Melting of the Arctic sea ice

Update 25 February 2013: Climate Dialogue summary now online
The summary of the first Climate Dialogue discussion on the melting of the Arctic sea ice is now online (see below). We have made two versions: a short and an extended version. The discussion between the experts is now officially closed. The public comments remain open. We apologize for the delay in publishing the summary.

Both versions can also be downloaded as pdf documents:
Summary of the Climate Dialogue on Arctic sea ice
Extended summary of the Climate Dialogue on Arctic sea ice

Introduction
The Arctic sea ice extent has been decreasing steadily for the past three decades. Scientists discuss the potential causes of this decrease. For practical reasons expert comments (comments by the invited scientists) are also separated from public comments. Anyone can comment. You need to subscribe once or use your own WordPress account. Public comments should be polite and on-topic and are moderated in advance.

Climate Dialogue editorial staff
Rob van Dorland, KNMI
Bart Strengers, PBL
Marcel Crok, science writer

Introduction Arctic sea ice

Melting of the Arctic
What are the causes of the decline in Arctic sea ice? Is it dominated by global warming or can it be explained by natural variability?

Introduction
Over the period 1979–2012, the Northern Hemisphere minimum sea ice extent for September—the end of the summer melt season— has declined by more than 11% per decade and the trend appears to be steeper for the last decade with record lows in 2007 and 2012. The decrease in winter sea ice extent is less strong, but the amount of thicker, older ice has decreased as well and therefore the decrease in total sea ice volume is even stronger than sea ice extent, both in summer and winter.

What is the cause?
Several studies have suggested that the decline in arctic sea ice is at least partly caused by global warming. An oft cited paper by Stroeve (2007)[1] and also more recent studies (i.e. Rampal 2011)[2] show that greenhouse forced climate models greatly underestimate the observed trend in arctic sea ice. A more recent study by Stroeve (2012)[3] shows that progress has been made in this area, but the climate models still cannot account for the full extent of the Arctic sea ice decline.

This could be explained as “it’s worse than we thought.” However it could also be interpreted as “models are yet unable to realistically simulate the sea ice behavior” and thus unable to conclude on the dominant role of global warming in the decline of Arctic sea ice. The low performance of climate models may be due to the difficulty in accounting for natural variations, or the physics associated with positive feedbacks. For example, it is not fully clear yet what role different oscillations have played like the Arctic Oscillation, the North Atlantic Oscillation and the Pacific Decadal Oscillation. Also, other anthropogenic forcings like black carbon could be important.

Discussion
A central question for the discussion is what is causing the recent decline in arctic sea ice. And can these processes be related to the emission of anthropogenic greenhouse gases?

Questions that are relevant for the discussion:

1) What are the main processes causing the decline in Arctic sea ice?

2) How unusual is the current decline in historical perspective?

3) What is the evidence for a substantial role of “global warming” in the current Arctic sea ice decline?

4) What is the evidence for a substantial role of natural variability (AO, AMO, NAO, PDO)?

5) What percentage of the recent decline would you attribute to anthropogenic greenhouse gases?

6) Do you think the Arctic could be ice free in the (near) future and when do you think this could happen?



[1] Stroeve, J.; Holland, M. M.; Meier, W.; Scambos, T.; Serreze, M. (2007). "Arctic sea ice decline: Faster than forecast". Geophysical Research Letters 34 (9): L09501

[2] IPCC climate models do not capture Arctic sea ice drift acceleration: Consequences in terms of projected sea ice thinning and decline; P. Rampal , J. Weiss , C. Dubois , J.-M. Campin; Journal: Journal of Geophysical Research , vol. 116, 2011, DOI: 10.1029/2011JC007110

[3] Stroeve, J., V. Kattsov, A. Barrett, M. Serreze, T. Pavlova, M. Holland, and W. N. Meier (2012a), Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations, Geophys. Res. Lett., doi:10.1029/2012GL052676

Guest blog Walt Meier
Arctic sea ice decline: past, present, and future

Walt Meier, Research Scientist, National Snow and Ice Data Center

Over the last 30+ years, Arctic sea ice has declined precipitously, particularly during summer. Summer extent has decreased by ~50%, including most of the older, thicker ice [1, 2]. Globally warming temperatures have been the primary cause of the long-term decline in Arctic sea ice [3]. Many processes effect the sea ice on several temporal spatial scales – e.g., winds, ocean currents, clouds – but the multi-decadal decline in all seasons, and in virtually all regions (Bering Sea in winter being an exception) cannot be explained without the long-term warming trend that has been attributed to anthropogenic greenhouse gas (GHG) emissions.

Unique
The current decline appears to be unique in at least the last 5000 years. While the consistent satellite record began only in 1979, earlier partial records indicate decreased extent in the Russian Arctic and the Greenland and Barents seas during the 1930s [4]. However, these reductions were regionally and temporally variable, unlike the pan-Arctic decline seen in recent decades. There are also indications that the North American side of the Arctic did not experience warm temperatures and thus low sea ice conditions during those years [5]. Thus, the 1930s period appears to be more of a regional event, as opposed to the pan-Arctic warming and sea ice decline we’re seeing now.

Earlier than the 1930s, proxy records from paleographic data (e.g., sediment cores) are essential to understand Arctic-wide sea ice conditions. The indicate reduced sea ice extent at levels near or possibly below current conditions during the Holocene Maximum, a period between 5000 and 10,000 years ago [6], though these are far from comprehensive. The next earliest potential period when ice conditions might have been low as now was during the Eemian period, the previous interglacial, about 130,000 years ago when temperatures were quite warm.

Global warming
The evidence for a substantial role of “global warming” in the current sea ice decline comes from the fact that the decline (1) correlates with the global warming temperatures over the past several decades, (2) is outside the range of normal variability over the past several decades and likely over the past several centuries, (3) the decline is pan-Arctic, with all regions experiencing declines throughout all or most of the year.  Also, model simulations of sea ice cover consistently show a response of declining sea ice to increasing GHGs (albeit slower than the observed decline); conversely, model runs over the last 30 years without GHG forcing do not show a decline [7, 8]. Finally, there does not appear to be a mechanism to sufficiently explain the long-term decline without including the effect of GHGs [9].

Arctic Oscillation
Along with the long-term GHG forcing, there is substantial natural variability in the sea ice system. The winter mode of the Arctic Oscillation (AO) or North Atlantic Oscillation (NAO) has been linked to summer sea ice conditions and the amount of multiyear ice in the Arctic [10]. A strong winter positive mode results in greater outflow of multiyear ice, resulting in a summer ice cover more prone to melt. Conversely, a negative mode tends to retain more multiyear ice, resulting in higher summer extents. However, the AO typically has a 3-7 year cycle, which does not correspond to the long-term trend. In addition, in recent years, the influence of the AO appears to have been broken, or at least weakened. For example, the 2009-2010 winter had the lowest AO on record (since 1950), and yet the summer 2010 minimum was among the lowest in the satellite record [11].

The Atlantic Meridional Overturning Circulation (AMOC) has some influence on sea ice extents in the Greenland, Barents, and Kara Seas, and thereby some effect on the total ice extent, particularly in winter [12]; it may explain some of the recent declining trend in sea ice [13]. Likewise, the Pacific Decadal Oscillation (PDO) affects winter ice conditions in the Bering Sea, but not elsewhere. These naturally varying climate oscillations cannot sufficiently explain the long-term decline in sea ice.

Attribution
It is difficult to put a precise number on how much of the decline is due to GHGs. There is strong natural variability, which is seen in observations and in model simulations. It is likely that at least some of the acceleration of the loss of sea ice in the past ~10 years is due to natural variability. A modeling study [14] suggested that about half of the observed September sea ice trend from 1979-2005 could be explained by natural variability, with the rest attributable to GHGs. There may also be some influence of black carbon, though how much is unclear.

Ice-free
The Arctic has been seasonally ice-free in the past under temperatures not much higher than in recent years. With continued GHG forcing and resulting increased temperatures, the Arctic will again become seasonally ice-free*. When this will occur is highly uncertain due to a number of factors. First, the ice cover has high interannual variability. Model simulations indicate periods of rapid ice loss, such as we have seen in the last decade [15]. However, periods of stasis or even increasing extent over several years are possible [14].

A couple of recent model studies have indicated a long-term linear response to GHG forcing [16, 17], suggesting that the recent acceleration in the decline is temporary and due to natural variability. Such a response would first result in ice-free conditions near the end of the century.  However, there are reasons to believe that a linear response is unlikely due to feedbacks and the response of the ocean to the loss of sea ice [18]. Over the satellite record, the observations are declining much faster than GCMs have indicated [7, 8]. IPCC models that match the historical record most closely indicate ice-free conditions by sometime in the 2030-2050 timeframe [19, 20]. This range seems reasonable, though it may not encompass the full range of possibilities.

However, even after ice-free conditions are reached for the first time, whether it be 2050, 2030, or even earlier, high interannual variability will continue. It is likely that there will be some subsequent years with more than 1 million square kilometers of sea ice remaining at the end of summer. Thus, prediction of sea ice conditions, particularly on decadal scales will be a challenge. Regardless of when ice-free conditions first occur, impacts of the sea ice loss are already being felt within the Arctic (and likely outside of the Arctic). These impacts will continue to increase well before summer ice-free conditions occur.

*There will likely be at least some ice throughout the summer, thick ice that piles up along the Greenland coast, ice in protected bays and inlets. Thus, it is important to define what is meant by “ice-free”. Here I will accept the 1 million square kilometers used in Wang and Overland (2009, 2012) as a reasonable threshold.

Biosketch
Dr. Walt Meier is a research scientist at the National Snow and Ice Data Center (NSIDC), part of the University of Colorado Boulder’s Cooperative Institute for Research in Environmental Sciences. His research focuses on studying the changing sea ice cover using satellite sensors and investigating impacts of the declining Arctic sea ice on climate. Dr. Meier also serves as lead scientist for NSIDC’s sea ice datasets. He has participated in several national and international activities, including a lead author on the AMAP Snow, Water, Ice and Permafrost in the Arctic (SWIPA) assessment report published earlier this year. He received a B.S. degree in from the University of Michigan, Ann Arbor in 1991 and an M.S. and Ph.D. degree from the University of Colorado in 1992 and 1998 respectively. From 1999 to 2001 Dr. Meier served as a visiting scientist at the U.S. National Ice Center in Washington, DC where he researched improved products for operational support of vessels in and near ice-infested waters. From 2001 through 2003 he was an adjunct assistant professor at the U.S. Naval Academy in Annapolis, MD teaching undergraduate courses in remote sensing and polar science.



References

[1] NSIDC Arctic Sea Ice News and Analysis, http://nsidc.org/arcticseaicenews/.

[2] Maslanik, J., J. Stroeve, C. Fowler, and W. Emery (2011), Distribution and trends in Arctic sea ice age through spring 2011, Geophys. Res. Lett., 38, L13502, doi:10.1029/2011GL047735.

[3] Overland, J.E., M. Wang, and S. Salo (2008), The recent Arctic warm period, Tellus, doi: 10.1111/j.1600-0870.2008.00327.x.

[4] Mahoney, A. R., R. G. Barry, V. Smolyanitsky, and F. Fetterer (2008), Observed sea ice extent in the Russian Arctic, 1933–2006, J. Geophys. Res., 113, C11005, doi:10.1029/2008JC004830.

[5] Overland, J.E., M.C. Spillane, D.B. Percival, M. Wang, H.O. Mofjeld (2004), Seasonal and regional variation of pan-Arctic surface air temperature over the instrumental record, J. Climate, 17, 3263-3282.

[6] Polyak, L., and several others (2010), History of sea ice in the Arctic, Quaternary Sci. Rev., 29, 1757-1778, doi: 10.1016/j.quascirev.2010.02.010.

[7] Stroeve, J., M.M. Holland, W. Meier, T. Scambos, and M. Serreze (2007), Arctic sea ice decline: Faster than forecast, Geophys. Res. Lett., 34, L09501, doi:10.1029/2007GL029703.

[8] Stroeve, J.C., V. Kattsov, A. Barrett, M. Serreze, T. Pavlova, M. Holland, and W.N. Meier (2012), Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations, Geophys. Res. Lett., 39, L16502, doi:10.1029/2012GL052676.

[9] Notz, D. and J. Marotzke (2012), Observations reveal external driver for Arctic sea-ice retreat, Geophys. Res. Lett., 39, L08502, doi:10.1029/2012GL051094.

[10] Rigor, I.G., J.M. Wallace, and R.L. Colony (2002), Response of sea ice to the Arctic Oscillation, J. Climate, 15, 2648-2663.

[11] Stroeve, J. C., J. Maslanik, M. C. Serreze, I. Rigor, W. Meier, and C. Fowler (2011), Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010, Geophys. Res. Lett., 38, L02502, doi:10.1029/2010GL045662.

[12] Mahajan, Salil, Rong Zhang, Thomas L. Delworth (2011), Impact of the Atlantic Meridional Overturning Circulation (AMOC) on Arctic surface air temperature and sea ice variability. J. Climate, 24, 6573–6581, doi: 10.1175/2011JCLI4002.1.

[13] Day, J.J., J.C Hargreaves, J.D. Annan, and A. Abe-Ouchi (2012), Sources of multi-decadal variability in Arctic sea ice extent, Env. Res. Lett., 7, 034011, doi: 10.1088/1748-9326/7/3/034011.

[14] Kay, J. E., M. M. Holland, and A. Jahn (2011), Inter-annual to multi-decadal Arctic sea ice extent trends in a warming world, Geophys. Res. Lett., 38, L15708, doi:10.1029/2011GL048008.

[15] Holland, M.M., Bitz, C.M. and Tremblay, B. (2006), Future abrupt reductions in the summer Arctic Sea ice. Geophys. Res. Lett. 33, L23503, doi:10.1029/2006GL028024.

[16] Tietsche, S., D. Notz, J. H. Jungclaus, and J. Marotzke (2011), Recovery mechanisms of Arctic summer sea ice, Geophys. Res. Lett., 38, L02707, doi:10.1029/2010GL045698.

[17] Amstrup, S.C., E.T. DeWeaver, D.C. Douglas, B.G. Marcot, G.M. Durner, C.M. Bitz, and D.A. Bailey (2010), Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence, Nature, 468, 955-958, doi: 10.1038/nature09653.

[18] Maslowski, W., J.C. Kinney, M. Higgins, and A. Roberts (2012), The future of Arctic sea ice, Ann. Rev. Earth and Planetary Sciences, 40, 625-654, doi: 10.1146/annurev-earth-042711-105345.

[19] Wang, M., and J. E. Overland (2009), A sea ice free summer Arctic within 30 years?, Geophys. Res. Lett., 36, L07502, doi:10.1029/2009GL037820.

[20] Wang, M. and J. E. Overland (2012), A sea ice free summer Arctic within 30 years: An update from CMIP5 models, Geophys. Res. Lett., 39, L18501, doi:10.1029/2012GL052868.

Guest blog Judith Curry

On the decline of Arctic sea ice

Judith Curry

I applaud the Dutch Ministry for establishing Climate Dialogue, and I am very pleased to participate in this inaugural dialogue on the decline of Arctic sea ice.

At my blog Climate Etc. http://judithcurry.com , I’ve written four lengthy articles on Arctic sea ice over the past 18 months:

Pondering the Arctic Ocean. Part I: Climate Dynamics

Likely causes of recent changes in Arctic sea ice

Reflections on the Arctic sea ice minimum: Part I

Reflections on the Arctic sea ice minimum: Part II

This essay presents an overview of my perspective on this topic; see the original articles for more details and references to scientific publications.

Observations

The conventional understanding of Arctic sea ice extent shows a general retreat of seasonal ice since about 1900, and accelerated retreat of both seasonal and annual ice during the latter half of the 20th century. Hints that this understanding may be overly simplistic in view of the uncertainties and ambiguities in the period prior to satellites are described in this presentation by John Walsh about plans for a gridded sea ice product back to 1870. Further, I’ve recently had some discussions about this with a historian that is investigating historical reports of sea ice extend during the period 1920-1950. He has found reports of reduced wintertime extent during this period, and a general lack of data from the Russian sector. While this material is not yet published, it reminds us that prior to 1979, we do not have a reliable data set of global sea ice extent. The lack of such a data set hampers our ability to test our ideas about the impact of natural variability versus anthropogenic forcing on sea ice variability and change.

Analysis of climate dynamics and sea ice physical processes

The following factors impact the sea ice fate during the melt season:

▪ Thickness and compactness of sea ice at the beginning of the melt season: ice that starts out thinner is more easily melted away. Further, first year ice has different optical and thermodynamic characteristics than multi-year ice.

▪ Transport of ice through the Fram Strait (between Greenland and Europe), which depends on a combination of atmospheric and ocean circulation patterns

▪ Weather patterns that act to either break up or consolidate the ice

▪ Radiative forcing (which is dominated by the cloud patterns)

▪ Melting from below by warm ocean currents.

▪ Melting from above by warm atmospheric temperatures.

▪ Geographic distribution of the sea ice, which depends on a combination of all of the above

And all this is complicated by the fact that the minimum sea ice extent in an individual season doesn’t simply reflect that season’s weather processes, but also reflects the decadal history of sea ice characteristics, sea ice export and atmospheric and oceanic circulation patterns. And the sea ice extent itself influences the atmospheric and oceanic circulation patterns. Hence, the sea ice characteristics tend to be out of equilibrium with the thermal forcing in a particular year.

Older ice
Here’s the basic story as I see it. During the late 1980s and early 1990s, the circulation patterns favored the motion of older, thicker sea ice out of the Arctic. This set the stage for the general decline in Arctic sea ice extent starting in the 1990′s. In 2001/2002, a hemispheric shift in the teleconnection indices occurred, which accelerated the downward trend. A local regime shift occurred in the Arctic during 2007, triggered by summertime weather patterns conspired to warm and melt the sea ice. The loss of multi-year ice during 2007 has resulted in all the minima since then being well below normal, with a high amplitude seasonal cycle. After 2007, there was another step loss in ice volume in 2010. In 2012, the basic pattern of this new regime was given a ‘kick’ by a large cyclonic storm in early August.

Anthropogenic
So, what is the contribution of anthropogenic global warming to all this? It’s difficult to separate it out. The polar regions are extra sensitive to CO2 forcing and water vapor feedback, owing the low amounts of water vapor. However, any radiative forcing from greenhouse gases is swamped by inter-annual variability in cloud radiative forcing. In the bigger picture sense, greenhouse forcing is involved in complex nonlinear ways with the climate regime shifts. So there is undoubtedly a contribution from CO2 forcing, but it is difficult to find any particular signal in this year’s record minimum, other than the contribution of greenhouse warming to a longer term trend. In the overall scheme of what is going on with the sea ice, I think 2007 was the most significant event, followed by 2010. The big event in 2012 was the cyclonic storm, and the impact on ocean mixing may turn out to be more significant than the sea ice minimum.

There is a complex interplay between natural internal variability and CO2 forcing, with complex interactions among ocean dynamics and heat transport, sea ice dynamics forced both by atmospheric winds and ocean currents, and atmospheric thermodynamic forcing acting to determine recent variations in multi-year sea ice extent. Hence sorting dynamical versus thermodynamic factors and attribution to increased greenhouse gases is not at all straightforward.

So . . . what is the bottom line on the attribution of the recent sea ice melt? My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range. Why such a ‘wishy washy’ statement with large error bars? Well, observations are ambiguous, models are inadequate, and our understanding of the complex interactions of the climate system is incomplete.

Whence an ‘ice free’ Arctic?

‘Ice free’ is put in quotes, because ‘ice free’ as commonly used doesn’t mean free of ice, as in zero ice. The usual definition of ‘ice free’ Arctic is ice extent below 1 M sq. km (current minimum extent is around 3.5 M sq. km). This definition is used because it is very difficult to melt the thick ice around the Canadian Archipelago. And the issue of ‘ice free’ in the 21st century is pretty much a non-issue if your require this thick ice to disappear.

What do the climate models have to say? Several recent papers have analyzed the CMIP5 simulations, and find near ice free conditions by mid-century, and even as early as the 2030’s. Whereas sea ice models are becoming quite sophisticated, most recently in terms of the radiative transfer, melt ponds, and aerosols, prediction of sea ice is hostage to predictions of the chaotic atmospheric and oceanic dynamics.

For the next two decades, natural variability will almost certainly trump any direct effects from anthropogenic warming by a long shot. The current sea ice situation does not seem stable, but it is not at all clear whether we can expect a reversion to the (more recently) normal state or yet a larger ice loss.

The issue is whether the ice is now sufficiently thin that it would be difficult to reverse the decline. Growing and diminishing the sea ice pack are not symmetric processes: ice export that contributes to diminishing the sea ice pack does not have a reverse counterpart; at best you stop the export and stop the decrease.

So the question then becomes what processes could contribute to a recovery of the Arctic sea ice on the time scale of two decades?

Recovery (?)

So, can we infer that the Arctic sea ice is caught in an irreversible ‘spiral of death’? Here are some processes that would contribute to a recovery of the sea ice:

▪ Reduction of the sea ice export through the Fram Strait

▪ Reduction of warm water inflow from the Atlantic and Pacific

▪ Fewer clouds in winter and/or more clouds in summer

▪ Less snow fall on ice in autumn and more in spring

▪ Less soot transported to the Arctic

▪ No rainfall on snow covered ice before mid-June

▪ Fewer storms in summer causing ice breakup, and more storms in autumn/early winter causing ice ridging/rafting

These processes depend on both random weather patterns and the teleconnection climate regimes. Can I predict how this might go over the next two decades? Heck no, other than that I suspect that the cool phase of the PDO will persist and at some point probably within two decades we will switch to the cool phase of the AMO.

And then there are the known unknowns: what solar radiation will do (looks like cooling), volcanoes are always a wild card, and then there are the less known unknowns such as cosmic ray effects, magnetic field effects, etc. And in terms of climate shifts, there may be something happening on much longer time scales (e.g. the Atlantic Meridional Overturning Circulation) that could influence the next climate regime shift. Focusing on CO2 as the dominant influence on the time scale of two decades seems very misguided to me.

Does ‘ice free’ matter?

The first issue to debunk is that an ‘ice free’ Arctic is some sort of ‘tipping point.’ A number of recent studies find that in models, the loss of summer sea ice cover is highly reversible.

The impact of September sea ice loss on the ice albedo feedback mechanism is interesting. The minimum sea ice occurs during a period when the sun is at low elevation, so the direct ice albedo effect isn’t all that large. Less sea ice in autumn means more snowfall on the continents, which can have a larger impact on albedo. The impacts of the freeze-thaw over the annual cycle influences ocean circulations. But sea ice would continue to freeze and thaw on an annual cycle.

Clouds would change, atmospheric circulation patterns would change. The net effect on climate outside the Arctic Ocean would be what? More snow during winter on the continents is the most obvious expected change. But we really don’t know.

There would likely be regional triggers that could feedback onto larger scale regime shifts. Would any of these patterns or extreme events fall outside the envelope of what we have seen over the past century? Hard to know.

Would melting sea ice trigger some sort of clathrate methane release into the atmosphere? Well in terms of thawing permafrost, it seems like more snow fall on the continents would inhibit permafrost thawing. Same for the stability of the Greenland ice cap.

These are all qualitative speculations, but I am not seeing a big rationale for climate catastrophe if the sea ice melts.

Biosketch
Judith Curry obtained her Ph.D. in Geophysical Sciences from the University of Chicago. She is currently Professor and Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology, and is also President of Climate Forecast Applications Network LLC. Her research addresses a range of topics in atmospheric and climate science, including sea ice and the climate dynamics of the Arctic http://curry.eas.gatech.edu/climate/arctic.htm. She is a Fellow of the AAAS, the American Geophysical Union, and the American Meteorological Society. She has recently served on the U.S. National Research Council Space Studies Board and Climate Research Committee. She currently serves on the U.S. Department of Energy Biological and Environmental Research Committee and the Earth Science Subcommittee of the NASA Advisory Council. Curry is an active spokesperson on issues related to integrity in scientific research. She is the proprietor of a blog Climate Etc. judithcurry.com, which is a forum to discuss topics related to climate science and the science-policy interface.

Guest blog Ron Lindsay

Melting of the Arctic
Ron Lindsay

I usually choose to focus on the mean ice thickness within the Arctic Ocean as opposed to all ice-covered seas because this limited system is better defined. The atmospheric forcing is more uniform over the region, the volume-thickness relationship is well established since it is a defined region and any residual summer ice will mostly be found there. In addition, ice thickness is a much more consistent climate indicator than ice area or extent. Trends in thickness explain much more of the inter-annual variability than sea ice area and even more than extent.

If we want to understand the fate of summer ice, it is the Arctic Ocean we need to look at. The peripheral seas in many respects don’t matter. I use the ice thickness estimates from the retrospective studies using the PIOMAS ice-ocean model. I am the first to say models are far from perfect, but the general pattern of ice thickness simulated by this model has been shown to be pretty good when compared to observations (Schweiger et al 2011[1]). If anything, the model may be a little conservative in estimating the decline in ice thickness.

Greenhouse gases
I believe fundamentally the main process causing the decline in Arctic sea ice is increasing greenhouse gases. Evidence for the role of greenhouse gases must come primarily from modeling studies. Only those can help us separate natural climate variations from variations caused by changes in greenhouse gases or other external forcing mechanisms (e.g. sun or volcanoes). Examining past climate records and asking questions about the forcing mechanisms responsible for changes can also help. For example there is some evidence that there was less sea ice about 9000 years ago when solar insolation was stronger.

But teasing out the actual mechanisms for the decline is very tricky (e.g. whether it is changes in the ocean or in the atmosphere or both or what processes are responsible). Observational evidence is difficult to interpret, since the decline itself modifies the lower atmosphere and the surface fluxes. What is cause and what is effect? One piece of evidence though is the high correlation (R = -0.72, 57 years through 2011) between the rate of melt (including export) in the Arctic Ocean and melt season (May to September) surface temperatures in the rest of the hemisphere, from 20N to 60N (NCEP-R1). The surface temperatures south of the Arctic are likely less influenced by ice loss and the trends are likely more influenced by global forcings. Sea ice basically responds to hemispheric conditions and is not on its own trajectory.

Unknowable
But the actual detailed mechanisms for the decline are currently unknowable. The trend in the latent heat content of the ice in September is less than 0.5 W/m2/year in September. It seems this means annual change in the net heat balance of the ice and the changes in the mean annual melt and growth rates are much too small to be accurately measured by any observational system that looks at the entire region. That the PIOMAS model gives reasonably good estimates of the mean ice thickness trends is because it has been tuned to the atmospheric forcing fields that we use. So while the total melt and growth rates must be about right (to get the correct thickness) an analysis of the individual components of the surface or oceanic heat fluxes and their trends likely won’t provide a useful answer. Because of the small shifts in energy needed to melt the ice it is perhaps no surprise that there is a wide scatter in sea ice trends between climate models.

Unusual
The current decline in ice extent and volume is highly unusual. Maybe the best way to show this is in the consistency in the trends. The linear trend in the September ice thickness from 1987 to 2012 explains 90% of the variability, much more than any other comparable interval since 1948. The observational record for sea ice is more spotty before this time, though researchers are piecing together a more comprehensive picture from various ship observations. So far that picture doesn’t suggest that large variations in sea ice extent were anything but regional over the last 120 years or so.

A reconstruction based on proxy records suggest that sea ice extent is now the lowest in 1450 years (Kinnard, 2011[2]). A recent review of the current state of knowledge (Polyak et al, 2010[3]) concludes: “This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.”

The evidence for a substantial role of “global warming” in the current Arctic sea ice decline is very strong, both from observations and from modeling studies. Of course neither can “prove” the role of greenhouse gases but there is overwhelming evidence it is true. To refute the evidence from models, one would have to show that they wildly underestimate natural variability (w.r.t to sea ice). Even in the NCAR CCSM4 which is one of the CMIP5 models with the highest “natural” variability, the sea ice extent trend over the last 30 years is still 50% due to greenhouse gases (Kay et al. 2011[4]).

Natural variability
For those that think this is not the case, they need to show some evidence that there are alternative explanations. Comparing ice volume instead of sea ice extent greatly reduces the natural variability compared to the trend and shows an earlier and more definitive separation than ice area between models run with or without increased greenhouse gas forcings (Schweiger et al 2011[5]).

While natural variability is very important for determining the ice extent, primarily through the action of the winds, I see a very consistent trend in the mean ice thickness with relatively little year-to-year variations. So while natural variability can strongly influence the ice area and extent, I doubt there is a strong component in the variability of the mean ice thickness within the Arctic Ocean. In the peripheral seas the winds are very important for determining heavy or light ice years and hence in these areas the variability associated with circulation changes can be very large, both for ice extent and thickness. There is evidence that an extended positive phase of the AO during the early 1990’s helped flush out older thicker ice and helped set up the subsequent decline in sea ice (Rigor et al. 2002[6], Lindsay et al. 2005[7]). Since then the ice decline cannot be explained by variations in the AO. Evidence from models (Day et al. 2012[8]) indicates that the AO may not play much of a role in sea ice variability. That same study suggest that the AMO indeed may indeed play a significant role in sea ice decline and that as much as 3%/decade of the 10%/decade trend in September sea ice extent between 1979-2010 may be due to AMO variability. There is also some observational evidence that sea ice extent may be influenced by the AMO but none of this evidence suggest that an arctic-wide change in ice extent as seen over the last decade is possible due to these type of modes of natural variability alone. It also appears ice thickness within the Arctic Ocean is less closely tied to the AMO.

As shown by Stroeve et al. (2012[9]), the CMIP5 models as a group underestimate the sea ice trend. But there is no requirement that reality should follow the group mean nor that any model that reproduces the observed trend any better than another is indeed the preferable model. In fact, there are ensemble members that match reality fairly well (e.g. Schweiger et al., 2011) but that shouldn’t fool us in to believing them more. Given that the CCSM4, a model with rather large (and possibly excessive) natural variability pins 50% of sea ice loss on greenhouse gases, probably more than this is due to the greenhouse emissions.

Ice free
The Arctic will likely be largely ice free at the end of some summers within a decade or two. Small bits of ice might remain some years, but they may not matter for much. Current research does not support the notion of any “tipping” points for summer sea ice so if we somehow magically could turn off the forcing that comes from greenhouse gases, sea ice would likely grow back relatively quickly. Unfortunately that is not likely to happen. Winter ice will remain for a long time, a century or more. How long probably depends mostly on the future rate of greenhouse gas emissions.

Biosketch
Ron Lindsay is an Arctic climatologist at the Polar Science Center Applied Physics Laboratory of the University of Washington in Seattle. Lindsay is interested in how the sea ice in the Arctic moves, grows, and decays in response to changing environmental conditions and how the changes in the ice pack are impacting the atmosphere above. To pursue these research themes he uses a wide variety of in situ and remote sensing data and numerical models. In support of these interests he has joined the IceBridge science team to help direct a NASA program to monitor ice thickness from aircraft. He is also developing a capability for modeling the response of the atmosphere to changing pack ice conditions in order to understand the extent to which the heat absorbed in the open water areas in the summer slows the growth of ice in the winter. Lindsay has been conducting Arctic research for over 35 years and has been with the Polar Science Center since 1988.



[1] Schweiger, A., R. Lindsay, J. Zhang, M. Steele, H. Stern, and R. Kwok. 2011. Uncertainty in Modeled Arctic Sea Ice Volume. J. Geophys. Res., doi:10.1029/2011JC007084

[2] Kinnard, C., C. Zdanowicz , D Fisher, and E. Isaksson, 2011: Reconstructed changes in Arctic sea ice over the past 1,450 years, Nature, 509-512, doi 10.1038/nature10581.

[3] Polyak, L., and several others (2010), History of sea ice in the Arctic, Quaternary Sci. Rev., 29, 1757-1778, doi: 10.1016/j.quascirev.2010.02.010.

[4] Kay, J. E., M. M. Holland, and A. Jahn (2011), Inter-annual to multi-decadal Arctic sea ice extent trends in a warming world, Geophys. Res. Lett., 38, L15708, doi:10.1029/2011GL048008.

[5] Schweiger, A., R. Lindsay, J. Zhang, M. Steele, H. Stern, and R. Kwok. 2011. Uncertainty in Modeled Arctic Sea Ice Volume. J. Geophys. Res., doi:10.1029/2011JC007084

[6] Rigor, I.G., J.M. Wallace, and R.L. Colony, Response of Sea Ice to the Arctic Oscillation, J. Climate, v. 15, no. 18, pp. 2648 – 2668, 2002.

[7] Lindsay, R. W. and J. Zhang, 2005: The thinning of arctic sea ice, 1988-2003: have we passed a tipping point?. J. Climate, 18, 4879–4894.

[8] Day, J.J., J.C Hargreaves, J.D. Annan, and A. Abe-Ouchi (2012), Sources of multi-decadal variability in Arctic sea ice extent, Env. Res. Lett., 7, 034011, doi: 10.1088/1748-9326/7/3/034011.

[9] Stroeve, J.C., V. Kattsov, A. Barrett, M. Serreze, T. Pavlova, M. Holland, and W.N. Meier (2012), Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations, Geophys. Res. Lett., 39, L16502,doi:10.1029/2012GL052676.

Summary of the Climate Dialogue on Arctic sea ice

Summary of the Climate Dialogue on Arctic sea ice

The decline of Arctic sea ice is one of the most striking changes of the Earth’s climate in the past three decades. In September 2012 the sea ice extent reached a new record low after an earlier record in 2007. Both ice extent and volume have decreased steadily and if things will continue this way the Arctic will be ice free in the summer some year in the future.

Given the recent new record the melting of the Arctic was the logical choice as the first topic on this new Climate Dialogue platform. We are very glad that Walt Meier, Ron Lindsay and Judith Curry took up the challenge to engage with each other. We also like to thank the many climate scientists and other interested readers who joined the discussion via the public comments. We had over 25,000 hits in the first three weeks, which exceeded our expectation for the first round of discussion.

This summary is solely based on the contributions of the three invited scientists Walt Meier, Ron Lindsay and Judith Curry. It’s not meant to be a consensus statement. It’s just the summary of the discussion and should give a good overview of how these three scientists view the topic at this moment, i.e. on what they agree and disagree and why. In our introductory article we presented six questions and we will treat each one separately.

1. What are the main processes causing the decline in Arctic sea ice?

Over the last 30+ years, Arctic sea ice has declined precipitously, particularly during summer. Summer ice extent has decreased by ~50%, including most of the older, thicker ice.

Source: http://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph/

Sea ice volume has decreased even more, with the monthly averaged ice volume for September 2012 of 3,400 km3, which is 72% lower than the mean over the period.

Source: http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/

There is no disagreement about these facts. However, it is less clear what are the main processes that caused the decline.
The discussants agree that relatively little heat (~0.5 W/m2) is necessary to explain the decline of Arctic sea ice in the past three decades. These changes are so small that our observational systems are unable (yet) to detect the main sources for this trend.
The discussants agree that in general melting from the ocean is much more effective than melting from the air. However there is little evidence that transport from either the Atlantic or the Pacific contributed much to the melting in the past decades.
A number of processes seems relevant: earlier snow melting in spring leads to melt ponds in the sea ice, opening the Arctic ocean for incoming solar radiation, which then melts the ice from both above and below the ice. Clouds are also an important player in these processes, although not much is known about the trends in clouds in this area.
The discussants stress that it’s difficult to separate cause and effect. The major forcings and feedbacks influencing the Artic sea ice can change from year to year.

Meier

Curry

Lindsay

The decline in sea ice extent since 1979 is very well documented/undisputed

5

5

5

The decline in sea ice volume since 1979 is very well documented/undisputed

5

4

5

Two thirds of the melting each summer is taking place from below the ice

3

x

x

Earlier snow melt in spring is playing a big role in the summer melting

4

4

4

By far the largest component causing the seasonal melting is the solar flux

5

5

5

The influx of warmer waters from the Atlantic has played a minor role in causing the decline in Arctic sea ice

x

x

x

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

2. How unusual is the current decline in historical perspective?

Lindsay and Meier have more confidence that the current decline is unprecedented in historical context. Curry stressed the lack of data before 1979 which hampers our understanding of the state of Arctic sea ice in the past. Meier on the other hand mentioned several studies that shed light on past sea ice conditions and how they differ from the current situation. The participants agree that during the Holocene Thermal Maximum (around 8000 ybp) the Arctic likely was ice free or near ice free as well in the summer. At that time temperatures in the Arctic were similar as today or even higher.

Meier

Curry

Lindsay

The current decline in ice extent is unprecedented in the last century

5

4

5

The current decline in ice extent is unprecedented in the last two millennia

3

x

3

The current decline in ice extent is unprecedented in the Holocene

3

x

2

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

3. Is there evidence for a substantial role of natural variability?

The discussants agree that a shift in the Arctic Oscillation (AO) in the late 80s seemed to have started the decline. A positive AO, especially in winter, pushed older thicker ice out of the Arctic through the Fram Strait. When the AO went back to normal however, the decline in sea ice continued. Meier and Lindsay conclude from this that oscillations like the AO, but also the NAO and PDO, probably played a minor role in the continuing decline. Model simulations suggest that the AMO might have contributed between 5% and 30% of the melting. Curry is not so sure about this. She mentions a hemispheric climate shift in 2001 that accelerated the decline followed by a local regime shift in 2007, that has resulted in all the minima since then being well below normal, with a high amplitude seasonal cycle. Lindsay and Meier also have more confidence in the models than Curry. Lindsay said it isn’t likely that they hugely underestimate natural variability, but this is exactly what Curry thinks the models do.

Meier

Curry

Lindsay

A shift in the AO to positive values started the decline in the early 90s

4

4

4

Now that the ice is thinner, the effect of natural oscillations on the sea ice trend is much smaller

4

3

4

Models underestimate natural variability considerably

2

5

1

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

4. What is the role of ‘global warming’?

There is disagreement about the role of global warming. Both Lindsay and Meier sum up evidence for a large role of “global warming” in the current decline in sea ice. Lindsay mentions the good correlation with the Northern Hemispheric temperatures, showing that the sea ice is not on its own regional trajectory but follows the trend of a larger area. Meier notes the fact that the warming now is pan-Arctic and outside the range of natural variability for the last few centuries. Curry acknowledges a role for global warming to the longer term trend. But at the same time she notes that locally any radiative forcing from greenhouse gases is swamped by inter-annual variability in cloud radiative forcing.

Meier

Curry

Lindsay

The evidence for a substantial role of “global warming” in the current Arctic sea ice decline is very strong

5

4

5

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

5. Quantification of the anthropogenic contribution to sea ice decline

The participants agree it is unlikely the contribution of greenhouse gases to the recent decline is lower than 30%. Curry even said she wouldn’t know any publishing climate scientist going lower than 30%. Curry proposed a range of 30 to 70% greenhouse gas contribution to the recent decline in sea ice extent. Her best estimate would be 50%. Lindsay agreed with this best estimate of 50% for extent. He added though that sea ice volume is his preferred metric because it shows less year to year variability. For sea ice volume he would go higher, say 70%. Meier proposed a smaller range of 50 to 70%.

Meier
%

Curry
%

Lindsay
%

What is your preferred range w.r.t. the contributions of anthropogenic forcing to the decline in sea ice extent?

50-95%

30-70%

30-95%

What is your preferred range w.r.t. the contributions of anthropogenic forcing to the decline in sea ice volume?

50-95%

30-70%

30-95%

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

6. Could the Arctic be ice free in the near future?

None of the participants is very enthusiastic about the idea that the Arctic could be ice free in the summer within a few years. Meier explained that so far the “easy” ice has melted but that now we’re getting to the “more difficult” ice north of Greenland en the Canadian Archipelago. “The predominant ice circulation pushes ice toward those coasts resulting in thick ice that tends to get replenished.”
Lindsay is most confident that even on a time scale of one or two decades greenhouse forcing should cause a further decline. Curry emphasized that on this time scale natural fluctuations will dominate the effect of CO2. For her a reverse of the trend is therefore possible. Meier “wholeheartedly” agreed with Curry that decadal prediction of sea ice is going be very difficult.
Curry stated that the currently used definition of “ice free” (being less than 1 million km2 of ice) is misleading as it is not really ice free. Meier defended the definition as being valid for all practical purposes like ship navigation, the albedo feedback and impacts on the ecosystem.
None of the participants believe in a tipping point. Lindsay noted that if we magically could turn off the forcing the sea ice could recover pretty quickly. Lindsay: “Unfortunately that is not likely to happen.”

Meier

Curry

Lindsay

The Arctic could be ice-free in a few years

1

1

1

The sea ice could (partly) recover in the next two decades due to natural variability

2

3

2

What is the most likely period that the Arctic will be ice free for the first time?

2030-2050

x

2020-2060

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

Extended summary of the Climate Dialogue on Arctic sea ice

Extended summary of the Climate Dialogue on Arctic sea ice

The decline of Arctic sea ice is one of the most striking changes of the Earth’s climate in the past three decades. In September 2012 the sea ice extent reached a new record low after an earlier record in 2007. Both ice extent and volume have decreased steadily and if things will continue this way the Arctic will be ice free in the summer some year in the future.

Given the recent new record the melting of the Arctic was the logical choice as the first topic on this new Climate Dialogue platform. We are very glad that Walt Meier, Ron Lindsay and Judith Curry took up the challenge to engage with each other. We also like to thank the many climate scientists and other interested readers who joined the discussion via the public comments. We had over 25,000 hits in the first three weeks, which exceeded our expectation for the first round of discussion.

This summary is solely based on the contributions of the three invited scientists Walt Meier, Ron Lindsay and Judith Curry. It’s not meant to be a consensus statement. It’s just the summary of the discussion and should give a good overview of how these three scientists view the topic at this moment, i.e. on what they agree and disagree and why. In our introductory article we presented six questions and we will treat each one separately.

1. What are the main processes causing the decline in Arctic sea ice?

Over the last 30+ years, Arctic sea ice has declined precipitously, particularly during summer. Summer ice extent has decreased by ~50%, including most of the older, thicker ice.

Source: http://nsidc.org/arcticseaicenews/charctic-interactive-sea-ice-graph/

Sea ice volume (as determined by the Piomas model[i]) has decreased even more. The model mean annual cycle of sea ice volume over the period 1979-2011 ranges from 28,700 km3 in April to 12,300 km3 in September. However, monthly averaged ice volume for September 2012 was 3,400 km3. This value is 72% lower than the mean over this period, 80% lower than the maximum in 1979, and 2.0 standard deviations below the 1979-2011 trend.

Source: http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/

There is no disagreement about these facts. However, it is less clear what are the main processes that caused the decline.

The discussants all agree that relatively little heat is necessary to get the melt rates of the recent past. Like Lindsay said: “[…] given the small amount of heat needed to melt the ice at the rate we have seen (less than 0.5 W/m2 annual average), is it a hopeless task to find a definitive mechanism, particularly since the dominant forcing for ice anomalies likely changes from year to year?”

These changes are too small to measure. Lindsay: “It seems this means annual change in the net heat balance of the ice and the changes in the mean annual melt and growth rates are much too small to be accurately measured by any observational system that looks at the entire region.” He adds: “[…] teasing out the actual mechanisms for the decline is very tricky (e.g. whether it is changes in the ocean or in the atmosphere or both or what processes are responsible). Observational evidence is difficult to interpret, since the decline itself modifies the lower atmosphere and the surface fluxes. What is cause and what is effect?”

Meier adds that given the small amount of heat necessary to melt the ice it is rather surprising that the sea ice has been relatively stable in the past. “In regards to the stability of the Arctic sea ice, I would agree with Ron [Lindsay] that it may be more surprising that it has been so stable over our years of observations, both in our modern satellite record (since 1979) and earlier. Given that the ice is quite thin (overall on average 2.5 meters or so, with multiyear being 3-4 meters), it doesn’t take much forcing, relatively speaking, to melt completely during summer (1 W/m2 or less).”

Ocean
The discussants agree that heat from the ocean is more effective in melting the ice than heat from the air. As Curry puts it: “Melting the ice from below is much more powerful than melting the ice from above, in terms of W/m2. Note that solar radiation penetrates into the mixed layer through open water leads and melt ponds and thin ice, so solar acts to melt from below as well as from above.”

Curry also referred to model calculations that tried to figure out how much heat from the atmosphere would be needed. “From the Arbetter et al. paper[ii], which asked how much IR forcing is needed to melt the ice from above, the answer depended on which sea ice model you used, but for a dynamic/thermodynamic sea ice model, the result was tens of W/m2.”

Meier: “The ocean is indeed a very important part of the sea ice melt story. Water is a much more effective mechanism to transfer heat to the ice compared to the atmosphere. This is seen in mass balance buoys presented by Don Perovich and colleagues at the U.S. Army Cold Regions Research and Engineering Lab that measure the relative contributions by the ocean and atmosphere to summer melt[iii]. […] near the ice edge bottom melting tends to dominate.”

It isn’t clear yet whether transport of warm water into the Arctic is contributing much to the melting from below. Lindsay: “I don’t know if it is possible to measure any additional heat being drawn from the warm Atlantic layer below the cold halocline.” Meier mentions some indications for transport into the Arctic: “This ocean contribution [to the melting] is due to in situ ocean warming or transport of warm water into the Arctic. There are some indications of influxes of warmer surface and near-surface water in the Pacific region (e.g. by W. Maslowski at the U.S. Naval Postgraduate School), but most of the heating is in situ due to solar insolation[iv]. Steele et al. also find that near the ice edge, bottom melt accounts for 2/3 of the thickness melt vs. 1/3 for surface melt from the atmosphere.”

This 1/3 vs. 2/3 ratio can’t be used for the Arctic as a whole yet. Lindsay: “I don’t agree that 2/3 of the melt comes from the ocean. How do we know that?” Adding: “If there is a trend in ocean heat flux I am not aware of it, except for solar heat absorbed by the ocean that subsequently melts ice.”

Solar insolation
Nevertheless a lot of the heat that is causing the seasonal melting now seems to come from in situ solar heating. Like Meier explains: “Even though the solar insolation maximum occurs when much of the Arctic Ocean is still ice-covered (i.e. June 21), a significant amount of heat is absorbed through the ocean. Buoy data[v] surface temperatures are >5°C, which is 7+°C above the melting point for the ocean water. These are surface temperatures, but the heat extends down several meters (via communication with Mike Steele). That is a lot of heat.”

With lots of the heat coming from in situ solar heating in the summer, a few processes are relevant: early snow melting in spring leading to melt ponds in the sea ice, opening the Arctic ocean for incoming solar radiation, which then melts the ice from both above and below the ice. Clouds are also an important player in these processes, although not much is known about the trends in clouds in this area. Curry: “With regards to the summer minimum, the clouds are contributing and seem to have been a major factor during 2007. Clouds are much more powerful radiatively than CO2, so if we are talking about radiative forcing, clouds should be front and center in the discussion.” This doesn’t mean though that Curry is thinking that clouds in general are the main driver for summer melting: "This response does not imply that I think clouds are the only or even the main driver of the summer sea ice minimum."

Lindsay: “It is very hard to really know what the long-term changes in the cloud radiative forcing is in the central Arctic, in part because satellite retrievals of cloud properties can be biased by changing surface properties, so if the surface changes (less ice) is the change in estimated cloud properties real or just an artifact?” Slightly later in the discussion Lindsay adds this: “As Judith says, clouds are the big player in radiative fluxes. How they are changing in response to changing ice in amount, composition, and vertical structure is still an open research question, so we don’t really know if cloud changes will be a positive or a negative feedback. Because they are so important I would not be surprised if they are found to be at least part of the source of the ice melt, but because cloud temperature and properties may change due to changing surface properties, sorting out cause and effect could be difficult.”

So snow and ice feedback could both be positive leading to larger melting in the summer. Lindsay: “Atmospheric fluxes are highly variable and accurately determining a long-term trend is difficult. A possible strong feedback is the lower albedo of melting snow in the spring so that an earlier onset of melt is amplified with earlier snow melt, earlier melt pond formation, and earlier lower albedo of bare ice[vi] which would amplify melt. In terms of melt, by far the largest component is the solar flux, so understanding how the surface albedo changes is crucial.”

Ice growth in winter
The extra heat in the oceans is quickly lost in the autumn though and first year ice is growing faster than multi-year ice. As Curry explains: “Ice volume increase during winter can actually be larger for first year (FY) ice than for a field dominated by multi-year (MY) ice. Thin ice grows at a much faster rate than thick ice. The change in ice volume for MY-dominated vs. FY dominated during summer is trickier. Thicker ice actually starts melting a bit earlier than thin ice owing to the larger sensible heat loss over the thin ice, but the thin ice may entirely disappear over the course of the summer by melting. A key issue is whether the FY ice can survive through the summer. This depends on the local thermodynamics, and also the export [through the Fram Strait] and also breakup induced by a big cyclonic storm. So following the time variation of the second year ice is another key to understanding what is going on (thermodynamics vs dynamics/export)[vii].

Lindsay: “A lot of different aspects of the system are changing and I can’t say which one is dominant, if any. I am not aware of observations that show the heat flux from the ocean is increasing. A lot of solar heat is now being dumped into the ocean in late summer, but much of this heat is quickly lost to space in the fall, so the impact on winter growth may be modest, again the thin ice growth rate feedback. How much of this new summer heat is sequestered and slows ice growth all winter is an open research question.”

Summary
Over the last 30+ years, Arctic sea ice has declined precipitously, particularly during summer. Summer ice extent has decreased by ~50%, including most of the older, thicker ice. Sea ice volume has decreased even more, with the monthly averaged ice volume for September 2012 of 3,400 km3, which is 72% lower than the mean over the period. There is no disagreement about these facts. However, it is less clear what are the main processes that caused the decline.
The discussants agree that relatively little heat (~0.5 W/m2) is necessary to explain the decline of Arctic sea ice in the past three decades. These changes are so small that our observational systems are unable (yet) to detect the main sources for this trend.
The discussants agree that in general melting from the ocean is much more effective than melting from the air. However there is little evidence that transport from either the Atlantic or the Pacific contributed much to the melting in the past decades.
A number of processes seems relevant: earlier snow melting in spring leads to melt ponds in the sea ice, opening the Arctic ocean for incoming solar radiation, which then melts the ice from both above and below the ice. Clouds are also an important player in these processes, although not much is known about the trends in clouds in this area.
The discussants stress that it’s difficult to separate cause and effect. The major forcings and feedbacks influencing the Artic sea ice can change from year to year.

Meier

Curry

Lindsay

The decline in sea ice extent since 1979 is very well documented/undisputed

5

5

5

The decline in sea ice volume since 1979 is very well documented/undisputed

5

4

5

Two thirds of the melting each summer is taking place from below the ice

3

x

x

Earlier snow melt in spring is playing a big role in the summer melting

4

4

4

By far the largest component causing the seasonal melting is the solar flux

5

5

5

The influx of warmer waters from the Atlantic has played a minor role in causing the decline in Arctic sea ice

x

x

x

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

2. How unusual is the current decline in historical perspective?

Lindsay is most outspoken that the current decline is remarkable in historical perspective. “The current decline in ice extent and volume is highly unusual. Maybe the best way to show this is in the consistency in the trends. The linear trend in the September ice thickness from 1987 to 2012 explains 90% of the variability, much more than any other comparable interval since 1948. The observational record for sea ice is more spotty before this time, though researchers are piecing together a more comprehensive picture from various ship observations. So far that picture doesn’t suggest that large variations in sea ice extent were anything but regional over the last 120 years or so.”

Curry on the other hand is much more focused on the uncertainties before the satellite measurements (1979) start. “The conventional understanding of Arctic sea ice extent shows a general retreat of seasonal ice since about 1900, and accelerated retreat of both seasonal and annual ice during the latter half of the 20th century. Hints that this understanding may be overly simplistic in view of the uncertainties and ambiguities in the period prior to satellites are described in this presentation[viii] by John Walsh about plans for a gridded sea ice product back to 1870. Further, I’ve recently had some discussions about this with a historian that is investigating historical reports of sea ice extend during the period 1920-1950. He has found reports of reduced wintertime extent during this period, and a general lack of data from the Russian sector. While this material is not yet published, it reminds us that prior to 1979, we do not have a reliable data set of global sea ice extent. The lack of such a data set hampers our ability to test our ideas about the impact of natural variability versus anthropogenic forcing on sea ice variability and change.”

Meier is closer to Lindsay. He thinks the historical evidence points towards lower ice extent in the 1930s but these changes were more regional: “While our most complete dataset, the one we have the highest confidence in, is the passive microwave record, there is fairly complete coverage from operational ice charts back to at least the mid-1950s. And there are Russian ice charts for the Eurasian Arctic back to the early 1930s. Though not complete, these do extend the record and I think provide some sense of the interannual and decadal natural variability of the ice. There are indications of lower ice in the 1930s in the Russian Arctic[ix], suggesting the influence of a multi-decadal cycle (AMO?), at least in the Russian Arctic. But the data show a different character in terms of the seasonality and regionality of the lower ice conditions compared to the recent decline.” In another comments he adds: “Before the 1950s, the 1930s are often mentioned as a warm period. However, this is primarily in the Atlantic region, where observations were more common. Ice charts from the Denmark[x] and Russia, indicate some periods of low summer ice, but on a more regional scale than we see now.”

Holocene
Going back further in time, both Lindsay and Meier refer to the reconstruction of Kinnard for the last 1.5 millennium: “A reconstruction based on proxy records suggest that sea ice extent is now the lowest in 1450 years[xi].” Even further back goes a review article of Polyak[xii] which concludes: “This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.” That same review of longer records indicates that the last time the Arctic had little or no summer ice was during the Holocene Thermal Maximum (~8000 years before present).

There has been little discussion about the uniqueness of the recent decline and the discussants indicate they are no expert on this matter. Meier has looked into the question though because at his institute NSIDC they receive a lot of questions about this. He offers an interesting thought experiment about what it could mean that the Arctic has been ice free in the past (~8000 ybp). “There are (at least) two ways of looking at it: If the Arctic has been ice-free during summer in the past, obviously it was due to natural forcing, so the current decline could also be due to natural forcing. If the Arctic has been ice-free during summer in the past due to natural forcing then anthropogenic forcing of a similar magnitude will have a similar effect. The first view is not implausible on its face, but it is simplistic because it doesn’t consider that the same result could be due to the same causes. Lightning starts forest fires, but that doesn’t rule out that a forest fire may be due to human actions. The second view is much more useful in my view because it has potential predictive value at least for the equilibrium state of the ice cover under a given forcing. For example, in the Holocene (~8000 ybp), the Arctic Ocean likely had ice-free or near ice-free summers and temperatures were similar to, maybe still a bit higher, than Arctic temperatures in recent years. Thus, the decline we’re seeing is entirely expected and we would expect to see it continue to near-zero summer extent in the coming years. The timing is still uncertain but it changes things from an “if the Arctic loses summer sea ice” to “when the Arctic loses summer sea ice”.

Summary
Lindsay and Meier have more confidence that the current decline is unprecedented in historical context. Curry stressed the lack of data before 1979 which hampers our understanding of the state of Arctic sea ice in the past. Meier on the other hand mentioned several studies that shed light on past sea ice conditions and how they differ from the current situation. The participants agree that during the Holocene Thermal Maximum (around 8000 ybp) the Arctic likely was ice free or near ice free as well in the summer. At that time temperatures in the Arctic were similar as today or even higher.

Meier

Curry

Lindsay

The current decline in ice extent is unprecedented in the last century

5

4

5

The current decline in ice extent is unprecedented in the last two millennia

3

x

3

The current decline in ice extent is unprecedented in the Holocene

3

x

2

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

3. Is there evidence for a substantial role of natural variability?

According to Lindsay and Meier, the short answer to this question is ‘no’. Curry is far less sure about this, emphasizing our lack of knowledge about the issue. So it is fair to say that there is disagreement about this topic.
Lindsay stated: “I think we all agree that the AO (Arctic Oscillation), NAO (North Atlantic Oscillation), and PDO (Pacific Decadal Oscillation) have little role in the long-term decline. I am less certain about the AMO (Atlantic Multidecadal Oscillation), although I am inclined to think it too is a minor player.” Curry on the other hand said: “Large scale atmospheric and ocean circulations vary on multi-decadal time scales, which influence circulation regions on shorter time scales as well, which among other things influences sea ice characteristics. Untangling how all this works has received far too little attention in my opinion.”

The kick
Let’s first discuss why Meier and Lindsay don’t see a large role for natural oscillations. They acknowledge that the AO and other oscillations have influence on the sea ice but stress that this influence now seems minor. For example all three see a role for the AO when the recent decline started in the late 80s/early 90s. Curry wrote in her guest blog: “During the late 1980s and early 1990s, the circulation patterns favored the motion of older, thicker sea ice out of the Arctic. This set the stage for the general decline in Arctic sea ice extent starting in the 1990′s.” Lindsay and Meier seem to agree with this view on the decline. In a comment Lindsay wrote: “[…] I once wrote a paper that raised the question of whether a tipping point had been passed in the late 1980‘s, when the current decline in ice thickness in the arctic ocean began in earnest, coincident with a shift in the AO, a shift I called “the kick” which started the decline. Despite a return to normal AO conditions the decline continued.” And Meier in a more general explanation wrote: “For example, the AO has been observed to have a large effect on summer ice condition. When the winter AO is positive, thick ice tends to get pushed out of the Arctic through the Fram Strait, leaving a thinner ice pack the following summer that is more likely to melt completely. The converse is true for a negative AO. However, the AO typically has a 3-7 year cycle, which does not correspond to the long-term trend. In addition, in recent years, the influence of the AO appears to have been broken, or at least weakened. For example, the 2009-2010 winter had the lowest AO on record (since 1950), and yet the summer 2010 minimum was among the lowest in the satellite record[xiii].”

So the discussants agree that the AO likely played a role in the early 90s to start the decline by pushing older and thicker ice out of the Arctic through the Fram Strait. Since then the correlation between the AO and Arctic ice has diminished, convincing Meier and Lindsay it now has a smaller role. In his guest blog Lindsay wrote: “Evidence from models[xiv] indicates that the AO may not play much of a role in sea ice variability. That same study suggests that the AMO may indeed play a significant role in sea ice decline and that as much as 3%/decade of the 10%/decade trend in September sea ice extent between 1979-2010 may be due to AMO variability. There is also some observational evidence that sea ice extent may be influenced by the AMO but none of this evidence suggest that an arctic-wide change in ice extent as seen over the last decade is possible due to these type of modes of natural variability alone. It also appears ice thickness within the Arctic Ocean is less closely tied to the AMO.”

Thin ice
Meier thinks the thinner ice has a different interaction with natural oscillations. Meier: “What is different now? The ice is thinner. Thinner ice is more easily moved around and out of the Arctic, is more easily broken up into smaller floes (that are more susceptible to melt), and is more easily melted completely during summer. We’ve seen this in recent years in the Beaufort Sea. Historically, this region has been a nursery of old thick ice and the ice moved in a clockwise direction in the Beaufort Gyre aging and thickening over many years. However, in recent years, the ice in the gyre has not survived the summer. The nursery has become a graveyard. There is likely some influence of ocean waters, which may have a cyclical natural varying component, but the thinner, more broken ice is the larger factor. Our expectations for how the ice responds to natural variability is based upon a thicker ice cover, which may no longer be valid.”

Another reason Lindsay doesn’t see a large influence of natural variability is that the sea ice thickness and/or volume (the preferred metric for Lindsay) is much less influenced by natural variability than the sea ice extent. “While natural variability is very important for determining the ice extent, primarily through the action of the winds, I see a very consistent trend in the mean ice thickness with relatively little year-to-year variations. So while natural variability can strongly influence the ice area and extent, I doubt there is a strong component in the variability of the mean ice thickness within the Arctic Ocean.”

Curry on the other hand sees a large role for so called climate shifts, a concept that has recently been picked up by papers of Swanson and Tsonis[xv] and David Douglass[xvi]. These shifts are related to several natural oscillations, although the physical processes behind it are far from clear yet. In her guest blog she wrote: “In 2001/2002, a hemispheric shift in the teleconnection indices occurred, which accelerated the downward trend. A local regime shift occurred in the Arctic during 2007, triggered by summertime weather patterns conspired to warm and melt the sea ice. The loss of multi-year ice during 2007 has resulted in all the minima since then being well below normal, with a high amplitude seasonal cycle. After 2007, there was another step loss in ice volume in 2010. In 2012, the basic pattern of this new regime was given a ‘kick’ by a large cyclonic storm in early August.”

Models
Another difference of opinion is originating in the confidence one should have in models. Lindsay defends the models: “To refute the evidence from models, one would have to show that they wildly underestimate natural variability (with regard to sea ice). Even in the NCAR CCSM4 which is one of the CMIP5 models with the highest “natural” variability, the sea ice extent trend over the last 30 years is still 50% due to greenhouse gases[xvii].” Adding later: “It is possible there are large unknown sources of long-term natural variability, but I think the models and the observations show CO2 is the major cause of the decline. Other sources of large long-term variability (say 30 to 100 years) that could contribute substantially to the decline are mostly speculation.”

Curry on the other hand does indeed think that models underestimate natural variability: “The relatively high attribution to AGW comes from climate models, which have substantial problems in simulating the Arctic climate […]. Not to mention that these climate models underestimate natural internal variability on multi-decadal timescales. […] I note that my group has just submitted a paper for publication analyzing the CMIP5 simulations of arctic sea ice. I am frankly trying to figure out how these models manage to produce any kind of sensible sea ice given that most of these models are biased cold (many are biased cold by 2°C or more). Our old friend ‘model calibration’ I assume, whereby 5 wrongs might make a ‘right’.”

So pretty strong disagreement here, mainly between Lindsay and Curry. Meier gives some consolation pointing out how complicated the sea ice system and its interaction with the AO might be: “One thing that I think is clear is that the sea ice system is complicated and that many factors that influence each other are changing, making separating them out difficult. Going back to a point I made earlier, I think an intriguing aspect is how the influence of natural variability on the sea ice (and vice versa) is changing. In other words, AO affects sea ice, but how is that effect changing with a changing ice cover and are the changes in the ice in turn influence the AO?”

Summary
The discussants agree that a shift in the Arctic Oscillation (AO) in the late 80s seemed to have started the decline. A positive AO, especially in winter, pushed older thicker ice out of the Arctic through the Fram Strait. When the AO went back to normal however, the decline in sea ice continued. Meier and Lindsay conclude from this that oscillations like the AO, but also the NAO and PDO, probably played a minor role in the continuing decline. Model simulations suggest that the AMO might have contributed between 5% and 30% of the melting. Curry is not so sure about this. She mentions a hemispheric climate shift in 2001 that accelerated the decline followed by a local regime shift in 2007, that has resulted in all the minima since then being well below normal, with a high amplitude seasonal cycle. Lindsay and Meier also have more confidence in the models than Curry. Lindsay said it isn’t likely that they hugely underestimate natural variability, but this is exactly what Curry thinks the models do.

Meier

Curry

Lindsay

A shift in the AO to positive values started the decline in the early 90s

4

4

4

Now that the ice is thinner, the effect of natural oscillations is much smaller

4

3

4

Models underestimate natural variability considerably

2

5

1

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

4. What is the role of ‘global warming’?

This question is of course closely related to the question about natural variability. So the positions on this topic are similar with Lindsay and Meier seeing more evidence for a large role of global warming than Curry. This is based on evidence from both observations and models.

In his guest blog Lindsay points out that the Arctic ice trends are correlated with temperature trends on the Northern Hemisphere. “One piece of evidence […] is the high correlation (R = -0.72, 57 years through 2011) between the rate of melt (including export) in the Arctic Ocean and melt season (May to September) surface temperatures in the rest of the hemisphere, from 20N to 60N (NCEP-R1). The surface temperatures south of the Arctic are likely less influenced by ice loss and the trends are likely more influenced by global forcings. Sea ice basically responds to hemispheric conditions and is not on its own trajectory.”

Meier has similar arguments: “The evidence for a substantial role of “global warming” in the current sea ice decline comes from the fact that the decline (1) correlates with the global warming temperatures over the past several decades, (2) is outside the range of normal variability over the past several decades and likely over the past several centuries, (3) the decline is pan-Arctic, with all regions experiencing declines throughout all or most of the year.” And later in a comment: “I base my view on the decline of not only summer extent but the rapid loss of old ice and the thinning of the ice cover, along with the apparent change in the response of the ice to natural fluctuations (such as the AO mode, as I discussed in my previous comment). Of course, natural variations have played a role and will continue to do so, but I don’t see a large enough effect to account for a substantial fraction of the observed change.”

Curry stated in her guest blog that the “lack of data [before 1979] hampers our ability to test ideas on contribution of natural variability versus anthropogenic forcing on sea ice decline”. However, during the discussion and also in her blog she highlights the role of natural variability in the current sea ice decline. In her post she talks about the “basic story” as she sees it and she then sums up all kind of natural factors and shifts. This leads to the following statement about the role of global warming: “So, what is the contribution of anthropogenic global warming to all this? It’s difficult to separate it out. The polar regions are extra sensitive to CO2 forcing and water vapor feedback, owing to the low amounts of water vapor. However, any radiative forcing from greenhouse gases is swamped by inter-annual variability in cloud radiative forcing. In the bigger picture sense, greenhouse forcing is involved in complex nonlinear ways with the climate regime shifts. So there is undoubtedly a contribution from CO2 forcing, but it is difficult to find any particular signal in this year’s (2012, red.) record minimum, other than the contribution of greenhouse warming to a longer term trend.” With the last sentence Curry’s view comes closer though to that of Meier and Lindsay. She acknowledges the role of greenhouse (global) warming in the decline of Arctic sea ice, although as we will see she tends towards a lower contribution of greenhouse gases than Lindsay and Meier.

Substantial
Models again play a role in the view of Meier and Lindsay. As Meier wrote: “Also, model simulations of sea ice cover consistently show a response of declining sea ice to increasing GHGs (albeit slower than the observed decline); conversely, model runs over the last 30 years without GHG forcing do not show a decline[xviii]. Finally, there does not appear to be a mechanism to sufficiently explain the long-term decline without including the effect of GHGs[xix].”

Lindsay again is the clearest about a large role for global warming: “The evidence for a substantial role of “global warming” in the current Arctic sea ice decline is very strong, both from observations and from modeling studies. Of course neither can “prove” the role of greenhouse gases but there is overwhelming evidence it is true. […] For those that think this is not the case, they need to show some evidence that there are alternative explanations. Comparing ice volume instead of sea ice extent greatly reduces the natural variability compared to the trend and shows an earlier and more definitive separation than ice area between models run with or without increased greenhouse gas forcings[xx].”

Curry on the other hand doesn’t place a lot of trust in model simulations of Arctic climate (see section 3 above).

Summary
There is disagreement about the role of global warming. Both Lindsay and Meier sum up evidence for a large role of “global warming” in the current decline in sea ice. Lindsay mentions the good correlation with the Northern Hemispheric temperatures, showing that the sea ice is not on its own regional trajectory but follows the trend of a larger area. Meier notes the fact that the warming now is pan-Arctic and outside the range of natural variability for the last few centuries. Curry acknowledges a role for global warming to the longer term trend. But at the same time she notes that locally any radiative forcing from greenhouse gases is swamped by inter-annual variability in cloud radiative forcing.

Meier

Curry

Lindsay

The evidence for a substantial role of “global warming” in the current Arctic sea ice decline is very strong

5

4

5

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

5. Quantification of the anthropogenic contribution to sea ice decline

Curry made what she called a ‘wishy washy’ statement about the attribution of the melting to anthropogenic forcing. She wrote: “So . . . what is the bottom line on the attribution of the recent sea ice melt? My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range. Why such a ‘wishy washy’ statement with large error bars? Well, observations are ambiguous, models are inadequate, and our understanding of the complex interactions of the climate system is incomplete.”

Later in a comment she simplified this statement a bit: “I think a simpler way to look at this would be to attempt to put bounds on the AGW contribution to the recent sea ice melt. I propose a range of 30-70%. Walt and Ron seem to be above 50% but not going higher than 70%.” And in another comment she said: “If I am interpreting their [Lindsay’s and Meier’s] assessments correctly, am I correct to infer that we are all in agreement within the range of uncertainty that we would each acknowledge? The disagreement seems to arise if we are each forced to pick a single attribution value: mine would be 50%; I infer that Lindsay’s in particular would be higher. But given the uncertainties, is there any particular reason to force this level of specificity and highlight disagreements?”

Meier replied that a 50-70% would be reasonable. “The 50-70% range for GHGs that Judith mentions is probably a reasonable spread in capturing the potential range. I would lean more toward the high side of that range because I don’t see the AMO and PDO having a large magnitude influence on summer ice. The AO does have a larger influence, but that has largely been lost in recent years.”

Note that here they refer to a different range. Curry’s range is wider, 30-70%. Lindsay replied that he also accepts a large uncertainty: “I agree with Judith that the percent decline in sea ice due to greenhouse gases is rather uncertain. It depends on the time intervals considered for the base case and current state (how much natural variability is averaged out).”

Curry even added she can’t think of many or even any climate scientist that would go either above 70% or below 30%. “One of the complaints from the comments is that the scientists with ‘extreme’ views (i.e. outside of this range) were not included. I wonder if Peter Wadhams would have gone above 70%? I am trying to think of any published scientists working on sea ice or Arctic climate dynamics that would go below 30%, and I can’t think of any.” However, both Lindsay and Meier quoted Day et al (2011)[xxi] in support of their position, who estimate natural variability having caused between 5% and 30% of the decline, which would allow for the anthropogenic contribution to be up to 95%.

Lindsay separates his estimates for ice extent and ice volume, leaning towards high percentages for ice volume: “I come back to the observation that ice volume is a much more consistent measure of the ice cover, showing much less year to year variability compared to the trend than ice extent or area. The CCSM3 model, for example, shows a clear separation in ice volume between the control and the A1B scenario as early as 1985, 10 to 15 years before the separation in ice extent[xxii]. The decline in volume is consistent with the PIOMAS estimates of ice volume (which is tied to the observed past weather and ice extent), given the uncertainties in both data sources. CCSM4 simulations show about a 50% decline in ice volume since the 1960’s with a typical ensemble spread on the order of 15%, so the CCSM4 runs indicate the decline in ice volume is about 3 times the natural variability, or about 70% of the decline is due to greenhouse gases. The decline in volume seen in the PIOMAS simulations is also very consistent, particularly if one focuses just on the Arctic Ocean since the late 1980’s. So I would go on the high side of the percentage loss due to greenhouse gases for ice volume and less for ice extent, maybe near 50%.”

Speculate
Later in the discussion all three acknowledged a great deal of uncertainty when making attribution statements. Meier for example wrote: “There seems to be a lot of wrangling over exactly what fraction of the observed change is attributable to GHGs vs. natural and other human (e.g., black carbon). There is clearly still uncertainty in any estimates and the models and data are not to point where we can pin a number with great accuracy. Judith is more on the lower end, rightly pointing out the myriad natural factors. Ron and I tend toward the higher end. I base my view on the decline of not only summer extent but the rapid loss of old ice and the thinning of the ice cover, along with the apparent change in the response of the ice to natural fluctuations (such as the AO mode, as I discussed in my previous comment). Of course, natural variations have played a role and will continue to do so, but I don’t a large enough effect to account for a substantial fraction of the observed change.”

And Lindsay wrote: “About the attribution of the decline to AGW vs. natural. The fact is we don’t really know and all we can do is speculate. That is not really science. Also the question is a little ambiguous. Are we referring to a linear trend, and if so over what period, or to a change for a particular year and against what base line? Do we assume natural variability is only contributing to the decline, or might it also slow it? So trying to put definite numbers on the ratio for the observed climate, even the uncertainty, is likely a futile effort. This can be done for ensemble model simulations of the climate, with all of the caveats that go with such studies, and the answer is a statistical summary for the model used, not a real-world analysis.”

Curry defended her focus on uncertainty by saying that “[…] when my uncertainty level seems higher than others, it is because I have a longer list of known unknowns than most others, which is traced back to my own publications and my service on the committees listed above.”

Summary
The participants agree it is unlikely the contribution of greenhouse gases to the recent decline is lower than 30%. Curry even said she wouldn’t know any publishing climate scientist going lower than 30%. Curry proposed a range of 30 to 70% greenhouse gas contribution to the recent decline in sea ice extent. Her best estimate would be 50%. Lindsay agreed with this best estimate of 50% for extent. He added though that sea ice volume is his preferred metric because it shows less year to year variability. For sea ice volume he would go higher, say 70%. Meier proposed a smaller range of 50 to 70%.

Meier
%

Curry
%

Lindsay
%

What is your preferred range w.r.t. the contributions of anthropogenic forcing to the decline in sea ice extent?

50-95%

30-70%

30-95%

What is your preferred range w.r.t. the contributions of anthropogenic forcing to the decline in sea ice volume?

50-95%

30-70%

30-95%

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)

6. Could the Arctic be ice free in the near future?

Meier explained why he is not very enthusiastic about Peter Wadhams’ prediction that the Arctic could be ice free within a few years. “While I won’t totally dismiss the possibility, I think it is a very low probability event. My rationale is that getting there relies on continuing to lose volume at the same rate as we’ve done over the last decade or so. I think there are a couple of very good reasons why this is unlikely. First, as Judith has particularly noted, there have been some extreme events in recent years that have helped kick down the summer ice and remove old ice. While I think there is room to debate how large of an effect these have had, we can’t depend on such events to happen in a timely manner in the next few years. But the larger reason for my doubts is that the rapid losses have come from the Siberian and Alaskan regions of the Arctic. The region along northern Greenland and Canadian Archipelago have not lost much summer ice – for good reason. The predominant ice circulation pushes ice toward those coasts resulting in thick ice that tends to get replenished. In other words, we’ve seen a rapid decline in the “easy” ice to lose, but now we’re getting to the “more difficult” ice. I think it’s likely that that will go more slowly.”

Although Lindsay agrees with Meier about the ‘Wadham hypothesis’, he does think the summers could be ice free within a decade or two. “The Arctic will likely be largely ice free at the end of some summers within a decade or two. Small bits of ice might remain some years, but they may not matter for much.”

Not surprisingly Curry is most reluctant in providing an estimate. She writes in her blog that: “prediction of sea ice is hostage to predictions of the chaotic atmospheric and oceanic dynamics.” In a comment she writes: “Pretending that extrapolating an observed trend or that CMIP5 simulations will produce a useful decadal prediction of sea ice is pointless (well there is a potential point but it is to mislead).” And in a comment to James Annan: “My point is that I don’t know with any high level of confidence what the sea ice will look like in 10 years or 100 years.” And finally she concludes that: “On timescales of two decades, I expect the natural variability to dominate, and this could still take us in either direction (more or less ice).”

Definition
Curry was also a bit annoyed about the generally accepted definition of ice-free. “[…] ‘ice free’ is usually taken to mean less than 1 million sq. km. This is far from ‘ice free’ in actuality (I find this use of ‘ice free’ to be highly misleading). So what is the point of talking about some sort of ‘tipping’ point, when even during summer, the Arctic Ocean is not really projected to be ice free?”

Following up from Curry in regards to what “ice-free” means, Meier agreed that this isn’t a particularly well-defined term, but he thinks it is nonetheless useful for thinking about changes in the ice cover and its impact. “It will indeed be difficult to reach completely ice-free (zero) ice because of the geography and dynamics of the system. Semi-enclosed bays and channels (e.g., the Canadian Archipelago) are more resilient to break-up and melt and, as I mentioned a previous post, the Greenland side of the Arctic gets replenished by ice moving across from Siberia. This ice can pile up into thick (several meters) ridges that are difficult to break up and melt completely.” Curry agrees: “This definition is used because it is very difficult to melt the thick ice around the Canadian Archipelago. And the issue of ‘ice free’ in the 21st century is pretty much a non-issue if your require this thick ice to disappear.”

For practical purposes Meier still thinks the definition is valid. “Instead of simply saying “ice-free”, my views is that it should be described as “ice-free for all practical purposes”. To me this means: seeing blue instead of white throughout the Arctic Ocean (except along the coasts), allowing ships to operate within the Arctic Ocean with little chance of seeing substantial ice, having a significant effect on the Arctic ecosystem, and having a significant effect on Arctic. (The last two are likely already occurring.) […] So I’m not worried too much about what we mean by “ice-free” or what specific number we put on it – that’s for gamblers placing bets to quibble about.”

Tipping point
The discussants agree there doesn’t seem to be a tipping point and that sea ice could recover pretty soon if the circumstances are right. Lindsay: “Current research does not support the notion of any “tipping” points for summer sea ice so if we somehow magically could turn off the forcing that comes from greenhouse gases, sea ice would likely grow back relatively quickly. Unfortunately that is not likely to happen. Winter ice will remain for a long time, a century or more. How long probably depends mostly on the future rate of greenhouse gas emissions.” And later in a comment: “I now believe a tipping point for summer sea ice is not a good way to characterize the system. The sea ice in the Arctic responds to global forcing in the atmosphere and ocean and is not on its own trajectory. A number of studies have supported this conclusion.” Curry wrote something similar: “The first issue to debunk is that an ‘ice free’ Arctic is some sort of ‘tipping point.’ A number of recent studies find that in models, the loss of summer sea ice cover is highly reversible.”

Also Meier and Lindsay point out that we might have several years with low ice-extent (or even near ice free conditions) followed by years with a higher extent, implicating that a ‘first’ year of being ice-free is not particularly meaningful. Meier indicates in his blog that IPCC models that match historical records indicate ice-free conditions in 2030-2050.

For the near future anything can happen according to Curry: “Whereas sea ice models are becoming quite sophisticated, most recently in terms of the radiative transfer, melt ponds, and aerosols, prediction of sea ice is hostage to predictions of the chaotic atmospheric and oceanic dynamics. For the next two decades, natural variability will almost certainly trump any direct effects from anthropogenic warming by a long shot. The current sea ice situation does not seem stable, but it is not at all clear whether we can expect a reversion to the (more recently) normal state or yet a larger ice loss.” And then, Curry adds, there are the known unknowns: “what solar radiation will do (looks like cooling), volcanoes are always a wild card, and then there are the less known unknowns such as cosmic ray effects, magnetic field effects, etc. And in terms of climate shifts, there may be something happening on much longer time scales (e.g. the Atlantic Meridional Overturning Circulation) that could influence the next climate regime shift. Focusing on CO2 as the dominant influence on the time scale of two decades seems very misguided to me.”

Lindsay though thinks the CO2 induced global warming will continue to cause a decline in the ice volume, even on a time scale of a decade or two. “I agree with Walt that the summer ice will come and go for a number of years, depending on the weather and the winds, but when it first goes to near zero is quite hard to predict.”

Meier “wholeheartedly” agrees with Curry that decadal prediction of sea ice is going be very difficult. “I have been involved in several meetings about the issue including the one that is the basis of the NRC report Judith references (Ron was also a participant). I will note that among those most skeptical of the models’ capability to capture decadal variability are the modelers themselves.”

The discussants agree that for a long time the Arctic will refreeze in winter. Curry notes that “sea ice would continue to freeze and thaw on an annual cycle”. Later in a comment she explains: “The massive cooling during the polar night causes substantial heat loss, which on land results in surface temperatures of -40°C and colder. Sea water in the Arctic Ocean freezes at a temp slightly warmer than -2°C. The only conceivable way to keep the Arctic Ocean ice free is to bring in much warmer ocean water from lower latitudes. Unless the geography of the Arctic basin dramatically changes, e.g. Alaska disappears, there is no way for this to happen. I don’t think that anyone would dispute these points.” Lindsay: “Winter ice will remain for a long time, a century or more. How long probably depends mostly on the future rate of greenhouse gas emissions.”

Summary
None of the participants is very enthusiastic about the idea that the Arctic could be ice free in the summer within a few years. Meier explained that so far the “easy” ice has melted but that now we’re getting to the “more difficult” ice north of Greenland en the Canadian Archipelago. “The predominant ice circulation pushes ice toward those coasts resulting in thick ice that tends to get replenished.”
Lindsay is most confident that even on a time scale of one or two decades greenhouse forcing should cause a further decline. Curry emphasized that on this time scale natural fluctuations will dominate the effect of CO2. For her a reverse of the trend is therefore possible. Meier “wholeheartedly” agreed with Curry that decadal prediction of sea ice is going be very difficult.
Curry stated that the currently used definition of “ice free” (being less than 1 million km2 of ice) is misleading as it is not really ice free. Meier defended the definition as being valid for all practical purposes like ship navigation, the albedo feedback and impacts on the ecosystem.
None of the participants believe in a tipping point. Lindsay noted that if we magically could turn off the forcing the sea ice could recover pretty quickly. Lindsay: “Unfortunately that is not likely to happen.”

Meier

Curry

Lindsay

The Arctic could be ice-free in a few years

1

1

1

The sea ice could (partly) recover in the next two decades due to natural variability

2

3

1

What is the most likely period that the Arctic will be ice free for the first time?

2030-2050

x

2020-2050

Scores (don’t know=x, very unlikely=1, unlikely=2, as likely as not=3, likely=4, very likely=5,)



[i] http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/

[ii] Arbetter, T., J.A. Curry, M.M. Holland, and J. M. Maslanik, 1997: Response of sea ice models to perturbations in surface heat flux. Ann. Glaciol., 25, 193-197.

[iii] http://www.chrispolashenski.com/docs/a57a188.pdf. Note Figure 1

[iv] Steele et al., 2010, http://www.agu.org/pubs/crossref/2010/2009JC005849.shtml

[v] Look at August and September ocean temperature data (from M. Steele and colleagues) here: http://psc.apl.washington.edu/UpTempO/Data.php

[vi] Perovich, D. K., S. V. Nghiem, T. Markus, and A. Schweiger (2007), Seasonal evolution and interannual variability of the local solar energy absorbed by the Arctic sea ice–ocean system, J. Geophys. Res., 112, C03005, doi:10.1029/2006JC003558

[vii] http://curry.eas.gatech.edu/currydoc/Schramm_JGR102.pdf

[viii] John Walsh presentation: http://nsidc.org/noaa/iicwg/presentations/IICWG_2011/Fetterer_Back_to_1870_Plans_for_a_Gridded_Sea_Ice_Product.pdf

[ix] Mahoney, A. R., R. G. Barry, V. Smolyanitsky, and F. Fetterer (2008), Observed sea ice extent in the Russian Arctic, 1933–2006, J. Geophys. Res., 113, C11005, doi:10.1029/2008JC004830.

[x] http://nsidc.org/data/docs/noaa/g02203-dmi/

[xi] Kinnard, C., C. Zdanowicz , D Fisher, and E. Isaksson, 2011: Reconstructed changes in Arctic sea ice over the past 1,450 years, Nature, 509-512, doi 10.1038/nature10581.

[xii] Polyak, L., and several others (2010), History of sea ice in the Arctic, Quaternary Sci. Rev., 29, 1757-1778, doi: 10.1016/j.quascirev.2010.02.010.

[xiii] Stroeve, J. C., J. Maslanik, M. C. Serreze, I. Rigor, W. Meier, and C. Fowler (2011), Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010, Geophys. Res. Lett., 38, L02502, doi:10.1029/2010GL045662.

[xiv] Day, J.J., J.C Hargreaves, J.D. Annan, and A. Abe-Ouchi (2012), Sources of multi-decadal variability in Arctic sea ice extent, Env. Res. Lett., 7, 034011, doi: 10.1088/1748-9326/7/3/034011.

[xv] Tsonis, Anastasios A., Kyle Swanson, and Sergey Kravtsov. "A new dynamical mechanism for major climate shifts." Geophysical Research Letters 34.13 (2007): L13705.

[xvi] http://judithcurry.com/2011/11/30/shifts-phase-locked-state-and-chaos-in-climate-data/

[xvii] Kay, J. E., M. M. Holland, and A. Jahn (2011), Inter-annual to multi-decadal Arctic sea ice extent trends in a warming world, Geophys. Res. Lett., 38, L15708, doi:10.1029/2011GL048008.

[xviii] Stroeve, J., M.M. Holland, W. Meier, T. Scambos, and M. Serreze (2007), Arctic sea ice decline: Faster than forecast, Geophys. Res. Lett., 34, L09501, doi:10.1029/2007GL029703 and Stroeve, J.C., V. Kattsov, A. Barrett, M. Serreze, T. Pavlova, M. Holland, and W.N. Meier (2012), Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations, Geophys. Res. Lett., 39, L16502, doi:10.1029/2012GL052676.

[xix] Notz, D. and J. Marotzke (2012), Observations reveal external driver for Arctic sea-ice retreat, Geophys. Res. Lett., 39, L08502, doi:10.1029/2012GL051094.

[xx] Schweiger, A., R. Lindsay, J. Zhang, M. Steele, H. Stern, and R. Kwok. 2011. Uncertainty in Modeled Arctic Sea Ice Volume. J. Geophys. Res., doi:10.1029/2011JC007084

[xxi] Day, J.J., J.C Hargreaves, J.D. Annan, and A. Abe-Ouchi (2012), Sources of multi-decadal variability in Arctic sea ice extent, Env. Res. Lett., 7, 034011, doi: 10.1088/1748-9326/7/3/034011

[xxii] Schweiger, A., R. Lindsay, J. Zhang, M. Steele, H. Stern, and R. Kwok. 2011. Uncertainty in Modeled Arctic Sea Ice Volume. J. Geophys. Res., doi:10.1029/2011JC007084

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Expert comments to Melting of the Arctic sea ice

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  • Marcel Crok

    Thank you Walt Meier, Judith Curry and Ron Lindsay for participating in this first discussion on Climate Dialogue.

  • Judith Curry

    I’ll kick off the discussion, focusing on the follow question:

    5) What percentage of the recent decline would you attribute to anthropogenic greenhouse gases?

    In my essay, I state:
    My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range. Why such a ‘wishy washy’ statement with large error bars? Well, observations are ambiguous, models are inadequate, and our understanding of the complex interactions of the climate system is incomplete.

    Walt Meier states:
    It is difficult to put a precise number on how much of the decline is due to GHGs. There is strong natural variability, which is seen in observations and in model simulations. It is likely that at least some of the acceleration of the loss of sea ice in the past ~10 years is due to natural variability. A modeling study [14] suggested that about half of the observed September sea ice trend from 1979-2005 could be explained by natural variability, with the rest attributable to GHGs. There may also be some influence of black carbon, though how much is unclear.

    Ron Lindsay states:
    I believe fundamentally the main process causing the decline in Arctic sea ice is increasing greenhouse gases. While natural variability is very important for determining the ice extent, primarily through the action of the winds, I see a very consistent trend in the mean ice thickness with relatively little year-to-year variations. So while natural variability can strongly influence the ice area and extent, I doubt there is a strong component in the variability of the mean ice thickness within the Arctic Ocean. There is also some observational evidence that sea ice extent may be influenced by the AMO but none of this evidence suggest that an arctic-wide change in ice extent as seen over the last decade is possible due to these type of modes of natural variability alone.

    From these statements by Meier and Lindsay, it seems that neither of them would state that there is high confidence that AGW is responsible for more than 70% of the recent melting of the sea ice? I also infer from both Meier’s and Lindsay’s statement that they would rule out with high confidence and attribution from AGW that is less than 50%?

    If I am interpreting their assessments correctly, am I correct to infer that we are all in agreement within the range of uncertainty that we would each acknowledge? The disagreement seems to arise if we are each forced to pick a single attribution value: mine would be 50%; i infer that Lindsay’s in particular would be higher. But given the uncertainties, is there any particular reason to force this level of specificity and highlight disagreements?

    • Ron Lindsay

      I agree with Judith that the percent decline in sea ice due to greenhouse gases is rather uncertain. It depends on the time intervals considered for the base case and current state (how much natural variability is averaged out).

      I think we all agree that the AO, NAO, and PDO have little role in the long-term decline. I am less certain about the AMO, although I am inclined to think it too is a minor player. The Day et al. (2012) study suggests a contribution on the order of +/- 0.5 M km^2 for sea ice extent so a reversal in the AMO probably won’t reverse the ice decline. But given the small amount of heat needed to melt the ice at the rate we have seen (less than 0.5 W/m2 annual average), is it a hopeless task to find a definitive mechanism, particularly since the dominant forcing for ice anomalies likely changes from year to year?

  • Walt Meier

    I agree with both Judith and Ron that there is still fairly high quantitative uncertainty in terms of the amount of influence of greenhouse gases. But I think we’re all in agreement that GHGs are playing a significant, but not exclusive, role in the long-term decline of Arctic sea ice with the magnitude of the decline is enhanced to some degree by natural variability. What the balance is between these two influences is still a largely open question.

    The 50-70% range for GHGs that Judith mentions is probably a reasonable spread in capturing the potential range. I would lean more toward the high side of that range because the I don’t see the AMO and PDO having a large magnitude influence on summer ice. The AO does have a larger influence, but that has largely been lost in recent years.

    One final comment on Judith’s about the data. While our most complete dataset, the one we have the highest confidence in, is the passive microwave record, there is fairly complete coverage from operational ice charts back to at least the mid-1950s. And there are Russian ice charts for the Eurasian Arctic back to the early 1930s. Though not complete, these do extend the record and I think provide some sense of the interannual and decadal natural variability of the ice. There are indications of lower ice in the 1930s in the Russian Arctic [Reference 4 in my post], suggesting the influence (AMO?) of a multi-decadal cycle, at least in the Russian Arctic. But the data show a different character in terms of the seasonality and regionality of the lower ice conditions compared to the recent decline.

  • Marcel Crok

    Hi Judith, Walt and Ron,
    many thanks for your first comments, which focus on one of the crucial questions, i.e. what is the contribution of greenhouse gases to the decline in Arctic sea ice.
    At first sight there doesn’t seem to be much disagreement between the three of you. Ron doesn’t mention a specific percentage in his comment, but in his guest blog he wrote: “I believe fundamentally the main process causing the decline in Arctic sea ice is increasing greenhouse gases.” Walt refers to the 50-70% range of Curry and that he would lean towards the high side.

    However I would first like to go back to Judith’s “wishy washy statement”:
    “My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range. Why such a ‘wishy washy’ statement with large error bars? Well, observations are ambiguous, models are inadequate, and our understanding of the complex interactions of the climate system is incomplete.”

    Now what exactly does this mean? Does it mean that there is a 2/3 chance that the range is anywhere between 30% GHG/70% Natural Variability (NV) and 70% GHG/30% NV? And there is a 1/3 likelihood it’s outside that range? Would Judith say that outside this range there is also a 50-50 split? In the sense that it is as likely the GHG contribution is lower than 30% or higher than 70%?
    I ask this because the rest of your (Judith’s) article mentions a lot of factors that you could summarize as “natural”. For example you wrote:
    “Here’s the basic story as I see it. During the late 1980s and early 1990s, the circulation patterns favored the motion of older, thicker sea ice out of the Arctic. This set the stage for the general decline in Arctic sea ice extent starting in the 1990′s. In 2001/2002, a hemispheric shift in the teleconnection indices occurred, which accelerated the downward trend. A local regime shift occurred in the Arctic during 2007, triggered by summertime weather patterns conspired to warm and melt the sea ice. The loss of multi-year ice during 2007 has resulted in all the minima since then being well below normal, with a high amplitude seasonal cycle. After 2007, there was another step loss in ice volume in 2010. In 2012, the basic pattern of this new regime was given a ‘kick’ by a large cyclonic storm in early August.”

    Nowhere in this basic story you talk about greenhouse gases. I read about circulation patterns, a hemispheric shift in 2001 (is this the shift that Swanson/Tsonis published about?), a local regime shift in 2007, summertime weather patterns and then finally a large cyclonic storm in 2012. So where in this basic story fits CO2/GHG’s? So I get the feeling you’re more inclined towards a low contribution of CO2 than a high contribution, is that correct? Can you explain why GHG’s play no role in your basic story?

    Would be nice to get a reaction first of Judith and then of Ron and Walt.

    Thanks, Marcel

  • Judith Curry

    Marcel,

    I think it a simpler way to look at this would be to attempt to put bounds on the AGW contribution to the recent sea ice melt. I propose a range of 30-70%. Walt and Ron seem to be above 50% but not going higher than 70%.

    One of the complaints from the comments is that the scientists with ‘extreme’ views (i.e. outside of this range) were not included. I wonder if Peter Wadhams would have gone above 70%? I am trying to think of any published scientists working on sea ice or Arctic climate dynamics that would go below 30%, and I can’t think of any.

    In terms of the climate shift paradigm, the AGW projects onto the natural internal modes, and hence contributes but is not easily separable from the natural variability. Note this paradigm is different from a secular warming trend superimposed on the large natural modes (e.g. AMO, PDO).

    Perhaps the more interesting issue is projecting the sea ice behavior forward in time. I think this is where you will find broader differences among members of the arctic climate dynamics community. While I have a very high opinion of the best sea ice models used in GCMs (e.g. CICE), the problem is with the atmosphere and ocean dynamics/thermodynamics in the Arctic. So I don’t have much faith in the climate model projections of sea ice. Alternatives include persistence (extrapolating current or longer range trends) or a climate dynamics approach (which is hampered by inadequate data in the early part of the century). On timescales of two decades, I expect the natural variability to dominate, and this could still take us in either direction (more or less ice.)

  • Walt Meier

    Following up from Judith’s comments:

    I agree that forced change (from GHGs) is intermixed with natural variability and separating out the two is difficult. And there interplay between the two, which I think is important because the impact of the natural variability on the ice may be changing as the ice changes in response to GHGs. For example, the AO has been observed to have a large effect on summer ice condition. When the winter AO is positive, thick ice tends to get pushed out of the Arctic through Fram Strait, leaving a thinner ice pack the following summer that is more likely to melt completely. The converse is true for a negative AO.

    Looking at plots of AO mode and September ice extent, the correlation is pretty good…until the early 2000s. Since then, the ice has continued downward even when the AO went strongly negative in the 2009/2010 and 2010/2011 winters.

    Similarly, we had a cold winter in the Bering Sea and a very late melt this past spring (perhaps related to the PDO). My thought was this year might be a relatively high year compared to recent years because that slow melt would impede later melt in the Beaufort and Chukchi Seas. But that did not happen. The August storm did help, as Judith mentioned earlier, but even without that storm we were heading toward a record or near-record low.

    What is different now? The ice is thinner. Thinner is more easily moved around and out of the Arctic, is more easily broken up into smaller floes (that are more susceptible to melt), and is more easily melted completely during summer. We’ve seen this in recent years in the Beaufort Sea. Historically, this region has been a nursery of old thick ice and the ice moved in a clockwise direction in the Beaufort Gyre aging and thickening over many years. However, in recent years, the ice in the gyre has not survived the summer. The nursery has become a graveyard. There is likely some influence of ocean waters, which may have a cyclical natural varying component, but the thinner, more broken ice is the larger factor.

    Our expectations for how the ice responds to natural variability is based upon a thicker ice cover, which may no longer be valid.

    I think this is one complicating reason why there is so much uncertainty in the proportion of human vs. natural influence and in what the future holds.

    My view of the future is that there will be increased variability in the ice pack and thus less predictability, at least for a time. When we reach “ice-free” conditions (i.e., <1 million sq km) is almost a moot point because that doesn't represent a point-of-no-return. The following year would likely have more ice and there will probably be a see-saw of very low vs. somewhat higher extents depending on the weather conditions. Even when first reach such conditions is uncertain due to such factors - how many storms will we get at key periods of the melt season, when will we have a strong AO winter that advects a lot of ice out during a winter, etc.?

    This is why projections from people like Peter Wadhams (who I agree would've been an interesting person to contribute) are not out of the realm of possibility even though I think they are highly unlikely. Nor would I disagree with Judith's comment that she doesn't have much confidence in projections in current projections

    By the way, I just saw that Peter Wadhams has an article in the upcoming issue of Scientific American, online here:

    http://www.scientificamerican.com/article.cfm?id=geoengineering-last-chance-save-sea-ice

    His comment on the latent heat physics is interesting, which may be an interesting jumping off point for another round of comments.

  • Ron Lindsay

    Estimates of the amount of sea ice decline due to greenhouse gases must come from models, and as Judith points out there are some uncertainties, but they are all we have … and they have a chance of being too conservative as well as too sensitive. I come back to the observation that ice volume is a much more consistent measure of the ice cover, showing much less year to year variability compared to the trend than ice extent or area. The CCSM3 model, for example, shows a clear separation in ice volume between the control and the A1B scenario as early as 1985, 10 to 15 years before the separation in ice extent (Schweiger et al 2011). The decline in volume is consistent with the PIOMAS estimates of ice volume (which is tied to the observed past weather and ice extent), given the uncertainties in both data sources. CCSM4 simulations show about a 50% decline in ice volume since the 1960’s with a typical ensemble spread on the order of 15%, so the CCSM4 runs indicate the decline in ice volume is about 3 times the natural variability, or about 70% of the decline is due to greenhouse gases. The decline in volume seen in the PIOMAS simulations is also very consistent, particularly if one focuses just on the Arctic Ocean since the late 1980’s. So I would go on the high side of the percentage loss due to greenhouse gases for ice volume and less for ice extent, maybe near 50%.

    It is possible there are large unknown sources of long-term natural variability, but I think the models and the observations show CO2 is the major cause of the decline. Other sources of large long-term variability (say 30 to 100 years) that could contribute substantially to the decline are mostly speculation. I also think the CO2 induced global warming will continue to cause a decline in the ice volume, even on a time scale of a decade or two. I agree with Walt that the summer ice will come and go for a number of years, depending n the weather and the winds, but when it first goes to near zero is quite hard to predict.

  • Judith Curry

    I have been asked by the moderator to comment on James Annan’s comment

    “Curry’s “attribution” statement implies that she believes the forced component to be about half of the recent trend, with natural contributing an equal amount.

    Under the reasonable assumption that the forced trend will stay roughly constant, and that natural contribution can be either sign, she is expecting the future observed trend to be half the historical one, albeit with substantial uncertainty.

    I think this is obviously nonsensical, it is certainly contrary to all published research in this area, and call upon her to either withdraw her statement, or clarify how I have misunderstood it (and to be precise, let’s hear her prediction for future trend in Arctic sea ice), or
    Justify it with reference to quantitative analysis.”

    I find this comment and inferences to be incomprehensible. As a challenge from a climate researcher (rather than an anonymous commenter), I find it to be very poorly argued and of a tone that does not promote reasoned dialogue. But since I have been asked by the moderator to respond, I will.

    I refer James Annan to read my published papers on Arctic sea ice and climate dynamics at the link provided in my biosketch, and also my 3 more extensive blog posts on this topic.

    The relatively high attribution to AGW comes from climate models, which have substantial problems in simulating the Arctic climate, among other issues that I have discussed at length elsewhere. Further, none of these future projections consider alternative scenarios of solar and volcanic forcing. Not to mention that these climate models underestimate natural internal variability on multidecadal timescales. So exactly why should I believe climate model simulations as a basis for future projections of sea ice extent? I note that my group has just submitted a paper for publication analyzing the CMIP5 simulations of arctic sea ice. I am frankly trying to figure out how these models manage to produce any kind of sensible sea ice given that most of these models are biased cold (many are biased cold by 2C or more). Our old friend ‘model calibration’ I assume, whereby 5 wrongs might make a ‘right.’

    My point is that I DONT KNOW with any high level of confidence what the sea ice will look like in 10 years or 100 years. If all other things remain the same as the period 1980-2000, plus additional greenhouse forcing, then yes the ice extent will shrink. Do I think that all other things will remain the same as the period 1980-2000? almost certainly not: we have seen a shift to the cool phase of the PDO and most projections are for reduced solar forcing. Further, the response of the climate is not linear with external forcing, so making projections on timescales less than 50 years solely on the basis of greenhouse forcing is unjustified

    Go back and read my paper Reasoning About Climate Uncertainty. http://www.climateaccess.org/sites/default/files/Curry_Reasoning%20about%20climate%20uncertainty.pdf
    I know you have read it once, please read it again.

    I know you are also not a fan of the Italian Flag. But the error in reasoning that you are making is to assume that a collection of publications that find a large contribution of AGW to sea ice melting means that this must be correct and that scientists should accept it as such. There is a great deal of ignorance on this subject: inadequate data prior to 1979, imperfect models, and incomplete understanding of the complex radiation and climate dynamics environment of the Arctic.

    As an example of the latter, in Peter Wadhams Scientific American article, he suggests geoengineering to modify the arctic clouds to keep the ice cool during summer. A very scary thing to do. If these were subtropical stratocumulus clouds over the ocean, then we have a pretty good idea that seeding the clouds would decrease the solar radiation reaching the ground. The situation is very different in the arctic, largely owing to the low sun elevation and the high surface albedo. In fact, for all but about ~2 months of the year, more liquid in the clouds would actually act to warm the sea ice surface. For background, I have published a number of papers on this issue, here are a few:
    http://curry.eas.gatech.edu/currydoc/Curry_JC5.pdf
    http://curry.eas.gatech.edu/currydoc/Benner_JGR106.pdf

    My point is that I feel that I have a fairly deep understanding of the dynamics and thermodynamics of sea ice, the radiative environment of the Arctic, and the regional climate dynamics of the Arctic and how it interacts with the global climate. The depth of my understanding is relative to other people; in terms of absolute understanding I acknowledge a great deal of uncertainty and ignorance (i.e. the white part of the italian flag).

  • Marcel Crok

    This is a comment from Bart Verheggen, who is a member of the Advisory Board of Climate Dialogue.

    Judith,
    In your answer to James Annan, you refer to predictions of a decreasing solar forcing and a cool phase of the PDO as reasons to expect the natural component of the ice shrinkage to decrease. This would mean, as Annan alluded to, that you predict ice loss in coming decades to be relatively less than in the past few decades (i.e. for the Arcit sea ice loss to decelerate), is that correct?

    However, solar forcing and PDO behavior are both very hard to predict, and changes therein of a similar nature as in the past century will most likely not have a large effect on temperature (see e.g. Feulner and Rahmstorf, 2010 on solar; http://skepticalscience.com/Pacific-Decadal-Oscillation.htm on PDO).

    You also state deep uncertainty as a reason for your 50-50 attribution (natural-anthropogenic). But uncertainty itself does not translate automatically into a 50-50 split (or any other particular split). What is the quantitative basis or evidence for your 50-50 assessment?

    Walt Meier and Ron Lindsay both state that according to them the
    anthropogenic influence is dominant (citing Day et al and Kay et al,
    who estimate 70-95% and ~50% anthropogenic, resp, where Lindsay deems
    the latter to be an overestimate)

    To them I would like to ask: What is your estimate of (or range for)
    the anthropogenic contribution to the decline in Arctic sea ice?

  • Judith Curry

    Bart,

    The US NRC recently published a new study on Seasonal to Decadal Predictions of Sea Ice: Challenges and Strategies
    http://www.nap.edu/catalog.php?record_id=13515

    Some excerpts:

    “At longer (decadal and greater) timescales, the role of trends in external forcings (e.g.,
    increasing greenhouse gases) and of factors that control the forcings is likely to provide some
    predictive potential because they account for increasingly large fractions of the change from
    present sea ice conditions. A critical point of uncertainty remains regarding the timescale at
    which a transition occurs between these two regimes, and there is likely to be an intermediate
    timescale for which the potential predictability is low. The primary challenge at these longer
    timescales is – improving the ability to simulate realistic forcings by the atmosphere and ocean
    using coupled climate models at decadal timescales, and to identify the model variable and/or
    processes that contribute to unrealistic simulations.

    In light of these challenges and while recognizing that there are limitations in current
    modeling and observational techniques, the committee offers possible strategies to significantly
    enhance our understanding and predictions of the Arctic sea ice cover over seasonal-to-decadal
    timescales (one of the recommendations):
    • Enhance the capabilities of numerical models through a coordinated experiment with
    multiple models to (a) identify which variables and processes are critical to simulating a
    realistic ice cover, (b) determine the sources of climate model drift, and (c) guide
    decisions regarding high-priority model development needs and the expansion of models
    to include additional capabilities and variables of interest to stakeholders”

    Basically, we don’t know how to make decadal predictions of sea ice. The problem just isn’t with sea ice, but GCM’s have been shown to basically have no skill on decadal predictions of regional climate change.

    Pretending that extrapolating an observed trend or that CMIP5 simulations will produce a useful decadal prediction of sea ice is pointless (well there is a potential point but it is to mislead).

    Recent published estimates of attribution of sea ice melt range from 5-40%. These estimates do not include solar cooling or account for the shift to the cool phase of the PDO and a like shift to the cool phase of the AMO. Since all of these lean towards cooling, I drop the AGW attribution to 50% with a large error bar.

  • Walt Meier

    A couple thoughts on the recent posts, both by Judith and Ron, and the public:

    There seems to be a lot of wrangling over exactly what fraction of the observed change is attributable to GHGs vs. natural and other human (e.g., black carbon). There is clearly still uncertainty in any estimates and the models and data are not to point where we can pin a number with great accuracy. Judith is more on the lower end, rightly pointing out the myriad natural factors. Ron and I tend toward the higher end. I base my view on the decline of not only summer extent but the rapid loss of old ice and the thinning of the ice cover, along with the apparent change in the response of the ice to natural fluctuations (such as the AO mode, as I discussed in my previous comment). Of course, natural variations have played a role and will continue to do so, but I don’t a large enough effect to account for a substantial fraction of the observed change.

    I wholeheartedly agree with Judith that decadal prediction of sea ice is going be very difficult. I have been involved in several meetings about the issue including the one that is the basis of the NRC report Judith references (Ron was also a participant). I will note that among those most skeptical of the models’ capability to capture decadal variability are the modelers themselves.

    There is great interest in decadal prediction by many groups – the U.S. Defense Department (what vessels need to be built in the next decade to patrol the Arctic), oil/gas companies (when/where can drilling be safely done), shipping companies (where/when can navigation be safely conducted) native populations (how will changing ice affect communities). There is also interest of course in the climate community, though less so based on my impression. This is because the climate focus is more multi-decadal and on such a timeframe, GHGs will be dominant.

  • Walt Meier

    Addressing some of the reader comments:

    One general thing I’ve seen is a question of balance, both in comments here and in post about this forum on RealClimate. One thing is notice is that there is criticism from both sides – that Judith, Ron and I are tilted too far toward acceptance of anthropogenic influence and those that think we are not tilted far enough. In my experience, this often means you got it about right.

    Those who think we are tilted too far toward an anthropogenic influence seem to be criticizing that we all accept such an influence and that there should be a contributor who does not. However, this is a scientific discussion. In science not all views are equally valid. A valid view must be backed by evidence. A view that anthropogenic GHGs do not influence climate is simply not supported by the evidence. I’m not going to go into detail, but there are myriad lines of evidence: the physical/chemical properties of GHGs, the paleoclimate record, the modern observational record, and climate models.

    As an example, I’ll note Douglas Keenan’s comment, 2012-11-14 21:08, that a significant trend in Arctic sea ice has not been demonstrated. This is wrong. Statistical significance tests have been conducted by numerous people (including myself) and trends are strongly significant at >99% confidence levels. Even breaking things into regions and months yields strongly significant trends in almost all regimes (the Bering Sea during winter months being the primary exception). These significance tests have not always accounted for autocorrelation, which does reduce significance, but auotcorrelation in the observational record is low (0.1 according to Stroeve et al., 2012 [my reference 8]) and thus has a minimal effect on the significance.

    On the “not tilted far enough” side, the main criticism seems to be that none of us (Judith, Ron, and I) are very enthusiastic for predictions that summer ice will be gone within the next few years (the “Wadhams hypothesis”). While I won’t totally dismiss the possibility, I think it is a very low probability event. My rationale is that getting there relies on continuing to lose volume at the same rate as we’ve done over the last decade or so. I think there are a couple very good reasons why this is unlikely. First, as Judith has particularly noted, there have been some extreme events in recent years that have helped kick down the summer ice and remove old ice. While I think there is room to debate how large of an effect these have had, we can’t depend on such events to happen in a timely manner in the next few years. But the larger reason for my doubts is that the rapid losses have come from the Siberian and Alaskan regions of the Arctic. The region along northern Greenland and Canadian Archipelago have not lost much summer ice – for good reason. The predominant ice circulation pushes ice toward those coasts resulting in thick ice that tends to get replenished. In other words, we’ve seen a rapid decline in the “easy” ice to lose, but now we’re getting to the “more difficult” ice. I think it’s likely that that will go more slowly.

  • Rob van Dorland

    Thanks Judith Curry, Walt Meier and Ron Lindsay for pointing out your view points and interaction so far.

    You seem to agree it is very complicated to put a number on the anthropogenic contribution in the sea ice decline. Nevertheless, you do have different positions in the debate. To summarize: Judith uses a wide range of 30-70 percent but in her story she focuses on the natural factors causing the decline and the uncertainty that almost prohibits to do a meaningful estimate. Also she believes that in the next two decades natural factors will be much more important than GHGs. Walt seems to believe that 50% is the best guess, where he focuses on the fact that thinner ice is much more prone to be melted due to natural factors (i.e. the Beaufort sea changing from a nursery into a graveyard). Ron tends to put a higher number on the anthropogenic contribution, based on model outcomes, using Ice Thickness in stead of Ice Extent.

    Important issues to discuss next in my opinion are:
    - Do you agree that Ice Thickness is a better indicator than Ice Extent to determine, among others, the relation with GHG-forcing? Walt already indicated he agrees (right?), but Judith didn’t comment on this yet.

    - Walt Meier stated that “our expectations for how ice responds to natural variability is based upon a thicker ice cover, which may no longer be valid”. Is that the reason that climate models do not show the observed steep decline of sea ice extent/volume? And if so, what processes are missing?

    - As brought in by Walt, Peter Wadham said in a recent interview that: “[…]the albedo—the fraction of solar radiation reflected back into space—drops from 0.6 to 0.1, which will accelerate warming of the Arctic […]the loss of the remaining summer ice will have the same warming effect on the earth as the past 25 years of carbon dioxide emissions.” I am very interested in your opinions on this, also because Judith Curry wrote in her introduction: ‘The impact of September sea ice loss on the ice albedo feedback mechanism is interesting. The minimum sea ice occurs during a period when the sun is at low elevation, so the direct ice albedo effect isn’t all that large. Less sea ice in autumn means more snowfall on the continents, which can have a larger impact on albedo.’

    - In this context the comment from Rob Dekker (first public comment) is interesting. He indicates that GCM projections are lagging 20 (CMIP5) to 40 years (CMIP3) behind, equivalent to 0.5-1.0 W/m2 forcing. He shows (with references) this might be caused by the fact that snow cover decline is underestimated by models. This seems to be contradictory to Judith’s claim that snowfall (and thus snowcover) has increased.Judith, do you also have a reference to a study that supports this view?

  • Judith Curry

    Responses to Rob’s questions:

    In terms of a single sea ice metric, I prefer ice volume. Ice thickness is tricky because of if its spatial variability. Ice volume, ice extent, and % ice age are my preferred metrics.

    The best sea ice models (e.g. CICE) have parameterizations that are a function of ice thickness. I think the disagreement between models and observations is mainly associated a range of problems in the model, and also natural internal variability.

    The past 25 years of carbon dioxide increase has contributed to less than 1 W m-2 in radiative forcing. There is no simple calculation to be made of the effect of the sea ice albedo change on the global energy balance. The better comparison is with a change in fractional cloud cover (which is highly variable), which dominates the planetary albedo far more than the arctic sea ice.

    Liu and Curry published a paper last year in PNAS on on sea ice/snow extent, here is a link
    http://judithcurry.com/2012/03/05/impact-of-declining-arctic-sea-ice-on-winter-snowfall/

  • Bart Strengers

    Also from my side I would like to thank Walt, Ron and Judith for the interesting discussion so far!
    At this moment I want to address some issues concerning Judith’s interesting paper (Liu et al 2012), also because there are several public comments that are related to the Liu et al study. The paper gives the relationship between the decline of ASI and increasing snowfall in the NH and concludes that:

    “The relationships documented here illustrate that the rapid loss of sea ice in summer and delayed recovery of sea ice in autumn modulates not only winter mean statistics (i.e., snow cover and temperature) but also the frequency of occurrence of weather events (i.e., cold air outbreaks). While natural chaotic variability remains a component of midlatitude atmospheric variability, recent loss of Arctic sea ice, with its signature on midlatitude atmospheric circulation, may load the dice in favor of snowier conditions in large parts of northern midlatitudes.”

    Suppose that this is a real effect, then a decline in sea ice in summer and autumn would enhance the albedo (mainly in spring since albedo effects in winter are small due to low solar insolation). In turn this would result in cooling the continents around the Arctic. I think there are three possibilities of the effects on the temperature of the Arctic Ocean:

    Possibility 1: more snowfall will cool the Arctic Ocean as well. Then, this is a negative feedback counteracting the decline in Sea Ice. Since a strong decline has been observed, shouldn’t there be another stronger process that explains the decline? And if so, what could that be?

    Possibility 2: It has no effect on the temperature of the Arctic Sea. In that case I would conclude the mechanisms in the Liu et al. paper is of no importance to the amount of ice in the Arctic Ocean.

    Possibility 3: It has a warming effect on the temperature of the Arctic Sea (a positive feedback).

    I would be very interested in your view on this issue. Also, I am interested in the opinions of Walt and Ron.

    Also, you state in the Liu et al. Paper that the decrease in albedo due to the decline in Arctic Sea Ice is an important effect.

    “When highly reflective sea ice is replaced by open water during the ice melting period, there is a substantial solar heat input directly into the ocean, increasing the heat stored in the upper ocean. For example, the cumulative solar heat input in the Beaufort Sea during the ice melting period in 2007 can be a factor of two to five higher than climatology, which is sufficient to warm the upper 5 m of the ocean by 5°C (24). The loss of sea ice in the Canada basin has also been accompanied by the widespread appearance of a near-surface temperature maximum at 25- to 35-m depth due to penetrating solar radiation (25). Warming of the upper ocean retards the recovery of sea ice during the fall freeze-up.”

    Could you indicate how this could be compatible with the mechanisms you have been discussing so far?

    Finally there is an interesting comment from Jos Hagelaars (and a comparable one from Arjen van Beelen) stating that:

    The Liu, Curry et al 2012 paper says the following on snow extent:
    “A decrease of autumn Arctic sea ice of 1 million km2 corresponds to a significantly above-normal winter snow cover (>3-12%) in large parts of the northern United States, northwestern and central Europe, and northern and central China.”
    The dataset from Rutgers University Snow Lab is used in the paper, that shows a small positive trend for the complete Northern Hemisphere snowcover during the winter period:

    http://climate.rutgers.edu/snowcover/chart_seasonal.php?ui_set=nhland&ui_season=1

    The snowcover trend for NH fall is flat and the trend is clearly negative in NH spring, when the incoming energy from the sun is increasing again.
    The following statement of Prof. Curry is therefore only relevant for the winter period, when the incoming solar energy is at a minimum:
    “Less sea ice in autumn means more snowfall on the continents, which can have a larger impact on albedo.”
    Looking at the dataset used for the Liu et al paper, it would be logical that the second part of the statement also applies to the spring period: less snow in spring has a large effect on the albedo. In this case a warming effect.
    Prof. Curry’s statement: “The minimum sea ice occurs during a period when the sun is at low elevation, so the direct ice albedo effect isn’t all that large.” also seems rather strange to me. The ice extent is declining in every season and not only when the sun is at low elevation.

    —END of comment

    Again it would be interesting to also hear the opnions of both Ron and Walt on this.
    Finally, in this context there is also a comment from Rob Dekker asking Ron to reply:

    Probably Dr. Lindsay could comment on this better than I could, but it seems to me that between GCMs and PIOMAS, PIOMAS is forced by NCEP/NCAR observational atmospheric data (at least for hind-casts), and thus has atmospheric effects of snow cover decline accounted for. So it may be no surprise that PIOMAS hind-casts appear to be more accurately simulating the ice volume and extent developments of Arctic sea ice extent.

  • Judith Curry

    There are some good questions in the general comments, let me respond to a few. Axel Schweiger raises the important question, as to whether the climate models are underestimating the forced variability.

    There are two parts to this issue:
    i) whether the global climate sensitivity to greenhouse forcing is too low as simulated by climate models
    ii) whether there are internal positive feedback processes within the Arctic that are too small or are neglected.

    With regards to point i), I don’t want to spend much time on that one since it is a worthy topic of a thread on its own. But I will state my own assessment that global climate model sensitivity both to greenhouse gas forcing and the aerosol indirect forcing are too large (these two factors cancel out to some extent, but two wrongs don’t make a right). I can expand on this and document this with references etc if the moderators deem it appropriate.

    But for this thread I would say it is more relevant to focus on ii). The possibilities seem to be:
    i) inadequate account for black carbon (in the atmosphere and on the surface)
    ii) inadequacies in the sea ice model parameterizations
    iii) inadequacies in cloud/aerosol/boundary layer parameterizations
    iv) inadequacies in ocean mixed layer parameterization and ice/ocean interactions

    Several years ago I gave an invited presentation at AGU entitled ‘GCM parameterization challenges at high latitudes.’ NASA has posted this on its website, can be found at http://map.nasa.gov/documents/3_07_Meeting_presentations/curry.pdf. It summarizes the major issues as I saw them about 5 years ago, here is a summary of the text:

    Clear sky radiative transfer

    The clear-sky radiative transfer is essentially solved
    • major breakthrough from SHEBA (“dirty window”)
    Remaining issues:
    • cloud overlap (CloudSat and Calipso should help)
    • consistency between microphysics code and r.t. code in specifying cloud optical properties
    • correct handling of the highly reflecting surface
    • (3D radiative transfer NOT a big issue in the polar regions)

    Problems with simulations of clouds:
    • Annual cycle is vaguely captured, though several models are out of phase.
    • Large variability between models.

    Possible reasons for poor simulations of Arctic clouds

    • Poor large scale dynamical fields
    • Inadequate boundary layer parameterizations
    • Incorrect surface temperature and surface state
    • Inadequate cloud microphysical parameterizations
    • Inadequate vertical resolution
    • Etc.

    Arctic Cloud Microphysics: Cloud Phase is the Dominant Issue

    • At -30C, more than half the clouds have liquid
    • Cloud phase has a substantial impact on radiative fluxes and precipitation

    Dual Moment Bulk Microphysical Models

    Microphysical elements that need parameterizing:
    • Liquid drop nucleation
    • Ice particle nucleation
    • Diffusional growth
    • Liquid droplet size spectra
    • Ice crystal size spectra
    • Fall speed
    • Particle collection and aggregation
    • Subgrid-scale supersaturation fluctuations
    Key issue is to get the microphysical elements interacting correctly with the aerosols to produce the correct indirect effect and getting new parameterizations into GCMs

    Boundary Layer Parameterizations

    Existing B.L. parameterizations work poorly in the Arctic, owing to:
    • Static stability and strong temperature inversions
    • Persistent negative surface heat fluxes
    • Large-scale subsidence
    • Mixed phase and crystalline clouds
    • Wintertime convection in leads
    Result in
    • Incorrect vertical profiles of T, q, u
    • Incorrect clouds
    • incorrect surface fluxes

    Issues: boundary layer

    To do list:
    • Prognostic equation for b.l. height accounting for subsidence
    • Investigation of missing mechanism in TKE generation;
    • LES studies of breaking waves in steep inversions
    • Thermodynamics for b.l. crystalline and mixed phase clouds
    • Observations of surface fluxes and b.l. evolution over wintertime leads

    Sea Ice Modeling

    Sea ice feedbacks are complex:
    • internal sea ice processes
    • interactions with local atmosphere and ocean
    • interactions with global processes
    Current sea ice models and parameterized interactions with the atmosphere and ocean are likely to be inadequate at simulating the climate in an altered sea ice regime.

    Needed Improvements to Sea Ice Models

    • Spectral radiative transfer: surface albedo, transmission through snow, sea ice, upper ocean.
    • Explicit melt ponds: albedo, latent heat, salinity effects
    • Snow: nonlinear conduction, metamorphism, redistribution
    • Ice age: optics, thermal conductivity, specific heat, etc.
    • Formation of snow/ice
    • Frazil ice formation
    • Ice deformation: brine rejection; enhanced decay of ridged ice
    • Lead width distribution: lateral melting, turbulent fluxes
    • Ice/ocean turbulent flux for ice thickness distribution
    • Fast ice: detailed ocean bathymetry,granular rheology

    Summary of parameterization issues

    Mostly solved issues:
    • radiative transfer
    • surface turbulent fluxes over ice/snow

    Issues ripe for major progress in short term
    • cloud microphysics and interactions with aerosols
    • cloud overlap
    • sea ice optics (and thermodynamics)
    • (cross-talking parameterizations)

    Issues limited by observations:
    • turbulent fluxes over leads
    • new ice formation, coastal sea ice, ridges

    Issues limited by physical understanding:
    • stable boundary layer
    • cloud-turbulence interactions
    • heterogeneous ice nucleation

    Here is a quick assessment of progress over the last 5 years as I know it, and I focus here on the NCAR climate model, since I am most familiar with that one and also because they have paid the most attention to the Arctic climate.

    There is no longer any excuse to get the clear sky radiative transfer incorrect, but I have not seen recent documentation as to which climate models are correctly treating the ‘dirty window.’

    There have been some breakthroughs in sea ice modeling, notably sea ice radiative transfer, melt ponds, and some implicit treatments of ice age thermodynamics. Allow me to brag about my former Ph.D. student Marika Holland, a scientist at NCAR who is now the lead scientist and SSC Chair of the NCAR CESM.

    There have been some breakthroughs in understanding mixed phase clouds and improving the microphysics parameterizations in the NCAR climate model. Allow me to brag about another of my former Ph.D. students, Hugh Morrison, who is the lead on NCAR’s cloud microphysical parameterizations for climate models.

    There are a lot of other items on my list where progress has not been made. If these issues were ‘fixed,’ in which direction would the climate models go (e.g. more or less ice). I can speculate on a few of these, but trying to reason through the impact of a particular parameterization change doesn’t work because of all of the complex feedbacks in the system.

    I note here that my perspective on all this arose from my service circa 1991-2003 on the World Climate Research Programme (WCRP) Arctic Climate System (ACSYS) Scientific Steering Group, my position as co-Chair of the SHEBA Science Working Group, Chief Scientist for the NASA FIRE Arctic Clouds Experiment, and Chair of the DOE ARM North Slope of Alaska Site Advisory Committee.

    So when my uncertainty level seems higher than others, it is because I have a longer list of known unknowns than most others, which is traced back to my own publications and my service on the committees listed above.

  • Judith Curry

    Neven raises an important point re how much heat does it take to melt the Arctic sea ice. He cites an article by Kwok and Untersteiner citing a number of 1 W m-2. Unfortunately, I am on travel and my laptop is having difficulty opening that article, I can only see the first two pages. So I don’t know exactly where that number comes from.

    Heat from the ocean is more effective at melting the ice than heat from the atmosphere. A while back I did some model experiments looking at how much heat from the atmosphere (a perturbation to the downwelling IR flux or surface air temperature) that it would take to melt the sea ice, as a function of different physics included in the sea ice model.

    I refer interested readers to the following publications:
    Holland, M., J.A. Curry, and J.L. Schramm, 1997: Modeling the thermodynamics of a distribution of sea ice thicknesses. Part II: Ice/ocean interactions. J. Geophys. Res., 102, 23093-23108. http://curry.eas.gatech.edu/currydoc/Holland_JGR102.pdf

    Holland, M.M., J.L. Schramm, and J.A. Curry, 1997: Thermodynamic feedback processes in a single-column sea ice/ocean model. Ann. Glaciol., 25, 327-332.

    Arbetter, T., J.A. Curry, M.M. Holland, and J. M. Maslanik, 1997: Response of sea ice models to perturbations in surface heat flux. Ann. Glaciol., 25, 193-197.

    Holland, M.M. and J.A. Curry, 1999: The role of different physical process in determining the interdecadal variability of Arctic sea ice. J. Climate, 12, 3319-3330. http://curry.eas.gatech.edu/currydoc/Holland_JC12.pdf

    Curry, J.A., J.L. Schramm, A. Alam, R. Reeder, T.E. Arbetter, P. Guest, 2002: Evaluation of data sets used to force sea ice models in the Arctic Ocean. J. Geophys Res., 107, art. no 3102. http://curry.eas.gatech.edu/currydoc/Curry_JGR107.pdf

    Unfortunately the Journal of Glaciology papers are not available online, I probably have hard copies buried somewhere in my office, I will try to put them online. From the Arbetter et al. paper, which asked how much IR forcing is needed to melt the ice from above, the answer depended on which sea ice model you used, but for a dynamic/thermodynamic sea ice model, the result was tens of W m-2.

    Melting the ice from below is much more powerful than melting the ice from above, in terms of W m-2. Note solar radiation penetrates into the mixed layer through open waterm leads and melt ponds and thin ice, so solar acts to melt from below as well as from above. See Holland et al. Part II paper for the details of physical processes of melting the ice from below.

    What fascinated me about the big August storm was the potential for deep mixing of the ocean down to the warm thermocline: this could have a much larger impact than any radiative forcing from above on the evolution of the sea ice. So what is going on in the Arctic Ocean is a combination of overall warming from GHG, as well as natural climate variability and weather roulette.

  • Judith Curry

    Philip Bradley raises a very interesting point:

    “The trend in the Arctic ice minimum extent is -8.2%/decade. While the trend in the maximum extent is -2.78%/decade. This means we are seeing both increasing summer ice melt and increasing winter ice formation (measured by extent).

This IMO points to decreased cloud cover as the primary cause of both, from increased summer insolation warming and increased winter radiative cooling.”

    I have been looking at this also. Refer to this diagram: http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.arctic.png
    During the period 1997-2006, there is a downward trend in overall sea ice extent, but the seasonal variability in sea ice extent is small and the trend seems equal for summer/fall min versus winter/spring max. Then, since 2007, we see a much larger annual cycle in sea ice extent, driven by the substantially lower summer extent, but but the recent winter extent is greater than in 2005, 2006, 2007.

    I suspect also that changing cloud patterns has something to do with this. There is a new paper that looks at the cloud characteristics over the Arctic since 2006, using Clousat and Calipso satellite radar and lidar. http://digitalcommons.unl.edu/usdeptcommercepub/344/. Comparing their Fig 4 (since 2006) with the previous climatologies (Fig 1), it seems that recent summer is lower than climatology and recent winter is higher than climatology. The lower cloud amount in summer is working in the right direction to reduce the sea extent at end of summer. But higher winter cloud amount points in the direction of less sea ice (in winter over the arctic, clouds warm the surface).

    So for winter, it seems like ice export or ocean heat transport are the main factors (I haven’t spotted recent measurements of Fram Strait ice export?). It will be VERY interesting to what the max winter sea ice extent is for 2013, I suspect that it might be low as a result of the ocean mixing from the August storm.

  • Judith Curry

    A response to Bart Strenger’s comment:

    With regards to the impact of increased snowfall on the Arctic Ocean during winter. If there is heavy snowfall during autumn, this will slow down the ice growth process, since snow has an insulating effect. If there is heavy snowfall in late winter/early spring, this can slow down the ice melt process since the sun spends its energy melting the snow before it can start melting the ice.

    I wouldn’t quite agree with any of the 3 possibilities put forward by Bart. I suspect that colder, snowier NH continents would primarily have an impact on the hemispheric atmospheric circulations and so influence ice export. And an indirect cooling effect on the Arctic Ocean during winter. So I think the dynamical response in terms of ice export is at least as important as any thermodynamical response.

    With regards to the albedo effect of changes to snow and ice cover, to first order this relates to the solar zenith angle (time of year, latitude) and the cloud cover. For low sun elevations (below 55 degrees), cloudiness will reduce the surface reflection of solar radiation relative to clear sky conditions. At higher sun elevations, the reverse is true.

  • Bart Strengers

    @Judith

    Thanks for your reply and your comments to public comments.
    There are many questions I would like to raise but for now I would like to focus on a data-issue I still don’get. You suggest there is MORE snowfall on the NH continents, however, as indicated by, for example, Arjen van Beelen:
    “To my knowledge, sea ice extent/area and snow area have tremendously decreased during the summer half year during which the effects of changing albedo are most significant. Snow cover trends are strongly negative during May, June and July. Though sea ice extent has most strongly decreased in late summer and early fall, decreases are still very large in May, June and July.”
    And Rob Dekker wrote:
    “The dataset from Rutgers University Snow Lab (as used in Judith’s paper) shows a small positive trend for the complete Northern Hemisphere snowcover during the winter period:
    The snowcover trend for NH fall is flat and the trend is clearly negative in NH spring, when the incoming energy from the sun is increasing again.”

    Could you shed a light on this?

  • Judith Curry

    Bart, I am not sure I understand the question. Our PNAS paper addressed wintertime snowfall. In some regions of the NH continents, there is a negative correlation between winter snowfall and autumn sea ice extent. The continental snow is melting earlier in spring. I don’t see a conflict between these?

  • Judith Curry

    Neven, if you look at the time series of PIOMAS ice volume
    http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/

    You see the same general behavior as for ice extent:
    • summer decrease is greater than the winter decrease
    • the amplitude of the annual cycle of ice volume is much larger since 2007 than for the preceeding several years

    Ice extent and ice volume give you two different pieces of information (albeit not completely independent pieces of information). Ice extent is more responsive to the current meteorology. Ice volume is a better indicator of climate change. To decipher the climate change (and understand the relative importance of forced versus natural variability), you need to have some understanding also of the shorter term meteorological and seasonal variability that is influencing the sea ice.

  • Judith Curry

    A response to Neven’s question:

    “1) You wrote: “models are inadequate”, ” I don’t have much faith in the climate model projections of sea ice” and “climate models, which have substantial problems in simulating the Arctic climate”.

    At the same time you write: “The first issue to debunk is that an ‘ice free’ Arctic is some sort of ‘tipping point.’ A number of recent studies find that in models, the loss of summer sea ice cover is highly reversible.”

    To a lay person there seems to be a contradiction there. Why do the tipping point models simulate Arctic climate better than sea ice projection models?”

    Climate models are able to simulate the annual cycle of sea ice, i.e. melting in the summer and freezing in the winter. So each winter, the sea ice cover recovers, more or less depending on the weather. No one disagrees with this.

    Further, ‘ice free’ is usually taken to mean less than 1 M sq km. This is far from ‘ice free’ in actuality (I find this use of ‘ice free’ to be highly misleading). So what is the point of talking about some sort of ‘tipping’ point, when even during summer, the Arctic Ocean is not really projected to be ice free?

    The massive cooling during the polar night causes substantial heat loss, which on land results in surface temperatures of -40C and colder. Sea water in the Arctic Ocean freezes at a temp slightly warmer than -2C. The only conceivable way to keep the Arctic Ocean ice free is to bring in much warmer ocean water from lower latitudes. Unless the geography of the Arctic basin dramatically changes, e.g. Alaska disappears, there is no way for this to happen.

    I don’t think that anyone would dispute these points.

    With regards to your question on PDO. I don’t know how to answer the question in the manner that you have posed it. Large scale atmospheric and ocean circulations vary on multidecadal time scales, which influence circulation regions on shorter time scales as well, which among other things influences sea ice characteristics. Untangling how all this works has received far too little attention IMO.

  • Judith Curry

    A response to Arjan van Beelen:

    “Dr. Curry wrote:

    “So for winter, it seems like ice export or ocean heat transport are the main factors (I haven’t spotted recent measurements of Fram Strait ice export?). It will be VERY interesting to what the max winter sea ice extent is for 2013, I suspect that it might be low as a result of the ocean mixing from the August storm.”

    I find this statement quite puzzling. I can understand the process (lower heat content in deeper waters), but this might lead to more rapid freezing in this area in fall (do we have any indication that this has occured?), and later opening up of this area during spring. Maximum extent is reached WELL outside the regions affected by the storm. These areas are always frozen over near maximum extent!”

    The Arctic Ocean has a very interesting vertical structure, the quickest thing I can reference you to is some figures from my text Themodynamics of Atmospheres and Oceans, the figures are posted online at http://curry.eas.gatech.edu/Courses/6140/lectures.html. Go to lecture 11, figure 11.6. The figure shows a plot of the average monthly vertical temperature and salinity profile for the top 100 m of the Arctic Ocean. From 50-100m, you see a relatively warm, salty layer. Look at the temperature curves for 7, 9 (corresponding to Jul, Sep). Mixing down to that layer would have brought warm, salty water to the surface. Apart from the warmth, the greater salinity means the ice would form at a slightly colder temperature. Ocean circulations would distribute the warm water away from its original mixing location. So unlike most of the global ocean, there is warmer water at depth. And if you go even deeper, say to 300 m, the water gets warmer and saltier yet (see this fig http://upload.wikimedia.org/wikipedia/commons/thumb/9/90/Arctic_sea_temperature_salinity_plot.svg/220px-Arctic_sea_temperature_salinity_plot.svg.png)

    Note, I haven’t seen any observations of Arctic Ocean temperature salinity profiles from last summer, I am not even sure any such measurements were even made. I hope that there were some measurements, this would be very illuminating.

  • Judith Curry

    Neven, Philip Bradley brought up the issue of clouds, I responded to that point. This response does not imply that I think clouds are the only or even the main driver of the summer sea ice minimum. With regards to the summer minimum, the clouds are contributing and seem to have been a major factor during 2007. Clouds are much more powerful radiatively than CO2, so if we are talking about radiative forcing, clouds should be front and center in the discussion.

    The loss of multi-year ice is the key issue, and ice export is a key part of this. I wish there was better data for sea ice volume export through the fram strait, especially the MY ice. But I like the polarbear page for this http://polarbear.colorado.edu/IceAge.html. The MY ice starts to decline around 1990, but 2000 isn’t all that much lower than 1990. A big part of what has happened since 2000 is enhanced ice export through the Fram Strait of MY ice. During May, this export has been particularly large for almost every year since 2000. You point to the land mass constraint: this is an absolute key, making Fram Strait export of dominant importance.

    Ice volume increase during winter can actually be larger for FY ice than for a field dominated by MY ice. Thin ice grows at a much faster rate than thick ice. The change in ice volume for MY-dominated vs FY dominated during summer is trickier. Thicker ice actually starts melting a bit earlier than thin ice owing to the larger sensible heat loss over the thin ice, but the thin ice may entirely disappear over the course of the summer by melting. A key issue is whether the FY ice can survive through the summer. This depends on the local thermodynamics, and also the export (and also breakup induced such as by a big cyclonic storm). So following the time variation of the 2nd year ice is another key to understanding what is going on (thermodynamics vs dynamics/export). If you want details, refer to this paper http://curry.eas.gatech.edu/currydoc/Schramm_JGR102.pdf.

    Locally, the ice albedo feedback is somewhat of a driver for the seasonal cycle, but the local solar heating in the shallow mixed layer is quickly lost as the autumnal cooling begins. If there is a big storm that mixes down further, the solar heating isn’t so easily lost and warmer water below can be brought to the surface. Which is why i find that Aug storm to be so interesting. Again, what happens with the clouds is also a huge deal; if the open water causes more clouds, then less solar will make it into the ocean.

  • Marcel Crok

    Thanks Judith, Walt, Ron and the many contributors to a very interesting first week of Climate Dialogue.
    If I summarize, we started discussing attribution right away. Judith came up with a range of 30-70% contribution from GHG’s although she seems to be inclined towards the lower end of this range while both Walt and Ron tend to go for the upper part of this range. All three agree that it is really difficult to pinpoint the exact number due to the myriad processes playing a role in the Arctic.

    During the last few days the discussion therefore goes deeper and deeper into these processes. In a (public) comment Neven came up with a paper of Kwok and Untersteiner (2011) which stated that (only) 1 W/m2 is necessary to explain the melt in the Arctic in the past half century. That paper by the way is online here:
    http://rkwok.jpl.nasa.gov/publications/Kwok.2011.PTO.pdf
    The APL Piomas page http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/ even mentions a lower number (0.4 W/m2) and agrees that this makes it extremely difficult to find causes for the decline, a conclusion that Kwok/Untersteiner also make:
    “At the moment, uncertainties in the heat-balance measurements observed at manned drifting stations and in the meridional heat transport calculated from radiosonde (balloon-based) observations around the Arctic perimeter prevent researchers from resolving those heat fluxes to an accuracy required to attribute the surplus of heat to any particular source or mechanism that explains the observed ice loss.”

    Judith stated in http://www.climatedialogue.org/melting-of-the-arctic-sea-ice/#comment-158 that the heat from the ocean is more effective for melting than heat from the air:
    “Heat from the ocean is more effective at melting the ice than heat from the atmosphere. A while back I did some model experiments looking at how much heat from the atmosphere (a perturbation to the downwelling IR flux or surface air temperature) that it would take to melt the sea ice, as a function of different physics included in the sea ice model.”

    Recently Roger Pielke sr. presented an analysis on his blog that suggests the warming of the troposphere is rather modest:
    http://pielkeclimatesci.wordpress.com/2012/09/21/arctic-lower-tropospheric-temperature-trends-since-1979/

    It would be interesting to get reactions from both Walt and Ron on this. Can we agree that the sea is more important than the atmosphere? And is like Pielke concluded warming of the troposphere too modest to explain the fast melting? What explains the difference between the 1 W/m2 of the Kwok/Untersteiner paper and the 0.4 W/m2 of the Piomas webpage?

    Marcel

  • Judith Curry

    Neven,

    Take a look at PIOMAS ice volume anomaly. Do the trend from 1979-2002. I think the latter half of this period saw sea ice that was generally in equilibrium with the circulations/forcing, which were slowly but steadily changing.

    In 2001/2002, there was a climate shift (analogous to the great climate shift of 1976). This has been documented in a number of papers, especially Tsonis (2007) and Tsonis and Swanson (2009) (note I discuss this more on my blog posts cited at the beginning of my essay here). The shift is arguably more complicated than just a switch to cool PDO (and includes AGW), but in the comment you referred to I referred to PDO rather than getting into the whole climate shift thing.

    As a result of the climate shift, the sea ice is out of equilibrium with the forcing and dynamics, and hence unstable. In 2007 we saw extreme sensitivity to internal Arctic processes (e.g. clouds), which then triggered another shift to the sea ice coming from the internal dynamics triggered by the 2007 ice loss.

    So what is the physical mechanism associated with the global climate shift that is causing the more rapid sea ice decline? there seems to be three choices:
    • changes in clouds (such changes are well known to occur with changes in ENSO phases; key aspect of the new regime is more La Nina events)
    • changes in atm/oce circulations, producing more ice export
    • changes in ocean heat content associated with transport through the Bering Strait

    The 3rd one, ocean heat transport is hard to call since I haven’t seen any observations at all.

  • Judith Curry

    Frank, that was a very thoughtful post. In the early 1990′s, i was working hard on trying to understand the forest, and believe me there wasn’t much to work with. By forest here, i mean clouds, radiation, sea ice, and the feedbacks among them. The culmination of this effort was my review paper
    Curry, J.A., D. Randall, and W.B. Rossow, and J.L. Schramm, 1996: Overview of arctic cloud and radiation characteristics. J. Clim., 9, 1731-1764.
    http://curry.eas.gatech.edu/currydoc/Curry_JC9.pdf

    In the early 90′s, i was one of a small handful of scientists working on these problems. Global climate scientists tended to stop at 60N, 60S.

    This work motivated the SHEBA experiment
    Uttal, T., Curry, J.A., and 26 others, 2002: Surface Heat Budget of the Arctic Ocean. Bull. Amer. Meteor. Soc., 83, 255-275.
    http://curry.eas.gatech.edu/currydoc/Uttal_BAMS83.pdf

    SHEBA brought the topic into the mainstream, and there has been a mini-explosion of people now working on these topics. With notable improvements to satellite observations, sea ice models, and cloud microphysics

    With the dramatic increase in interest associated with sea ice decline, we haven’t really seen a synthesis of what is going on. In 1996, my article cited about 100 papers, and I really had to dig into some old Russian papers. Now, there are probably a thousand papers to look at. When I retire, maybe I can tackle this one. Or maybe we need a scientific assessment specifically on this topic, with an international team of people.

    I agree that we are collectively not yet seeing the forest on this one.

  • Ron Lindsay

    There have been a number of interesting questions addressed in the public comments. While there is of course plenty of drivel in some public comment sections of blogs, I am often impressed with the level of understanding exhibited in some of the posts. Let me express my take on some of the issues, in no particular order.

    On tipping points…I once wrote a paper that raised the question of whether a tipping point had been passed in the late 1980‘s, when the current decline in ice thickness in the arctic ocean began in earnest, coincident with a shift in the AO, a shift I called “the kick” which started the decline. Despite a return to normal AO conditions the decline continued. I now believe a tipping point for summer sea ice is NOT a good way to characterize the system. The sea ice in the Arctic responds to global forcing in the atmosphere and ocean and is not on its own trajectory. A number of studies have supported this conclusion.

    On ocean influences vs atmospheric influences, I agree with the concept that the heat fluxes required to melt the ice at the rate we have observed are very small and attributing this flux to a particular source over decades may be futile. Perhaps the remarkable thing is not how quickly the ice is declining but that it is so stable over the many years we have of observations…that natural variability is not much larger. This is due, I think, to the very strong negative feedback that Judith mentioned, the thin-ice-growth feedback in winter which insures strong growth of thin ice.

    The storm last summer likely melted additional ice due to increased ocean mixing, but it is not clear that in the long run it made much difference…the ice it removed was quite thin and may have melted anyway. The volume anomaly in PIOMAS shows a downward blip when the storm occurred, but it does not show the September volume or extent was strongly affected by the storm.

    A lot of different aspects of the system are changing and I can’t say which one is dominant, if any. I am not aware of observations that show the heat flux from the ocean is increasing. A lot of solar heat is now being dumped into the ocean in late summer, but much of this heat is quickly loss to space in the fall, so the impact on winter growth may be modest…again the thin ice growth rate feedback. How much of this new summer heat is sequestered and slows ice growth all winter is an open research question. The point is that most of the Arctic Ocean mixed layer is close to the freezing point so the heat flux to the ice does not change radically. I don’t know if it is possible to measure any additional heat being drawn from the warm Atlantic layer below the cold halocline.

    Atmospheric fluxes are highly variable and accurately determining a long-term trend is difficult. A possible strong feedback is the lower albedo of melting snow in the spring so that an earlier onset of melt is amplified with earlier snow melt, earlier melt pond formation, and earlier lower albedo of bare ice (Perovich et al., 2007) which would amplify melt. In terms of melt, by far the largest component is the solar flux, so understanding how the surface albedo changes is crucial.

    On the possibility of a winter time ice-free arctic see Winton (2006). He discusses model results under a quadrupling of CO2, admittedly a very high level.

    Perovich, D. K., S. V. Nghiem, T. Markus, and A. Schweiger (2007), Seasonal evolution and interannual variability of the local solar energy absorbed by the Arctic sea ice–ocean system, J. Geophys. Res., 112, C03005, doi:10.1029/2006JC003558.

    Winton, M. (2006), Does the Arctic sea ice have a tipping point?, Geophys. Res. Lett., 33, L23504, doi:10.1029/2006GL028017.

  • Walt Meier

    Lots of interesting comments, both from Ron and Judith, and from the public. I second Ron’s comment that there are many incisive comments from the public – far more than I could hope to delve into, but I’ll try to respond to some. I thank Marcel for moderating and bringing some of the more interesting questions to our attention.

    The ocean is indeed a very important part of the sea ice melt story. Water is a much more effective mechanism to transfer heat to the ice compared to the atmosphere. This is seen in mass balance buoys presented by Don Perovich and colleagues at the U.S. Army Cold Regions Research and Engineering Lab (CRREL) that measure the relative contributions by the ocean and atmosphere to summer melt. There are numerous papers and other resources available online; just one example is this paper: http://www.chrispolashenski.com/docs/a57a188.pdf. Note Figure 1 – near the ice edge bottom melting tends to dominate. This ocean contribution is due to in situ ocean warming or transport of warm water into the Arctic. There are some indications of influxes of warmer surface and near-surface water in the Pacific region (e.g., by W. Maslowski at the U.S. Naval Postgraduate School), but most of the heating is in situ during to solar insolation (Steele et al., 2010, http://www.agu.org/pubs/crossref/2010/2009JC005849.shtml). Steele et al. also find that near the ice edge, bottom melt accounts for 2/3 of the thickness melt vs. 1/3 for surface melt from the atmosphere.

    Even though the solar insolation maximum occurs when much of the Arctic Ocean is still ice-covered (i.e., June 21), a significant amount of heat is absorbed through the ocean. Buoy data (look at August and September ocean temperature data (from M. Steele and colleagues) here: http://psc.apl.washington.edu/UpTempO/Data.php. Surface temperatures are >5 C, which is 7+ C above the melting point for the ocean water. These are surface temperatures, but the heat extends down several meters (via communication with Mike Steele). That is a lot of heat.

    That heat must be lost to the atmosphere before ice can form in the autumn. But as Judith and Ron point out, once the heat is loss, ice growth is very rapid because the atmosphere has gotten cold. Ice growth is exponential – very fast at first and the gradually slowing. So delaying the start of the ice growth a few weeks doesn’t necessarily have much of an effect on the end of winter ice thickness.

    One thing that I think is clear is that the sea ice system is complicated and that many factors that influence each other are changing, making separating them out difficult. Going back to a point I made earlier, I think an intriguing aspect is how the influence of natural variability on the sea ice (and vice versa) is changing. In other words, AO affects sea ice, but how is that effect changing with a changing ice cover and are the changes in the ice in turn influence the AO?

    Following up from Judith in regards to what “ice-free” means, I agree that this isn’t a particularly well-defined term, but I think it is nonetheless useful for thinking about changes in the ice cover and its impact. It will indeed be difficult to reach completely ice-free (zero) ice because of the geography and dynamics of the system. Semi-enclosed bays and channels (e.g., the Canadian Archipelago) are more resilient to break-up and melt and, as I mentioned a previous post, the Greenland side of the Arctic gets replenished by ice moving across from Siberia. This is can pile up into thick (several meters) ridges that are difficult to break up and melt completely.

    I look at “ice-free” in two ways:

    1. Instead of simply saying “ice-free”, my views is that it should be described as “ice-free for all practical purposes”. To me this means: seeing blue instead of white throughout the Arctic Ocean (except along the coasts), allowing ships to operate within the Arctic Ocean with little chance of seeing substantial ice, having a significant effect on the Arctic ecosystem, and having a significant effect on Arctic. (The last two are likely already occurring.)

    2. Reaching “ice-free” conditions is not going to be like flipping a switch. The impacts will be felt as that is approached (and indeed are already being felt).

    So I’m not worried too much about what we mean by “ice-free” or what specific number we put on it – that’s for gamblers placing bets to quibble about.

  • Ron Lindsay

    Just a couple of comments:

    As far as ocean vs atmosphere, I still think the dominant terms of the heat budget for the ice are the solar and infrared radiative fluxes and that variability in these are large, particularly when albedo and cloud changes are considered. If there is a trend in ocean heat flux I am not aware of it, except for solar heat absorbed by the ocean that subsequently melts ice.

    About the attribution of the decline to AGW vs natural. The fact is we don’t really know and all we can do is speculate. That is not really science. Also the question is a little ambiguous. Are we referring to a linear trend, and if so over what period, or to a change for a particular year and against what base line? Do we assume natural variability is only contributing to the decline, or might it also slow it? So trying to put definite numbers on the ratio for the observed climate, even the uncertainty, is likely a futile effort. This can be done for ensemble model simulations of the climate, with all of the caveats that go with such studies, and the answer is a statistical summary for the model used, not a real-world analysis.

  • Rob van Dorland

    Thanks for the input and for looking at relevant questions made in the public comments.

    I think you all agree on the statement that ice melt from below (ocean) is dominant as compared to ice melt from above (atmosphere).

    Can we also agree on the next statements?
    - (made by Walt Meier) that the Arctic Ocean gets warmer due to a) in situ warming and b) transport of warm water into the Arctic?

    - That most of the in situ warming is due to solar insolation? As a consequence less sea ice leads to more insolation (and hence absorption of solar energy) into the ocean (albedo feedback), increasing the temperature of the mixing layer of the ocean.

    - (made by Ron Lindsay) that the dominant terms of the heat budget for the ice are the solar and infrared radiative fluxes and that variability in these are large, particularly when albedo and cloud changes are considered. And also that there is a strong (negative) trend in albedo in summer and autumn. A related question may be whether there are indications of a large negative trend in cloudiness over the last couple of decades? And if so, how does it compare to the trend in surface albedo?

    - That there is a strong temperature trend in the Arctic of 0.33 °C/decade (for JJA, based on UAH) and 0.47 °C/decade for the complete year is 0.47 °C/decade, which would result in 30 years to 1.4 °C?

    - That the term ‘ice free’ is a little bit misleading, but that we define it here as ‘seeing blue instead of white throughout the Arctic Ocean (except along the coasts)’ (Walt Meier)

    Judith, it surprised me that in your reply on the comment by Neven you summed up three possible physical mechanisms for the rapid sea ice decline (clouds, atm/oce circulation, ocean heat transport through the Bering Strait), but forgot to mention the surface albedo changes (which may be the dominant effect). Can you comment on that?

    I suggest that after clarifying these points, we will push the discussion towards the second question in the introduction of this subject: ‘How unusual is the current decline in historical perspective?’ Ron Lindsay made in his contribution on the 19th of November a relevant statement: ‘Perhaps the remarkable thing is not how quickly the ice is declining but that it is so stable over the many years we have of observations…that natural variability is not much larger.’

  • Judith Curry

    Rob, you misinterpret my comment. It was made in the context of a global climate shift (e.g. large scale circulation change), rather than with reference to in situ processes going on in the Arctic

  • Walt Meier

    In regards to the stability of the Arctic sea ice, I would agree with Ron that it may be more surprising that it has been so stable over our years of observations, both in our modern satellite record (since 1979) and earlier. Given that the ice quite thin (overall on average 2.5 meters or so, with multiyear being 3-4 meters), it doesn’t take much forcing, relatively speaking, to melt completely during summer (1 W/m2 or less).

    So how unique is the current decline in a historical context, to the best of our knowledge? It’s a difficult question to answer, and I don’t think say too much with high confidence. And neither Judith, Ron, nor I are paleoclimatologists. It is a question we get asked frequently at NSIDC, so I’ve looked into research a bit, so I can give you my best understanding of the current knowledge.

    Before I summarize my understanding, first, I would say that the more interesting issue that if the Arctic has been ice-free in the past, what would it mean for our interpretation of the current decline? There are (at least) two ways of looking at it:

    1. If the Arctic has been ice-free during summer in the past, obviously it was due to natural forcing, so the current decline could also be due to natural forcing.
    2. If the Arctic has been ice-free during summer in the past due to natural forcing then anthropogenic forcing of a similar magnitude will have a similar effect.

    The first view is not implausible on its face, but it is simplistic because it doesn’t consider that the same result could be due to the same causes. Lightning starts forest fires, but that doesn’t rule out that a forest fire may be due to human actions.

    The second view is much more useful in my view because it has potential predictive value at least for the equilibrium state of the ice cover under a given forcing. For example, in the Holocene (~8000 ybp – see below), the Arctic Ocean likely had ice-free or near ice-free summers and temperatures were similar to, maybe still a bit higher, than Arctic temperatures in recent years. Thus, the decline we’re seeing is entirely expected and we would expect to see it continue to near-zero summer extent in the coming years. The timing is still uncertain but it changes things from a “if the Arctic loses summer sea ice” to “when the Arctic loses summer sea ice”.

    Now to summarize my understanding of the pre-satellite historical record:First, pre-1979, we have information from sea ice charts created by various countries. These were (and still are) produced primarily to support ships in the area. They were done primarily manually (and still have a strong manual component in terms of integration of different satellite sources) using ship observations, aerial reconnaissance and, starting in the 1960s, early satellite data. The data are not complete and often a fair amount of guess-work, albeit guess work by experienced analysts. The focus was not on making a consistent climate time series, merely doing the best chart possible at any given time. Since about 1953, the coverage has been reasonably complete – enough to create monthly fields. This was original done by John Walsh and colleagues at the University of Illinois. This has been stitched together with the satellite record by people at UK Hadley Centre, but not in a particularly consistent manner.

    Forgive me for a brief shameless promotion, we’ve just published a homogenized version of this product that is consistent our NSIDC satellite record: http://www.the-cryosphere.net/6/1359/2012/tc-6-1359-2012.html (open access), which includes background on these and other sources of 20th century Arctic sea ice extent.Before the 1950s, the 1930s are often mentioned as a warm period. However, this is primarily in the Atlantic region, where observations were more common. Ice charts from the Denmark (http://nsidc.org/data/docs/noaa/g02203-dmi/) and Russia, indicate some periods of low summer ice, but on a more regional scale than we see now.Before that, other than sporadic, very limited records, we reliant on paleo records (sediment cores, ice-drifted debris, etc.). This information is as one might expect extremely sparse, both in space and time. A synthesis by Kinnard et al. (2011) indicates the current decline is unique in the last 1450 years. A review of longer records (Polyak et al, 2010) indicate that the last time the Arctic had little or no summer ice was during the Holocene Thermal Maximum, ~8000 ybp.

    Happy Thanksgiving to all the U.S. readers!

    Kinnard, C., C.M. Zdanowicz, D.A. Fisher, E. Isaksson, A. de Vernal, and L.G. Thompson, 2011. Reconstructed changes in Arctic sea ice over the past 1,450 years, Nature, 479, 509-512, doi: 10.1038/nature10581.

    Meier, W.N., J. Stroeve, A. Barrett, and F. Fetterer, 2012. A simple approach to providing a more consistent Arctic sea ice extent time series from the 1950s to the present, The Cryosphere, 6, 1359-1368, doi:10.5194/tc-6-1359-2012.

    Polyak, L., and several others, 2010. History of sea ice in the Arctic, Quaternary Science Reviews, 29, 1757-1778, doi:10.1016/j.quascirev.2010.02.010.

  • Rob van Dorland

    After some pause respecting thanksgiving, I would like to address the topic of Arctic Sea Ice in the past.

    Thanks Walt for addressing this topic already in your posting at November 22 (I think your promotion is very relevant). I like the way you split the subject into 1) What do we know about sea ice in the pre-satellite era from observations and 2) What are the mechanisms for changes in the sea ice extent/volume.

    Concerning the observations Walt distinguishes the period with reasonably complete data (1953 – 1979) and older periods with rather incomplete data in terms of space and time coverage.

    The paper by Meier et al., 2012 concludes: ‘The results indicate that trends [of ice extent] through the 1960s were largely positive (though not statistically significant) and then turned negative by the mid-1970s and have been consistently negative since, reaching statistical significance (at the 95% confidence level) by the late 1980s.’ @Walt, did you also consider the correlation between sea ice extent and (global mean or Arctic air/sea) temperatures? (This point was issued also by Jos Hagelaars in his public posting at 2012-11-23 00:06:10)

    It seems that there are (at least) two relevant papers (Kinnard et al., 2011 and Polyak et al, 2010) addressing the situation before 1950 and indicating that the current decline is unique in the last 1450 years. @Judith, may I invite you to comment on these studies?

    Concerning the mechanisms of changes in sea ice extent/volume Walt made a clear statement, coupling (local) forcing to (equilibrium) sea ice amount: ‘If the Arctic has been ice-free during summer in the past due to natural forcing then anthropogenic forcing of a similar magnitude will have a similar effect.’ @Ron, can you confirm that this coupling is also evident in climate models (albeit that many models underestimate the current decline)?

    Rob Dekker brought up very interesting points in his public posting at 2012-11-22 09:08:10: ‘This multi-decadal development is amazingly consistent, and relentlessly downward. It is hard to find any “natural variability” due to “uncertainty” in clouds, in this graph. Which brings us back to feedbacks, negative and positive. If the negative feedback of faster ice growth in fall (which is very nicely explained by Frank) indeed would be significant, than should we not see a ‘levelling off’ of this volume anomaly graph? Then why is it that it seems that instead of levelling off, ice volume is declining even faster (about 2X) than before the major extent losses occurred (since 2005). It seems to me that ice extent and ice volume graphs both indicate that positive feedbacks in the Arctic are still stronger than negative feedbacks at this point, and one may ask when that would change. Could it be that currently Arctic sea ice volume is simply not stable, and will continue to decline until the Arctic warms up substantially?’ It would be interesting to hear the views of all discussants.

  • Ron Lindsay

    Rob asked “Could it be that currently Arctic sea ice volume is simply not stable, and will continue to decline until the Arctic warms up substantially?’

    I think that for time scales of a decade or more the ice volume is largely in equilibrium with the hemispheric mean temperature, but on shorter time scales it is not. While the current volume is relatively low compared to the hemispheric mean temperature, it is premature to project a continued anomalous decline relative to the hemispheric temperature. In other words I don’t think the ice is unstable, going on it’s own trajectory independent of the larger-scale climate.

  • Bart Strengers

    Ron, Walt and Judith,

    While writing a summary of the discussion so far, the following question came to my mind (you all already made remarks related to this, but I would like to focus more):
    since you all indicate it is very difficult to really prove a significant contribution of GHGs (or global warming) to the decline in Arctic Sea Ice, I wonder to what extent you agree with the reasoning that observed natural variability since 1950 cannot explain the decline as observed in past decades (see for example in Notz (2012) who concludes that: ‘We find that the available observations are sufficient to virtually exclude internal variability and self acceleration as an explanation for the observed long-term trend’). This reasoning leads to the conclusion that observations alone are sufficient to prove there must be an anthropogenic factor in the current decline of Arctic sea ice.

    So the question is: To what extent do you agree with this reasoning? (maybe also taking into consideration the two studies mentioned by Rob that the current decline is unprecedented in the past 1450 years and the study from Spielhagen (2011) that shows a 2 C increase in temperature of Atlantic Water entering the Arctic Ocean during the 20th century, unprecedented in the past 2000 year.)

  • Rob van Dorland

    I would like to consider the role of clouds in the Arctic Sea Ice decline a little bit more.

    We probably agree that there is a huge annual cycle in the Arctic in solar insolation, temperature (hence IR fluxes), cloudiness, latent and sensible heat fluxes. There are many feedback loops between these entities. Yet, we observe a steep decline in sea ice volume already starting in the 80s. IMO this suggests that there are first order forcing mechanisms (perhaps only one dominant), which trigger the observed decline, possibly via positive feedbacks (e.g ice albedo).

    As we agreed that most of the melt (2/3) is from below and the remaining (1/3) is caused by the atmosphere, the dominant forcing mechanism is the increase of ocean heat content, in particular the increase in the upper layers. (we may discuss the reason for this, but a good candidate is anthropogenic forcing).

    Considering the smaller (1/3) effect of changes in the atmosphere on the decline:
    Judith stated in her contribution (at the 18th of November): ‘Clouds are much more powerful radiatively than CO2, so if we are talking about radiative forcing, clouds should be front and center in the discussion.’ However, as stated in her guest blog there is a strong seasonal cycle in the effects of clouds, warming in the winter and cooling in the summer.

    So, my first remark is that there will be months where the CO2 (surface) forcing is more important than cloud forcing as the sign of the latter reverses during the year.

    More importantly, is there agreement that latent heat changes related to the decline in sea ice extent is much larger than (radiative surface) forcings due to cloud and CO2 changes?

    Thirdly, might there be a negative feedback (in summer and autumn) of enhanced latent heat release, hence more (low) clouds, implying less forcing from above. If so, it will be difficult to believe that changes in cloudiness is a main driver of the decline.

    I would be very pleased if you (all) can comment on these points.

  • Ron Lindsay

    Let me respond to a couple of Rob’s comments.

    I don’t agree that 2/3 of the melt comes from the ocean. How do we know that?

    It is very hard to really know what the long-term changes in the cloud radiative forcing is in the central Arctic, in part because satellite retrievals of cloud properties can be biased by changing surface properties, so if the surface changes (less ice) is the change in estimated cloud properties real or just an artifact?

    Global climate forcing (greenhouse gasses plus aerosols plus volcanos plus solar) is on the order of 1-2 W/m2 globally (Hansen et al 2011). This is enough to produce the observed ice volume loss rate if it were distributed evenly over the surface of the globe. But that is not the case and I don’t know just how the surface downwelling radiative flux changes over sea ice due to changes in CO2 alone. As Judith says, clouds are the big player in radiative fluxes. How they are changing in response to changing ice in amount, composition, and vertical structure is still an open research question, so we don’t really know if cloud changes will be a positive or a negative feedback. Because they are so important I would not be surprised if they are found to be at least part of the source of the ice melt, but because cloud temperature and properties may change due to changing surface properties, sorting out cause and effect could be difficult.

  • Rob van Dorland

    Thanks Ron for your reply. I thought there was consensus about the 2/3 ocean and 1/3 atmosphere issue in relation to ice melt. Walt brought this up referring to Steel at al.

    I think you made a very relevant statement: ’Because they [clouds] are so important I would not be surprised if they are found to be at least part of the source of the ice melt, but because cloud temperature and properties may change due to changing surface properties, sorting out cause and effect could be difficult.’

    Therefore let’s consider first order feedbacks in the Arctic due to ice decline (without pointing to the initial cause):
    1) ice – albedo feedback:
    less ice -> more SW absorption by the ocean -> higher ocean temperatures -> more ice melt
    2) Latent Heat – Cloudfeedback
    Less ice -> more LH -> more (low) clouds -> positive or negative feedback depending on surface albedo and season
    3) Snowcover – Arctic temperature feedback
    Less ice -> higher temperatures in the Arctic -> Less snow cover over continent surrounding the Arctic –> higher temperatures in the Arctic region (positive feedback). Or it might as well be a negative feedback if higher temperatures in the Arctic result in more snow cover.

    I would appreciate if we could make a list of first order feedbacks in the Arctic region and rank them in terms of sign and strength. I also invite Judith and Walt to give ideas and comments on this.

  • Marcel Crok

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    We hope you will appreciate this new initiative to move the global warming debate forward.

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  • Rob Dekker

    Thank you Climate Dialogue staff, for starting this venue with a discussion on Arctic sea ice developments.

    And thank you Dr. Meier, Curry and Lindsey for providing a great overview of scientific findings attempting to explain the sharp (unprecedented in at least a few thousand years) reduction in Arctic sea ice cover from the past 4 decades.

    Since the Arctic is a major regulator of Northern Hemispheric weather patterns, our understanding of the process is extremely important for future estimates of Northern Hemisphere weather projections. In that regard, the overview given by Dr. Meier and Dr. Lindsey, sustained with references to scientific publications, are very helpful.

    In the discussion of “causes” of Arctic sea ice decline, it seems important to note that “natural variability” is not an explanation for a trend, since it can goes TWO ways. The best we could say is that such-and-such part of the decline COULD be caused by natural variability if natural variability is currently “negative”.

    Here, it is important to note that Arctic sea ice extent dives way below “natural” variability, and there is no “recovery” in sight :
    http://neven1.typepad.com/.a/6a0133f03a1e37970b017744cf5360970d-pi

    So, I think that before we start speculating about how much of Arctic sea ice decline is “natural” and how much is “anthropogenic”, we should FIRST understand why GCMs are underestimating Arctic sea ice decline even if we add both these factors in the models !

    Here, I noticed that GCM projections are lagging some 20 years (CMIP5) to 40 years (CMIP3) behind actual Arctic sea ice decline. Apparently, we are currently experiencing Arctic “climate” conditions that were not expected until another 40 – 80 ppm increase in CO2 concentration (which implies some 0.5 – 1.0 W/m^2 forcing).

    So, could it be that there is an additional heat source that is not correctly modeled, which causes the models to ‘delay’ the response to anthropogenic forcing ?

    Derksen et al 2012 noticed that snow cover is quite significantly underestimated in CMIP5 simulations :
    http://www.nature.com/news/arctic-snow-cover-shows-sharp-decline-1.11709
    We are talking about very significant reductions in snow cover, which just set a record of a whopping 6 million km^2 snow cover anomaly in June 2012 :
    http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=6

    What kind of forcing would such a large anomaly in snow cover create ?
    Tamino did a first estimate using observational data and a simple model for insolation, and assessed that the albedo changes for NH ice and snow over the past couple of decades causes an extra 1150 TW to be absorbed by our planet :
    http://tamino.wordpress.com/2012/10/08/snowice-by-request/
    1150 TW is some 0.9 W/m^2 if spread out over the entire Northern Hemisphere.
    If this albedo-induced heat is kept closer to the Arctic, that number goes up even more.

    This is certainly in the ballpark of the forcing mentioned above, and thus can quite plausibly explain why Arctic sea ice decline is 20-40 year ahead of GCM estimates.

    If underestimate of high-summer snow cover decline is the cause of GCMs underestimate of Arctic sea ice decline, then the search for “causes” of Arctic sea ice decline would shift to finding causes for the rapid decline in Northern Hemisphere summer snow cover.

    Which would take the scientific discussion to a slightly different area of the planet, with slightly different physics and different implications about the future….

  • Lennart van der Linde

    Walt Meier in his endnote 18 refers to Maslowski et al (2012):
    http://www.oc.nps.edu/NAME/Maslowski%20et%20al.%202012%20EPS%20Future%20of%20Arctic%20Sea%20Ice.pdf

    They write on p.639:
    “The modeled evolution of Arctic sea ice volume appears to be much stronger correlated with changes in ice thickness than with ice extent as it shows a similar negative trend beginning around the mid-1990s. When considering this part of the sea ice–volume time series, one can estimate a negative trend of −1,120 km3 year−1 with a standard deviation of ±2,353 km3 year−1 from combined model and observational estimates for October–November 1996–2007. Given the estimated trend and the volume estimate for October–November of 2007 at less than 9,000 km3 (Kwok et al. 2009), one can project that at this rate it would take only 9 more years or until 2016 ± 3 years to reach a nearly ice-free Arctic Ocean in summer. Regardless of high uncertainty associated with such an estimate, it does provide a lower bound of the time range for projections of seasonal sea ice cover. (We do note that other published estimates also have large or indeterminate uncertainties.) At the same time, observational proxies of ice thickness (Maslanik et al. 2011) and independent model estimates (Polar Science Center 2011) of sea ice volume suggest a further decline of ice volume since 2007.”

    According to this reasoning there seems to be a fair chance that the Arctic will be ice free at the end of summer before the end of this decade. I’m curious to know how large the participants in this discussion estimate this chance to be.

  • Arjan van Beelen

    Jim Cripwell, before discrediting this blog could you please elaborate on your theory that the observed changes in Antarctic and Arctic sea ice extent/volume are caused by changes in cloud cover? I don’t see why the albedo of clouds above Arctic sea ice is larger than above Antarctic sea ice, I’d also like to see some studies/observations of that.) Preferably I would like to see some observations and studies backing up your conclusions.
    I have seen studies and observations backing up the theory you seem to call CAGW (?, though it is not clear what is your definition of that?). I have also seen studies describing why we expect to see large sea ice changes in the Arctic (see the discussion above), and not in the Antarctic and possible reasons why we observe slight increases in Antarctic sea ice (e.g. see (very recent) http://www.the-cryosphere-discuss.net/6/931/2012/tcd-6-931-2012.pdf , refs and especially discussion therein). (FYI: sea ice changes in the Arctic are 4x larger than in the Antarctic, changes in the latter are barely significant; global sea ice trend is strongly negative.)

  • Bob Brand

    I would like to say I appreciate the efforts by Drs. Meier, Curry and Lindsay to participate in this dialogue. All three of the guest blogs are really informative. Also, I happen to disagree with the comments made by Jim Cripwell concerning the choice of experts: all three are excellent. Although I sometimes disagree with the comments made by Dr. Curry on her blog, she is certainly one of the most rational, influential and well-informed of the ‘skeptic’ voices in the blogosphere.

    Judith Curry rightly asks: “What percentage of the recent decline would you attribute to anthropogenic greenhouse gases?

    We ought to keep in mind that anthropogenic forcings are the sum of (at least) greenhouse gases, ozone, direct and indirect effects of aerosols and also soot (‘black carbon’), if you want to mention that separately from aerosols:

    http://www.ipcc.ch/publications_and_data/ar4/wg1/en/fig/figure-ts-5-l.png

    And I guess we can forget about Urban Heat Islands in the Arctic. ;-)

    I would suggest the proper answer to Dr. Curry’s question might well be: “> 100 per cent”, because anywhere from 20% to 70% of the effect of extra greenhouse gases may have been masked by extra aerosols (as you can see in the IPCC radiative forcings table, linked above).

    A separate reason that the attribution of this decline to extra GHG’s may actually be “> 100%”, is that naturally the insolation at higher Northern latitudes is now (very slowly) decreasing – because of orbital forcings (Berger and Loutre 1992). Since we are very slowly nearing the later part of the current interglacial, one would actually expect a trend towards an *increase* in Arctic sea ice.

    I would appreciate it very much if all three experts would briefly comment on these considerations.

  • Jos Hagelaars

    Dear editors and advisory board,
    A very good initiative to facilitate a professional scientific discussion about the very interesting subject: the climate of the world we all live in. I find it also laudable to give the interested public an opportunity to react or ask questions.
    Thanks very much.

    I see there is some kind of agreement between the experts on the attribution of the decline in the Arctic sea ice to greenhouse gases (50-70%). Dr. Meier and Dr. Lindsay state that without the long-term warming trend of GHG’s this decline can’t be explained, with some references to research indicating that this decline appears to be unique in at least the last 5000 years.
    Does Prof. Curry agree with this statement?

    The natural variability could even cause the Arctic sea ice to grow again for some decades (Kay 2011), but due to the seemingly unstoppable trend in growing GHG concentrations in the atmosphere the long term trend will be one of less and less ice in the Arctic. A unique ecological habitat could be lost then.
    According to Yamamoto et al 2012 the rate of ocean acidification (dropping CO3(2-) concentration) in the Arctic is not only influenced by the rising of the atmospheric CO2 concentration but also by the loss of sea ice. This also has a negative influence on ecological life in the Arctic Ocean.
    What’s the opinion of the experts on this matter?

  • Neven

    Sorry, here’s another try for a better layout:

    I agree that it would’ve been nice if Dr Peter Wadhams of the University of Cambridge had been invited to give his views. This initiative was announced in a Dutch news paper as a negotiation between alarmist scientists and skeptics. Dr Meier and Dr Lindsay are not in the least alarmist. Wadhams could be labeled as such, despite the fact that he has been largely right about the unfolding of events in the Arctic so far. An unfolding which, of course, is alarming.

    It’s good to see though that all expert participants agree on an anthropogenic factor of at least 50%. Given the magnitude of the event and the rate at which it is progressing, one then inevitably moves on from ‘could there possibly be a problem ever?’ to ‘what can and should be done about this anthropogenic factor?’. It seems that after one day ClimateDialogue has been so successful in reaching agreement concerning the reality and risks of AGW (which is clearly reflected in the Arctic situation) that it has made the dialogue about all other scientific aspects of climate change irrelevant. Well done, chaps.

    Now, of course, many will say: But is there a problem related to the disappearing of Arctic sea ice? I personally think there very well could be several problems and have co-written an article about it for the Arctic Sea Ice blog, called Why Arctic sea ice shouldn’t leave anyone cold. Maybe Drs Curry, Lindsay and Meier could expand some more on potential consequences of disappearing Arctic sea ice? In my view saying “we don’t know” isn’t really comforting. Rather the opposite, with, again, the magnitude of the event and its rate of progress in mind. We absolutely need to know this, right? This is the crux of the matter.

    So some more please on Arctic Amplification, Northern Hemisphere snow fall patterns (positive anomaly in winter, very negative anomaly in spring and summer) and the influence on atmospheric patterns. Permafrost and methane clathrates are less relevant at this point.

  • Neven

    Now, of course, many will say: But is there a problem related to the disappearing of Arctic sea ice? I personally think there very well could be several problems and have co-written an article about it for the Arctic Sea Ice blog, called Why Arctic sea ice shouldn’t leave anyone cold. Maybe Drs Curry, Lindsay and Meier could expand some more on potential consequences of disappearing Arctic sea ice? In my view saying “we don’t know” isn’t really comforting. Rather the opposite, with, again, the magnitude of the event and its rate of progress in mind. We absolutely need to know this, right? This is the crux of the matter.

  • Rob Dekker

    Judith Curry said :

    A modeling study [14] suggested that about half of the observed September sea ice trend from 1979-2005 could be explained by natural variability, with the rest attributable to GHGs.

    Judith, I have seen similar statements about Day et al 2011 on blog sites, which seem to originate from this statement from their paper :

    Division of the ensemble mean CCSM4 1979 – 2005 trend (-0.49%/year) by the observed 1979 – 2005 trend (-0.87%/year) implies that approximately half (56%) of the observed September trend is externally forced and approximately half results from internal variability.

    Two notes on this :

    (1) Their CCSM4 model runs show can attribute about half (56%) of the decline is sea ice as “external forcing” (GHG forcing).
    The remaining trend (which they call “internal variability”) of the difference with observation they could NOT explain.

    Which is kind of opposite from what you say.

    (2) Their analysis runs until 2005. Since then, Arctic sea ice extent dropped a whopping 2 million km^2.
    This drop since 2005 brings the observed trend since 1979 to -1.42%/year, the 20 year trend becomes -2.5%, and the 10 year trend -4.2%/year.

    Checking these numbers with their Table 1 results, shows that all of these observed trends are outside of even the COMBINED “internal” and “external” variability range of the CCSM4 models for the longer term trends. Only short term variability is still consistent with observation.

    Since CCSM4 models only show a -0.49%/year trend due to external forcing, the CCSM4 models are clearly missing something very significant in the long term trend (even as short as 10 years), and unless we find out what the cause is of the missing long term trend, and correct the models, there is really no way of stating how much of this missing trend is natural and how much is anthropogenic.

    But we better hurry up fixing our models, since the trend is clearly accelerating…

  • Faustino aka Genghis Cunn

    Judith writes: “So . . . what is the bottom line on the attribution of the recent sea ice melt? My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range.”

    That is, there is at least a 2 in 3 chance that the contribution to sea ice melt will be in the range of 30nv-70af to 70nv-30af. And perhaps a 1 in 3 chance that it will be outside that range. In short, anthropogenic forcing could be a very minor element (say 20%) or a very major element (say 80%). We don’t know; as Ron Lindsay says, it “is rather uncertain.”

    The bigger question is: does it matter? Is the extent of Arctic sea ice a great concern? Should we fear or celebrate a reduction? If the latter, then the question of attribution is of only academic interest; we should be pleased if human emissions are accelerating ice loss.

  • Hajo Smit

    I think this whole issue starts wioth a completely false statement that “biases” any debate that might ensue. It reads:

    The Arctic sea ice extent has been decreasing steadily for the past three decades. Scientists discuss the potential causes of this decrease.

    It should read:

    The Arctic sea ice extent goes up and down with the seasons in an almost perfect sinoidal oscillation as one would expect from the perfectly sinoidal changes in incoming energy from the sun. Superimposed on this unchanging sinus there are relatively minor year tot year variations in the minimum and maximum sea ice extent. Exactly as we have it with the tides at our shores. Since 1979 seas ice extent is measured by sattelite. In september 2007 and 2012 the minima have been exceptionally low (in both cases within weeks the line was back to the regular sinus). Depending on the interval it is possible to conclude that there is a downward trend. Scientist discuss the potential causes of this decrease if it is statistically significant at all given that older datapoints from the 30′s also show low ice extent.

    If the other topics in this “climate dialogue” will also be so badly skewed from the onset in the definition of the topic. Then I am 100% sure that the whole dialogue will fail. We will end up with the anwers to the wrong questions.

  • Lennart van der Linde

    Judith Curry writes in her guest blog:
    “Focusing on CO2 as the dominant influence on the time scale of two decades seems very misguided to me.”

    And:
    “The first issue to debunk is that an ‘ice free’ Arctic is some sort of ‘tipping point.’ A number of recent studies find that in models, the loss of summer sea ice cover is highly reversible.
    The impact of September sea ice loss on the ice albedo feedback mechanism is interesting. The minimum sea ice occurs during a period when the sun is at low elevation, so the direct ice albedo effect isn’t all that large. Less sea ice in autumn means more snowfall on the continents, which can have a larger impact on albedo. The impacts of the freeze-thaw over the annual cycle influences ocean circulations. But sea ice would continue to freeze and thaw on an annual cycle.”

    And:
    “Would melting sea ice trigger some sort of clathrate methane release into the atmosphere? Well in terms of thawing permafrost, it seems like more snow fall on the continents would inhibit permafrost thawing. Same for the stability of the Greenland ice cap.
    These are all qualitative speculations, but I am not seeing a big rationale for climate catastrophe if the see ice melts.”

    This would all be quite comforting if it would make sense. But does it? Not according to the arguments of scientists like Jim Hansen.

    What’s the influence of CO2 on the time scale of two decades? Over the past two decades CO2-concentrations increased by about 36 ppm (from about 356 to about 392 ppm, almost 2 ppm/year on average). Over the past two centuries CO2 increased by more than 100 ppm from about 280 ppm to the current 392 ppm, so more than 0.5 ppm/year on average. The current growth rate is more than 2 ppm/year:
    http://www.esrl.noaa.gov/gmd/ccgg/trends/

    Jim Hansen gives some useful context to these data in this article with Makiko Sato:
    http://arxiv.org/ftp/arxiv/papers/1105/1105.0968.pdf

    The natural rate of CO2 change during deglaciations is about 100 ppm in 10.000 years (from about 190 to about 290 ppm), so on average about 1 ppm per century. At the current growth rate, which shows no sign of slowing yet, we can expect to reach 560 ppm, a doubling from preindustrial, before the end of this century with an average rate of increase of about 1 ppm/year over three centuries. That would bring us back to a CO2 level that earth has not seen in probably more than 40 million years, so before the start of the glaciation of Antarctica, with an average speed over three centuries that is about 100 times faster than during recent deglaciations.

    This is the focus of Jim Hansen, and that seems very reasonable to me. I don’t understand why Judith Curry seems to think this focus is ‘misguided’.

    Hansen thinks the loss of Arctic sea ice is a potential ‘tipping point’ because of several potential positive feedbacks, such as what he calls the ‘albedo flip’. Loss of albedo does not start at ice area minimum, but much earlier in the season when insolation in the Arctic is at its peak. That makes the ice albedo effect potentially much larger than Curry seems to think.

    More snow fall on the continents in autumn/winter doesn’t automatically mean more snow and albedo in spring. To the contrary, as Rob Dekker points out, studies show that there seems to be less and less snow in spring on the continents, so less albedo, faster warming and more melting of permafrost.

    This also affects warming and melting on Greenland, just as the warming ocean water does, with the risk of fast and large sea level rise. Why does Judith Curry seem to take this risk not very seriously?

    Melting of permafrost and clathrates would be another positive feedback by releasing CO2 and methane, although there seems to be quite some discussion about the potential speed/time scale of that feedback. If however Arctic sea ice melts away much faster that thus far expected, this feedback could also kick in much faster than expected.

    I don’t see why we should ignore these quite serious risks, as Judith Curry seems to advise.

  • Elmar Veerman

    I must say I am surprised that none of these three scientists mentiones the possibility that more than 100% of Arctic sea ice decline is due to anthropogenic greenhouse gases.

    That needs an explanation, of course.

    In my opinion it is entirely possible that what we call ‘normal’ (ice extent before 1979) wasn’t normal at all. Warming had already started long before 1979, at least 2000 years ago. Without anthropogenic greenhouse gases, the next ice age might have started. Arctic sea ice extent would have been much greater than it was right before 1979.

    It is strange to pretend the ocean oscillations can be a cause of the decline if there would have been growth in a situation without anthropogenic greenhouse gases.

  • capt.dallas

    There has been a bit of recent research that indicates that the shorter term climate oscillations like the PDO and AMO may have much longer term oscillations or be parts of other longer term ocean oscillations related to Thermohaline circulation. Tuggweilder et al for example indicate that variation of surface wind velocity in the Antarctic convergence can have significant, (10 to 30 Sverdrup) impacts on the North Atlantic AMOC on time scales of ~150 years. Since there has been a shift in the diurnal temperature range trend starting in ~1985, where Icelandic diurnal temperature ranges are increasing, would not this be indication of stronger natural internal variability impact?

  • Bert Amesz

    Arctic sea ice

    Congratulations with your initiative. Also my compliments to the three experts for their guest blogs. Apparently there is agreement regarding the nature of the individual processes that affect Arctic sea ice. However, at the same time they conclude that the interaction and feedbacks are complex and not (yet) well understood. Evidently, I am not in the position to provide any clarification on this complicated matter. Nevertheless I have some questions and remarks.

    My first remarks concerns question (2) of the introduction: ‘how unusual is the current decline in historical perspective?’ Walt Meier concludes that ‘the current decline appears to be unique in at least the last 5000 years’. But in the report ‘Past Climate Variability and Change in the Arctic and at High Latitudes’ (US-CCSP, 2009) I read that, somewhere between 750 and 1500 AD, ‘the Northwest Passage was open, at least during some summers’. Does this mean that, at that time, the situation was comparable to present day conditions? My question/remark may be relevant since the mentioned period seems to coincide with the Medieval Climate Anomaly (MCA). It should be noted that during the same period the Aletsch glacier retreated as well.

    My second remark relates to the first sentence of the introduction: ‘is the decline dominated by global warming or can it be explained by natural variability? Maybe it’s just semantics, but the two phenomena aren’t mutually exclusive. I suppose that ‘global warming’ must be read as ‘atmospheric warming [by GHG’s]’? As to the natural variability, I would like the make to following remarks. The behavior of the world ocean (THC/AMOC, ENSO, AMO, PDO) is indeed extremely complex. So is it’s interaction with the cryosphere (sea ice, ice shelves, NADW, AABW) and atmosphere (AO/NAO, snow/ice-albedo). The system is not only intricate – it’s also extremely slow. Climate feedbacks take place on a century (or even millennium?) timescale. In all major or abrupt climate changes (Big Freeze, the 8,2Ka-event, DO-events, etc), the coupled ocean system played a dominant role. Is it, given this slow response, misplaced to assume that, since early 19th century, our climate is still recovering from LIA? And that the warming of the atmosphere in the 20th century is, at least partly, a long term ‘natural variability’? IPCC did not (yet) ‘find hard evidence’ for such a hypothesis. Maybe the answer can be found in the Arctic.

  • Neven

    Dr. Curry wrote:

    The net effect on climate outside the Arctic Ocean would be what? More snow during winter on the continents is the most obvious expected change.

    and

    Well in terms of thawing permafrost, it seems like more snow fall on the continents would inhibit permafrost thawing.

    Snow works as an insulator, according to this report from the University of Alaska Fairbanks:

    “Snow cover influences the exchange of heat between the air and the ground and also affects the distribution of permafrost. A heavy snowfall in the autumn or early winter will slow down frost penetration, soil freezing and the formation of permafrost because the insulating blanket of snow retards heat loss from the ground. On the other hand, a thick snow cover that persists on the ground in spring will delay thawing of the underlying frozen ground.”

    That thick snow cover is obviously not persisting in spring, so thank you for pointing out another positive feedback.

  • Arthur Smith

    I would like to understand Judith Curry’s confidence in attributing the remarkably low levels Arctic ice plunged to this year to the brief Arctic cyclonic storm in August. Cyclonic storms in the Arctic are rare but not unknown. Why hasn’t such a storm caused this sort of thing before? If this storm was in some ways unique, would not climate change be expected to be itself causative in the formation of such a storm, so it cannot be referred to as natural variability in the first place?

    NSIDC reported on the storm here: http://nsidc.org/arcticseaicenews/2012/08/a-summer-storm-in-the-arctic/ including the interesting comment – “Summers dominated by low pressure systems over the central Arctic Ocean tend to end up with greater ice extent than summers dominated by high pressure systems.” Why did that not happen this time? Attribution without a physical causative mechanism doesn’t sound like scientific explanation to me…

  • Albert Jacobs

    As “Faustino” asks: “Does it matter?” What is the quest about?

    First, It is to prove or disprove whether GHG (aka carbon dioxide, mostly) are capable of causing catastrophic global warming. We are still waiting for that proof. It is not supplied by scenario-based computer models based on a more than a century-old paper, revised by its author ten years later and accepted as a basic dogma for parameter input. Its programs have also been seriously challenged.

    Second, to investigate in depth the natural causes of climate change, in the geological past and at present times. So far the IPCC has paid only lip service to alternatives. Hypotheses involving the sun and the oceans have been developed, which need support for testing and verification, not obstruction.

    Third, the applicability of the Precautionary Principle has to be examined in view of failing computer predictions of the last twenty years. Meanwhile the abatement and mitigation scam has taken a trillion dollars out of the world economy without much benefit to climate. It is not sufficiently realised how much secondary consequences of EU carbon policy have contributed to economic problems of today.

    In the light of the above, I must agree that the question of Arctic ice cover, is not of primary relevance, in particular when we are so uncertain about the causes and supposed mechanism.

  • Douglas J. Keenan

    This post claims that there is a “trend” in Arctic sea ice extent. A trend, in order to exist, should be demonstrated to be statistically significant. There has been no such demonstration, by anyone. Moreover, I do not believe that there could be such a demonstration, given the shortness of the time series.

    In other words, the claimed “trend” might be reasonably ascribed to random variation. As an analogy, if we flip a coin four times and get the same side each time, that does not imply that the coin is biased: getting four in a row can reasonably be ascribed to random variation (the probability of getting four in a row is 1/8).

    The techniques for evaluating significance that are taught in introductory statistics courses are based on assumptions that do not hold for the Arctic ice (e.g. the assumption that there are no autocorrelations). Thus, more specialized techniques need to be used.

  • Bart Verheggen

    Thank you to Walt Meier, Judith Curry and Ron Lindsay for participating in this new platform!

    Both WM and RL attribute most of the decline in Arctic sea ice to anthropogenic activities and cite Day et al (2012) and Kay et al (2011) in support of their assessment. These studies estimate between 5 and 30% and approx 50% of the decline to natural causes. Reasons for a dominant anthropogenic role is that the current decline is unique in probably thousands of years, Arctic-wide, correlates with the global warming trend (which is predominantly anthropogenic) and is quantitatively inexplicable if anthropogenic contributions are excluded. JC thinks it’s about 50-50 natural-anthropogenic, but it is not clear to me what she bases her assessment on: Her post lists many uncertain factors, but these would merely mean that the error bars are very large; uncertainty itself does not translate automatically into a 50-50 split (or any other particular split).

    So my q uestion to Judith Curry would be: What is your basis for assessing a 50-50 split?

    In a more general sense, could natural variability not also have contributed to cooling, thus having masked some of the anthropogenic warming (as e.g. solar trends may have over recent decades)? What is the evidence that natural unforced variability has actually contributed to warming?

    Short comment: I purposefully distinguish anthropogenic versus natural causes, since they must add up to 100%. GHG and natural causes do not need to add up to 100%, since other anthropogenic forcings, notably aerosols, are then left out of the picture. Since these are very likely negative, the total would add up to more than 100%, but that is easily lost in the argumentation.

  • Neven

    Dr. Meier wrote:

    Our expectations for how the ice responds to natural variability is based upon a thicker ice cover, which may no longer be valid.

    Bingo…

  • jdannan

    Curry’s “attribution” statement implies that she believes the forced component to be about half of the recent trend, with natural contributing an equal amount.

    Under the reasonable assumption that the forced trend will stay roughly constant, and that natural contribution can be either sign, she is expecting the future observed trend to be half the historical one, albeit with substantial uncertainty.

    I think this is obviously nonsensical, it is certainly contrary to all published research in this area, and call upon her to either

    Withdraw her statement, or
    Clarify how I have misunderstood it (and to be precise, let’s hear her prediction for future trend in Arctic sea ice), or
    Justify it with reference to quantitative analysis.

  • Rob Dekker

    Bert said :

    alt Meier concludes that ‘the current decline appears to be unique in at least the last 5000 years’. But in the report ‘Past Climate Variability and Change in the Arctic and at High Latitudes’ (US-CCSP, 2009) I read that, somewhere between 750 and 1500 AD, ‘the Northwest Passage was open, at least during some summers’.

    It took me a bit of time to find that report, but here it is :
    http://downloads.climatescience.gov/sap/sap1-2/sap1-2-final-report-all.pdf
    Regarding your claims, take a look at the evidence :

    Figure 6.8 shows the bowhead whale bone findings on which this statement was based.

    They found 5 specimens of bowhead whale bones on the shore of the Beaufort sea that dated around 1000 AD.
    There was no significant increase in bowhead whale bones found in the Central Canadian Archipelago over the 750-1500 AD period, nor any significant increase on the East side of the Canadian Archipelago.

    So, maybe the Beaufort sea was not completely frozen over in summers during that time, but I think that the authors do not present enough evidence to claim that the Northwest passage was open during some summers over that period.

    What do you think ?

  • Rob Dekker

    Bert said

    The system is not only intricate – it’s also extremely slow. Climate feedbacks take place on a century (or even millennium?) timescale.

    Bert, this statement is puzzling.
    As far as I know, if snow or ice disappears, the albedo (feedback) effect is immediate.
    After all, how could the sun know that it should react slowly to a change in albedo of any particular part of the planet ?

  • Elmar Veerman

    So… all three experts think natural variability has contributed substantially to recent sea ice loss in the Arctic. But they can’t point to a significant source of this variation from outside the system (the only candidate, the sun, fails to meet the criteria). So it’s internal variability we’re talking about. This implies that this variability is not part of climate change, just part of the present climate. And that in turn means the effect should reverse in the not too distant future, adding extra ice. Indeed all three seem to think that 2012 ice cover was an exception, which will be followed by years with more ice.

    I’m not an expert, but I am confident that they are wrong. That’s because sea ice volume in the Arctic has steadily declined since 1979. A virtually ice-free Arctic seems inevitable before the end of 2015, but could happen next year. My question to Walt Meier, Judith Curry and Ron Lindsay would be: if this happens, will it change your view about the proportion of ice loss that can be contributed to anthropogenic greenhousgases? Especially Walt Meier, since you call total ice loss in 2015 highly unlikely. If it happens, that will surely change your view?

  • Bert Amesz

    Rob Dekker:

    Arctic sea ice during the Medieval Climate Anomaly

    I’m not an expert on bowhead whales. I’m simply referring to the conclusion on page 146 of the report (US Climate Science Program, 2009) that reads:

    “A final peak of bowhead bones dated
    about 1.5–0.75 ka has been found in all
    three regions, suggesting an open
    Northwest Passage during at least
    some summers. During this interval
    the bowhead-hunting Thule Inuit
    (Eskimo) expanded eastward out of the
    Bering Sea region and ultimately
    spread to Greenland and Labrador”

    Thus it seems that, during the MCA, there was a (significant) natural variability in sea ice extent. Comparable to the present day situation? I don’t know.

  • Eli Rabett

    Several above have pointed out that lower albedo due to more open water in September is not as important because the sun is low, however, since the lower fall ice cover means that there will be more, thin, first year ice grown during the winter, which will melt faster during the spring and summer.

    Thus since there will be less ice cover in the spring and summer (see this figure at cryosphere today which shows that the decrease in ice cover is for the entire year) the albedo will be significantly lower during the spring and summer. The first effect, of course, will be to warm the Arctic ocean even more, and melt further ice.

  • Eli Rabett

    It is quite clear from Judith Curry’s response to James Annan that her only justifications for stating that the loss of sea ice is her gut feeling about sea ice and her mistrust of models. To her it is a coin toss, 50/50. Now some, not Eli to be sure, might be tempted to point out that those who relied on gut feelings and their mistrust of models, were badly wrong in predicting the US election last week, but the point is not as troll like as one might imaging.

    James points out that the second word in natural variation is variation, that is the natural variation of sea ice cover will go up and will go down. We see this in the record. The decline since 1979 when we began to have useable satellite coverage is not steady, but a jiggling imposed on the larger trend. One observes ups and downs on a time scale of one to a few years but not on a ten to longer year timescale. On the other hand greenhouse gas forcing predicts a steady decline in the average of the trend which is what is observed.

    James Annan is asking Judith Curry to specify a mechanism that is driving the naturally driven component of sea ice area downwards.

    Further, since we expect the greenhouse driven component of the forcing to increase, or at best remain constant in the foreseeable future, for the sea ice not to go to zero in the Fall (or even earlier) at some point in the half century future, that natural forcing has to be LARGER than the greenhouse gas forcing to stop or reverse the decline.

    Something that large has to be obvious. So, what is it?

  • Dan H.

    Elmar,
    Did you read the paper to which Walt referenced about the Russian data dated back to 1933? It may give you more insight on the extent of the Arctic se ice prior to the satellite record.

    http://www.agu.org/pubs/crossref/2008/2008JC004830.shtml

  • Hank Roberts

    “… the retreat in recent decades is pan-Arctic and year-round in some regions, whereas the early twentieth century retreat was only observed in summer in the Russian Arctic. The AARI ice charts indicate that a significant transition occurred in the Russian Arctic in the mid-1980s, when its sea ice cover began to retreat along with that of the rest of the Arctic.”

    “… ice extent began to decrease rapidly in the mid-1980s for most seasons and regions….
    … overall there is no correlation between our results and the Arctic Oscillation index.”

    “… Had the AARI charts been available to Meier et al. they may have instead concluded that a more significant change had occurred since our results show a transition from advance to retreat during this time.”

    http://www.agu.org/pubs/crossref/2008/2008JC004830.shtml
    doi:10.1029/2008JC004830, 2008

    Cited by 8: http://scholar.google.com/scholar?hl=en&lr=&cites=10638625586393882405

  • Jos Hagelaars

    Prof. Curry says in her 5.43 pm comment, with reference to the study of the National Research Council: “The problem just isn’t with sea ice, but GCM’s have been shown to basically have no skill on decadal predictions of regional climate change.”

    ‘No skill’ is not what the NRC report says:
    “Some global coupled climate models are able to realistically simulate the past behavior of Arctic sea ice (e.g., Jahn et al., 2012). Figure 1.2 compares a single realization by the Community Climate System Model Version 3 (CCSM3) with observations of the actual ice cover, demonstrating the model’s success in capturing not only the decadal-scale pace of ice loss, but also realistic interannual variability. Of particular note is the ability of the modeled ice extent to undergo a decade of recovery within the inexorable downward trend.”

    Jahn et al 2012 indicate that the sea ice extent has a large internal variability on a 24-year scale but that over longer periods the decreasing trend in ice extent can be captured well:
    “In other words, approximately one in three ensemble members has a sea ice extent trend for 1981–2005 that is not statistically significant, which again highlights that the internal variability is large and can hide (or amplify) a forced trend over this relatively short period, complicating the detection of a forced trend. Over longer periods (1970–2005, or longer), however, all ensemble members show a decreasing trend in the ice extent that is significant at the 95% level, resulting from the smaller contribution of internal variability compared to the trend.”

    - Why this ‘no skill’ statement?

    Dr. Meier said: “…because the I don’t see the AMO and PDO having a large magnitude influence on summer ice. The AO does have a larger influence, but that has largely been lost in recent years.”
    Dr. Lindsay said: “I think we all agree that the AO, NAO, and PDO have little role in the long-term decline.”
    But now I read in Prof. Curry’s comment:
    “Recent published estimates of attribution of sea ice melt range from 5-40%. These estimates do not include solar cooling or account for the shift to the cool phase of the PDO and a like shift to the cool phase of the AMO. Since all of these lean towards cooling, I drop the AGW attribution to 50% with a large error bar.”
    To me these statements are contradictory, a little role / no large magnitude influence versus a drop from 10-45% with large error bars.

    - Why this large difference in opinion on natural variation?

  • Guido van der Werf

    Excellent initiative and many thanks to all involved. I enjoy the discussion but feel it would benefit greatly from showing a few graphs in the beginning. Especially for those that are not expert on the subject and for the press this could be helpful to better frame the discussion. I made a few graphs that might be relevant, please see here but I am sure folks at KNMI could do better. Please consider doing this for the next topics.

    Not being an expert I do think these graphs clarify few things when making the assumption that temperature and sea ice are highly correlated, thus being able project sea ice area back in time (which is backed up to some degree by the Russian data Walt Meier referred to). First and foremost, there has to a mixture of natural and anthropogenic causes at play: the overall upward trend is difficult to explain without anthropogenic sources while the 1940-1970 downward trend is most likely explained by natural causes. If true then it is very likely that the upward trends in the other time periods were at least partly aided by natural factors.

    A simple multiple linear regression of Arctic temperature driven by CO2 and AMO (yes, highly simplified) can explain about 70% of the variability. It does a poor job on interannual variability but captures the trends very well. Now, AMO is defined as SST so I am not sure what is the chicken and what is the egg but Judith Curry brought the AMO up and statistically it makes sense. It yields scalars of 1.4 K for AMO SST and 1.2 K for each Watt of radiative forcing, indicating anthropogenic factors are at the moment more important than natural ones. Again, a huge simplification but still illustrative I think and I hope this will encourage adding some graphs for the follow-up topics.

  • william

    Best wishes for your new endeavour. I have some preliminary comments at http://scienceblogs.com/stoat/2012/11/14/climatedialogue-org/.

    Meanwhile, I’m with those (Bart, James, Eli) interested in the three estimates of anthro contribution, but rather puzzled by the confidence in the estimates of natural contribution. Fundamentally, it seems to me (guv) that you can only do attribution from the models (as Ron said) but that means that if you don’t trust the models (as JC clearly doesn’t) you have to admit you have no real basis for estimating anthro vs natural contributions. No amount of “gut feeling” is going to fix that up.

    On a slightly meta note, I think this experiment will only work if the 3 invited folk mix in and address peoples comments; so I find JC’s obvious reluctance to deal with James’s comments very much against the spirit of this blog. James is a published researcher in the field of attribution; indeed his credentials in this area are better than JC’s. I don’t think her rather dismissive “go off and read a pile of other stuff” is satisfactory. But this isn’t all about JC: I’d be interested in Walt or Ron’s reaction to James’s comments.

    Lastly, I’ve just read:

    “Recent published estimates of attribution of sea ice melt range from 5-40%…. Since all of these lean towards cooling, I drop the AGW attribution to 50% with a large error bar.”

    and can make no sense of it. If the published estimates of (presumably) anthro attribution are 5-40%, changing that to 50% is an increase, not a drop.

  • RobertInAz

    Re: Ice free Arctic. Once we get to an “ice free” state – if the annual winter freeze always gets to 15 million square kilometers, is there any additional heat (energy) stored year to year? In other words, would the deep Arctic be gradually warming even if the surface completely refreezes each winter – no matter how thin the ice cover? Would additional energy absorbed through lower albedo be stored in other places? My sense is that heat taken into the Arctic in the summer/fall would get released over the winter.

  • ronallarson

    I’d like to emphasize two resources identified above – but not strongly enough.

    First there have been two earlier cites to the 2012 paper by Prof. Maslowski on modeling. Maslowski there gently criticizes most models, but not strongly enough stating his own that have correctly predicted the trends. Many years ago he was predicting ice disappearance in just a few more years – well before the three panelists are still doing. (And I have seen no reference to the fact that ice area, extent, volume, and thickness all have to go to zero together; area/extent must bend over very rapidly very soon.)

    The second resource being missed in this otherwise good dialog is the website maintained by Neven, a commenter above (and I recognize other regular contributors [I am a lurker]). See

    http://neven1.typepad.com/blog/2012/11/climatedialogue-a-new-initiative.html

    and especially his section on graphs:

    https://sites.google.com/site/arcticseaicegraphs/

    and especially the various equations to fit the Piomas data found at:

    https://sites.google.com/site/arctischepinguin/home/piomas

    and especially:

    https://14adebb0-a-62cb3a1a-s-sites.googlegroups.com/site/arctischepinguin/home/piomas/piomas-trnd1.png?attachauth=ANoY7cp8mZ9xk1mPEVA1zY04tix9MlNgvKVNNRXSXKRrDJ2Zzw8Z6rK7D_6bd4Rjjm_0DUTF0Pec9lZLMSQuzZSam7uYVpHHQY-1e2xmOojGv80RJkxeFW67bGTV6SuazCZD41GarkszzQM5sGniUamysOxOk1J957lStTGB3Z5hqparqELb4CLP6nqykY7oyl6_1iDYtWa80a2rIIQCHtT-aafbvrdaMssxJLVwQr6w7W-n-h7E_qY%3D&attredirects=0
    https://sites.google.com/site/arctischepinguin/home/piomas

    I see terrible (but common) error in using a linear fit to any arctic ice data – especially area/extent.

    Ron

  • axel_schweiger

    Judy
    Good discussion. As you point out, in the absence of longer term (pan-arctic) sea ice records, it is difficult to assess whether or not climate models capture multi-decadal sea ice variability correctly. We therefore have to allow for the fact that they may underestimate internal variability (e.g. PDO, AMO). But if this is the case, don’t you think that we also have to allow for the fact that they quite possibly underestimate “forced” variability and that this and not natural variability is chiefly responsible for the discrepancy in sea ice trends between IPCC models (as a group) and the observations, as has been widely suggested. In coming up with your 50/50 assessment it appears you are accepting the former but are discounting the latter. Am I interpreting you correctly?
    On establishing longer-term sea-ice records: Those interested can participate in doing so by helping to transcribe ship logs: http://www.oldweather.org/

  • jdannan

    That was an awfully long-winded way to avoid answering.

  • janama

    I offer this section from Timothy Casey’s article on volcanic CO2.

    http://carbon-budget.geologist-1011.net/

    “Irrespective that some authors may neglect to allow for significant volcanogenic CO2 input to the atmosphere, volcanoes represent an enormous CO2 source that is mostly submarine. Furthermore, volcanic activity beneath both ice caps and localized to the regions of most intense melting has demonstrated an obvious cause of stronger Spring melts at the Poles. It is evident from the observations of Sohn et al. (2008) & Reves-Sohn et al. (2008) that the Northwest Passage was opened up by powerful volcanic activity under the Arctic Ice along the Gakkel Ridge, while West Antarctic melting (as opposed to thickening of ice throughout the rest of Antarctica) can be explained by recent volcanic activity beneath the ice (Corr & Vaughan, 2008). Moreover, there are simply too many volcanoes to deny that the atmospheric concentration of the most erupted gas next to water is predominantly controlled by the balance or lack thereof between volcanic activity and photosynthesis. Furthermore, there is simply no established volcanic CO2 fingerprint by which we may distinguish atmospheric proportions of anthropogenic and volcanogenic contributions. This leaves us with no empirical method by which we may attribute the 20th century rise in CO2 to human energy consumption.”

  • cohenite

    The Arctic is not experiencing anything unusual today. Petr Chylek’s work shows that:

    http://www.lanl.gov/source/orgs/ees/ees14/pdfs/09Chlylek.pdf

    This is also helpful in putting the current Arctic conditions in a historical context:

    http://www.worldclimatereport.com/index.php/2004/12/10/open-letter-to-senator-mccain/

  • Rob Dekker

    Dr. Curry said

    Recent published estimates of attribution of sea ice melt range from 5-40%. These estimates do not include solar cooling or account for the shift to the cool phase of the PDO and a like shift to the cool phase of the AMO. Since all of these lean towards cooling, I drop the AGW attribution to 50% with a large error bar.

    It seems to me that this statement has little or no scientific evidence to back it up.
    The 50% of “natural variability” factors Dr. Curry mentions are either neutral or already negative :

    The PDO is negative, with the harshest winter in at least 30 years in the West Arctic this year, the sun is particularly weak in this solar cycle, and the “natural” part of the AMO is hardly noticeable : North Atlantic waters have warmed, but not warmed more than the rest of the planet over the past 30 years.

    So why did Arctic sea extent decline another 2 million km^2 (30%) even after the attribution studies that were presented in 2005 ?

    And in absence of any multi-decadal “natural variability” cause, can anyone scientifically disprove the hypothesis that 100% of the multi-decadal decline is caused by external forcing (AGW), and that natural variability is just doing it’s normal thing : be variable, year-to-year ?

  • Sam_H

    First off, thanks to everyone involved in setting up this debate, it’s a fantastic idea, and thanks to Judith, Ron and Walt for taking the time to participate, it really is appreciated by many folk!

    A few questions for whoever would like to answer them.
    Firstly, what do ye think might be lacking in the models that result in them failing to capture the accelerating loss of Arctic sea ice in recent years? Something missing/inaccurate in observations or an issue with the models themselves?
    Also, given how studies are beginning to demonstrate the influence of this ice loss on Arctic and mid-latitude weather, how might the models inability to capture the ice loss trend impact predictions of regional climate change in the next few decades?

    Cheers,
    Sam

  • Rob Dekker

    Regarding Arctic sea ice extent prior to satellite records, DMI has been making ice extent maps since 1898, based on ship logs.

    Since some “skeptics” refer to the 30′s as having a “lower” ice extent, it may be interesting to look at this DMI 1933 report, to see how “low” that extent really was :
    http://brunnur.vedur.is/pub/trausti/Iskort/Pdf/1933/1933.pdf

    Look at August 1933 (close to minimum extent), and notice that ice is still present in the Kara sea, ice packed against the coast of Siberia, just east of Yamal, and on the other side against the coast of the Beaufort (we would need to go back 30 year to see that in August), some ice still in Baffin Bay, and Svalbard still has ice on the east coast.

    In fact, it looks like there was more ice on the Atlantic side at the minimum extent in August 1933 than there is now in November 2012.

    Dr. Curry herself referred to the work done by Chapman and Walsh, who used these DMI charts, and also the Russian AARI data, and a spectrum of other pre-satellite reports, and came up with this chart for Arctic Ice extent since the 1880′s :
    http://nsidc.org/noaa/iicwg/presentations/IICWG_2011/Fetterer_Back_to_1870_Plans_for_a_Gridded_Sea_Ice_Product.pdf

    Kinnard et al 2008 confirm these 20th century results, using paleo-climate data :
    http://tamino.files.wordpress.com/2010/10/polyakfig2.jpg

    If ice extent (or variability) earlier in the 20th century was really completely different than what Chapman and Walsh or Kinnard et al reconstructed, then why did nobody publish any paper contradicting their results ?

    Further back, Kinnard et al 2011 reconstructed Arctic sea ice extent 1400 years back, using paleo climate proxies :
    http://tamino.files.wordpress.com/2011/12/kinnard_2011_sea_ice.jpg?w=500
    Notice that, yes, this does go all the way through the LIA (which seems to have a interesting dip in ice extent (maybe “warm Arctic, cold continent” effect)) and the MWP as well.

    Just to indicate how absurdly low Arctic sea ice extent has gone, somebody added 2012 minimum into the Kinnard et al graph :
    http://img849.imageshack.us/img849/5994/kinnaird2012.jpg

    Does anyone still want to argue about the “low” ice extent of the 30′s, the MWP, or suggest that somehow, after decades of AGW ice thinning, this cliff that Arctic sea ice is falling off in the past few decades is “natural variability” ? Or that there may be a 50/50 chance that it would “recover” somehow ? Or that “we don’t know how to make decadal predictions of sea ice”, or “I DONT KNOW with any high level of confidence what the sea ice will look like in 10 years or 100 years” ?

    Sometimes you don’t need to be a scientist to make a prediction about the future.

    A picture says tells more than a thousand words.

    So can we all please face reality by taking a good look at this last picture, and see where this is going ?

  • Bert Amesz

    @Rob Dekker 2012-11-15 08:32:38 (and various other bloggers):

    Natural variability / climate feedback on a multi century timescale

    The ocean circulation is an important climate feedback on a multi century timescale. And Arctic sea affects the intensity of this world wide circulation. This is roughly how it works.

    In the (sub) tropics, the sun heats the (shallow) ocean. On its turn, the ocean radiates (IR) to the atmosphere where heat is trapped by GHG’s. But not all the heat is released instantly. The reason for that is that the shallow (heated) ocean is part of the global ‘ocean conveyor belt’ (THC/AMOC). The ocean redistributes this excess (sub)tropical heat towards the polar regions. There the deep ocean is fed by freezing cold water (NADW and AABW). As a consequence, enormous bodies of warm and cold water are being pumped incessantly around the globe. During the process, waters are ‘mixed’, warm water wells up and heat is released to the atmosphere. Note that the heat storage capacity of the ocean is thousand times larger than the one of the atmosphere, while the circulation period is more than a thousand years. However, the strength of the THC/AMOC is not constant. One of the factors that affects the intensity of the THC/AMOC, is the formation of North Atlantic Deep Water (NADW) in the Arctic. In this formation process, Arctic sea ice plays an important role.

    Now let’s go back to the Little Ice Age (LIA). LIA was – probably – caused by an extremely inactive sun in combination with a series of volcanic super eruptions. As from the 18th/19th century, the sun regained strength and the heat flux to the (shallow) ocean increased. Ocean’s circulation starts to change, Arctic sea ice (and glaciers) start to retreat, earth’s albedo decreases, etc . Due to the inertness of the ocean system (heat capacity, circulation period, interplay with cryosphere, release of heat to atmosphere), it may take several centuries to reach a new state of equilibrium. So, in my view, a part of present day atmospheric warming can be explained by the presence of a secular warming trend since the end of LIA.

  • new site of interest: Climate Dialogue « iclimate

    [...] up, the causes of the decline in Artic sea ice: http://www.climatedialogue.org/melting-of-the-arctic-sea-ice/ Share this:TwitterFacebookLike this:LikeBe the first to like [...]

  • TRM

    Do any of the models take into account ocean floor thermal vents and other volcanic activity? Do we even know how many are in the arctic? Where? How big? How much energy they contribute?

  • Ed_B

    A better start would be to ask how ocean temperature data, ENSO, PDO, wind data, solar wind changes, planetary dynamics, etc etc can explain the ice loss. Without a handle on natural variabilty, the model results are necessarily junk.

    Thus I conclude that this discussion is a very poor start for any scientific “Climate Dialogue”.

  • Oso Politico

    I thought the point of the exercise was to correlate and show causation between rising CO2 levels and loss of Arctic ice. But beyond some theorizing and guesswork I see nothing – no data, no air temperatures, sea temperatures, heat content – nada, nothing, nichts. As there has been no significant rise in global temperatures for 16 years or so, the loss of sea ice must be attributable to something else – or did I miss something?

  • Neil Hutton

    I am surprised that the focus has been totally on the Arctic, though clearly that is where the ice is melting. We are however actually dealing with the entire planetary system and at the opposite pole the Antarctic Ice cover is at a maximum since satellite coverage began. It is then difficult to argue that the change in Arctic Ice cover can be related to atmospheric CO2 content since it is essentially the same at both Poles, the difference between Northern Hemisphere and Southern Hemisphere atmospheric CO2 is minimal and certainly not in the range to explain the differences in behaviour of the Polar Ice. This suggests that the the Arctic melt is not related to AGW but occurs as a result of the major oceanic oscillations. It is the oceans which control the atmospheric temperatures and not the reverse. The conclusion on this basis is that we are observing a dominantly natural cycle such as has been observed previously in the 20s and thirties of the last Century

  • MSchopp

    Dear Dr. Meyer, I have 3 questions:

    1 You wrote:

    “The current decline appears to be unique in at least the last 5000 years. While the consistent satellite record began only in 1979, earlier partial records indicate decreased extent in the Russian Arctic and the Greenland and Barents seas during the 1930s [4]. However, these reductions were regionally and temporally variable, unlike the pan-Arctic decline seen in recent decades.”

    This does not agree with research published decades ago, see here

    From 1957:
    “Northpole ice has decreased by something as 40% in volume…this has been going on for 30-40 years”
    Also predicting no ice in year 2000 if trend continues
    http://i680.photobucket.com/albums/vv161/Radiant_2009/popularmechanics1957-2.jpg

    From 1947
    “The Arctic is melting says scientist”
    http://trove.nla.gov.au/ndp/del/article/22429983?searchTerm=climate%20change&searchLimits=

    From 1922
    “The changing Arctic”
    “The Arctic seems to be warming up…all point to a radical change in climatic conditions
    http://docs.lib.noaa.gov/rescue/mwr/050/mwr-050-11-0589a.pdf

    Various more references here:
    http://www.real-science.com/new-giss-data-set-heating-arctic

    2. I think you were co-author of todays most prominent sea ice chart, that shows very little variation in sea ice before the satellite era. How can this be conciliated with the above historic evidence ?

    3. You wrote
    “Ice-free
    The Arctic has been seasonally ice-free in the past under temperatures not much higher than in recent years.” and “…the current decline appears to be unique in at least the last 5000 years”.

    Does this suggest, that you presume lower temperatures during the last 5000 years ?

    Did you use Hockey Stick temperature reconstructions for this opinion about temperature ? Most temperature reconstructions suggest that temperatures have been higher a 1000 years ago and as well during sevaral episodes in the last 5000 years.

    Would this exclude temperature as the main driver for todays decline or perhaps suggest, that
    longer term data is not suitable to exclude ice free Arctic during the past 5000 years, perhaps not even 1000 years ?

    Thanks

  • Ivan

    I am wondering, what happened to the Antarctic sea ice. It appears to be increasing, not as much as the Arctic ice is declining, but increasing nevertheless. My question is: what kind of models predicted this? Is it really possible that the planet Earth has that kind of bipolar disorder, that the Northern hemisphere exhibits all the features the GHG-dominated models predict, while the Southern Hemisphere is doing exactly the opposite? If the Arctic ice melt is anthropogenic, is the Antarctic ice gain also anthropogenic? Or maybe in the Southern Hemisphere some natural causes are overwhelming the anthropogenic forces? If so, what is the guarantee that the Arctic melt is not also dominated by some natural forces that would have melt the ice even in the absence of C)2 increase? And above all, not only that the Antarctic sea ice is increasing, the continental ice sheets are increasing as well and the temperature trend over most of the continent is flat or declining. Antarctica is a perfect hot-spot for the greenhouse warming because of an extremely dry atmosphere and almost complete isolation from the oceanic influences. If the recent warming was predominantly CO2 driven, it should be the most pronounced there. But it is not, on the contrary.

    The only way of dealing with this for scientists was to fabricate some highly implausible and ad hoc assumptions to explain away the inconvenient Antarctic lack of warming and melt, and go full steam ahead with the Arctic scare stories. But, that ain’t gonna work, I am afraid.

  • Pieter Folkens

    The present behavior of Arctic sea ice should be viewed in the context of sea ice around both poles and what is known about polar ice during Pleistocene and Holocene Interglacials. If Arctic sea ice anomalies are diminishing while Antarctic sea ice anomalies increase, a global condition cannot be reasonably recognized without a clear explanation for the difference.

    If it can be shown that present sea ice conditions are unremarkable compared with conditions in the recent and ancient past, one must be cautious about rushing to conclusions and making bold statements using words like “unprecedented” and “record-breaking.”

  • njcons

    I see very little commentary regarding NASA’s finding that a large part of the ice loss has been due to the Transpolar Ice Drift. This has been well documented and studied. NOAA says in part:

    Nghiem said the rapid decline in winter perennial ice the past two years was caused by unusual winds. “Unusual atmospheric conditions set up wind patterns that compressed the sea ice, loaded it into the Transpolar Drift Stream and then sped its flow out of the Arctic,” he said. When that sea ice reached lower latitudes, it rapidly melted in the warmer waters.

    winds causing this trend in ice reduction were set up by an unusual pattern of atmospheric pressure that began at the beginning of this century,” Nghiem said.

    http://www.nasa.gov/vision/earth/lookingatearth/quikscat-20071001.html

    Comments?

  • Jos Hagelaars

    I had the impression this should lead to a more scientific discussion between experts. When Rob van Dorland asks for some references, Prof. Curry gives a link to a blog-post in her comment on November 16, 2012 at 7:49 pm. The paper she refers to is published in PNAS:
    http://www.pnas.org/content/109/11/4074.long

    This Liu, Curry et al 2012 paper is about the influence of the loss of Arctic ice on winter snowfall in some recent winters. The paper says the following on snow extent:
    “A decrease of autumn Arctic sea ice of 1 million km2 corresponds to a significantly above-normal winter snow cover (>3-12%) in large parts of the northern United States, northwestern and central Europe, and northern and central China.”
    In the methods-section of the paper it is clear that the dataset from Rutgers University Snow Lab is used. This dataset shows a small positive trend for the complete Northern Hemisphere snowcover during the winter period:
    http://climate.rutgers.edu/snowcover/chart_seasonal.php?ui_set=nhland&ui_season=1
    The snowcover trend for NH fall is flat and the trend is clearly negative in NH spring, when the incoming energy from the sun is increasing again.

    The following statement of Prof. Curry is therefore only relevant for the winter period, when the incoming solar energy is at a minimum:
    “Less sea ice in autumn means more snowfall on the continents, which can have a larger impact on albedo.”
    Looking at the dataset used for the Liu et al paper, it would be logical that the second part of the statement also applies to the spring period: less snow in spring has a large effect on the albedo. In this case a warming effect.

    Prof. Curry’s statement: “The minimum sea ice occurs during a period when the sun is at low elevation, so the direct ice albedo effect isn’t all that large.” also seems rather strange to me. The ice extent is declining in every season and not only when the sun is at low elevation.

    It is my opinion that statements that are incorrect should be addressed.

  • Gary Swift

    Amature question here:

    Why only look at natural variability in regard to the last 9000 years? Clearly, we are in a global slump in regard to ice volume, even when you look at the most icy years we have on record.

    The decline since the last ice age is rather stark in comparison to the paltry differences in arctic ice in the past few thousand years. Compared to the real “normal” amount of Northern Hemisphere ice, the northern hemisphere is basically already ice free, isn’t it?

    How do climate models explain the loss of continental ice sheets which led to our current ‘normal’ level of arctic ice? Is there a viable explaination as to why we think our modern millenium should be more stable than previous times?

  • Neven

    I have two questions for Dr. Curry, which I hope she’ll answer if she deems them good enough:

    1) You wrote: “models are inadequate”, ” I don’t have much faith in the climate model projections of sea ice” and “climate models, which have substantial problems in simulating the Arctic climate”.

    At the same time you write: “The first issue to debunk is that an ‘ice free’ Arctic is some sort of ‘tipping point.’ A number of recent studies find that in models, the loss of summer sea ice cover is highly reversible.”

    To a lay person there seems to be a contradiction there. Why do the tipping point models simulate Arctic climate better than sea ice projection models?

    2) How does a cool PDO influence sea ice differently than a warm PDO? Isn’t the word ‘cool’ causing misunderstandings? The definition seems to be US-centric, meaning that the PDO is cool or warm depending on SSTs off the Pacific coast. But looking at this image (left is warm PDO, right is cool PDO). If this image is largely correct there looks to be more warm SSTs near Bering Strait when the PDO is cool than when the PDO is warm.

    But let’s say that when the PDO is cool, colder water enters the Arctic through Bering Strait. Is that water really colder compared to the long-term average? Because if I’m not mistaken, the PDO is defined as either cool or warm after “the monthly mean global average SST anomalies
    are removed to separate this pattern of variability from any “global warming” signal that may be present in the data” (source.

    So, again, how will the PDO add to a slowdown or reversal of the negative trend in Arctic sea ice cover? If it’s not through changes in SST, is it through changes in SAT or changes in atmospheric patterns (Beaufort Gyre, etc)?

    I suspect the same question applies to the AMO, but I haven’t looked into it enough.

  • Philip Bradley

    The trend in the Arctic ice minimum extent is -8.2%/decade. While the trend in the maximum extent is -2.78%/decade. This means we are seeing both increasing summer ice melt and increasing winter ice formation (measured by extent).

    This IMO points to decreased cloud cover as the primary cause of both, from increased summer insolation warming and increased winter radiative cooling. This also explains why Antarctic sea ice is increasing, as black carbon is almost absent there, and the albedo difference (compared to the Arctic) results in less summer ice melt.

    But I am interested in hearing the views of the experts on what causes the increasing winter Arctic sea ice formation trend.

  • troppo19

    Arctic sea ice perhaps not the best starting point. As others have observed, it is unwise to overlook the contrasting situation in the Antarctic.

    I once had an opportunity to examine a Viking map, tattooed into a piece of leather, clearly showing routes that have rarely been navigable since.

    Comments above include a lot of side-assumptions, eg GHGs trapping heat radiating from tropical oceans. If the “standard” model of atmospheric heat transfer (as per Trenberth etc) is correct, then my location (19° 11′ 38″S, 146° 40′ 31″E) would be uninhabitable, rather than as it is, benign – most of the time :-)

    Another theme puzzling me is the speculation about CO2 levels, eg are the Mauna Loa records reliable, representative, is CO2 a well-mixed component of the atmosphere etc.
    The Mauna Loa monitoring was originally established for using CO2 as one proxy for detecting changes in volcanic activity, and no doubt useful for that purpose. There are places not far north of here, on the Ring of Fire, where almost neat CO2 continually bubbles up from the sea bed, like out of a can of soft drink, and yes, there are healthy reef flora and fauna, except in the immediate vicinity of fumaroles of course.

    It is now possible to buy an accurate 1% CO2 datalogger for as little as $US65. No excuses for speculation any more – get out there and start logging. I have detected “spikes” in CO2 concentration during summer late afternoons, probable evidence of the West Pacific “carbon pipe” (out-gassing) phenomenon. Can’t be any anthropogenic source, occurs in daylight, so not to be confused with the natural increase of +/- 50 ppm that happens after sunset.

  • Neven

    I’d also make one more remark on the influence of CO2/GHGs on dimininshing Arctic sea ice over, and it has to do with semantics. When speaking of CO2/GHGs one somehow imagines the GHGs over the Arctic to trap the heat and reflect it back, melting the ice. Although this is one of the factors behind massive temperature anomalies during winter, it isn’t accurately describing the process.

    What we’re talking about is the accumulated heat in the ocean-atmosphere system by greenhouse gases since the start of the Industrial Revolution. If I’m not mistaken, this heat or energy amounts to 2 Hiroshima bombs per second since 1960. Here’s a good graph that shows the heating (from Nuccitelli et al 2012).

    As Kwok and Untersteiner wrote in this 2011 article:

    “The surplus heat needed to explain the loss of Arctic sea ice during the past few decades is on the order of 1 W/m2.”

    Now this heat is not going away, so the only way it cannot influence Arctic sea ice, is if it doesn’t get into the Arctic to begin with. But as long as the North Pole is colder than the equator, energy will be transported to it.

    Anyway, I thought it’d be better to talk of accumulated heat by GHGs than by just GHGs as an influence on the diminishing of the Arctic sea ice cover. GHGs don’t melt ice, heat does.

  • Gerald Wilhite

    Words are important. Words need to mean what they say, especially important words like “ice free”. It’s worse than the absurd phrase “climate change’. Everybody here says “ice free” isn’t descriptive so please quit using it.

    It is extremely important that you come up with an accurate phrase that means what it says.

  • Douglas J. Keenan

    Walt Meier, November 15, 2012 at 11:57 pm, states that “Statistical significance tests have been conducted by numerous people (including myself)” and cites in particular the paper of Stroeve et al. [GRL, 2012], of which he is a co-author. Walt has kindly sent me the Arctic ice data used in the paper, which allowed me to check the paper’s analysis. Following are some comments.

    In statistical analyses, inferences are not drawn directly from data. Rather, a statistical model is fit to the data, and inferences are drawn from the model. We sometimes see statements such as “the data are significantly increasing”, but this is loose phrasing. Strictly, data cannot be significantly increasing, only the trend in a statistical model can be.

    In order for a statistical analysis to be considered valid, the model must be demonstrated to be plausible on both statistical and scientific grounds. Yet no one has attempted to demonstrate that the model used by Stroeve et al. is plausible on either statistical or scientific grounds. In other words, the model was simply adopted by proclamation. The failure to present any evidence or logic to support the selection of the model is a serious violation of basic scientific principles—indeed, it means that the paper of Stroeve et al. is not true science.

    Not only is the model of Stroeve et al. unjustified, it is unjustifiable. Moreover, this is easily seen.

    First, consider total ice volumes on time scales relevant to Milankovitch cycles. A key breakthrough in understanding Milankovitch cycles came with the realization that it is the changes in ice volume that should be directly studied. For details, see Roe [GRL, 2006; doi:10.1029/2006GL027817]. (Milankovitch forcing of the ice ages was really only established with the publication of Roe’s work.) Hence, we should at least consider a model where the annual changes, rather than the ice extents, are modeled by an autoregressive process.

    A key characteristic of AR(1) processes is that only the current value has a direct effect on the next value. That seems dubious for Arctic ice: if the current year has extremely high/low ice extent, then it is at least plausible that the current year will directly affect years after the next year. Hence, we should at least consider models where the changes are AR(p), with p > 1.

    Putting the above together leads naturally to considering ARIMA(p,1,0) models, with p > 1. I checked the simplest of those models: a driftless ARIMA(2,1,0).

    The model of Stroeve et al. is a straight line with AR(1) residuals. We can directly compare that model to a driftless ARIMA(2,1,0) model, using the primary data set of the authors (September ice extents during 1953-2011). The relative likelihood of the straight line with AR(1) residuals is 0.013. In other words, there is extremely strong evidence for rejecting the model of Stroeve et al. Thus any conclusions drawn by Stroeve et al. should be regarded as unfounded.

    This does not imply that a driftless ARIMA(2,1,0) model is an appropriate model for Arctic ice. There might well be other models that are better. Selecting a model would require a research project. If a driftless ARIMA model were selected, though, that would imply that the changes in Arctic ice extent should be attributed to random variation: there is no trend.

    For some elaboration on the above, see the op-ed piece that I published in The Wall Street Journal last year:
    http://www.informath.org/media/a42.htm

  • Arjan van Beelen

    Rob van Dorland wrote: “This seems to be contradictory to Judith’s claim that snowfall (and thus snowcover) has increased. Judith, do you also have a reference to a study that supports this view?”

    I am quite interested in Dr. Curry’s answer to this. To my knowledge, sea ice extent/area and snow area have tremendously decreased during the summer half year during which the effects of changing albedo are most significant. Snow cover trends are strongly negative during May, June and July: http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=6 and sea ice . Though sea ice extent has most strongly decreased in late summer and early fall, decreases are still very large in May, June and July. http://nsidc.org/cgi-bin/bist/bist.pl?annot=1&legend=1&scale=75&tab_cols=2&tab_rows=2&config=seaice_extent_trends&submit=Refresh&hemis0=N&img0=trnd&hemis1=N&img1=plot&mo0=06&year0=2012&mo1=07&year1=2012 . (Note that sea ice area shows larger decreases early in the season than extent!) We are talking about areas of up to 5-8 million km2 less ice/snow cover in recent years, to me it seems that this must have very large climate effects, especially in the areas close to where the ice has disappeared. Dr. Curry, do you agree with this, and if you do why do you not acknowledge this, but try to downplay this by changing the subject to clouds and focus on their uncertainty? Do you have data showing that there is very large global cloud cover variability on decadal time scales, and indications/proof that this has (had) a much larger influence on planetary albedo than the recent decrease in spring/summer snow cover and sea ice? See for a first order approximation of the energy associated by the albedo change: http://tamino.wordpress.com/2012/10/05/snow-2/ and http://tamino.wordpress.com/2012/10/08/snowice-by-request/#more-5756 .

  • Rob Dekker

    Judith Curry said :

    Liu and Curry published a paper last year in PNAS on sea ice/snow extent, here is a link
    http://judithcurry.com/2012/03/05/impact-of-declining-arctic-sea-ice-on-winter-snowfall/

    Thank you for your study, which seems to collaborate the findings by Dr. Francis on how extreme weather events are linked to declining Arctic sea ice :
    http://www.agu.org/pubs/crossref/2012/2012GL051000.shtml

    Also collaborating your study are the findings from is Cohen et al 2012
    http://web.mit.edu/jlcohen/www/papers/Cohenetal_ERL12.pdf
    who state :

    Though we cannot conclude definitively that warming in the summer and autumn is forcing winter regional cooling, analysis of the most recent observational and modelling data supports links between strong regional cooling trends in the winter and warming trends in the prior seasons. A warmer, more moisture-laden Arctic atmosphere in the autumn contributes to an increase in Eurasian snow cover during that season. This change in snow cover dynamically forces negative AO conditions the following winter. We deduce that one main reason for models failing to capture the observed wintertime cooling is probably their poor representation of snow cover variability and the associated dynamical relationships with atmospheric circulation trends

    Still, your reference to winter snow cover does not seem to address the discussion topic that Rob van Doorland brought up, regarding summer snow cover decline, and to which extent the significant underestimate of multi-decadal snow cover decline in models could explain the underestimate of multi-decadal decline in Arctic sea ice extent in IPCC GCMs.

    Probably Dr. Lindsay could comment on this better than I could, but it seems to me that between GCMs and PIOMAS, PIOMAS is forced by NCEP/NCAR observational atmospheric data (at least for hind-casts), and thus has atmospheric effects of snow cover decline accounted for. So it may be no surprise that PIOMAS hind-casts appear to be more accurately simulating the ice volume and extent developments of Arctic sea ice extent.

    Maybe one of the other two experts could comment on this difference between GCMs and PIOMAS ?

  • Faustino aka Genghis Cunn

    I appreciate that the invited authors are taking the time to respond to comments and each other. The format which groups their comments separately from general users works well, readers can follow a concise debate if they wish without wading through all comments. Separating out off-topic comments is also a good idea, as long as you have the resources to do this.

    I’d still be interested in a response to my earlier comment, though. Is the loss of Arctic ice a concern, or is it advantageous, e.g. for transport and resource access? If AGW is occurring and increasing ice loss, should this be in the benefits column?

  • David Springer

    The attributions are gratuitous.

    Take Curry’s 30% – 70% anthropogenic with 66% confidence.

    What? If your doctor said that about whether you had cancer or not how would you interpret it?

    Why not say 0% – 100% anthropogenic with 100% confidence. Incredible.

  • manacker

    Dr. Curry’s assessment that there is a greater than 66% likelihood that 50%+/-20% of the recent melt was caused by anthropogenic forcing.

    Do we have any data on earlier melts of Arctic sea ice (1920s-1940s)? As I recall, there was a Russian study by Polyakov that showed similar melting to today, as well as a study by Chylek, which showed Greenland temperatures warming at the same rates as today. The temperature record for Illulissat, Greenland, shows this early 20thC warming trend:
    http://farm3.static.flickr.com/2620/3797223161_16c1ac5e39_b.jpg

    If these data show similar sea ice decline in the 1920-40 period, before there was much anthropogenic CO2 increase, this might help narrow down the anthropogenic portion of the recent decline.

    Max

  • manacker

    Here is a link to an article, which quotes Dr. Polyakov, who is now at IARC, Fairbanks:
    http://seagrant.uaf.edu/news/00ASJ/08.30.00_MeltingIcecap.html

    Dr. Igor Polyakov is a physical oceanographer at the International Arctic Research Center in Fairbanks. He says the open water tourists saw is more the result of wind and ocean currents than climate change. He also says sea ice thickness varies according to large-scale ocean-atmosphere oscillations that take decades to unfold.

    POLYAKOV: “We found a 60- to 70-year cycle with many Arctic parameters, such as surface temperature, air pressure, and ice thickness variability. And we believe this signal comes from the North Atlantic and is induced by very slow anomalies in the circulation in the North Atlantic. We believe that this cycle is very important for the Arctic environment, because all major parameters show this slow variability.”

    I’ll see if I can also find the link to the Russian study, coauthored by Polyakov.

    Max

  • manacker

    Couldn’t find that link to the Polyakov study, but here is a paper by Dr. Arnd Bernaerts on the Arctic warming of the early 20th century (EAW):
    http://noconsensus.wordpress.com/2009/11/04/past-arctic-warming-also-created-by-currents/

    From this paper

    “How is the EAW explained today

    Although 90 years have passed since the earlier Arctic Warming (EAW) commenced, it seems that the issue is still one of the most puzzling climatic anomalies of the 20th century (Bengtsson, 2004:4055), and there are many questions not answered yet. Instead the matter is often sidelined by regarding it as:
    • Natural variability is the most likely cause (Bengtsson, 2004:4045);
    • We theorize that the Arctic warming in the 1920s/1930s was due to natural fluctuations internal to the climate system (Johannessen, 2004:341)
    • The temperature anomalies are due primarily to natural variability in the weather system (Overland, 2008:81).

    Such notions explain too little. The matter becomes even more critical if claimed without sufficient prove, for example: That the past 100 years are significant for the changeover of a climate system dominated by natural forcing to a climate system dominated by anthropogenic influences, as done recently by S. Brönnimann et al., while admitting that “Our understanding of the climate mechanisms operating in the Arctic on different timescales is still limited”. (Brönnimann, 2008: 3, 20) Is it helpful to dramatize the shrinking sea ice during a recent time period, if one is not fully aware of what happened in the early years of the last century?

    Actually, few but sufficient air temperature data are available since long time. The paper will use them to show that the early warming was initiated and sustained over two decades by the West Spitsbergen Current, a branch of the Gulf Current in the North Atlantic. Naming the sea as the cause of the Arctic warming from 1919-1939 could help to understand better the current situation in the Arctic.”

    End of quote.

    Will keep looking for the original Polyakov study.

    Max

  • cwschoneveld

    I propose that writers in this blog ban the word “may” from their texts since the term always implies is opposite “may not” at the same time. Casual readers sometimes overlook the uncertainty present in it. An example from the comments?”:

    Neven
    2012-11-14 22:31:10

    Dr. Meier wrote:

    Our expectations for how the ice responds to natural variability is based upon a thicker ice cover, which may no longer be valid.

    Bingo…

  • R. Gates

    Great dialog on sea ice with a nicely balanced team of experts. Maybe would have been interesting to have Stroeve, Wadhams and Maslowski weigh in as well. Bur the important thing is we’re having a dialog.

    This discussion about attribution (50 to 70% of sea ice decline anthropogenic etc) seems as misplaced as the discussion about the role of anthropogenic climate change and superstorm Sandy. A systemic or wholistic approach (rather than fractionalizing causative factors) seems to me more likely to lead to a more productive perspective. In nonlinear responses such as we are seeing in the Arctic, there are two ways of looking at it. We may reach certain bifurcation points based on natural variability that would not tip without the extra “kick” from anthropogenic forcing, or we may reach the bifurcation point from anthropogenic forcing and natural variability kicks us over. Either way, the system tips and would not do so unless the whole system was primed for the tip, and thus it is artificial to try and put percentages on attribution. What can be said is that if a system is naturally ready for tipping to a new regime, the presence of anthropogenic forcing increases the likelihood of tipping. It could also be said that without anthropogenic factors, the system might approach a tipping point through natural variability but not tip with the extra nudge.

    The issue of NH snowpack and it’s late spring/early summer downward trend certainly needs further discussion. Of special interest should be the role this plays in both increasing regional heating both of land and air, but also of the rivers feeding into the Arctic ocean. Some persistent areas of warmth in the ocean are where their are rivers discharging into the Arctic, and with less snowpack later the season we are seeing river tempertures increase and thier peak discharge date come earlier.

  • Jim Cripwell

    Faustino, you write “I’d still be interested in a response to my earlier comment, though. Is the loss of Arctic ice a concern, or is it advantageous, e.g. for transport and resource access?”

    Speaking as a Canadian, I welcome any resource access, as long as it is under national control; and, therefore, subject to government regulation. I dread the use of the Arctic Ocean for trasnsport. The US claims that the Northwest Passage is international waters, so we will have no control. However, if there is any sort of disaster, we do not have the resources close by to clean up any mess, which could be disasterous. You need to go to places like Vancouver, or St. John’s, Newfoundland, to find the resources needed to mount any relief operation. So, please let us pray that the Northwest Passage never opens up. I strongly suspect that the Russians will, have a completely different approach for anyone attempting to use the Northeast Passage.

  • capt.dallas

    Rob Dekker, “It seems to me that this statement has little or no scientific evidence to back it up.
    The 50% of “natural variability” factors Dr. Curry mentions are either neutral or already negative :”

    It seems to me that this statement has little or no scientific evidence to back it up. :) There is a degree of uncertainty involved and either natural or GHG forcing can amplify the impact of the unknowns. How many kilometers squared of Arctic ice are cleared each year to allow shipping? Would that ice build or become fixed if it were not cleared? One of the points Dr. Curry tries to make is don’t assume, which has an old joke attached.

  • Michael Lowe

    My comment as a lay person is that you shouldn’t use the term ‘ice free’ when there is stillice there. Redifining a common sense term in this way sounds duplicitous. How about ‘effectively ice free’ or ‘crtically low ice’ or something like that.

  • Neven

    It’s an honour to have been mentioned by Dr. Curry, but it would’ve been even better if she had taken that time to address my two questions.

    Something else Dr. Curry wrote, caught my eye:

    Philip Bradley raises a very interesting point:

    “The trend in the Arctic ice minimum extent is -8.2%/decade. While the trend in the maximum extent is -2.78%/decade. This means we are seeing both increasing summer ice melt and increasing winter ice formation (measured by extent).

This IMO points to decreased cloud cover as the primary cause of both, from increased summer insolation warming and increased winter radiative cooling.”

    This might be a very interesting point until one realizes that 1) we’re talking about extent here, whereas volume would be a much more useful measurement to compare the declines in maximum and minimum, and 2) the Arctic Ocean is constrained by land masses, otherwise we might see just as big a maximum decline.

    Of course, sea ice experts realize this, which is why you won’t see Dr. Meier or Lindsay bring it up.

  • Neven

    Thank you for that excellent link, Manacker. Thanks also for mentioning it links to a radio script from 2000.

    Some other interesting tidbits from the radio script:

    Not to worry, however. Polyakov and others say the cycle shows signs of shifting back toward a colder Arctic climate.

    POLYAKOV: “I would be very careful with forecasts. But available data suggests that we are very close to the situation when everything will go to a cold climate regime, with thicker ice, colder air temperature, higher atmospheric pressures and colder water in the ocean.”

    Well, well, I wonder how Dr. Polyakov looks back at that quote.

    Here’s another interesting one:

    For the moment, many scientists believe that natural cycles are exerting a more powerful influence on the Arctic’s ice cover than are the impacts of global warming.

    Again, that was back in 2000.

  • Arjan van Beelen

    Dr. Curry wrote:

    “So for winter, it seems like ice export or ocean heat transport are the main factors (I haven’t spotted recent measurements of Fram Strait ice export?). It will be VERY interesting to what the max winter sea ice extent is for 2013, I suspect that it might be low as a result of the ocean mixing from the August storm.”

    I find this statement quite puzzling. I can understand the process (lower heat content in deeper waters), but this might lead to more rapid freezing in this area in fall (do we have any indication that this has occured?), and later opening up of this area during spring. Maximum extent is reached WELL outside the regions affected by the storm. These areas are always frozen over near maximum extent!

  • Philip Bradley

    Judith, thanks for your response. I’d like to add that it’s not generally appreciated how much solar radiation the Arctic gets in summer. In fact, in mid-summer, above the Arctic Circle gets more solar radiation than the Tropics. Which makes summer cloud albedo changes more important than generally appreciated.

    http://earthobservatory.nasa.gov/Features/EnergyBalance/page3.php

    See second figure

  • don penman

    Autumn is still lingering in the UK the leaves are still falling off the trees,there would need to be a rapid change to support the idea that Arctic Sea Ice loss equals severe winter weather.
    The growth in Sea Ice and cold weather seems to favour the Pacific side of the Arctic as it did last year.
    http://www.natice.noaa.gov/pub/ims/ims_gif/DATA/cursnow_asiaeurope.gif

  • Rob Dekker

    manacker said

    Do we have any data on earlier melts of Arctic sea ice (1920s-1940s)?

    Did you check my post 2012-11-16 10:05:17 ? This mentions the DMI charts from the 30′s, and the Chapman and Walsh reconstruction over the past century. Or the Kinnard et al reconstruction over the past 1400 years, with 2012 filled in :
    http://img849.imageshack.us/img849/5994/kinnaird2012.jpg
    Does that help ?

    As I recall, there was a Russian study by Polyakov that showed similar melting to today

    I have not seen any claim by Polyakov that showed “similar melting to today”. Not even in your reference to Polyakov’s pre-2000 study. Where did you get that statement from ?

  • TINSTAAFL

    cwschoneveld
    2012-11-17 13:53:04:

    “I propose that writers in this blog ban the word “may” from their texts”

    in the same comment:
    “Dr. Meier wrote:

    Our expectations for how the ice responds to natural variability is based upon a thicker ice cover, which may no longer be valid.”

    Bingo?

  • Neven

    Dr. Curry, I apologize for the veiled sneer, I was just surprised by the eagerness with which you seemed to take up Philip Bradely’s comment. I’m not disputing anything you say about cloudiness, as I don’t know much about the subject. My point is that if you would want to say something about it by invoking the difference between minimum and maximum decline, extent is not the most useful metric to do so. Simple example: Ice cover at maximum can reduce from 2 metre on average to 1 metre, with extent hardly changing.

    My other point concerning the Arctic Ocean being constrained by land masses: if the Arctic Ocean weren’t constrained, maximum might have been much bigger before than it is now, meaning that decline in maximum would have been bigger too (read for instance this blog post from Tamino discussing the Eisenman 2010 paper). Or in other words, you would see similar big swings from minimum to maximum before 2007. And of course, ice growth gets bigger as ice melt gets bigger. It’s called winter, and it’s still around.

    So my point was that if you want to say something by invoking the difference in decline rate between minimum and maximum extent (or area for that matter), you’re going about it the wrong way. One of the commenters at the ASI blog looked at it from another perspective:

    To me the obvious effects to explain this are 1. albedo feedback means that as ice reduces, the summer melt can be greater because of the extra energy captured. 2. In winter as the ice gets thinner, more heat can be lost through the ice allowing more ice formation.

    These are not the only effects but they are the obvious ones. In view of this, how does Curry think that this points to reduced cloud cover?

    Models and PDO in next comment.

  • Arjan van Beelen

    Dr. Curry wrote: “The past 25 years of carbon dioxide increase has contributed to less than 1 W m-2 in radiative forcing. There is no simple calculation to be made of the effect of the sea ice albedo change on the global energy balance. The better comparison is with a change in fractional cloud cover (which is highly variable), which dominates the planetary albedo far more than the arctic sea ice.”

    Rob van Dorland wrote: “This seems to be contradictory to Judith’s claim that snowfall (and thus snowcover) has increased. Judith, do you also have a reference to a study that supports this view?”

    Though increased snowfall in winter in recent years (is this trend significant?), and decreased snow area in other seasons are not incompatible, this is not what I commented on.

    I wanted to point out that, in contrary to the possible small changes in snow area in winter, the total sea ice + snow area has strongly decreased during spring and summer (5-8 million km2). See the links in my previous post. This does lead to a large albedo effect (which might actually feedback on the sea ice extent in summer). This must have very large climate effects, especially in regions previously covered by snow.

    I was wondering if Dr. Curry agrees with this, and if she has any data backing up her comment that cloud cover variations (during similar timescales..) dominate the changes in planetary albedo over the observed sea ice + snow area changes in summer. Is there any reliable data showing that there are such large trends in cloud cover?

    I see you have adressed part of my second question. Thank you very much for explaining why enhanced mixing by the storm decreases the heat content of the ocean column (I was already aware of this (not of details though), but for other readers it might be much clarifying). However, this has not answered my question. It is a direct comment on what you wrote.

    Dr. Curry wrote:

    “It will be VERY interesting to what the max winter sea ice extent is for 2013, I suspect that it might be low as a result of the ocean mixing from the August storm.”

    Personally, I don’t see how this might strongly influence winter (max) extent, because the area affected by the storm is well outside the region where the max extent is reached. The storm affected areas which are always frozen in winter.

    I can understand that the storm would lead to faster freeze up in fall (is there any indication that this has occured? Maybe Neven knows?), maybe thicker ice in this area in winter and later melt during spring. I do however NOT see how this would strongly influence max extent.

    Again, when I read Dr. Curry’s comments, I read uncertainty here, uncertainty there, snow is increasing and the ice might restore next year because of the storm. (Exaggerating a bit here of course). The reader might get the impression that these things are the dominant changes currently going on in the Arctic; I think this is not a good representation!

    This topic is starting to become more and more interesting, I’d like to thank the authors and hosts for their efforts!

  • Jos Hagelaars

    Prof. Curry raised an interesting point about the increase in amplitude from winter to summer (actually early spring to early fall) in ice volume and ice extent since 2006. However there is a difference between the two. The average amplitude in sea ice extent over 2007-2012 is about 16% higher than over the period 1979-2000, and, regarding the same periods, the ice volume amplitude is about 13% higher (if my calculations are correct).
    See this image for a comparison in ice volume and sea ice extent anomaly.
    The ice extent anomaly is based on the same data as the graph Prof. Curry referred to in her comment on November 17, 2012 at 3:30 pm. The image also shows that the decline in extent as well as in volume is accelerating.
    (Data obtained from NSIDC FTP site and KNMI Climate Explorer).

    Prof. Curry mentions changes in cloud cover and changes in ice export or ocean heat transport as possible influences for this increased variability after 2006 (larger amplitude). To me the explanation given by Neven in his comment on 2012-11-18 17:14:29 seems very plausible:
    “My other point concerning the Arctic Ocean being constrained by land masses: if the Arctic Ocean weren’t constrained, maximum might have been much bigger before than it is now, meaning that decline in maximum would have been bigger too”.
    Neven mentions the paper by Eisenman 2010. Eisenman states the following in his conclusions:
    “These results suggest that the seasonal asymmetries in the evolution of Arctic sea ice extent are overwhelmingly the consequence of blocking by coastlines.”

    What is the opinion of Dr. Meier and Dr. Lindsay about this increased variability after 2006? Do they have an explanation?

  • arctic

    A few comments concerning Judy’s division between the natural variability and GHG forced sea ice extent.
    The mean (June to November) Arctic sea ice extent is highly correlated to the mean high Arctic temperature (just look at the data for sea ice extent available from the National Snow and Ice Data Center and the temperature at high Arctic met stations available from e.g. the NASA GISS data). Polyakov et al (Clim Dyn 2009) finds that about 60% of North Atlantic post 1970 warming was due to the multi-decadal variability. Chylek et al (Geophys. Res. Lett. 2010) finds that about a half of the Arctic post 1975 warming was due to the anthropogenic GHGs and about half to the AMO (Atlantic Multi-decadal Oscillation). Mahajan et al (J. Clim. 2011) finds that the GFDL climate model simulations shows the Arctic sea ice extent highly correlated to the AMOC (Atlantic Meridional Overturning Circulation).
    All these points towards a large natural variability of the Arctic temperature and sea ice extent. If AMO will continue its 60-70 year cycle (as seen in the 20th century) we can expect the natural climate variability to start counteracting the GHG anthropogenic warming and slow down or stop the Arctic warming during the next few decades. If on the other hand the AMO will continue rising (which would be against hundreds or thousands years of the AMO records – Delworth and Mann 2000, Gray et al, Geophys. Res. Lett. 2004) the Arctic will continue warming as predicted by climate models. However, the climate models (CMIP3) are not able to reproduce the 20th century Arctic temperature variability (Wang et al 2007, J. Clim.), so their prediction of the future Arctic climate is in doubt.

  • Neven

    Given the interesting questions regarding NH snowfall and amplitude (I’ve made a graph of PIOMAS max and min data, and it looks like the difference in decadal decline between max and min is smaller than the difference for extent; I’ll report the exact numbers), I’ll just restrict myself to a clarification of my question regarding Dr. Curry’s remarks on the PDO, and leave the models be for the time being.

    To recap, Dr. Curry wrote:

    Do I think that all other things will remain the same as the period 1980-2000? almost certainly not: we have seen a shift to the cool phase of the PDO

    Thereby implying that a cool PDO (as well as solar forcing and the AMO) might slow down or reverse the steep decline in Arctic sea ice loss.

    And so I asked (click on the link to see the basis of my question):

    how will the PDO add to a slowdown or reversal of the negative trend in Arctic sea ice cover? If it’s not through changes in SST, is it through changes in SAT or changes in atmospheric patterns (Beaufort Gyre, etc)?

    Dr. Curry’s answer:

    With regards to your question on PDO. I don’t know how to answer the question in the manner that you have posed it. Large scale atmospheric and ocean circulations vary on multidecadal time scales, which influence circulation regions on shorter time scales as well, which among other things influences sea ice characteristics. Untangling how all this works has received far too little attention IMO.

    I will now try to clarify:

    Dr. Curry, you wrote “Heat from the ocean is more effective at melting the ice than heat from the atmosphere.” Ocean heat flux may well have played a dominant role in the extent/area/volume decline since 1979.

    I don’t know if I’m correct, but I’m assuming that the main influence the PDO can have on Arctic sea ice is via SSTs (probably ocean heat flux through Bering Strait). Now, when the PDO is ‘cool’ the waters in front of the entrance of Bering Strait are much warmer than when the PDO is ‘warm’. Besides, even if those waters were termed ‘cool’ compared to the other sign of the PDO, they’re probably still as warm or warmer than the average because mean global average SST anomalies are removed (see this graph for clarification). I personally don’t believe the PDO influences Arctic sea ice much via SSTs (the most important way it can), and therefore ask(ed) you if you would agree with that.

    You say that not a lot is known about how the PDO influences sea ice, still you seem to imply that the PDO could be one of the factors to slow down the steep decline from the last decade. So you must have some idea how that happens. How?

  • Neven

    I can understand that the storm would lead to faster freeze up in fall (is there any indication that this has occured? Maybe Neven knows?)

    Arjan, I don’t actually know, but if the summer storm brought up heat from lower layers in the Arctic Ocean, it must have gone somewhere else, because the areas that were most affected by the storm (East Siberian Sea, Laptev Sea), have frozen up relatively fast, as you can see on this regional graphs page. The Beaufort Sea was anomalously warm for most of the melting season, but is now filled with ice, and the Chukchi Sea is also freezing relatively fast.

    Given the SSTs in the North Pacific, I wouldn’t be surprised to see the same thing happening as last year: lots of cold and ice on the Pacific side of the Arctic, and a very slow freeze on the Atlantic side of the Arctic (Kara Sea has finally begun to freeze, Barentsz is lagging).

  • MJonas

    Neven referred to Polyakov in 2000 saying “I would be very careful with forecasts. But available data suggests that we are very close to the situation when everything will go to a cold climate regime, with thicker ice, colder air temperature, higher atmospheric pressures and colder water in the ocean.
    and then you say
    Well, well, I wonder how Dr. Polyakov looks back at that quote.“.

    If I read this correctly, then Neven is thinking of the Arctic sea ice losses in recent years, and concluding that Dr Polyakov was wrong.

    It really is too early to conclude that. We don’t know how much of the melting has been caused by wind and currents. We don’t know the temperature cycles’ causes, and we don’t know when the current cycle(s) will peak, but when the peak does occur the waters around the Arctic will still be warmer than before, and will probably stay warm for several years. Whatever ice melting has been caused by the warmer waters will therefore probably continue for several years.

    One thing is clear: the Antarctic has not been losing sea ice, although the IPCC report expected sea ice loss at both poles [AR4 ch.10 Snow and Ice “There is a projected reduction of sea ice in the 21st century in both the Arctic and Antarctic with a rather large range of model responses.“].

    It seems to me that no-one really knows enough about any of this, that the computer models are useless, and the initial question by climatedialogue.org has only one possible answer: We just don’t know.

    PS. I have been unable to login to climatedialogue.org using my normal WordPress account, and have had to create a new one. My normal signin is as “Mike Jonas:.

  • Frank

    Those of us who are not sure how much to trust GCM’s would have appreciated a summary of the basic physical processes occurring in the Arctic. The average volume of ice in the Arctic has diminished by 310+/-100 km^3/year over 1979-2011 (PIOMAS). Wikipedia says the area of the Arctic Ocean is 14,056,000 km^2 (but the areas defined by Arctic sea ice and the official Arctic Ocean certainly aren’t the same. Dividing gives a rough approximation of 22 mm/yr of decreasing ice thickness. The enthalpy of fusion for ice is 334 kJ/kg times 916.7 kg/m3 for 306,000 kJ/m3 or 306 kJ/m2/mm. Assuming these calculations reasonably and correctly approximate the situation, we need 6800 kJ/m2/yr or 0.21 W/m2 to melt 22 mm/yr of ice.

    If one wants to attribute the change in sea ice to a change in anthropogenic GHGs, the next question should be: How is the surface radiative balance changed by GHGs With a standard atmosphere, there is roughly a 1 W/m2 decrease in upward flux at the surface for 2X CO2, but the Arctic is drier, colder and stratified. Of course, only the increase DLR absorbed by sea ice can directly cause melting.

    Do traditional feedbacks apply to the Arctic with its stratified atmosphere, temperature inversions and subsistence? WIth surface temperature pegged near freezing during most of the melting season and with little vertical mixing, is water vapor feedback important? The change in energy flux associated with melting is massive: Hudson calculated that the current reduction in sea ice has produced a GLOBAL sea ice albedo feedback of 0.1 W/m2 (from 2-3% of the earth’s surface), but this could be negated by a 2.3% increase in Arctic cloud cover. (Hudson, S. R. (2011), Estimating the global radiative impact of the sea ice-albedo feedback in the Arctic, J. Geophys. Res., 116, D16102.) Unfortunately, melting of sea ice in the Bering Sea and Hudson Bay in June are unlikely to have any impact on whether sea ice at 85 degN melts in late August. Even inside the Arctic Ocean itself, convection is needed to transfer heat from regions melting earlier than normal to the remainng sea ice. Late in the season, convection moves floating sea ice, reducing its effectiveness. Changes in clouds and convection are potentially much larger than radiative forcing. It isn’t obvious why I should believe that GCMs are remotely capable of accurately modeling these convective phenomena. This is particularly true when I read how sea ice in the ECHAM GCM was “tuned” for AR5: Mauritsen, T., et al. (2012), Tuning the climate of a global model, J. Adv. Model. Earth Syst., 4, M00A01, doi:10.1029/2012MS000154. Uncertain albedo causes major difficulties for even modern weather forecasting programs near the rain/snow line for many days after a winter storm.

    Under these circumstances, attributing some fraction of the decrease in sea ice to GHGs and another fraction to natural variability appears to represent hubris. Climate science should be able to say with some confidence that the increase in DLR associated with increased GHGs is (or is not) large enough to provide the energy needed to melt roughly 20 mm per year of Arctic sea ice*, but this doesn’t mean these changes were caused by GHGs. After all, the same change in DLR isn’t causing a similar change in Antarctic sea ice. Modelers can tune their GCMs to reproduce the sea ice observed during the 1980s or the 2000s, but fiddling with multiple interacting parameters doesn’t make such models suitable for attribution or prediction. Are the same sea ice parameters used at each pole?

    *Even simple linear trends can be misleading. Consider a simplified Arctic Ocean permanently and stably covered with thick ice, 5 meters at the maximum and 3 meters at the minimum; with 2 m of ice melting in the summer matched by 2 m of ice thickening during the winter. Now increase the amount of DLR so that 50 mm of additional ice melts every summer. One would predict ice thickness varying between 2 and 4 meters after 20 years. As the ice gets thinner, (exponentially) more heat will escape through the ice during the winter, the linear trend will diminish and stability will eventually be restored. After 2012′s record melt, it has taken about 1 month longer than in 1980 for the Arctic Ocean to freeze to the shores of Asia and North America. (igloo.atmos.uiuc.edu/cgi-bin/test/print.sh?fm=10&fd=10&fy=1980&sm=11&sd=10&sy=2012) Some areas on the edge of the Arctic Ocean (Kara and Barents seas) are lagging further behind. Instead of thickening for at least six months as in 1980-1, this winter the ice will have about one month less to thicken. However, how much does sea ice actually thicken during the last month of the freezing season when the heat of fusion presumably must travel through more than one meter of ice by conduction and the air above the ice has begun to warm? Do GCMs produce reasonable results for the increase in thickness of first year sea ice with time?

    The three professors commenting above have personally struggled with many aspects Arctic climate for decades, figuratively studying many trees in a forest of challenging phenomena. Amateurs (like me) may spend a few hours flying above this forest with some back-of-the-envelop calculations, wondering if the experts are only seeing the part of the forest where scientific progress is being made. (That’s the ultimate in hubris, of course.) Above Professor Curry notes that a radiation transfer problem with clear sky radiative transfer has been solved with the “dirty window”, but she isn’t sure which models incorporate this correction. Unfortunately for my confidence, clear-sky radiation transfer is the “simplest tree in this forest”.

  • gillibrandpa

    While I understand Judith Curry’s caution about the role of natural variability in the decline of Arctic sea ice and of assigning too much importance to AGW, surely the natural cycles she mentions (PDO, AO and NAO) have all varied significantly over the past century without causing the precipitous drop in sea ice extent and volume that we have seen over the past couple of years. This seems to imply strongly that the increasing temperatures in the Arctic, and the northward oceanic transport of heat (due to a warming Atlantic), are overriding the natural variability she describes.

    It seems to me that the clearest lesson we have learned over the past couple of decades is that the natural caution of scientists has led us to consistently underestimate the scale and rate of the global changes that are occurring as a result of AGW. I’m not saying scientists shouldn’t be cautious, but events don’t seem to be waiting for them !

  • Eli Rabett

    Winter surface ice area/extent has little to say about summer/fall extent in the Arctic Ocean, because the Arctic Ocean completely freezes over during the winter. The areas which add to winter ice extent (Hudson’s Bay, Baltic Sea, Kamchatka Sea, etc.) are guaranteed to melt during the summer/fall. Where they provide some indication as to trends is the date at which they are ice free, which is, indeed earlier.

    Anyone pointing to total winter sea ice extent as an indicator of what is happening in the summer/fall is selling you a McGuffin

  • Eli Rabett

    Rob Dekker points out that

    Here, I noticed that GCM projections are lagging some 20 years (CMIP5) to 40 years (CMIP3) behind actual Arctic sea ice decline. Apparently, we are currently experiencing Arctic “climate” conditions that were not expected until another 40 – 80 ppm increase in CO2 concentration (which implies some 0.5 – 1.0 W/m^2 forcing).

    In this regard it is interesting to note that the annual swing of CO2 concentrations is about 15 ppm between spring and late summer so there would be substantially less ghg forcing in August/September and more in April/May. Is this accounted for in the models?

  • Neven

    Dr. Curry wrote:

    Clouds are much more powerful radiatively than CO2, so if we are talking about radiative forcing, clouds should be front and center in the discussion.

    Again, talking about CO2 causes misunderstandings (see Frank’s comment). It’s not the CO2 over the Arctic that is causing the Arctic sea ice to melt, it’s the accumulated heat (see this graph that shows total heat content) in the Earth system that is most probably causing the sea ice to melt so precipitously.

    Dr. Curry also wrote:

    Neven, Philip Bradley brought up the issue of clouds, I responded to that point. This response does not imply that I think clouds are the only or even the main driver of the summer sea ice minimum.

    If you are going to encourage Philip Bradley (“Philip Bradley raises a very interesting point”), you should also tell him that his methodology isn’t adequate as evidence for his hypothesis. By encouraging him you also tend to make others think you agree with his flawed methodology. Your latest comment seems to imply that you agree with me on this point (or else you would have addressed it, I assume), which means my explanation of volume as a better metric for comparing max and min decadal decline and geographical constraints hasn’t been for nothing.

    That’s important to me, because my wife told the geographical constraints and PDO to go to hell last night. :-)

  • Ibrahim

    Neven,

    You refer to: Dana Nuccitelli, Robert Way, Rob Painting, John Church, John Cook: 2012: Comment on “Ocean heat content and Earth’s radiation imbalance. II. Relation to climate shifts” . Physics Letters A

    David Douglass reply:
    D.H. Douglass, R.S. Knox, 2012: Reply to “Comment on ‘Ocean heat content and Earth’s radiation imbalance. II. Relation to climate shifts’ ” by Nuccitelli et al. Physics Letters A

    You should read it.

  • Roger Knights

    What this site is doing is terrific. Even if it raises more questions than answers, it’s great to have all the issues laid out knowledgeably and civilly in one place, instead of being scattered all over the Internet. This site should have been set up a dozen years ago.

    (One suggestion is to increase the type size of headings like “Public Comments” so they’re easier to find. And it would be nice if the site automatically converted items in link format to active links, the way some sites do.)

    My peanut gallery comment is a reply to this comment (excuse me if someone else has already done so):

    Elmar Veerman
    2012-11-15 11:27:59
    . . . Indeed all three seem to think that 2012 ice cover was an exception, which will be followed by years with more ice.

    I’m not an expert, but I am confident that they are wrong. That’s because sea ice volume in the Arctic has steadily declined since 1979. A virtually ice-free Arctic seems inevitable before the end of 2015, but could happen next year.

    But there’s a reason the trend of “steady decline” shouldn’t continue: because the high arctic doesn’t ever get above freezing–or only very briefly. (Right?)

  • Cooter

    I will just throw a couple of points out there;

    1) Ron said; “Winter ice will remain for a long time, a century or more. How long probably depends mostly on the future rate of greenhouse gas emissions.”

    Really? Looking at the current arctic temperature profile, the arctic would have to warm by close to 30C for winter sea ice to be a thing of the past. I am unaware of any science that says we can or will see that as a result of AGW. Can you point me in the right direction?

    2)At what point did 1 million sq km of ice become ‘ice free’? This is some kind of absurd language trick whereby you can make a million square kilometers of ice just disappear in the minds of the public who will have no idea what you mean. I am okay with setting some level as a definition of ice free, but it should not be a level at which there is still a very substantial amount of ice sheet in the arctic ocean. This is a ‘consensus’ which defies the English language and should not be acceptable.

    3) The notion that the arctic ice sheet’s decline correlates well with increased surface T is wrong. To wit; the increase in global average atmospheric surface temperature stopped about 16 years ago. Most of the decline to arctic sea ice has happened since that time. Further, antarctic sea ice has actually increased in the time frame. Something is terribly wrong with the notion that CAGW is supported by declining sea ice when temperatures stopped increasing but sea ice continues to decline, but only in the norther hemisphere. This is a case of scientists turning a blind eye to the data that does not match their working hypothesis. And yes; I am comfortable with the notion that an oven continues to warm for some time after the heat element comes on. It does not, however, continue to warm after the element goes off, even as certain areas absorb heat and others deliver their heat. Think about what that means for CAGW as a working theory.

    4) The notion that scientists must better communicate the science in order to stave off catastrophy is ludicrous. Science must explain naturally occuring phenomena. Period. End of story. Anything beyond that is politics and or religion. If you had stuck to the science we would be in a much better position to inform on the facts. As it is people like Hansen, Jones and Mann are making a mockery of science and leaving real damage in their wake.

    You go around crying wolf every time a hurricane makes landfall and try to scare people into doing what is ‘right’ and you will eventually lose all credibility. “Whoever undertakes to set themselves up as a judge of truth and knowledge is shipwrecked by the laughter of the gods.”

    If you want to figure out what is really happening you will need to study ENSO, PDO etc. You have alluded to this in your articles, but failed to give them their obvious due. They correlate much much better with sea ice and even surface T than CO2. Obviously; liquid water has a heat capacity several orders of magnitude greater than atmospheric gases. And the last time I checked; Trenberth still had not found the missing heat in them.

    And mind you; I do not deny that CO2 influences global atmospheric temperature, nor do I deny the anthropogenic increase on CO2. I just highly doubt that ‘about 50%’ adequately captures true natural variability and am amazed at how little we understand about the effects of oceanic cycles, solar maxima and minima, Milenkovich cycles and how ‘scientists’ are so willing to dismiss them out of hand in favor of a theory that really only matches a little tiny bit of the data. I am further amazed at how a few of these ‘scientists’ have gone way way out on a limb in their efforts to ‘prove’ their pet theory and how they’ve been allowed to do so by academic institutions that simultaneously condemn any and all religion for the exact same behavior.

    If CAGW is a serious problem we have not been served well by the scientists in the field. They’ve been so busy trying to ‘convince’ that they have forgotten to ‘prove’ and have been left in a great many cases with egg on their faces even as they throw eggs at those who scoff at them and their pet cause. See comment 1) above about winter sea ice.

  • Jos Hagelaars

    @Marcel Crok

    “Judith came up with a range of 30-70% contribution from GHG’s although she seems to be inclined towards the lower end of this range..”

    This way of summarizing suggests that Judith Curry would think that the attribution to anthropogenic forcings is somewhere between 30 and 50%. That is clearly not what she said:
    “My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range.”
    and
    “The disagreement seems to arise if we are each forced to pick a single attribution value: mine would be 50%”
    This means she thinks it’s 50%, could be 20% higher or 20% lower, but she also said that there is probably no scientist around who thinks it’s below 30%.

    Ron Lindsay mentioned 70% for the attribution value (referring to ice volume decline) and Walt Meier said: “The 50-70% range for GHGs that Judith mentions is probably a reasonable spread in capturing the potential range.”

    To me the correct summary for the question no.5 of the introduction (“What percentage of the recent decline would you attribute to anthropogenic greenhouse gases?”) would be:
    The experts conclude that the contribution of anthropogenic forcings to the sea ice decline is probably in a range of 50-70% with an uncertainty of 20%.

  • Lennart van der Linde

    Having followed the discussion so far my main conclusion is: Walt, Judith and Ron agree about a significant human influence causing the Arctic sea ice to melt, but they disagree about the probable relative proportions of human and natural factors, and about the probable speed at which the remaining sea ice will melt.

    My main question then is: what are the most important implications of this conclusion?

    My own answer would be: looking at the unprecedented speed at which we increase the human influence, currently by more than 2 ppm of CO2 per year, and looking at the current CO2-concentration of almost 400 ppm (a level not seen during maybe the past 15 million years, according to Tripati et al), it seems quite certain that the Arctic will be ice free by the end of summer before the end of this century, probably this will happen before the middle of this century, and possibly it will happen before the end of this decade. This then implies a strong positive feedback thru lower albedo and release of GHG’s, with a risk of much earlier than expected onset of these feedbacks. The significance of that risk seems large enough to urge governments around the world to reduce their GHG-emissions as quickly as possible.

    It would be interesting to learn the views of Walt, Judith and Ron on this.

  • Eli Rabett

    Roger Knights wrote

    But there’s a reason the trend of “steady decline” shouldn’t continue: because the high arctic doesn’t ever get above freezing–or only very briefly. (Right?)

    Without getting into the data weeds it is important to realize that the sea ice extent/area as recorded by, for example, Cryosphere Today, extends beyond the Arctic Ocean, so it includes things like Hudson’s Bay, the Baltic, etc. If you look at the winter extent maps at Cryosphere, you will see a steady decline of ice on the edges since 1979, which accounts for the winter decline. It is on the fringes that the system gets above freezing and the problem is that the edge is moving to higher latitudes fairly rapidly in all seasons.

  • billc

    I hope one of the experts can weigh in on a line of reasoning that I have not heard explored much. We hear lots of talk on the global average surface temperature having slowed its rise; we also hear about the arctic sea ice melting faster than expected. Why not combine the two trends? In one of those back-of-the-envelope moments I tried this using PIOMAS ice volume. The energy required to drive tropospheric temperature swings and arctic ice volumes appeared to be around the same order of magnitude for, respectively, multiannual trends and intra-annual fluctuations. While I am aware there are lots of other energy balance considerations, it is interesting that the combined metric essentially eliminated both the slowdown in warming and the acceleration in ice melt. It also seems exactly the sort of thing that internal dynamics could drive.

  • Jos de Laat

    There are two recent papers on the impact of soot and dust on Arctic sea ice.

    Goldenson, N., Doherty, S. J., Bitz, C. M., Holland, M. M., Light, B., and Conley, A. J.: Arctic climate response to forcing from light-absorbing particles in snow and sea ice in CESM, Atmos. Chem. Phys., 12, 7903-7920, doi:10.5194/acp-12-7903-2012, 2012.

    http://www.atmos-chem-phys.net/12/7903/2012/acp-12-7903-2012.html

    and

    Holland, Marika M., David A. Bailey, Bruce P. Briegleb, Bonnie Light, Elizabeth Hunke, 2012: Improved Sea Ice Shortwave Radiation Physics in CCSM4: The Impact of Melt Ponds and Aerosols on Arctic Sea Ice*. J. Climate, 25, 1413–1430. doi: http://dx.doi.org/10.1175/JCLI-D-11-00078.1

    http://nldr.library.ucar.edu/repository/assets/osgc/OSGC-000-000-010-676.pdf

    Although neither study specifically investigates how much the deposition of soot and dust on ice and snow may have contributed to recent Arctic sea ice decline, Holland et al. [2012] did perform a historical run, and results indicate that soot/dust and melting ponds may have contributed to recent Arctic sea ice decline. Furthermore, results from Goldenson et al. [2012] indicate there may also be a coupling with changes in circulation patterns. It is also interesting to note that effects are different between the Arctic and Antarctic. Either way, the magnitude of the soot/dust-on-snow/ice effect certainly warrants further investigation.

  • Jos Hagelaars

    @Marcel Crok 2

    The warming trends Pielke shows on his blog are based on the NCEP/NCAR reanalysis data for only June, July and August and they happen to be lower than the trend over the complete year.
    Comparing the UAH data for the North Pole for JJA, their trend is 0.33 °C/decade, about the same as the NCEP/NCAR reanalysis. The UAH trend for the North Pole for the complete year is 0.47 °C/decade, which would result in 30 years to 1.4 °C.
    Comparing this with the global average, UAH gives 0.14 °C/decade. So the Arctic is warming about 3.4 times faster than global average according to the dataset of Spencer/Christy. I think this is called Arctic Amplification. See also this analysis of Tamino:
    http://tamino.wordpress.com/2012/10/13/arctic-amplification/

    About the 0.4 W/m2 used for melting the ice, this was already mentioned by Ron Lindsay in his comment on November 13, 2012 at 4:53 pm:
    “But given the small amount of heat needed to melt the ice at the rate we have seen (less than 0.5 W/m2 annual average), is it a hopeless task to find a definitive mechanism, particularly since the dominant forcing for ice anomalies likely changes from year to year?”

    This 0.4 W/m2 is probably based upon the average size of the Arctic and the fact that the water after the melting will get warmer than 0°C.
    The data for the calculations are also given by Frank in the comments and can easily be found on the internet, for 310 km3 ice per year, melting and warming to 5 °C:
    310•10^9 m3 * 334 kJ/kg * 917 kg/m3 + 5 * 310•10^9 m3 * 917 kg/m3 * 4.19 kJ/kg = 1•10^20 J
    The average area covered with ice in the Arctic is about 9•10^12 m2, this leads to:
    1•10^20 J / 9•10^12 m2 per year = 0.36 W/m2

    Kwok et al use data from Trenberth (ref 14) which is also about 9•10^19 Joule per year but they recalculated it over 30 years and to a global heat surplus, see the following quote:
    “..the net heat required to account for the average loss of ice during the past three decades is of similar magnitude to a 1-W/m2 global heat surplus”.
    I’m not sure what they mean with their ‘global heat surplus’, maybe the experts can elucidate it.

    Church & White 2011 come up with 2.5•10^21 Joule used for melting sea ice over 1972-2008 (table 2) which comes to 0.25 W/m2. As comparison, they give 2•10^21 for gain in heat content for the atmosphere over the same period, lower than what’s used for melting the sea ice. The heat stored in the oceans is about 100 times more according to Church & White.

  • Lennart van der Linde

    Tripati et al 2009 say it may haven been 15 millions years since CO2 levels were over 400 ppm (I hope the link works):
    http://newsroom.ucla.edu/portal/ucla/last-time-carbon-dioxide-levels-111074.aspx

    During the Pliocene, several million years ago, CO2 levels came close to 400 ppm, and Arctic temps were probably about 19 degrees C higher than today, according to Ballantyne et al 2010:
    http://geology.gsapubs.org/content/38/7/603.full

    So today, are we on our way to an Arctic at least 19 degrees warmer, excluding the effects of positive feedbacks and continuing emissions? How long would it take for the Arctic to warm that much? What would be the effects on global and regional climates, sea level, food production, migration, political tensions, and so on? To what extent could we adapt to such effects? To what extent could strong mitigation policy still prevent some of these effects? What are the uncertainties, risks, costs and benefits of different policies? Do we know enough to answer such questions, or do we need to understand the Arctic climate system better before anwering them?

    I’m not a climate scientist (my background is in public administration), but I would say we know enough to argue for strong mitigation policies. It would be nice to hear to what extent Walt, Judith and Ron agree.

  • Toby

    Cooter
    (1)

    Eh?

    (2) The definition of “ice-free” is arbitrary – the questions are in what months(s)? what minimum extent? I think the North Pole free of ice for three months (July-Sept) plus unobstructed passage for shipping across the Arctic Ocean from Fram Strait to Bering Strait in that time would qualify, irrespective of the actual extent of the ice. That is quite possible by 2030.

    (3) Antarctic sea ice has not increased in a statistically significant sense.

    (4) Anything that improves the public’s understanding of science is a good thing, whether is is HIV, acid rain, nuclear weapons or climate change.

    CAGW is a superfluous concept – a quick slaughtering by Occam’s Razor is surely in order.

  • MJonas

    Cooter -
    1. The relationship is not linear. Probably the closest is that rate of ice loss relates to temperature and to ice thickness from last year. ie, if the sea currents are warm they could continue to melt ice even if they aren’t getting any warmer, and the thinner the ice is to start with, the faster the ice loss is likely to be.
    2. Agree. “Ice free” should mean no ice, but it could reasonably be defined as (eg.) free of all ice that could impede shipping. Whatever, the definition being used needs to be defined, and in the absence of explicit definition it must retain its plain english meaning – “no ice”.
    3. The element in the oven is still on so that part of your argument is invalid (the element hasn’t got any hotter for a while and may start getting cooler soon, but it is still pretty warm today). But the failure to look at the Antarctic is disgraceful, and is as you say “a case of scientists turning a blind eye to the data that does not match their working hypothesis.”. Particularly as the IPCC report states clearly that sea ice loss is expected at both poles [AR4 ch.10, "Snow and Ice"].
    4. Agree totally. The only way science properly progresses is with theories open to testing and with actual evidence.

  • Marcel Crok

    @Jos Hagelaars
    http://www.climatedialogue.org/melting-of-the-arctic-sea-ice/#comment-204
    Jos, you are totally right about Judith Curry, see did indeed said 50% if she would have to pick a single number. I will forward your summary statement to them and let hem respond.
    Marcel

  • Charles

    Jim Cripwell writes:
    “What GHG warming? There always seems to be the assumption that…adding CO2 to the atmopshere is actually causing warming. There is no empirical data to support this claim; none whatsoever. The rate of rise of global temperatures has not changed since GHGs supposedly started rising alarmingly around 1970. See http://www.vukcevic.talktalk.net/MidSummer-MidWinter.htm and http://bit.ly/V19Im8

    The first link shows long-term temperature trends for Central England only, so there’s nothing global about it. The second link resolved to a web address that seemed to indicate a lot of processing, but it’s hard to tell. The graph seems to start at about 1979 and shows a familiar, noisy signal with a clear overall rise over time.

    “If the rate of rise of global temperatures from the actual measured data shows that there has been no change since around 1970, then … the total climate sensitivity of CO2 is indistinguishable from zero.”

    By “rate of rise” do you mean slope? Are you looking for changes in slope after 1970, or a change in slope around 1970, or else a positive slope after 1970? Or something else? It doesn’t seem clear. And, the graphs linked don’t seem to clarify things.

  • Lennart van der Linde

    I have a question about the amount of energy that’s melting Arctic ice as a percentage of the global energy imbalance. Above several estimates have been given about the energy that’s needed to explain the melting of Arctic ice: from a maximum of almost 1 W/m2 to about .25 W/m2. But how much is this energy as a percentage of the global energy imbalance?

    Last year Jim Hansen and others wrote an interesting paper about the global energy imbalance:
    http://pubs.giss.nasa.gov/docs/2011/2011_Hansen_etal.pdf

    They conclude that the current energy imbalance is about .75 W/m2 averaged over the 11 yr period of the solar cycle. They also seem to show in their figure 8 that over the past 10 years about about 2% (.015 W/m2) of that extra energy has been used to melt sea ice, and that the amount of energy melting sea ice seems to be growing quite rapidly. I assume that practically all of this energy is being used to melt Arctic sea ice.

    Do I understand this correctly, and what do Walt, Judith and Ron think of this estimate of Hansen et al? And also: by how much can we expect the global energy imbalance to grow over the coming decades and what could that imply for the amount of energy that goes into melting Arctic sea ice? Would the part of the global energy imbalance that goes into melting the sea ice grow or stay the same? I’m also curious to hear what others besides the three guest bloggers think on this.

  • Dan H.

    MJonas and Toby (reply to Cooter),

    Winter ice is likely to reform every year for as long as the Earth remains in its current interglacial temperature realm. The Arctic ocean temperature simple falls well below the maximum temperature for an ice-free state.

    Ice-free can be defined by the minimum area, as the floating ice attched to Greenland may take much longer to melt than the unattached sea ice.

    Antarctica is simply not reacting to the same forcings as the Arctic. The extreme cold fosters continual glacial buildup on the continent. The sea ice responds to both the land-based glaciers and ocean currents. There is significantly less turnover in the Anarctic waters than the Arctic.

    Ditto on the scientific evidence. Expanding scientific knowledge can only serve to expand understanding, even among the masses. Too many other sites attempt to stifle this type of dialogue, because it runs contrary to their own belief system.

  • Lennart van der Linde

    Reading the discussion so far it seems the question on the potential importance of ice albedo positive feedback hasn’t been properly answered yet. Or maybe I’ve missed it?

    At first Judith seemed to say it isn’t an important effect, or maybe even non-existent. Several questions for clarification haven’t been clearly answered, but give the impression that there is some relevant effect after all, although a (negative?) cloud feedback would seem more important to her.

    So for further clarification, could all three guest bloggers please answer this question: what are the indications for a positive ice albedo effect and a possibly negative cloud feedback, and what estimates for their magnitude have been found thus far?

  • Lennart van der Linde

    And another (maybe implicit) question that hasn’t really been answered so far: based on paleo data what approximate CO2 level/range roughly corresponds to a global equilibrium state with an ice free Arctic during summer? Would that be about 350 ppm, as Jim Hansen seems to think? Or some other number/range?

    And related: CO2 levels are currently approaching 400 ppm and rising by more than 2 ppm/yr, while during the last deglaciation the average rise seems to have been about 1 ppm/century, from about 190 to 290 ppm as a feedback to orbital forcing. The current rise seems to be about 200 times faster than the natural rise in the past, and further rises because of several relatively slow carbon feedbacks can be expected. How fast can we expect Arctic sea ice to respond to this forcing, that with time would seem to overwhelm the not precisely known negative aerosol forcing?

    And what will be the effects of an Arctic Ocean more and more free of ice, for example on the melting of Greenland ice, sea level rise and carbon release from melting/eroding permafrost and the ocean sea bed? So far not many words have been said by the guest bloggers on these possibly very important effects. Maybe the discussion so far has been focussed too much on the trees and not enough on the forest?

  • Nabil Swedan

    Walter Meier says “The ocean is indeed a very important part of the sea ice melt story. Water is a much more effective mechanism to transfer heat to the ice compared to the atmosphere.”

    Surface temperature rise is 0.00000003 C/hour. At this rate, heat transfer coefficient between water or air and ice is zero. Water or air can never melt ice. The only way the observed ice can melt is by water vapor condensation, which has a heat transfer coefficient in the order of 2,450,000 J/(hr m2 C).

  • Neven

    I agree with Lennart van der Linde and would like to hear more from the experts, if possible, about their views on the possible consequences of diminishing Arctic sea ice. I know Dr. Curry keeps stressing that a lot is still unknown and not well-understood, but given the trends so far and a melting season behind us that shattered all records despite weather conditions that were very much unlike those of the perfect melting season of 2007, I don’t find that a comforting idea. Not at all, in fact. It seems to me that uncertainty cuts both ways. We cannot exclude worst-case scenarios for instance. I wish we could.

    I hope this question doesn’t make the experts uncomfortable. I know how they do not like to make statements on things that aren’t certain to happen, and like Dr. Kerry Emanuel wrote in a recent article:

    For scientists, an asymmetric reward structure means that it is better to be a little late in what proves to be an important discovery than to publish too soon and be proved wrong. As a result, scientists often ignore apparent patterns in their data if there is as little as a 5 percent probability that they could have arisen by chance. But while this philosophy makes sense for science, it can be disastrous when applied to risk assessment.

    It is fine to discuss the science and its uncertainties in an initiative like Climate Dialogue, but once it is agreed that at least half of the decline in Arctic sea cover (and thus Arctic climate change) is caused by man-made global warming, you cannot remain silent about the implications. Arctic sea ice is not just about Arctic sea ice (and when it will be gone), it’s about much more. Talking about it doesn’t automatically mean you’re advancing one policy or the other. Saying nothing or downplaying potential risks is.

  • Everette L. Wampler

    Energy to Melt Glaciers
    Regarding the energy levels necessary to melt Earth’s glaciers. I computed the energy to extract Earth out of the Younger Dryas Event at ≈ 11,700 yBP to be ≈ 123 times solar radiation or ≈ 170 kilowatts per square meter. Solar is ≈ 1.368 kilowatts per square meter in space,. This energy level acted for ≈ 150 years at the NGRIP ice core site. That is ≈ 1.13 kw/m^2 per year. See the next paragraph for solar only melting glaciers. The GISP-2 ice core site had lower energy levels lower than 35 kw/m^2 for ≈ 189 years. A level of 0.185 kw/m^2 per year. So it appears that solar could not have been the cause of deglaciation in such a short period. If you examine my work you will discover the cause of glacial cycles over long periods and some sediment cores predict millions of years.

    Some of my other research indicates solar energy would have accomplish the same glacial melting ending about 5000 years in the future. See Ill 3.0 in the text book. So this means that solar equivalent is ≈ 1.36 kilowatts per square meter for ≈ 35,000 years vs ≈ 150 years with energy supplied by the external source.

    My illustration, Ill 7.7, predicts that Earth is well past, ≈ 5000 years, the point where it would have begun returning to low temperatures leading to glaciation. The controlling factor is the climate servos, two primary, a few secondary and an unknown number as tertiary feedback control systems and a new atmospheric state. These are distributed control systems rather than being in a black box as they are generally understood. Feedback control systems suffer from noise input. Modern Man is a noisy bunch. They also fail and that can be in positive or negative directions of the controlled variable, in this case temperature. In the case at hand, it is an excess of feedback variables, moisture and CO2, which are to be considered.

    So, it is obvious that high levels of energy are needed to melt the glaciers in a relative short period as we see in dispersal of the high level glaciation existing from ≈ 27,500 to ≈ 10,000 yBP. I called the Global Glacial Maximum in Antarctica the Quiet Period. It appeared that nothing was happening with the climate, just cold, cold in that period. I later developed a theory for what caused the Quiet Period. It is a shocking revelation. And, may I add, it could happen again starting tomorrow.

    That melting from ≈ 30,000 to ≈ 10,000 yBP produced a sea level rise of ≈ 120 meters, 130 meters by some estimates. If the poles continue to melt today, then global warming will have proven itself with disastrous results. The saltwater/freshwater interface of rivers will move upstream a frightening distance world wide

    It is not a case of what is the cause of the warming. It is warming and our new task is to work with Nature to mitigate that state as best we can. I think an excellent example of man made environmental disasters is demonstrated by the media production from Florentine Films and the USA Public Broadcasting/Educational television station with call letters WETA, under direction of Ken Burns. WETA is located in the Washington, D. C., USA metro area. Here we see a graphic example of the suffering of humans caused by humans. However, with some excellent work those same humans ended that disaster. The tropical storm(?) Sandy is still another example along with those disasters around the globe which are not weather related. The common thread is, can Modern Man gain control of his unusual talents and mitigate all disasters.

    Incidentally, I am selling my research. It took three years to produce and no outside financial support. The series title of my work is:
    “ THE ADVENT of MODERN MAN. “
    And Volume II title: “ The End of The Last Ice Age. “
    Actually, I should have ended it with All Ice Ages. Those of at least the last several million years.
    ISBN 9780984918119 Find it at:
    http://www.omega-spacepublishingusa.com. And, at Barnes & Nobel when administrative tasks are complete.

    Everette L. Wampler

  • chris colose

    I’d like to comment on the question by Lennart and Neven regarding the broader feedback implications of Arctic sea ice loss, which have only briefly been touched upon, but serve as the cornerstone for understanding the long-term evolution of the climate at high latitudes.

    It must be recognized that while Arctic sea ice loss is a big “tipping point” at an ecosystem, regional climate, and probably socio-political-economic level, that from the global climate system perspective it’s still relatively small potatoes. For present and warmer climates, ice-albedo feedback itself is one of the smallest feedbacks when looked at from the view of the global top-of-atmosphere energy budget, well behind water vapor and probably cloud responses (and the uncertainties are larger for these as well). Ice-albedo is an extremely important contributor to the near-surface regional climate, and is likely a big factor in observed and projected low-level (say 1000-500 mb) high-latitude amplification (relative to the global mean) which has all sorts of interesting dynamical implications. Beyond this however, caution needs to be taken when making connections to global climate sensitivity estimates or to (more recently) synoptic-scale weather feedbacks.

    Regarding high-latitude cloud feedbacks, much like the global response, we simply don’t know very well how clouds will act to amplify or dampen the forced component of climate change. There is a known anti-correlation between sea ice extent and low-level cloud cover (moreso in Autumn than summer), a relationship supported in various model studies, lidar/radar observations, and even paleoclimate arguments from tree-ring based correlations of temperature and solar radiation (Gagen et al., 2011). However, in the prevailing climate, low clouds in the Arctic (unlike in the global mean) has a net warming effect at the surface due to the longwave response throughout the year overwhelming the shortwave component that is dominant only over a few months of the warm season. However, the details depend on the vertical cloud distribution, among other things (e.g., Palm et al 2010). I agree with Judith that clouds are very important energetically, but it’s simply baseless to assume they will be more dominant regionally than the surface sea ice direct radiation feedbacks.

  • Frank

    Judith: Thank you for your kind reply. I did look at your references. I still think a good answer to the attribution issue would be set aside GCM’s (which sometimes are tuned to predict today’s sea ice using their temperatures – which may be colder than the LIA), and focus on what you do know with high certainty: radiative forcing and possibly water vapor feedback. Did these well-understood phenomena provide enough energy at the surface to have melted the sea ice lost from 1980-2012. However, it dawns on me that the radiative forcing for 2X CO2 may change sign when an inversion is present: DLR will be emitted from a lower, colder altitude and deliver less energy to the surface!

  • Neven

    Beyond this however, caution needs to be taken when making connections to global climate sensitivity estimates or to (more recently) synoptic-scale weather feedbacks.

    Caution also needs to be taken with being too cautious and be silent about potential worst-case scenarios. Again, Emanuel: “This philosophy makes sense for science, it can be disastrous when applied to risk assessment.”

    It must be recognized that while Arctic sea ice loss is a big “tipping point” at an ecosystem, regional climate, and probably socio-political-economic level, that from the global climate system perspective it’s still relatively small potatoes.

    Please, define ‘regional’. Does that include the NH land masses? Or does a potential increase in blocking patterns and anomalous snowfall patterns stay restricted to the Arctic Ocean? How about the Greenland Ice Sheet and Arctic glaciers?

    If all of that is small potatoes, where does that leave us from the risk assessment POV?

  • billc

    Chris – to shamelessly self-promote and repeat a comment I made earlier – if you look at a “climate shift” in 2001-2002 and the trends in 1) TLT and 2) arctic sea ice, the total energy trend is not shifted; less TLT warming but more arctic sea ice (PIOMAS volume) loss. Perhaps this helps explain Judith’s 3 items (as Rob van Dorland has asked her to clarify).

  • chris colose

    Neven,

    I can’t imagine that replacing, say, a 60% albedo surface over much of the surface at high latitudes with a 20% albedo surface will have no impact on the general circulation (and thus have far-field impacts, perhaps on snow cover or blocking patterns, which will obviously propagate into some sort of mid-latitude response). However, these are very much research-level questions, and the links to changes in future weather patterns are pretty much speculative at best. Everyone likes to talk about the links to sea ice nowadays whenever a blocking pattern or extreme event happens, but even ignoring the issue of natural variability, there is currently no consensus on how wave heights or blocking frequency might change in a warming climate. Elizabeth Barnes and Dennis Hartmann at UWashington, for example, have some recent results from the CMIP5 models that seem to suggest the opposite of the Francis et al. hypothesis. I discussed some of the things going on in a blog post following up on Hurricane Sandy.

    From a dynamics perspective, I can’t imagine what a “worst case” scenario might be, or whether it will be that big of a deal outside the atmospheric science community. It could be, but it’s difficult to envision just what that might be or whether Kerry’s precautionary advice even applies. From a global climate sensitivity perspective though, and especially with respect to science fiction views on methane catastrophes or runaway greenhouses, there’s no basis for thinking about the Arctic region as the difference between manageable and catastrophic levels of climate change. More sensitive models for example, don’t inflate climate sensitivity because of more ice loss, but usually because of more low cloud dissipation.

    There is much more to worry about in the Arctic though with respect to biodiversity, the natives to the Arctic region, and even national security (e.g., increased access to exploration and the hunt for potential natural resources has already led to Arctic nations posting overlapping and disputed claims of territory).

  • Lennart van der Linde

    Another attempt to get some clarification from Judith Curry. In her guest blog she wrote:

    “The impact of September sea ice loss on the ice albedo feedback mechanism is interesting. The minimum sea ice occurs during a period when the sun is at low elevation, so the direct ice albedo effect isn’t all that large. Less sea ice in autumn means more snowfall on the continents, which can have a larger impact on albedo… Would melting sea ice trigger some sort of clathrate methane release into the atmosphere? Well in terms of thawing permafrost, it seems like more snow fall on the continents would inhibit permafrost thawing. Same for the stability of the Greenland ice cap… I am not seeing a big rationale for climate catastrophe if the see ice melts.”

    Ice albedo feedback does not only occur when the sun is at low elevation, but is particularly relevant when the sun is at high elevation. Ice area is also decreasing before September, so the direct ice albedo effect is apparently substantially larger than Curry proposes.

    Net albedo on the continents is also decreasing because snow is melting faster in spring than it is increasing in fall/winter, as several commenters have argued with references. So the point that Curry is trying to make here doesn’t make sense either.

    The same goes for her next point on more snow on the continents in fall/winter possibly preventing permafrost and Greenland thawing. Permafrost and Greenland already are thawing and there seems to be a significant chance that this thawing will accelerate over the coming decades. Also carbon release thru increasing coastal erosion and from the sea bed seems an important probable effect of decreasing sea ice.

    So why does Curry say she sees no big rationale for climate catastrophe if the sea ice melts?

    Her arguments to support this view appear to be incorrect, so that would make the rationale for potential climate catastrophe quite a bit bigger than she argues.

    The sea ice is melting fast. How fast it will melt over the coming decade(s) we will see, but however fast it will turn out to be, even if there would be only a small rationale for climate catastrophe, that risk would seem urgent enough to start taking as strong preventive measures as possible.

    Even Curry seems to accept there is at least some rationale in arguing a risk of climate catastrophe. This risk seems substantially higher than she acknowledges.

    Maybe Walt and Ron can comment on their assessment of this risk? Have I misunderstood something, or is Curry’s reasoning on this point indeed incorrect? Or if I have misunderstood, maybe she can try once more to clarify and substantiate her argument?

    One more point: Curry seems to think there’s a good chance of sea ice recovery over the coming two decades. But she also thinks it’s likely that the sea ice decline of the past decades was for about 50% forced by increasing GHG’s and for about 50% by natural variability. So even if natural variability over the coming decades would by itself reverse this trend, then continuing GHG forcing would still at the most leave sea ice area at about the current low level. The chance for substantial recovery would seem quite small. On the other hand, the chance for continued fast decline seems significant, since natural variability could just as well continue to reinforce the downward trend. Why does it seem so hard for Curry to acknowledge this?

  • Bert Amesz

    @ Walt Meier d.d. Nov 22, 2012

    You seem to support the conclusion that the current decline is unique in the past 1450 years (or even 8000 years). This seems to be the opposite of the conclusions in the report ‘Past Climate Variability and Change in the Arctic and at High Latitudes’ (US-CCSP, 2009)’. On page 176 they conclude that between 750 and 1500 AD parts of the Arctic were open, at east during some summers, while during LIA sea ice extent was excessive. So apparently there exist a strong natural variability. These conclusions contradict with the sources you list in your post. Can you comment on this? To me it is puzzling.

    http://downloads.climatescience.gov/sap/sap1-2/sap1-2-final-report-all.pdf

  • Rob Dekker

    Similar to Lennart van der Linde, Neven, and various other commenters, I am surprised how much the experts (specifically Dr. Curry) address uncertainty in modeling “natural variability” (AMO, clouds, etc) while barely touching on any feedbacks that could explain the difference between climate model projections and reality.

    In general, the emphasis by Dr. Curry on uncertainties over explaining long term trend in the Arctic ice decline seems rather misplaced. On a linear trend over the past 30 years, the standard deviation of Arctic sea ice is something line 500 k km^2, and on a quadratic down trend it is even less (something like 300 k km^2 IIRC). At the same time, the models (CMIP3/CMIP4/CMIP5) are pretty good in reproducing this uncertainty, but fail miserably on the long term trend (underestimated by 20-40 years).

    So, why is Dr. Curry talking so much about uncertainties (such as the influence of clouds) while the real problem seems to be that models underestimate the long term (AGW) trend ?

    Since ice extent modeling shows more variability than ice volume modeling, there seems to be a consensus among the experts that ice volume is the best way to assess multi-annual developments in Arctic sea ice, when it comes to separating natural variability and long term anthropogenic trend. Dr. Lindsay even explicitly mentioned that modeling with ice volume shows a much earlier divergence that modeling extent :

    The CCSM3 model, for example, shows a clear separation in ice volume between the control and the A1B scenario as early as 1985, 10 to 15 years before the separation in ice extent (Schweiger et al 2011).

    Indeed it is clear that ice volume development has even less “natural variability” than ice extent :
    http://psc.apl.washington.edu/wordpress/wp-content/uploads/schweiger/ice_volume/BPIOMASIceVolumeAnomalyCurrentV2.png?%3C?php%20echo%20time%28%29%20?

    This multi-decadal development is amazingly consistent, and relentlessly downward. It is hard to find any “natural variability” due to “uncertainty” in clouds, in this graph.

    Which brings us back to feedbacks, negative and positive.
    If the negative feedback of faster ice growth in fall (which is very nicely explained by Frank) indeed would be significant, than should we not see a ‘leveling off’ of this volume anomaly graph ?
    Then why is it that it seems that instead of leveling off, ice volume is declining even faster (about 2X) than before the major extent losses occurred (since 2005).

    It seems to me that ice extent and ice volume graphs both indicate that positive feedbacks in the Arctic are still stronger than negative feedbacks at this point, and one may ask when that would change. Could it be that currently Arctic sea ice volume is simply not stable, and will continue to decline until the Arctic warms up substantially ?

  • Bart Strengers

    The next comment is from Wayne Davidson,copied from RealClimate.org:

    Judith Curry wrote:
    “So . . . what is the bottom line on the attribution of the recent sea ice melt? My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range. Why such a ‘wishy washy’ statement with large error bars? Well, observations are ambiguous, models are inadequate, and our understanding of the complex interactions of the climate system is incomplete.”

    Natural variability may have the same impact as CO2… That is incorrect. Natural variability is part of any process but sea ice thinning gradually , year by year, is not quite variable.

    Judith Curry:
    “Older ice
    Here’s the basic story as I see it. During the late 1980s and early 1990s, the circulation patterns favoured the motion of older, thicker sea ice out of the Arctic. This set the stage for the general decline in Arctic sea ice extent starting in the 1990′s. In 2001/2002, a hemispheric shift in the teleconnection indices occurred, which accelerated the downward trend. A local regime shift occurred in the Arctic during 2007, triggered by summertime weather patterns conspired to warm and melt the sea ice. The loss of multi-year ice during 2007 has resulted in all the minima since then being well below normal, with a high amplitude seasonal cycle. After 2007, there was another step loss in ice volume in 2010. In 2012, the basic pattern of this new regime was given a ‘kick’ by a large cyclonic storm in early August.”

    A single cyclone “done in” the sea ice for 2012, while everything started in 2007 by the not mentioned Arctic dipole. The decline was slow and gradual for decades reaching a critical point where any cyclone would appear to be having an impact (depending on the animation watched). Flushing through Fram Strait occurs almost constantly, no matter how thick the ice is, or what Oscillation dominates, its a natural phenomena of great consistency. The thinning of the ice, decreasing in over all sea ice volume yearly declines appears to be unnatural . The replenishment process involved in creating thicker multi-year ice has been dwarfed by the extra heat present in the Arctic. Of which flushing has very little to do with it.

  • Bart Strengers

    The next comment is from Gavin Schmidt, copied from RealClimate.org:

    “So . . . what is the bottom line on the attribution of the recent sea ice melt? My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range. Why such a ‘wishy washy’ statement with large error bars? Well, observations are ambiguous, models are inadequate, and our understanding of the complex interactions of the climate system is incomplete.”

    This statement is meaningless. The number you are trying to estimate is uncertain and so has to be characterised by some kind of distribution (which is to be estimated). A statement of likelihood is a quantification of the area under that curve between some limits (see http://www.realclimate.org/index.php/archives/2012/01/the-ar4-attribution-statement/ for examples). This means that the the likelihood of any single value (i.e. 50% or whatever) is actually zero. Rather, statements need to be couched as follows: the probability of the number being greater than 50% is XXX, or of lying between this range is YYY etc.

  • Jim Cripwell

    I would like to draw attention to two sources of empirical data on Arctic and Antarctic sea ice, namely:-
    http://arctic.atmos.uiuc.edu/cryosphere/
    http://nsidc.org/arcticseaicenews/
    These show how the freezing of Arctic sea ice, and the melting of Antarctic sea ice is progressing. Please note that neither of these sources is, or ever can be, refereed or peer reviewed.

  • Jos Hagelaars

    There are some references here made by Marcel and Prof. Curry to Swanson en Tsonis 2012. Prof. Curry wrote:
    “As a result of the climate shift, the sea ice is out of equilibrium with the forcing and dynamics, and hence unstable. In 2007 we saw extreme sensitivity to internal Arctic processes (e.g. clouds), which then triggered another shift to the sea ice coming from the internal dynamics triggered by the 2007 ice loss.”
    Followed by a list of 3 points (clouds, atmospheric/ocean circulations, OH transport).
    The reader (or is it just me) could get the impression that Prof. Curry thinks that climate shifts are an explanation for the steady decline of the arctic sea ice and therefore could be lead astray.

    I use the word ‘steady’ after staring a while at these two figures:
    - Sea Ice Extent 1953-2011 (also present in the recent article of Dr. Meier in The Cryosphere).
    - The Cryosphere Today.

    Variability is clearly present, but superimposed on a long term declining trend. Also in contrast to atmospheric global temperatures, the short term trend (10 years) gives no indication of any ‘pause’ in the decline. Neither the opposite is present: a sudden steep acceleration. To me there is a remarkable steady decline, starting at least around or even before the 1970′s.

    Coming back to Swanson & Tsonis 2012 (article can be found online here). The word ‘ice’ or ‘Arctic’ is not present in their paper at all. The article is about resonance and coupling between major modes in the Northern Hemisphere climate variability and mentions the ‘pause’ in the increase in atmospheric temperatures after 2000:
    “Here, a new and improved means to quantify the coupling between climate modes confirms that another synchronization of these modes, followed by an increase in coupling occurred in 2001/02. This suggests that a break in the global mean temperature trend from the consistent warming over the 1976/77–2001/02 period may have occurred.
    If as suggested here, a dynamically driven climate shift has occurred, the duration of similar shifts during the 20th century suggests the new global mean temperature trend may persist for several decades.”

    There is a nice commentary on RealClimate regarding this article written by the lead author, he says:
    “What do our results have to do with Global Warming, i.e., the century-scale response to greenhouse gas emissions? VERY LITTLE, contrary to claims that others have made on our behalf.”
    and:
    “.. our paper is fundamentally about inter-decadal variability in the climate system and its role in the evolution of the 20th century climate trajectory, as well as in near-future climate change.”

    I’m glad Prof. Curry wrote that she was misinterpreted (November 21, 2012 at 7:54 pm).
    To clarify it, did she mention this Swanson paper only as a sort of an explanation for the short term variability in the arctic sea extent?
    If so, there should be some peer reviewed article then where evidence is presented for a ‘climate shift’ in the Arctic. I haven’t found any, but maybe the experts could present us such a paper?

  • Jos Hagelaars

    Dr. Meier said in his comment on ‘November 22, 2012 at 2:00 am’ that there is paleoclimatic evidence “that the last time the Arctic had little or no summer ice was during the Holocene Thermal Maximum, ~8000 ybp”.
    That would make the near future Arctic ice free summer – not an “if”, but a matter of ‘when” according to Dr. Meier – pretty unique on the human time scale.

    Logically there is a relation for long term variations in the amount of sea ice with temperature. Looking at some temperature reconstructions e.g. Vinther 2009, Richard Alley’s GISP2 ice core data or this well-known Wikipedia picture, it seems that the temperature is dropping since about ~8000 years ago. ‘Something’ changed this long term temperature decline in the Arctic area around 1900 as is visible in the graph of Kaufman 2009. As they put it:
    “The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.”
    When on longer timescales the Arctic gets warmer, the amount of ice decreases. Or the other way around. The multi-decade warming trend in the Arctic is about 0.47 °C/decade (UAH since 1979): even more warming = even less ice. Seems very logic to me.

    What is the opinion of the experts about this long term relation of temperature in the Arctic and the amount of ice?

  • Rob Dekker

    Bert Amesz

    This is the second time you bring up this statement from the US-CCSP 2009 report (the first time was in your post from 2012-11-14 12:52:29).

    In my reply 2012-11-15 08:12:48 to your post, I point out that “They found 5 specimens of bowhead whale bones on the shore of the Beaufort sea”, and that “I think that the authors do not present enough evidence to claim that the Northwest passage was open during some summers over that period”.
    To which you replied “I’m not an expert on bowhead whales. I’m simply referring to the conclusion on page 146 of the report”.

    Now, it is fine with me if you accept anything that anyone writes in any report as long as it conforms with your beliefs, but if you get confronted with an assertion (like mine) that the authors do not present enough evidence to sustain the statement, then why don’t you address that in a scientific way, by debunking my assertion, instead of simply repeating your statement and asking an expert (Dr. Meier) to look into it ?

    Unless climatedialogue moderators feel that the remark on page 176 of the US-CCSP 2009 report requires continued discussion on this blog beyond the posts made already, I would suggest that both Bert Amesz’ last post (2012-11-22 09:01:25) and my response here get moved to the “off-topic” section.

  • Bert Amesz

    @Rob Dekker, Nov 23th

    I did address my open question – without any form of prejudice – to Walt Meier for the simple reason that he introduced the topic in his opening post. In another post, he listed some references. I’m not trying to debunk any of them, as you suggest in a rather insulting manner. I merely wanted to point out that they seem to contradict with the US-CCSP study. In my turn, I’m tempted to suggest that you debunk that study because it doesn’t confirm with ‘your beliefs’. But I won’t. Let’s keep Climate Dialogue a platform for open minded people. 

  • Dan H.

    Bart,
    If someone from the realclimate website wishes to post here, then let them do so. I fear than many of them try to avoid an open and honest dialogue, as opposed to their own site. If those comments mimic your own, then I believe that the clinetele here would be happy to hear your own views.

    I am surprised that no one has mentioned the motion of the NA warming trend, which began in Alaska in the mid-70s, moved eastward to Canada in the 90s, and is currently occurring in Greenland. The decine of the Arctic sea ice seems to follow this eastward trend. Maybe, the Arctic will follow the cooler (or lack or warming) tha began in Alaska in the 80s, and migrated eastward in the 2000s.

  • Rob Dekker

    Bert Amesz,

    I am sorry that my tone felt “insulting” to you. It was not intended as such.
    I was disappointed however that TWICE in this blog post your brought up the claim that :

    between 750 and 1500 AD parts of the Arctic were open, at east during some summers, while during LIA sea ice extent was excessive.

    Where you use page 176 of the US-CCSP, 2009 report as your evidence, but so far you did not engage in a scientific dialogue about this statement.

    I suggested that :

    I think that the authors do not present enough evidence to claim that the Northwest passage was open during some summers over that period.

    What do you think ?

    My main argument was that the 5 species of bowhead whales dated to around 1000 B.P. in the Beaufort sea is not enough evidence to conclude that the NW passage was open. In fact, the graphs from the US-CCSP 2009 report suggest that bowhead whale bones have been found through all three areas of the Arctic dated over the past 5 thousand years, with a small “west” (towards the Beaufort) concentration during 1000 B.P. and a small “eastern” (towards Baffin Bay) concentration 250 years later, with no significant change in bowhead whale bone finds in the Central Canadian Archipelago corridor over the past 6000 years.

    Secondly, the scientific papers mentioned as the original source of the data are Dyke et al 1996 and Savelle et al 2000.
    Neither one of these studies supports the US-CCSP conclusion of an open NW passage around 1000 AD. In fact, Dyke et al 1996 states :
    http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/1200/1225

    At 1 ka B.P., the bowhead range was similar to that at 2 ka B.P.; the range appears to have expanded in places and to have retracted in others (Fig 19). The pattern of occupation of Prince Regent Inlet seems to have switched: earlier, whales seem to have occupied the east side but not the west; later, the west side but not the east.

    which suggests regional climate changes that shifted sea ice back and forth (east and west) during that time, but no suggestiond of an “open” NW passage at all.
    Lavelle et al 2000 barely mentions 1000 AD as special, apart from this remark :

    Although the range apparently expanded slightly at approximately 1000 B.P., this occurred during an otherwise overall reduction in the bowhead range relative to the 5500-2500 expansion.

    http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/871

    which also suggests regional changes in an otherwise cooling pan-Arctic climate.
    So the US-CCSP 2009 page 176 conclusions seems not sustained by the original data it quotes, and that is why I suggested that they do not have enough evidence to sustain their statement.

    Thirdly, bowhead whales are amazing marine mammals, perfectly adjusted to Arctic sea ice, and I would not be surprised if they have been crossing the NW passage continously over the entire Holocene, through the LIA and MWP and any other regional or pan-Arctic climate change periods too.

    Lavelle et al 2000 makes another statement that is interesting in this respect :

    Regarding predation, note that although we have recorded thousands of bowhead bones and tens of beluga, narwhal, and walrus bones in the CAA, we have yet to record one bone of a killer whale, the only known predator of bowhead whales besides humans.

    After all, sea ice is their nich, where the hide from their predators (killer whale) and reach feeding areas where no other whale can get to. They are quite literally the living “ice breakers” of the Arctic, and over the past 10 million years even evolved an immensely strong head bone which allows them to break through sea ice of 2 feet thick. The Arctic is their home, and noone else comes even close.

    So, I think they have been traveling through the NW passage over the entire Holocene period.

    What do you think ?

  • Rob Dekker

    Bert Amesz,

    Also, Polyak et al 2010, in their excellent summary paper of “History of sea ice in the Arctic” seemed to have mellowed out the US-CCP 2009 page 176 statement on bowhead whale findings :

    A final peak of bowhead bones appears to have culminated shortly prior to 1000 A.D. in the Beaufort Sea and somewhat later in the eastern CAA (Fig. 10), suggesting the possibility of temporarily open channels.

    http://bprc.osu.edu/geo/publications/polyak_etal_seaice_QSR_10.pdf

    So I think that the statement that “the Northwest Passage was open, at least during some summers”, flat out, without any “suggest” or “possibility” disclaimers, and then suggesting that these findings “seem to contradict” the references that Dr. Meier gave, is simply not scientifically sustainable without providing a lot more evidence.

  • Neven

    Rob and Bert,

    Thirdly, bowhead whales are amazing marine mammals, perfectly adjusted to Arctic sea ice, and I would not be surprised if they have been crossing the NW passage continously over the entire Holocene, through the LIA and MWP and any other regional or pan-Arctic climate change periods too.

    Indeed. Bowhead whales probably don’t need a completely open NWP to make it from one end to the other, or intermingle in between. All they need is leads and small polynyas to breathe.

    In 5 of the last 6 years the NWP has been completely open, with ships, yachts, catamarans and even kayaks going through. Nowadays there are boats making the passage without reinforced hulls! The last two melting seasons saw several expeditions going through the NWP and the Northern Sea Route in one season, effectively circumnavigating the Arctic sea ice pack and North Pole.

    There is very little evidence that this has happened since the Holocene Climatic Optimum, when 8% more solar radiation (+40 W/m2) reached the Northern Hemisphere in summer (that is not the case in the current Rapid Ice Loss Event). The only evidence, ie remnants of bowhead whales, that can be and is drummed up by Bert Amesz is weak at best.

  • Jim Cripwell

    Neven, You write “In 5 of the last 6 years the NWP has been completely open, with ships,”
    I would like you to expand on what you mean by “ships”. It is absolutely true that in recent years, nimble, small, shallow draught vessels have been able to transverse the NWP with little difficulty. But ships? Routinely, for decades, the Canadian Coast Guard icebreakers escort various cargo vessels to communities in the Canadian Arctic, bringing them their yearly supplies of heavy goods that are uneconomical to bring by air. The ultimate destination each year is Eureka.

    But so far as I am aware, no commercial cargo vessels have gone through the NWP, unescorted, at all. The last ship to do so, I believe, was the Manhatten, which was exceptional. But even then, there were icebreakers with her.

    So could you expand on what you precisely mean by “ships”.

  • Bert Amesz

    Rob Dekker (and Neven)

    Rob, apologies accepted and thanks for your comprehensive reaction. Again: I wasn’t ‘claiming’ anything, just pointing out some puzzling discrepancies between the various studies. But you convinced me that studies on the basis of bowhead whales only, lead to inconclusive results. I’m not a scientific researcher, just a simple – but unbiased – hydrogeologist who tries to understand what’s happening in the Arctic. To me it’s clear now that the current decline, in extent and thickness, is unprecedented in recent history.

    But I have another remark, now concerning LIA. I’ve read the Polyak paper and I saw the graph of Kinnard (2011). Only his graph, because the paper is behind a pay wall. Kinnard concludes a relatively low extent during LIA, while Polyak shows the opposite (which looks logical to me). Moreover, Kinnard’s current decline seems dazzling compared to Polyak. Hence, quite different results. Is this also due to the proxies they use?

  • Rob Dekker

    Bert Amesz said

    I’ve read the Polyak paper and I saw the graph of Kinnard (2011). Only his graph, because the paper is behind a pay wall. Kinnard concludes a relatively low extent during LIA, while Polyak shows the opposite (which looks logical to me). Moreover, Kinnard’s current decline seems dazzling compared to Polyak. Hence, quite different results.

    Bert, as a hydrologist, you had a scientific education. As a computer scientist, so did I.
    So now that I cleared up the question you had about the US-CCSP 2009 page 176 conclusion, maybe this time could you could try to clear up your second question that “Polyak shows the opposite” from Kinnard et al 2011 about the LIA.

    For starters, could you give a reference to exactly which figure in exactly which Polyak paper you are looking at ?
    Then, can you please check the caption on that figure and check if it pertains to the same pan-Arctic area that Kinnard et al reconstructed ? Then please let us know your findings.

  • Rob Dekker

    P.S. Here is a non-paywall version of Kinnard et al 2011 :
    http://www.geotop.ca/pdf/devernalA/Kinnard_et_al_nature_2011.pdf

  • Bert Amesz

    Rob Dekker

    Thanks for the copy of Kinnard et al 2011. Be assured that I understand the difference in ‘Arctic’ and ‘Nordic Seas’ ice extent. What I mean is the following. In his paper (2010, fig 12), Polyak tries to match the ice extent in the Nordic Seas (Svalbard, Scandinavia) with the findings of Kinnard (2008) regarding Arctic ice extent over the period 1870-2003. He concludes ‘a close match, except for an obvious discrepancy in the early 20th century ‘. So far, so good.

    Now have a look at another period: LIA. From Polyak (Fig 12) one may conclude that, in Nordic Seas, the ice cover was relatively extensive. Which seems the opposite of the findings of Kinnard (2011, Fig 3a) regarding late-summer Arctic extent. According to Kinnard (2011), ice coverage during LIA was even lower than during the Medieval Warm Period. He concludes that the low ice extent during LIA (and the Dark Ages Cold Period) was due to an increased northward advection from warm Atlantic water into the Arctic. Nevertheless: while Polyak was looking for a match between Nordic Seas and the Arctic for a more recent period, it appears to me that such a match doesn’t exist for LIA. I suppose that an increased advection of warm Atlantic water would have affected the ice extent in the Nordic Seas as well? Unfortunately, Kinnard (2011) doesn’t compare his findings with the ones of Polyak (2010).

    Then there is another striking difference between the two graphs: the Polyak paper (fig 12) shows a more gradual decline (with ups and downs) since early 19th century (end of LIA), while according to Kinnard (2011, fig 3c) the decline starts more than a century later, mid 20th century. Hence the word ‘dazzling’ in my previous post.

    So while the bowhead whales have been discarded, I’m still stuck with the fact that two – I assume – eminent research groups come up with different findings with regard to an important topic: natural variability.

  • Jos Hagelaars

    @Rob Dekker/Bert Amesz

    I don’t want to mingle in your discussion, but I just was looking into the data of Macias Fauria et al 2009, where the Polyak 2010 – fig.12 graph is based upon, when I read the comment of Bert Amesz on 2012-11-25 14:44:18.
    Some trends from these Macias Fauria data in sq km2 per year:
    1700-1799: +326
    1800-1899: +146
    1900-1997: -1136
    The data can be downloaded here:
    http://www.helsinki.fi/science/dendro/data/DATA-Finland-Dendro-team.xls

    I hope it is of any use regarding your discussion.
    Regards, Jos

  • Neven

    Bert, maybe you should ask Kinnard and Macias-Fauria what it is exactly they did. For which regions? For which parts of the year (max, min, whole year)? You also might want to check eventual differences between Kinnard 2008 and Kinnard 2011. And be careful not to mix up Polyak and Polyakov.

    Polyak was looking for a match

    (…)

    his findings with the ones of Polyak (2010)

    Polyak et al. didn’t look, there are no findings. In their paper Polyak et al. describe the history of Arctic sea ice, and towards the end compare the findings of two papers to show “the pan-Arctic nature of the modern ice loss”.

    I don’t know what it is you would like to get at, but I’m amazed at how much info you seem to get out of eyeballing a couple of graphs and reading the subscript. Maybe you could teach me that. :-)

    What you also might find interesting from that final paragraph is the following:

    The remarkable modern warming and associated reduction in sea-ice extent are especially anomalous because orbitally-driven summer insolation in the Arctic has been decreasing steadily since its maximum at 11ka, and is now near its minimum in the precession cycle

    Which is why some people here asked why accumulated heat due to GHGs could not be responsible for more than 100% of the recent rapid ice loss.

  • Bert Amesz

    @Neven – Nov 25th

    As to your last remark, I found an interesting paper from Spielhagen et al (2011) regarding the temperature of Atlantic Water in Fram Stait during the past 2000 years. He reports a rapid and unprecedented temperature increase since 1850. Here the link for (the paywalled) paper.

    http://www.sciencemag.org/content/331/6016/450.abstract

    Here another (paywalled) paper from Cronin et al (2012) on Arctic Ocean warming during the last glacial cycle.

    http://www.nature.com/ngeo/journal/v5/n9/full/ngeo1557.html

    PS: ‘One picture is worth a thousands of words’, is a saying.

  • Dan H.

    Bert,
    Correct me if I am wrong, but does the Cronin paper not indicate that warming of the intermediate layer occurs during a decrease in glacial melting. Would not added melt from Greenland lead to a decrease in this water temperature?

  • Neven

    Bert, do you have a copy of the Spielhagen paper?

  • Rob Dekker

    Bert Ametz,
    Thank you for the Spielhagen et al 2011 publication on Atlantic Water (AW) temperatures.
    For starters, here is a non-paywall version of that paper :
    http://instaar.colorado.edu/~marchitt/reprints/spielhagenscience11.pdf

    This reconstruction shows an unprecedented (in the 2000 year period) 2 C increase in temperature of Atlantic Water during the 20th century. This makes sense, since the Arctic overall has warmed about 2X the global rate.

    Thus, so far, it seems that this publication confirms a 100% anthropogenic cause for 20th century warming.

    As usual with sedimental core reconstructions using foraminifers, their time resolution is a bit coarse (on the order of 20-50 years). As Spielhagen notes : the gradual transition may be an artifact caused by bioturbation mixing of foraminifer-poor sediments from the late LIA and foraminifer-rich sediments from the Modern Period But other than poor temporal resolution, what a great analysis, and clearly explained reconstruction of ocean water temperatures at 50-200 meter in the Western Svalbard current.

    I’m not sure which point you want to make with this paper, but it is interesting to note that Spielhagen et al’s analysis does show nice multi-decadal variability over the full 2000 year reconstruction, and found that the AW temperature during the MWP was close to what Fram Strait experienced around the start of the 20th century.

    Incidentally, the AW temperature that Spielhagen reconstructed is the water that gets inserted underneath the Arctic sea ice, and thus any increase in temperature will likely increase bottom melt (especially for thick ice).

    This brings up to another (beside NH snow cover anomaly) uncertainty in modeling Arctic sea ice development in a warming world : ocean heat flux, where a difference of 0.5 W/m^2 can change the long term Arctic average sea ice thickness very significantly.

    Here, I would like to as Dr. Lindsay to comment : To which extent is ocean heat flux (heat from below the halocline) involved in the PIOMAS ice volume hind-cast simulation from the past 4 decades ? Is ocean heat flux an ‘input’ into the PIOMAS model and if so where do you get the ocean heat flux data, or is ocean heat flux simply part of the calibration of the model by ice-thickness measurements over the decades (submarine measurements, ICESat, ICEbridge etc) ?

  • Bert Amesz

    @ Rob Dekker

    I googled on ‘heat flux fram strait’ and found this paper from Schauer et al (2004):

    http://ftpout.npolar.no/oan/backup/Undervisning/UNIS/U.Schauer_Fahrbach2003JC001823.pdf

    During 1997-2000 they measured the heat flux in Fram Strait and report a strong increase in the West Spitsbergen Channel. The net increase amounts to some 25 TW and its due to two equally important factors: stronger flow and higher water temperatures. In conclusion they suggest ‘ that a warming signal from the late 1990s is presently spreading in the interior Arctic Ocean’.

    Let’s assume that the net increase of 25 TW is uniformly divided over the Arctic north of 80°. This would result in 5 W per square meter which is more than the radiative effect of GHG’s. So your conclusion of ‘100% AGW’ is a little premature. But I agree with your conclusion that Arctic sea ice is being attacked from top (atmospheric conditions) and bottom (warm ocean currents).

    It would be nice to know whether the Schauer-measurements had a follow up. I would think that permanent monitoring would be useful.

  • Andries Rosema

    Increased cloudiness likely cause of sea ice melting

    Changes in net radiation have a significant influence the melting of sea ice in the arctic region. Here we want to compare two first order effects. Meteosat data for the period 1982-2006 show that cloudiness has increased by about 10%. Starting from an average cloud cover of 0.50, this would imply an increase to 0.55. We will compare this effect with that of the reported increase in atmospheric CO2 content. The net radiation (In) received by the earth surface may be written as:

    In = (1-A) I – (1-E) L

    Here A is the albedo, I the global radiation, E the atmospheric emissivity and L the long wave black-body emission. A and E may be expressed in terms of the cloud cover (C):

    A = As + C (Ac –As)
    E = Ea + C (1-Ea)

    As and Ac are the surface and cloud albedo, respectively. Ea is the downward emissivity of the cloud free atmosphere. Inserting these expressions in the equation for the net radiation, we obtain

    In = [1-As-C(Ac-As)] I – (1-c) (1-Ea) L

    The cloud free atmospheric emissivity Ea may be estimated with the formula of Angstrom in dependence of atmospheric humidity. The values for the Atlantic and Arctic are about 0.82 and 0.75 respectively. The effect of a CO2 increase can also be expressed in terms of emissivity. From 280 to 400 ppm we get an emissivity increase of 0.028xln(400/280) = 0.01.

    We will now calculate the effects on the net radiation of (1) an increase in cloudiness from 0.5 to 0.55 and (2) and increase of CO2 from 280 to 400 ppm, for both the Atlantic region and for the Arctic sea ice region. The following table presents the various applicable parameter values as well as the calculation results.

    ATLANTIC ARCTIC
    Refer. +Cloud +CO2 +Both Refer. +Cloud +CO2 +Both
    Cloud albedo Ac 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6
    Surface albedo As 0.05 0.05 0.05 0.05 0.7 0.7 0.7 0.7
    Global rad. I 340 340 340 340 120 120 120 120
    Atm. emiss. Ea 0.82 0.82 0.83 0.83 0.75 0.75 0.76 0.76
    Blbody emission L 400 400 400 400 300 300 300 300
    Cloud cover C 0.50 0.55 0.50 0.55 0.50 0.55 0.50 0.55
    Netrad.(W/m2) In 194 188 196 190 5 9 6 10
    Rad.forc(W/m2) -5.8 2.0 -4.0 4.3 1.5 5.7
    Icemelt(m/yr) 0.41 0.14 0.54
    Temp.change(K) -0.29 0.10 -0.20

    Note that cloud cover and atmospheric emissivity values are adapted to represent the two causes of radiative forcing: +Cloud and +CO2. Also the combined effect is calculated in the column +Both. The calculation outcomes are presented in the lowest 4 lines, in terms of “radiative forcing” as well as the equivalent effects on ice melt and surface temperature. To estimate the latter effect we have assumed an overall heat exchange coefficient (radiation, sensible and latent heat) of 20 W/m2K.

    Actual melting rates will be notably smaller than indicated in the table because of competing heat transfer processes. We estimate that only 1/4 of the values in the table will actually be used for melting. Melting rates would then be 10 cm/year for the increase in cloudiness and 3.4 cm/year due to increased CO2. Rothrock et al (2003) state that during the 10 year period 1987-1996 ice thickness decreased with 6 to 9 cm per year. It seems that the CO2 effect alone is not a sufficient explanation and that the increase in cloudiness plays a dominant role.

    Another interesting element in the above table is that the increase in cloudiness would have an opposite, cooling effect in the Atlantic. From Meteosat we do indeed find a decrease of surface radiation temperatures during the period 1982-2006. This also indicates that, with respect to arctic sea ice melting, we have to assign a dominant role to increased cloudiness.

  • Andries Rosema

    Formula’s are ok but I do not succeed in producing a proper table. How can we have a proper discussion then? For those who want to know the proper figures, please send me an email at andries.rosema@ears.nl

  • Jim Cripwell

    There are a wealth of sites, clearly not peer reviewed, which report on the daily, weekly, and monthly state of Arctic and Antarctic sea ice. Just to mention three, there are:-
    http://nsidc.org/arcticseaicenews/

    http://arctic.atmos.uiuc.edu/cryosphere/

    http://www.ec.gc.ca/glaces-ice/default.asp?lang=En&n=CEC7AE99-1

    What these are currently showing is that Arctic sea ice is rapidly regaining all the ice it lost at the nadir of the summer melt. While at the same time, the Antarctic sea ice extent remains above the recent average. However, this seems to be carefully neglected by the warnists, who clearly want to spread the myth that somehow the amount of sea ice in the Arctic is controlled by the amount of CO2 in the atmosphere. It is a pity that we will have only one more week of Canadian data.

  • Jim Cripwell

    Bart Strengers. You write “So the question is: To what extent do you agree with this reasoning? (maybe also taking into consideration the two studies mentioned by Rob that the current decline is unprecedented in the past 1450 years and the study from Spielhagen (2011) that shows a 2 C increase in temperature of Atlantic Water entering the Arctic Ocean during the 20th century, unprecedented in the past 2000 year.)”

    We have good data on Arctic sea ice extent since satellites were available in 1979. Prior to this, such data as we have is largely anecdotal. Some of this data indicates that nothing unusual is happening in the Arctic; some indicates that unusual things are happening. I cannot see how you can possibly come to any conclusions on the basis of empirical data that was collected prior to 1979. And post 1979, there is simply insufficient data to tell us what causes what is happening.

  • Eli Rabett

    The links that Mr. Cripwell pointed to are respositories of data which have been peer reviewed and the algorithms for processing new data coming down from satellites have been peer reviewed as well as having multiple levels of peer review for the construction and validation of the instruments, satellite tracking and more.

    That the Arctic refreeze is covering the surface with a thin layer of new ice is no surprise. One simply needs to have followed any discussion about first year ice increasingly dominating the Arctic ice pack as the volume falls rapidly or peeked in at any of those sites mentioned by Mr. Cripwell.

    Some things are obvious

    As obviously, the variation of maximum ice extent in the Arctic is an indicator of conditions outside the Arctic Ocean basin, places such as Hudson’s Bay. That ice will always melt in the summer, so it has little to no effect on minimum ice extent.

  • Bob Brand

    Hi Bert Amesz, considering your comment 2012-11-29 12:38:16:

    The 5 Watt/square meter from Schauer et al (2004) might of course be the result of ‘100% AGW’, if this heat has accumulated over a larger area of the Atlantic ocean. It need not be accumulated in the same year when it was measured in Fram Strait, but might be a warming signal from any number of years during the 1990s.

    The distinction between (1) in-situ warming of the Arctic sea ice and (2) the additional heat from atmosphere/ocean currents does seem really useful to me, but please consider that (2) may be the accumulated result of AGW transported from a very large area at lower latitudes.

  • Rob Dekker

    Bert Amesz,
    Thank you for your response.

    I think that if your assessment of 5 W/m^2 increase in ocean heat flux is correct, then it would likely explain the dramatic multi-decadal decline in Arctic sea ice volume (some 75% at the September minimum over the past 3 decades) as registered by the PIOMAS model :
    http://img.photobucket.com/albums/v224/Chiloe/12_Climate/sea_ice_PIOMAS_min.png

    Note that this PIOMAS volume overview is still right on track to hit “ground zero” volume around 2020, and there seems to be no “negative feedback” pushing back at the accelerated rate of ice volume loss.

    Unfortunately, from a scientific point of view, it is not so easy to make that claim, nor to blame increased ocean heat flux for this decline. Allow me to explain :

    For starters, it may be good to realize that from basic physics we know that ocean heat flux affects thick ice (MYI) especially in winter much more than thin ice (FYI). The thicker the ice, the more it insulates, and thus the less bottom-freeze occurs during winter, but without ocean heat flux it will still grow a bit each winter. In fact, without any ocean heat flux the Arctic ocean would freeze solid all the way to the bottom eventually. Think about it. However, if there is any ocean heat flux, even if the atmosphere is below zero, thick ice can still be bottom-melting while thin ice is growing. So ocean heat flux reduces thickening of MYI, and shortens MYI freezing period as well. A double whammy as they say here in the US. Thus, if ocean heat flux increases (over the decades), the MYI gets thinned the most, which affects ice volume, but not ice extent. Since this (ice volume reduced, MYI reduced, while ice extent is still hanging in there) is what we have seen over the past 3-4 decades, as witnessed by the PIOMAS volume results, I believe that ocean heat flux may have played an important role in “preparing” the Arctic sea ice for what now seems to be an imminent collapse.

    Secondly, it is not certain that all heat that gets injected underneath Arctic sea ice through the West Spitzbergen current actually will contribute to ocean heat flux that melts MYI from beneath. The ocean underneath sea ice in the Arctic is strongly stratified, which can prevent deep ocean heat from reaching the ice cover. In fact, the paper you quote from Cronin et al (2012) on Arctic Ocean warming during the last glacial cycle suggests that during the last glacial cycle, this stratification was so strong that virtually none of the medium depth heat inserted from the Atlantic made it to the surface. Thus, ocean heat flux must have been very low, and basic physics thus suggests that sea ice must have been very thick during the last glacial period.

    When trying to model this stratification, and the resulting ocean heat flux, the problem appears to be inherently non-linear. In fact, modeling ocean heat flux from below the halocline in a stratified Arctic has been an immense theoretical challenge which has not been solved yet, and may never be. The main problem is that the heat flux is dictated by turbulence and thus the Navier Stokes equations, which in 3D do not even have a mathematical solution, even if you have the boundary conditions.

    Needless to say, modeling ocean heat flux has been a real challenge, and a more empirical approach may be more useful in the case of Arctic sea ocean heat flux. This is why I asked Dr. Lindsay to clarify how ocean heat flux is incorporated in the PIOMAS model.

    In absence of clarification on PIOMAS, a “must read” paper is Polyakov et al 2010 (“Arctic Ocean Warming Contributes to Reduced Polar Ice Cap”), which spends a great deal on the issue of ocean heat flux.

    Most sites show only the abstract, and charge for the paper itself, but the great people from Woods Hole Oceanographic Institution (WHOI) provided not just the Ice Tethered Profiler (ITP) buoys that supplied data for this paper, but were also kind enough to share the paper with all of us :

    https://darchive.mblwhoilibrary.org/bitstream/handle/1912/4345/2010jpo4339.1.pdf?sequence=1

    One quote from the paper, which seem applicable in the context of your assessment (5 W/m^2), I think you are in the ballpark of what analytical models suggests, although you maybe a bit on the high side. From Polyakov et al :

    Estimates of upward heat flux from the AW yield values ranging from 1.3 W m^2 (analytical model, Rudels et al. 1996), to 2.1 W m^2 (1D mixed layer model, Steele and Boyd 1998), to 3-4 Wm^2 (parameterization for the bulk heat transfer coefficient from the mixed layer temperature, Krisfield and Perovich 2005), to as high as 4-6 W m^2 (heat budget estimates for the eastern Nansen Basin, Walsh et al. 2007).

    Another quote, one of the most comprehensive statements from this paper, cutting through all the theoretical deliberations, is this one :

    Until recently, maximum (~2-3 C) AW temperatures have been found in the Nansen Basin, while in the Canadian Basin the AW temperature has remained near 0.58C (Fig. 2a). This decrease of AW temperature with distance from its Arctic entrance region implies that AW heat must be lost along the AW spreading pathways.

    which suggests that at least a great deal of the increasing AW heat makes it to the bottom of the Arctic sea ice, thus indeed contributing to ocean heat flux. Especially check figure 2 in the paper, since it suggests that even as recently as the past decade, warming AW has increased the temperature of the deep water under the Arctic basin (where the thick MYI ice hangs out )quite dramatically, while there does not seem to be much of increase in the temperature of the out flowing ocean waters. Thus, much of this heat may have been ‘lost’ to the surface and thus melting thick ice…

    Also, Polyakov et al’s own modeling (which may very well be an underestimate) suggests that 0.5 W/m^2 increase in ocean heat flux over the past 50 years, which they then used in a 3D model and found that it causes a 28-35 cm of ice thickness reduction, which is something like 30% of the ice volume decline.

    Unless we understand how PIOMAS models ocean heat flux, we may not know if that assessment is realistic or not.

  • Jim Cripwell

    Eli makes some excellent points. Let me answer some of them. I am sure as we get to other topics, the discussion will, inevitably, come to the validity of models, and whether the output of these models is comparable with empirical data. There is always a cry from the warmists that the only papers which are worthwhile discussing are those that have been peer reviewed. The point I am making is that the actual data that is reported on a routine basis is not peer reviewed. It is what it is. As Eli so correctly points out, if the way it is collected has been vetted thoroughly, then it must be accepted by the scientific community as indisputable fact. So I am laying the groundwork for future discussions.

    As to ice, in such places as Hudson Bay, the warmists cannot have it both ways. When the ice in this location was late in freezing, as it has been recently, then this was said to be caused by CAGW, and the poor polar bears could not get onto the ice fast enough, and so were suffering, and have some sort of status as an endangered species. Now that the ice is forming at closer to the usual time, then the ice is thin and has no bearing on what is really happening. It is sort of heads you win, tails I lose.

    It is absolutley true that in the Arctic sea ice volumes are decreasing. In the Antarctic, sea ice volumes are increasing. I am deeply suspicious of trying to draw any conclusions as to what will happen in the future on the basis of such a limited time over which we have accurate data. It was a wind event in 2007 that caused the very low minimum sea ice extent in the Arctic. There was a storm this year which had a similar effect. The extent to whether these events are connected to CAGW is unknown. You cannot make 7 year ice in 5 years. If the Arctic sea ice is going to recover, as I fully expect it will, it will take time. In 2005, the warmists claimed that the intense hurricane season in the North Atlantic was a sure sign of CAGW. Since which, the activity in the NA has returned to normal, but we still get the warmists referring to Katrina, as if this storm was proof of CAGW. And we see the same with Sandy this year. Arctic sea ice is one of the few remaining factors where the prophesies of CAGW still seem to be holding. I think it would be wise to wait for a few more years of empirical data before we pass judgement.

  • Bert Amesz

    @Bob Brand

    My remark referred to the ‘100%’ only, not to AGW as such. As I stated, Schauer reports an increased heat flux due to (on a 50/50 basis): (i) increase of flow velocity and (ii) higher water temperatures. You can’t attribute both effects for 100% to humans. I think that a significant part of the increased heat flux is caused by natural variability in AMO and/or AMOC.

  • BWTrainer

    I must say, I completely disagree with Bart Strengers synopsis of where the discussion is at so far (his post on 11/29) when he writes: “since you all indicate it is very difficult to really prove a significant contribution of GHGs (or global warming) to the decline in Arctic Sea Ice”. The words ‘very’ ‘really’ ‘prove’ and ‘significantly’ are incredibly vague and to me do not at all represent what the scientists have said.

    Here is Walt Meier: “the multi-decadal decline in all seasons, and in virtually all regions (Bering Sea in winter being an exception) cannot be explained without the long-term warming trend that has been attributed to anthropogenic greenhouse gas (GHG) emissions.” and “The evidence for a substantial role of “global warming” in the current sea ice decline comes from the fact that the decline…” Dr. Meier seemed to ultimately agree that the high end of a 50-70% range seemed appropriate.

    Ron Lindsay’s opening statement included “I believe fundamentally the main process causing the decline in Arctic sea ice is increasing greenhouse gases.” And he likewise seemed to settle in the 50-70% range.

    Even the skeptical Judith Curry, whose analysis has been quite contested, seems to think at least 30% of the decline is related to GHG, while allowing for the possibility of the 70% figure. 30% definitely seems “significant”, to use Bart Strengers word.

    Finally, it seems to me that trying to “prove” a precise number is a fool’s errand anyway.

  • hippo

    Nice post, Dr Curry

    What I miss in the discussion on polar ice melt, is the following.
    Sea water is salt, contains sufficiently to decrease the freezing pint by 5 to 6 degrees Celsius.
    Refreezing requires temperatures well below zero, so you will get ice derived from salt water. Although a certain amount of the salt will be expelled and not incorporated into the ice, this ice is also likely to thaw earlier than ice, composed of snow, which does not contain any salt. This ice will thaw at 0 degrees, and freeze at 0.

    As far as I know (and I do not know everything), this has not been addressed in the various studies about thawing of the Arctic.

    Please, your opinion.

  • Rob Dekker

    Jim Cripwell,
    As I asked before, who are these “warmists” that you are talking about, and where is your definition of your theory of “CAGW” that you keep on mentioning ?
    Could you please give at least ONE link to a scientific paper that sustains your opinions ?

  • Rob Dekker

    Bert Amesz said

    Schauer reports an increased heat flux due to (on a 50/50 basis): (i) increase of flow velocity and (ii) higher water temperatures. You can’t attribute both effects for 100% to humans.

    Of course you can’t. Schauer analyzed a 3 year period (1997-2000), which is decidedly in the short term variability noise.
    Why do you think this study is relevant for human attribution to multi-decadal Arctic sea ice decline ?

    I think that a significant part of the increased heat flux is caused by natural variability in AMO and/or AMOC

    Which evidence do you have to sustain that opinion ?
    According to Day et al 2011, AMO/AMOC (as well as PDO, AO, NAO) can explain AT MOST 30% of the observed multi-decadal Arctic sea ice decline, with the remaining 70 % anthropogenic.
    And they use the extremely conservative assumption that influence of anthropogenic global warming on Northern Atlantic SSTs is only linearly increasing over the past century. Which is certainly an underestimate of anthropogenic GHG influence.

  • Andries Rosema

    In my contribution of 29 November I have argued, using radiation balance calculations, that increased rates of melting in the arctic are predominantly due to an increase of cloud cover. With Meteosat we observe a 10% increase of cloud cover since 1982. This observation is consistent with the increase of rainfall reported for the same period by the IPCC 4th Assessment Report.

    My contribution was however difficult the read because the table collapsed. Therefore (with thanks to Theo Wolters) here is a link to the correct text and table: http://www.nlslash.nl/climatetheory/seaicemelting.doc

    The theory put forward predicts a simultaneous negative radiative forcing and decrease in surface temperature in the Atlantic. This is confirmed by our Meteosat surface radiation temperature data, also since 1982.

    I would appreciate feedback from the experts and public on this view.

  • Bert Amesz

    @ Rob Dekker

    Plse note that conclusions by Day et al 2012 relate to September ice extent only.

    Mahajan et al 2011: AMOC no correlation with summer ice extent, but the strengthened AMOC could have contributed to decline of winter ice. Here:

    http://curryja.files.wordpress.com/2011/11/mahajan_amoc_arctic.pdf

  • Rob Dekker

    Bert Amesz said :

    I think that a significant part of the increased heat flux is caused by natural variability in AMO and/or AMOC

    Mahajan et al 2011: AMOC no correlation with summer ice extent, but the strengthened AMOC could have contributed to decline of winter ice.

    Thank you for mentioning Mahajan et al 2011, the findings of which were confirmed by Day et al 2011. It’s pretty clear that both studies place the influence of warming Atlantic waters on Arctic sea ice in the Northern Atlantic marginal seas (Nordic Seas and West Greenland). Of course, Arctic sea ice does not know if that warming is caused by the “natural variability” of AMO, or simply because the entire Northern Atlantic is warming up with the rest of the planet. So even that 30% “long term variability” will have an anthropogenic factor.

    Either way, if “natural variability” of AMO/AMOC only correlates well with winter sea ice decline, one may wonder what caused the jaw-dropping summer sea ice decline over the past 3 decades, no ?

  • Rob Dekker

    Andries,

    All climate models predict an increasing cloud cover over the Arctic when the rest of the planet warms, and even Dr. Curry admits that increased cloud cover causes warming in the Arctic (apart from a few weeks during summer).

    So if cloud cover indeed increases over the Arctic, then this is a sure sign that clouds are a part of Arctic amplification of Arctic and lower latitude warming.

    Conforming with model expectations, it is clear now that at least in late summer and autumn, cloud cover increased, specifically over the now ice-free areas of the Arctic.

    However, there have been some contradictory reports on weather Arctic cloud cover in other seasons is actually increasing over other parts of the year and adding to warming as well or not (on a multi-decadal timeframe). For example, Screen and Simmonds 2010 reports that Changes in cloud cover, in contrast, have not contributed strongly to recent warming.
    http://sciences.blogs.liberation.fr/files/arctique-ann%C3%A9es-2000-tures.pdf

    So, if increased cloud cover in other seasons were also confirmed, it would add confidence to GCM projections, and a confirmation that cloud cover is part of Arctic amplification in a warming world (rather than ONLY “natural variability” as some experts here assert).

    So, could you please give a reference to the Meteosat surface radiation temperature data that you mention, or a reference to a scientific paper that addresses the changes in cloud cover over the Arctic in recent decades and how these changes add to Arctic amplification of global warming ?

  • Herman Vruggink

    Perhaps it’s an idea to make a summary when the discussion is over? What have we learned out of this discussion so far, what’s in common, what’s not.

  • Bert Amesz

    @ Rob Dekker

    One may argue as follows. In wintertime, the increased AMOC/AMO affects the volume (and extent) of multiyear sea ice. See also NSIDC:

    http://nsidc.org/images/arcticseaicenews/20111004_Figure6.png

    So at spring, the starting conditions deteriorate gradually. The spring sea ice extent is increasingly dominated by one year ice. Subsequently, this thin ice disappears rapidly due to atmospheric conditions in spring and summer. This would imply an indirect relation between AMOC/AMO and summer ice extent. The AMO, often seen as fingerprint of AMOC , is a natural climate variability. Also during the fifties, the AMO was positive and sea ice extent was low. But I agree with you: in addition to the natural AMO-variability, there is an overall warming trend in North Atlantic waters.

  • Andries Rosema

    @ Rob Dekker

    You wrote “All climate models predict an increasing cloud cover over the Arctic when the rest of the planet warms”. In my contribution of 29 November I argued by energy balance calculations that increased cloudiness results in a positive forcing and melting in the Arctic and a negative forcing and cooling in the Atlantic area. This is not in line with your statement.

    In addition I believe that “all climate mosdels predict” and “even Dr. Curry admits” are not scientific arguments. I presented some very simple calculations in my previous contribution. What is wrong there?

    With respect to the cloud data, these have not yet been published. At EARS we have 30 year of hourly VIS and TIR Meteosat data and are continuing to receive. The cloud data are classified in height classes on the basis of their cloud top temperature. Cloud duration data fields in percent are then derived for each day and each dekad. The cloud durations are input to our rainfall mapping system. They are also used for excessive precipitation insurance.

    I have extracted dekad cloud durations series for 30 land and 25 sea locations for the period 1982-2006. These data show pre-dominantly an increase in cloudiness over land and ocean/sea during this period. The average increase for the ocean/sea locations is:
    +18% for the MediumLow cloud level (260-279K)
    +6% for the MediumHigh cloud level (240-260K)
    +8% for the High cloud level (226-240K)
    +9% for the VeryHigh or “Cold” cloud level (<226 K)

  • Rob Dekker

    Andries,

    I’m sure you have the best intentions, but in your posts you have not given a single reference to the (apparently 30 years) data from Meteosat, nor any reference to any scientific publication at all. Neither about the data, nor about your own assessment of radiative forcing, nor any reasoning about what is cause and what is effect.

    Could you please respond to the findings of Screen and Simmonds 2010
    http://sciences.blogs.liberation.fr/files/arctique-ann%C3%A9es-2000-tures.pdf
    who report that Changes in cloud cover, in contrast, have not contributed strongly to recent warming., a conclusion based on the ERA-interim re-analysis dataset, as confirmed by satellite observations ?

  • Arjan van Beelen

    @Andries Rosema:

    You show potentially interesting information (quite large trends btw), but what are the locations of these stations, and how are they selected? How do you define a ‘cloud’ using satellite imagery? Why hasn’t it been published, I think (reliable?) data on cloud cover changes are of the utmost importance. Is there any data on the period up to more recent years, when most of the arctic sea ice melting occured?

  • Rob Dekker

    Dr Lindsay said

    I don’t agree that 2/3 of the melt comes from the ocean. How do we know that?

    to which Rob van Dorland replied :

    I thought there was consensus about the 2/3 ocean and 1/3 atmosphere issue in relation to ice melt. Walt brought this up referring to Steel at al.

    I think there was a misunderstanding here. Steele et al 2010 refers to the diurnal cycle of Arctic sea ice melt, whereas I think Dr Lindsay refers to the multi-decadal loss of volume recorded by PIOMAS.

    The two (estimates of ocean heat melt versus atmospheric heat melt) may indeed be completely unrelated.
    After all, bottom-melt in the ice margin during the summer melt season mainly originates from ocean warming due to the change in albedo in the ice margin (ice to dark ocean), and thus both bottom and top melt originates from the atmosphere (and Arctic summer sun).

    In contrast, for multi-decadal volume loss, ocean heat (and bottom melt) typically refers to heat flux through the cold halocline in the Arctic, caused by influx of Pacific and Atlantic water underneath the ice pack. This ocean heat flux affects mostly thick multi-year ice during winter (since heat flux through thick is in winter is much smaller than through thin ice), and thus is of a completely different nature than the diurnal cycle bottom melt in the ice margin in summer.

    To address Dr. Lindsay’s question “How do we know that?” regarding bottom melt due to increased ocean heat flux from Atlantic and Pacific waters, the best scientific estimate that I have found is (once again) Polyakov et al 2010 :
    https://darchive.mblwhoilibrary.org/bitstream/handle/1912/4345/2010jpo4339.1.pdf?sequence=1

    They suggest that over the past couple of decades, ocean heat flux (due to Atlantic water temperature increase) has increased 0.5 W/m^2 under the ice, meanwhile noting that ocean heat flux through the halocline is mostly determined by turbulence, which is notoriously non-linear. Also, they note significant geographical differences of ocean heat flux :

    there is a wide spread of flux magnitudes depending on geographical location. For example, Padman and Dillon (1987) estimated heat fluxes above the AW core (320-430 m) using microstructure profiles from the Beaufort Sea to be in the range 0.02-0.1 W/m^2. Heat fluxes in the Canada Basin at the base of the mixed layer and below ice were estimated as 0.3-1.2 and 0.2 W/m^2 ;over the Chukchi Borderlands the estimates were higher, 2.1-3.7 and 3.5 W m^2 (Shaw et al. 2009)….etc etc

    Still, when inserting their estimate of an overall 0.5 W/m^2 increase in ocean heat flux in their 3D model, they found that it causes a 28-35 cm of ice thickness reduction, which is something like 30% of the observed ice volume decline.

    Dr. Lindsay, can you please comment on these ocean heat flux findings by Polyakov et al 2010 ? Specifically, does the PIOMAS model confirm or deny their findings, and is their estimate (of a multi-decadal volume loss attributed to increased ocean heat flux due to warmer AW influx) in the ballpark of the PIOMAS ocean heat flux estimates ?

    It would be REALLY interesting to understand PIOMAS’ findings/modeling of ocean heat flux over the past decades a bit better, and if anyone has performed any experiments with PIOMAS in varying ocean heat flux, to determine how sensitive overall volume decline is to increased Atlantic ocean water influx..

  • Jim Watkins

    In the first place I would like to thank the individual scientists that are engaged here discussing the topics from the grounding of their specialties. To have you discuss from the position of the passion you have for your work in open forum is actually a rare access for the public versus the craft of science writing which distills down the science for the public pallet.

    In your discussions, there seems to be a recurring theme of the limits of data based on the introduction of satellites in the late 70s and other limitations. I would suggest there is a vast trove of data that I have not seen referred to and this is the data from all the military traffic in the arctic by the Russians, the Americans and any other country with nuclear submarines, as these boats and crews would have a very strong interest in sea ice conditions above them and would have recorded huge amounts of data as they plied their various courses at varying times of the year.

    Another point is the factor of changing salinity and its affects on ice formation and retention. As referenced in one of the abstracts I looked at.

    http://www.nature.com/nature/journal/v481/n7379/fig_tab/nature10705_F1.html
    http://www.nature.com/nature/journal/v481/n7379/full/nature10705.html

    If arctic warming is a fact then the water flow of the feeder continents of Asia the North America through permafrost melting and all the other sources of runoff which could include glacial melt and the potential of changing rain volumes across the continents would seem likely to impact on ice formation and retention.

    Then there could be the interactions and feedbacks from the weather. The cyclonic event of august 2012 was just one of many recorded cyclonic and anti-cyclonic events recorded over time. These events are related to the high pressure ridges and positions of the jet stream as it changes over the course of a year. A storm can have significant impact on the breakup of sea ice depending on the strength of the the storms systems at critical times in the melting phase of summer.
    Regrettably I can not find the original abstract that referred to specific years of intense activity of these storm periods but this piece infers a direction.

    http://link.springer.com/article/10.1007%2FBF01030491?LI=true

    The impacts in the general ecology of the Arctic Ocean of the loss of sea ice can also be a venue to be taken account of. What impacts there are can be inferred from such events as drowning polar bears unable to reach ice flows for seal hunting as the distance to the ice is too far and to other aspects of the total ecology that perhaps can feed into ice formation and melting regimes, even on a microbial level. Life forms shape ecologies as they are shaped by them. What they are in the Arctic is likely subtle but likely not without impact.

    In the dialogues going forward, the ability of the scientific community that focuses on the Arctic to communicate what is known and the possible futures will likely need to find new methods that could contribute to the public and policy makers awareness. One such project that is quite impressive is the Vulcan Project.

    http://vulcan.project.asu.edu/

    To create such granular visualizations of as many aspects of the complexity of the Arctic by the use of video is something that would, I believe, be a fantastic way to engage the vested interests of all the partners.

  • Hank Roberts

    > a vast trove of data that I have not seen referred to …
    > with nuclear submarines

    Prob’ly before your time, youngster.

    Here ya go.
    First few results are news and science articles, plus a typical (*) from WTF:

    https://www.google.com/search?q=“gore+box”+arctic+submarine+data
    About 194 results (0.31 seconds)

    Newly Declassified Submarine – National Science Foundation
    https://www.nsf.gov/news/news_summ.jsp?cntn_id=102863
    Map of Gore Box. Map of Arctic Ocean where formerly classified submarine data are now being released for study. …

    nsf.gov – News – Newly Declassified Submarine Data Will Help …
    http://www.nsf.gov/news/news_images.jsp?cntn_id=102863...
    “Gore Box:” The area outlined in the Arctic Ocean where formerly classified submarine data are now being released for scientific study, named for Vice President …

    Submarine Upward Looking Sonar Ice Draft Profile Data and Statistics
    nsidc.org/data/docs/noaa/g01360_upward…/index.html
    This data set includes submarine data collected in the Arctic Ocean by U.S. Navy … original “Gore Box” (so called because of Vice President Gore’s advocacy for …

    And the (*) from WTF:

    Thinning Arctic Ice; More Al Gore Aided and Abetted Misinformation …
    wattsupwiththat.com/…/thinning-arctic-ice-more-al-gore-aided…
    Oct 9, 2012 – Guest post by Dr.Tim Ball Al Gore did more to bring melting Arctic ice … which environmental data from Arctic submarine exercises could be released. It was called the “Gore Box” by the USN, so there is little doubt of the origin.

  • Jim Cripwell

    The summary can best be described as “all sound and fury; signifying nothing” (Shakespeare, Macbeth). Three confirmed, ardent, warmists write what they think, and the summary is supposed to mean something? I dont think so.

    We now have a few more months of data with respect to both Arctic and Antarctic sea ice extent. The Antarctic has been setting maximum extent values for the date as the summer progressed, and looks likely to start the refreeze a little early, with the minimum extent being the second highest value since records began. I know there is a pal reviewed article which “explains” why CAGW has no effect on Antarctic sea ice. But then, the warmists have a pal reviewed article on any aspect of CAGW, where the empirical daya does not support the religious belief that CAGW is real. Then the warmists do their best to see that counter articles never get published; just look at what happened to Livingston and Penn, Roy Spencer, and Anastassia Makerieva.

    Meanwhile, Arctic sea ice extent made a spectacular recovery from the minumum set in September 2102. The latest data shows that Arctic sea ice extent is just within the 2 sigma limit of the average of precious years. Further, the temperature north of 80 is significantly below average. This could well signify a late start to the melt of that ice which needs to melt if the Arctic is to be ice free next summer, or at least set another record for the minimum extent.

    I presume that, sometime, there will be a pal reviewed article which explains why CAGW only affects Arctic sea ice extent in the summer. While the empirical data shows the dramatic loss of summer sea ice, it shows that winter sea ice extent is far less affected. I wonder why. But I am sure someone will invent a good reason, and get it published.

    All in all, not a very promising start to this blog.

Off-topic comments (click to expand)
  • Jim Cripwell

    I have not seen any comments about Antarctic sea ice extent. My reading of the data is that Arctic and Antarctic sea ice extent are negatively correrlated. This does not indicate that CAGW plays any role in the decrease of Arctic sea ice extent that has been observed in recent years. Rather it indicates that clouds may play a major role. The albedo of clouds is greater than the surface everywhere on earth except Antarctica, where the albedo of the ice is greater that that of clouds. So more clouds cause cooling everywhere else except Antarctica, where they cause warming; and vice versa. A change in cloud cover is more indicative of what is happening to total sea ice extent.

    A note to those who run this blog. It seems to me that discussing Arctic sea ice extent in isolation is a very biased way of starting discussions on this blog. If you want to appear to be unbiased, then you ought to have included Antarctic sea ice extent in the intiial discussion subject.

  • Elmar Veerman

    Hi, good to see the discussion has started (dialogue to me sounds like there are just two sides, which would be an oversimplification!) May I ask how these three scientists for the first discussion were selected? Are they chosen to represent the full range of opinions in climate science about this topic? I ask because I have the feeling the scientists who are most concerned about the Arctic are missing. For example, I would like to hear what Peter Wadhams (Cambridge)has to say about this. Or Wieslaw Maslowski, an oceanographer who made a model in 2007 that predicted an ice-free Arctic in the summer of 2013.

  • Jim Cripwell

    Elmar, you ask how the “experts” were chosen. All three are well known supporters of the idea that adding CO2 to the atmosphere causes CAGW, and hence believe this is the cause of the extensive melting of Arctic sea ice. I have great fears that this blog will be just another way of promoting The Cause on behalf of The Team. I hope I am wrong.

  • Marcel Crok

    @Jim Cripwell
    Judith Curry clearly is the most skeptic of the three. She has written critically about attribution. One of our criteria is that invited scientists have published in the peer reviewed literature about the topic under discussion. Which skeptical scientist would you have suggested?
    Marcel

  • Jim Cripwell

    To Marcel Crok.

    It is clear that you do not read Judith’s Climate Etc. She routinely chooses topics for discussion which assume CAGW is correct. Surely it is not up to me to choose experts who disagree with CAGW; that is your job. I merely point out that the three who you chose just happen to be proponents of CAGW. I hope that this is not deliberate.

    I seriously doubt that there are not people who have published on Arctic and Antarctic sea ice, and who are climate skeptics, but who they are I dont know. I suggest you contact people like Anthony Watts, Richard Courtney, Christopher Monkton, Richard Lindzen, or thousands of others who are well known climate skeptics, who would be far more likely than myself to know as to who would be suitable candidates. I just have doubts that you have searched very diligently.

    Please note, I am a retired scientist who has no access to what is going on in the scientific world, except what I can glean from the Internet. Surely you have far better access as to who should be chosen as experts than I do. But if you want this blog to be impartial, I suggest you dont introduce a topic unless you can guarantee that both sides of the discussion are represented as experts.

  • Jim Cripwell

    To Arjan van Beelen. You write “I don’t see why the albedo of clouds above Arctic sea ice is larger than above Antarctic sea ice,” I did not say that. I do wish people would actually read what is written. The albedo of clouds is the same the world over. The albedo of Antarctic ice (not sea ice) is greater than that of clouds. I do not have a reference for this. I read it somewhere, and did not keep the reference.

    As to CAGW, I accept that adding CO2 to the atmosphere causes global temperatures to rise, so AGW is real. The question is, how much do temperatures rise? Only if the rise is Catastrophic (the C) does it matter. Hence the use of the term CAGW.

    You must remember that just about anything that supports CAGW can be published in the peer reviewed literature. Publishing anything that disputes CAGW is extremely difficult., Just ask Roy Spencer. So the majority of papers opposing CAGW are not found in the peer reviewed literature, they are found on blogs.

  • Arjan van Beelen

    @Jim, I meant to comment on your statement that the albedo of clouds is greater at the surface everywhere except at Antarctica. I do not see why the same is not true for the Arctic. (Above sea ice is relevant for the surface radiation budgets.) Can you explain why this would be the case?

    So there are no literature studies. No references, you read it somewhere.. on some blog(?). How can we discuss science without any reference to a study?

    Instead you divert the discussion even further to your suggestion that this blog is biased (who would you suggest as a SEA ICE expert “skeptic” for this topic?), and the literature is biased…

    Show us studies, data, equations, results! These are things we can discuss. All the rest is useless handwaving and rumors. You should know as a retired scientist… I will certainly leave this blog if things go that way (again…), as I am not interested in rumors, suggestions and handwaving which can not be checked nor discussed. Marcel, is it possible to create a topic/place where people can leave comments which are off topic (or leave suggestions for this blog) so that they do not interrupt the scientific discussion?

  • William Steiner

    We have seen a lot of conjecture with regard to whether there is global warming and if man is the cause of global warming. Sadly, conjecture becomes fact if it is repeated often enough. When one says that “man may cause global warming because of higher carbon dioxide levels” without the data to support it, that is bad science and it is conjecture.
    There is NO data to support man caused global warming, also known as anthropogenic global warming, due to carbon dioxide forcing. In fact, the carbon dioxide readings that state the carbon dioxide levels have significantly increased were taken on the side of the Mauna Loa volcano, an active volcano. They are false readings with regard to man’s contribution to carbon dioxide levels because volcanos release carbon dioxide. Furthermore, the proponents of man caused warming have also used an organic chemistry formula which shows the conversion of carbon based fuels into carbon dioxide. That is also false because it assumes that all carbon from the fuel become carbon in carbon dioxide. A 100% conversion of carbon from fuel to carbon dioxide, also known as CO2, never happens and never will happen.
    In fact, the Vostok Ice Core Studies have shown that higher CO2 levels are the RESULT of warming oceans/warming climate and not the cause of warming. It’s a cause and effect thing and the man caused theorists have it backwards. According to the logic of man caused theorists, cancer would cause smoking.
    There is NO data to support universal global warming as the man caused warming people state. University of Alabama-Huntsville global temperature mapping has shown that parts of the globe are becoming cooler while other parts are becoming warmer.
    Man caused warming theorists have totally ignored geologic time and have almost totally dismissed the biggest determining factor of climate change, plate tectonics and volcanism. They need to simply study the Eocene Epoch and man was not here.
    We have seen a significant increase in the degree of undersea volcanism in the last forty years. When JK Hilliar of Cambridge U. found over 200,000 volcanic sea mounts in just a portion of the earth’s oceans, that was significant. Why? These sea mounts have volcanic vents that can turn on or off in a geological instant. When on, they heat the water uo to 750 degrees Fahrenheit and there are a lot of vents.
    The oceans are the largest reservoirs of carbon dioxide on the earth. Undersea vents heat the water releasing CO2 from the vents and from the water itself because a warmer solution holds less gas. However, the biggest green house gas is increased water vapor caused by warming oceans.
    Undersea volcanism causes global warming as it increases the real greenhouse gas called water vapor. Terrestrial or above ground volcanism causes global cooling because it releases reflective particles which reflect solar energy. Our planet lies in a balance between these two most dynamic natural forces. Man is but a flyspeck on the window when it comes to climate change.
    We all seek a cleaner planet. We all seek to lessen pollution. However, we must find correct solutions for real problems and man caused warming is not it.

  • William Steiner

    Regarding the melting of Arctic Ocean ice. Undersea volcanism has increased worldwide and it includes the Arctic Ocean. In 1999 and explosive volcano erupted under the Arctic Ocean with such force it left a 10 sq km debris field. The cause of that explosive volcano was a CO2 buildup in the crust under the ocean, according to the Woods Hole Observatory. They also stated it released 10X more CO 2 than originally thought. It continues to erupt along a vent line, heating the water to 752 degrees Fahrenheit.

  • William Steiner

    The Vostok Studies have shown CO2 levels change AFTER climate change. That makes sense as oceans warm, with oceans being the biggest temperature regulator, less CO2 can be held in solution. Warmer oceans release more water vapor, the real greenhouse gas. Its simple physics.
    To say the CO2 causes climate change is the equivalent of saying cancer causes smoking. It is just backwards to real cause and effect.
    Then when we air condition our homes to make them cooler we remove water vapor from the air to cool them. We do not remove CO2 from the air to cool them.

  • Schuur

    @ Jim Cripwell,
    Marcel Crok has stated clearly that invited scientists must have pubished in peer reviewed literature. Those are the real experts in the field. They could ask for contributions of economists, experts on Slovakian literature, dentists or truck drivers for all I care. But that would make no sense, would it? It would be like a bunch of car salesmen, who claim to possess all knowledge about baking bread, while discrediting real bakers. Your suggestion to invite people like Monckton or Courtney holds no ground at all. For all intents and purposes, I think this is a weblog about scientific knowledge, not about deliberately misleading the public. I do appreciate the input from real scientists, including the minority on the sceptical side, but as soon as such people start publishing here, the whole website would lose its scientific credibility and reliability.

  • Neven

    I agree that it would’ve been nice if Dr Peter Wadhams of the University of Cambridge had been invited to give his views. This initiative was announced in a Dutch news paper as a negotiation between alarmist scientists and skeptics. Dr Meier and Dr Lindsay are not in the least alarmist. Wadhams could be labeled as such, despite the fact that he has been largely right about the unfolding of events in the Arctic so far. An unfolding which, of course, is alarming.

  • Neven

    It’s good to see though that all expert participants agree on an anthropogenic factor of at least 50%. Given the magnitude of the event and the rate at which it is progressing, one then inevitably moves on from ‘could there possibly be a problem ever?’ to ‘what can and should be done about this anthropogenic factor?’. It seems that after one day ClimateDialogue has been so successful in reaching agreement concerning the reality and risks of AGW (which is clearly reflected in the Arctic situation) that it has made the dialogue about all other scientific aspects of climate change irrelevant. Well done, chaps.

  • Neven

    So some more please on Arctic Amplification, Northern Hemisphere snow fall patterns (positive anomaly in winter, very negative anomaly in spring and summer) and the influence on atmospheric patterns. Permafrost and methane clathrates are less relevant at this point.

  • Albert Jacobs

    I agree with Jim Cripwell: I admire Judy, but she is not the strongest one for arguments to defang the CAGW myth. I can shake another half dozen published sceptics out of my reference list, Marcel, some of whom will have stronger arguments against any sizeable CO2 influence.

    What about Peter Chylek, Nils-Axel Morner, Christopher Kinnaerd, Masahiro Ohashi, A.Polyankov, George Taylor for starters?

    The important aspects to be discussed on Arctic ice cover include the actual satellite measurements, the influence of the wind and currents (gyre), the greater influence of the influx of Pacific and Atlantic warmer water on melting and the solar flux. An examination of the reasons for the negatively correlation with the Antarctic ice cap is also a must. Also, Arctic ice cover can not be discussed without attention to the historic perspective. We can not depend on a forty year window of satellite observations when major earthy cycles are sixty years. There is non-scientific, non-continuous data to be had from historic sea-farers, which speak of low Arctic ice cover in past centuries. Arctic Ice cover changes are mostly a natural event and geological history is long. It has varied from ice sheets covering half of North America to forests on Ellesmere Island.

    I am happy with the concept of ClimateDialogue and wish it a good future.

  • Jim Cripwell

    Arjan, you are trying to make my remarks mean far more than I intended. I must go back to Square 1. There are various blogs which discuss CAGW. To take but 3 examples, there is RealClimate, which is blatantly warmist, and WUWT, which is equally blatantly skeptic. In between there is Climate Etc. which is definitely warmist, but far more neutral than the other two blogs. When I heard of Climate Dialogue from the Global Warming Policy Foundation, it seemed that this new blog would be somewhere between Climate Etc. and WUWT.

    So when I came here intially, I was deeply disappointed to find a blog that, at first blush, is just an unmoderated version of RealClimate; a blatantly pro-warmist blog. The first subject was Arctic sea ice, heavily biased to the warmist side, with no experts from the skeptic side. What I tried to do was point out how biased this first article was, in the hopes that Marcel might change his approach. In support of this I tried to suggest that it would be far better to include a discussion of Antarctic sea ice, and see if there was an reason, other than CAGW, which explains the differences between the two poles.
    Now I am fully aware that the warmists have all sorts of excuses, some published in the peer reviewed literature, that try and dismiss Antarctic sea ice, so that they only need discuss Arctic sea ice, and show that it really does prove that CAGW is real. All I was attempting to do is to suggest that there is a hypothesis which tries to explain the difference between the two poles, and which does not involve CAGW. Has this hypothesis been fully tersted? Is there lots of data etc to show that it might be correct? No, of course not. It is merely an idea which tries to deal with both poles at the same time; something this first artcile on the blog fails miserabely to do.

    I sincerely hope that in the future, Marcel will take this blog so that it truly lies between Climate Etc and WUWT. Should this fail to happen, I wont be around at all.

  • Maunder

    As per so many of the above comments, good initiative.
    It is fitting for the dutch to start with it, and that is not meant sarcastic but a compliment.
    Throughout the ages the dutch have always been the more likely nation to accept that there are two, or more, sides to every issue.

    It is clear from all of the above that other then “belief” in computer models and predictions no one has got any real clue as to what is going on.
    What is also clear, like it or not, is that similar ice disappearing discussions were in the news in the 1930′s with similar predictions of doom.
    We can of course go back 1000 years and ask the Vikings for advice on how to farm on Greenland. Or even further back and ask Hannibal about crossing the Alps with elephants, that path is blocked by ice and snow at the moment.

    What would also appear obvious is that nothing that is happening at the moment is new or unprecedented except in the mind of some and those that wish to follow every prediction of doom.

    We are not seeing any weather event that is outside natural limits or has not happened in similar fashion in the last 100 years. We have just put more people in harms way which is just about the only anthropogenic part in the whole issue.
    Simplistic reasoning? Perhaps.
    But so is the notion that an increase in CO2 is the cause of a slight increase in temperature after a 30 year cooling period. Whereas the CO2 has been increasing supposedly since the mid 19th century and has by now increased about 33%, assuming that the starting point is correct.
    There has been no increase, some would say there has been a decline, in temperature for the last 14 years. Which by itself flies in the face of the theory.
    The sea level is not rising any faster then it has done on average for the last 100 years.
    Etc.
    I know they are all the old arguments from a non AGW believer.
    But then I like to live with facts rather then models which, the 3 experts here agree to, are not accurate.
    The debate here would appear to be about how inaccurate the models are and how can we defend the predictions.

    History and facts are clearly not on the side of the models.
    Life is looking up and if it is warming in the long term rather then part of a cycle it will, overall, be good for the human race.
    Our species has always done better in times of warmth. Darn history again.

    No problem with finding long term energy solutions which do not require carbon based fuels on the basis that logic would indicate that within the next 150 years we will have used most of it and we will be forced to rethink those energy sources.
    But we are certainly waisting excessive mental energy and public funding on CO2 is causing unprecedented warming models and trying to explain every gust of wind with that model and classify it as “predicted”.

    Let’s put the mental energy and public funds into something useful for the future.

  • Jesuswept

    @ William Steiner

    2012-11-13 17:59:55
    “”In fact, the carbon dioxide readings that state the carbon dioxide levels have significantly increased were taken on the side of the Mauna Loa volcano, an active volcano. They are false readings with regard to man’s contribution to carbon dioxide levels because volcanos release carbon dioxide.””

    I appreciate the idea behind the website which I understood was about debate on AGW/CC, about finding a consensus/agreement so that we can finally move on and take action. Before making such a claim here you should have asked the good folks at MLO how they do their measurements and perhaps mention to them what you’ve just said… ;)

    “The concentration of carbon dioxide in the atmosphere of Barrow, Alaska, reached 400 parts per million (ppm) this spring, according to NOAA measurements, the first time a monthly average measurement for the greenhouse gas attained the 400 ppm mark in a remote location. Carbon dioxide (CO2), emitted by fossil fuel combustion and other human activities, is the most significant greenhouse gas contributing to climate change.

    “The northern sites in our monitoring network tell us what is coming soon to the globe as a whole,” said Pieter Tans, an atmospheric scientist with NOAA’s Earth System Research Laboratory (ESRL) in Boulder, Colo. “We will likely see global average CO2 concentrations reach 400 ppm about 2016.”

    Carbon dioxide at six other remote northern sites in NOAA’s international cooperative air sampling network also reached 400 ppm at least once this spring: at a second site in Alaska and others in Canada, Iceland, Finland, Norway, and an island in the North Pacific.”

    http://researchmatters.noaa.gov/news/Pages/arcticCO2.aspx

  • Aaron Lewis

    Climate science cannot have it both ways. Either anthropogenic warming (AGW) exists and affects all of our weather, or AGW has not occurred and therefore affects none of our weather. It is an all or nothing proposition. The trend of temperatures tells us that AGW is real, and therefore affects the entire weather system, all the time.

    AGW has been affecting all of the weather on Earth as long as AGW has been perceptible. We were ready for variations in the old, lower energy weather system. The early effects of small amounts of extra CO2 were tiny, and, we just did not notice that the weather was intrinsically different. We thought the pattern of warming was just natural variation or another natural cycle of warming – the natural variation of a system in equilibrium. Now, greenhouse gas concentrations have increased, the system is not in equilibrium, and AGW is much greater. We are not ready for the more powerful weather system that results from the extra energy from AGW. It is time to get “real” and tell the truth.

    The truth is that energy from AGW is a part of the heat content of all phases of our weather system. That includes the 2012 weather process that produced “Sandy”. Sandy, without the energy from AGW, would not have been “Sandy”. AGW was a part of the 2010 Russian Heat Wave and the Pakistan Floods. AGW was a part of the 2011 Texas Drought. Without the extra heat from AGW, these would all have been very different events – “normal weather”. Likewise, the great snow events were internal work done by the global weather system, driven to greater intensity, by the extra energy from AGW.

    AGW provided the extra heat that reduced Arctic Sea Ice extent. This is a special set of weather processes because Arctic Sea Ice extent affects all other northern hemisphere weather. Loss of sea ice leverages the impact of AGW on the global weather system. Anyone who doubts this needs to go back and think about the thermodynamics of weather.

    AGW is extra heat that humans and Earth’s ecosystems are not adapted to withstand. AGW is that straw, which when added to a load of straw, breaks the camel’s back.

  • Nabil Swedan

    Rob Decker says, “But we better hurry up fixing our models, since the trend is clearly accelerating…”

    Knowing how wrong is the basic climate energy equation, we sure have to hurry up in fixing our models-The potential energy of the atmosphere is missing from the equation, and there cannot be any worst than that. Bureaucrats have to hold onto the climate regulations until the climate models are fixed and print something that makes sense. Otherwise, most of us will be poor and poverty is the worst enemy to the climate.

  • climatedialogue.org – Stoat

    [...] Dekker makes the first comment that really attempts to discuss the science. After that it gets better, with four or five comments actually about science. Those comments [...]

  • Eli Rabett

    Well, conversation about this attempt has already started many other places, but some, not Eli to be sure, fear that it will not go well as presently structured because it encourages the insertion of many things which are not necessarily so (or ever were). For example, and Eli picks on this because he has looked into these matters in some detail, William Steiner writes

    There is NO data to support man caused global warming, also known as anthropogenic global warming, due to carbon dioxide forcing. In fact, the carbon dioxide readings that state the carbon dioxide levels have significantly increased were taken on the side of the Mauna Loa volcano, an active volcano. They are false readings with regard to man’s contribution to carbon dioxide levels because volcanos release carbon dioxide. Furthermore, the proponents of man caused warming have also used an organic chemistry formula which shows the conversion of carbon based fuels into carbon dioxide. That is also false because it assumes that all carbon from the fuel become carbon in carbon dioxide. A 100% conversion of carbon from fuel to carbon dioxide, also known as CO2, never happens and never will happen.

    The observation of CO2 concentrations at Mauna Loa have been confirmed at many other sites, including in a series of aircraft flights as well as at multiple locations across the globe. While the latter have a different annual range (less in the southern hemisphere than the northern for interesting reasons) the annual means travel in lockstep. Moreover, Steve Riley, who has made a study of the effects of the volcanic emissions on the Mauna Loa record, has conclusively shown that a) it is zilch (a ppm or less on average, a few ppm during infrequent eruptions) b) any eruptions are clearly marked and monitored, and their effects eliminated from the ML record.

    Ferdinand Engelbeen has a good introduction to the measurements of atmospheric CO2

    As to all of the carbon in fuels being converted to CO2, well, that is an interesting discussion, but Eli fears that it will not go precisely where William Steiner wishes. But to start that one, where else does it go and what happens to it then? As a hint, it should be pointed out that anyone designing an engine or generator that burns fossil fuel has the precise aim of converting all the fuel into CO2 and water vapor in order to extract the maximum heat energy from the process.

    IEHO, the moderators need to find a way of dealing with such insertions that assume things that are simply not so. While there is a place for opinion and everyone is so entitled, there is also a need for correcting clear misbeliefs so the discussion does not degenerate. Also, it is disappointing that for this topic Neven, a person of Dutch citizenship, and perhaps the best informed amateur on the subject of Arctic ice has not been given a more central role.

    It is conceivable that this comment will not be posted, so it goes, but I would point out to the moderators that a similar inattention to reality and a favoring of obviously unfounded opinions by posters and commentators lead rather quickly to the irrelevance and later end of Nature;s climate science blog.

  • Jim Cripwell

    Schuur you write “Your suggestion to invite people like Monckton or Courtney holds no ground at all.”

    I do wish people would read what I actually write, instead of assuming that I wrote something they would have liked me to have written. What I said was “I suggest you contact people like Anthony Watts, Richard Courtney, Christopher Monkton, Richard Lindzen, or thousands of others who are well known climate skeptics, who would be far more likely than myself to know as to who would be suitable candidates.”

    In other words, I suggested that Marcel consulted some of the real skeptics of CAGW to find out who the experts on sea ice are, and who believe CAGW is a hoax. Not pseudo-skeptics like Judith Curry. Maybe you want me to look foolish by suggesting that the people I mentioned wrote artciles on sea ice, but that was not what I said.

    If Marcel really wants a dialogue from both sides of the debate, which I am beginning to doubt, then he must actively solicit the views of people who, like myself, strongly believe that the true physics shows conclusively that adding CO2 ot the atmopshere has absolutely no bad effects whatsoever; and certainly has a negligible effect on raising global temperatures. CO2 is a plant food, and the more we have of it in the atmosphere the better. It will help us feed an ever growing world population.

    I believe one of the future subjects to be discussed will be climate sensitivity. If I am right, then let me suggest here and now, that he invite Terry Oldberg and Tomas Milancovic to write on the subject.

  • Elmar Veerman

    @Jim Cripwell: people who believe adding CO2 to the athmosphere does not contribute to warming can never be experts. They are just wrong, which has been demonstrated over and over again. And who is ‘Tomas Milancovic’? The scientific literature makes no mention of him. If you meant Milutin Milankovic, he died in 1958.

  • OPatrick

    This should be an interesting initiative to follow, but to help it stay so can I request a 3-tiered commenting system (or 4 tiered depending on whether it would be necessary to keep the Off-topic comments section)? The expert discussion and separate comments section for all general comments as it is, but with an intermediary section where commenters who appear to have particularly pertinent points and some evidence of expertise can comment. These contributors could be elevated from the melee if their comments there appear consistently worthwile (and thrown back into it if they don’t justify their promotion) and allowed to carry on a secondary discussion which might be worth reading for purpose other than pure entertainment.

  • Nabil Swedan

    Rob Dekker says “But we better hurry up fixing our models, since the trend is clearly accelerating…”

    Well, the basic energy equation of the climate used in the models is so wrong; it is missing the potential energy of the atmosphere and it cannot be any worst. Sure we have to hurry up fixing the climate model. Until then, bureaucrats have to hold onto the unreasonable climate regulations. Otherwise, most of us will be poor and poverty is the worst enemy of the climate.

  • Jim Cripwell

    Elmar Veerman, you write ” @Jim Cripwell: people who believe adding CO2 to the athmosphere does not contribute to warming can never be experts. They are just wrong, which has been demonstrated over and over again. And who is ‘Tomas Milancovic’?”

    To answer the second question, both Terry Oldberg and Tomas Milancovic have commented extensively on Judith Curry’ blog, Climate Etc. on the subject of Climate Sensitivity. They claim to have shown that the whole concept of no-feedback climate sensitivity has no place in physics. It is a meaningless concept, for which there can never be any empirical data to support it. The physics they have presented, so far as I can see, is above reproach. What qualifications they have, I have no idea, but the physics they present is excellent.

    As to all climate skeptics being wrong, we will see. Hopefully at some poiut of the discussion on this blog we will get to the subject of the empirical data which supposedly supports the idea that adding CO2 to the atmosphere causes global temperatures to rise at an abnormal rate. We have experienced, according to the IPCC, an abnormal rate of rise in the CO2 in the atmosphere since around 1970. There is absolutely zero empirical data in any temperature/time graph that shows any abnormal change in the rate of rise in temperature. Zero, nada, zilch. As I say, when this subject comes up for discussion, I look forward to crossing swords with you. I am an empiricist, and I only trust empirical data. The meaningless, hypothetical arguments that the IPCC ludicrously puts forward as “proof” of CAGW need to be assigned to the garbage cans of history as soon as possible. And the empirical data is very emphatically on my side.

  • j.ruis

    Elmar:
    How can you be so confident that experts are wrong, not being an expert yourself? The argument for your confidence is based on “the steady decline of arctice sea ice since 1979″. First: this is no argument that experts are wrong: they are familiar with the decline. Second, this decline was not constant at all: the rate of decline is largely consistent with the AMO and less so with CO2. See: http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.arctic.png
    And other factors like soot may also contribute. And you may ask this question to yourself: if the decline decreases in the coming decade, would you reconsider your view that CO2 is the main contributor?

  • DikranMarsupial

    “Pretending that extrapolating an observed trend or that CMIP5 simulations will produce a useful decadal prediction of sea ice is pointless (well there is a potential point but it is to mislead).”

    I’m sorry, but I think the moderators should not allow accusations of deception, such as this, even when made by the expert contributors.

  • Howard

    Great Blog, Thanks! Hopefully the experts can help me out with some simple questions:

    Is there an effect from carbon black pollution that helps to melt the ice?

    To what extent has GHG warming influenced large natural modes (AMO, PDO, etc.) that might enhance melting?

  • Jim Cripwell

    Howard writes “To what extent has GHG warming influenced large natural modes (AMO, PDO, etc.) that might enhance melting?”

    What GHG warming? There always seems to be the assumption that the models are correct, and that adding CO2 to the atmopshere is actually causing warming. There is no empirical data to support this claim; none whatsoever. The rate of rise of global temperatures has not changed since GHGs supposedly started rising alarmingly around 1970. See http://www.vukcevic.talktalk.net/MidSummer-MidWinter.htm and http://bit.ly/V19Im8

    If the rate of rise of global temperatures from the actual measured data shows that there has been no change since around 1970, then it follows, as surely as night follows day, that the total climate sensitivity of CO2 is indistinguishable from zero.

  • Marcel Crok

    Several people have asked why we didn’t ask Peter Wadhams to participate. Well the answer is, we did ask him. He was really enthusiastic about our initiative and agreed to participate. When the deadline came closer, it turned out, unfortunately, that he was too busy, and in the end he was unable to write his guest blog. We heard this only last week. I then asked Maslowski as a logical ‘substitute’ of Wadhams, but he didn’t answer my email.
    We also asked Jamie Morison of UW in Seattle. He couldn’t make it as well and suggested amongst others to contact Ron Lindsay. Lindsay agreed to write his guest blog in a very short period, for which I really thank him.
    This is of course all part of this new initiative. We want the best/most relevant scientists to participate, but in general they are really busy.
    At the moment the review of the SOD of IPCC’s AR5 WG1 report is going on. I have to write review comments myself as well.
    Marcel

  • Jim Cripwell

    Our host writes “This is of course all part of this new initiative. We want the best/most relevant scientists to participate, but in general they are really busy.
    At the moment the review of the SOD of IPCC’s AR5 WG1 report is going on. I have to write review comments myself as well.
    Marcel ”

    What a revealing comment! It seems Marcel was only concerned with contacting people who are concerned with the writing of AR5. Clearly he was not the slightest bit interested in contacting any skeptics who might disagree with the idea that GHGs are causing the Arctic sea ice to melt. I can assure him, there are NO skeptics who are concerned with the AR5. It will turn out to be just as much a load on nonsense as the previous 4 efforts of the IPCC.

    I went to http://www.pbl.nl/en/news/newsitems/2012/pbl-knmi-and-crok-launch-climate-discussion-platform-climatedialogueorg
    and find the following
    @@@

    ClimateDialogue.org is the result of a request by the Dutch parliament to facilitate the scientific discussions between climate experts representing the full range of views on the subject. It is funded by the Dutch Ministry of Infrastructure and the Environment.
    The aim of ClimateDialogue.org is to establish what the discussants agree on, where disagreements remain and what the possible or likely reasons behind these disagreements are. The project by no means aims to solve controversies nor give an objective, scientific final judgment on the topics under discussion.
    and
    PBL Netherlands Environmental Assessment Agency together with the Dutch Royal Meteorological Institute (KNMI) and science journalist Marcel Crok launched their joint website ClimateDialogue.org – an international blog where invited scientists discuss controversial topics in climate science. There are several blogs that facilitate discussions between climate experts, but since the climate debate is highly polarised and politicised, blog discussions between experts with opposing views are rare.
    @@@

    Let me emphasise key parts of this. “It is funded by the Dutch Ministry of Infrastructure and the Environment.” to ” to facilitate the scientific discussions between climate experts representing the full range of views on the subject.” So clearly pulic money is funding Climare Dialogue, to encourage these discussions. Further ” There are several blogs that facilitate discussions between climate experts, but since the climate debate is highly polarised and politicised, blog discussions between experts with opposing views are rare.” It would seem that one of the objects of this expenditure of Dutch public funds is to promote discussions between warmists and skeptics. If this interpretation is wrong, then please correct me as to why Climate Dialogue has been started.

    I suggest that it IMPOSSIBLE to encourage a dialogue between two sides of an argument if our host deliberately excludes, ab initio, ANY input from the skeptic side of the argument. We skeptics are simly too “ignorant” to have any views that are worthy of consideration.

    I have news for you, Marcel. Either you should shape up, and do what the Dutch Parliament intended you do, or this blog is going to turn out to be a pale imitation of RealClimate; just another mouthpiece for The Team to prosletize The Cause. I am deeply disappointed.

  • Dan H.

    Bert,
    Yes, these types of natural climate forcings seem to get lost on many people. Determining accurate natural changes are critical to calculating manmade changes. Without these determinations, the models are uselss.

  • HarryWiggs

    In reply to janama, at 05:44:15, who asserted this: “Furthermore, there is simply no established volcanic CO2 fingerprint by which we may distinguish atmospheric proportions of anthropogenic and volcanogenic contributions. This leaves us with no empirical method by which we may attribute the 20th century rise in CO2 to human energy consumption.”

    That particular meme is utterly debunked, and has been for quite some time. reference the below link, from the USGS. Asa practicing geologist, I find this false meme trotted out quite often, and it is not supported by the current state of peer-reviewed geological findings.

    http://hvo.wr.usgs.gov/volcanowatch/archive/2007/07_02_15.html

    Thanks to the moderators and professional scientists who’ve provided this site, for rational and data-based discussion to take place.

  • HarryWiggs

    Jim Cripwell on 2012-11-16, @13:13:40: Respectfully, your assertions are so wrong, as to not EVEN be wrong. I could point you to long-established (over a 150-year period, in fact) of exactly how CO2 does cause warming, causes it as it rises (ever heard of a really hot place, called “Venus?”) but something tells me you wouldn’t accept ANY rational scientific data as valid, given the wildly-incorrect nature of your statement. Saying it loudly, a lot, and all over the Internet does NOT make your opinion anything more than what it is: an opinion, and one not well-supported by any extant scientific data and research.

  • Mike Haseler

    To say I am disappointed by the site is an understatement.

    The reason climate researchers have got into this mess is because they constantly ask questions of the form “what can possibly cause … “, then without any real knowledge think up possible answers and delude themselves that their “best” answer is “science”. IT ISN’T

    I would liken it to someone going onto the internet with a vague symptom and reading through all the possible illnesses that they may possibly have and deciding that their pain in the head is a brain tumour.

    If however you go to your doctor what will they say? Will they also discuss all the possible things that could cause you to have a pain in the head? Or will they ask whether there are any symptoms that are out of the ordinary and reassure the patient, that quite often you get aches and pains and no one really knows what causes them, but if they feel unsure and need reassurance or if something bad does really start to happen … do come back.

    NEXT PATIENT PLEASE!

    And to be blunt I’m sick to the back teeth of reading idiotic newspaper articles that start “scientists say that global warming could …”. Except for planet earth hypochondriacs, who cares what global warming “could”?

    Let’s start with a simple question: “what do we know global warming is doing”? Perhaps when I see an honest answer to that question, I might just pay a bit more attention to those who ask “what could…”

  • Mike Haseler

    “Scientists discuss” … No they don’t.

    Arts studects discuss, theological students, philosophers, etc. discuss. Real scientists create testable hypothesis and then test them against actual data. That is what makes them scientists.

  • Kip Hansen

    I would like to see a “reply” option on Public Comments, so that Public Commenters can reply to specific public comments.

    I would also like to see a reliable method of addressing a comment to one of the Dialogue Participants — at least to the point where the moderator will CC: a Dialogue Participant if a Public Comment is directed to them.

    Thank you,

  • Kip Hansen

    PS: I like the Off Topic Comments section!

  • Dr Inferno

    I notice all the proclaimed experts in the discussion unquestionably accept the existence of so-called “carbon” gases in our atmosphere. Surely for a legitimate dialogue you need experts who are willing to question the very foundations of PCAGW.

    How for example does carbon dioxide manage to float within the air itself being that it is heavier than air? Anyone who has held a diamond or a piece of graphite can attest that carbon is a solid, not a gas. As a gas it would simply fall to the ground as and so become solid. We see on Mars that the polar caps are made of carbon dioxide in it’s true solid state.

  • Eric H.

    So far so good, Climate Dialogue. My take home on this was the honesty of the three scientists in saying that they don’t know exactly what is causing the melt. Of course I learned more from their explanations of “I don’t know” then I knew before, so this was a good read. My thanks to Judith, Ron, and Walt.
    Probably letting my biases take over, I can see no reason at this point in the evolution of climate science where we need government to tax or try to control carbon except where inherently practical. This includes government subsidy of “renewable” or “sustainable” (whatever that means) energy production.
    To keep this blog from turning into a mud sling it would be nice to see the usual derogatory name calling kept to a minimum. If you wouldn’t have the courage to say it to my face (a 220lb body builder) then you shouldn’t say it in here. My .02.

  • Jim Cripwell

    HarryWiggs, you say “Saying it loudly, a lot, and all over the Internet does NOT make your opinion anything more than what it is.”

    I base my opinion on empirical data; or in the case of CAGW the almost complete lack of any empirical data to support the conclusion that CAGW exists. I am quite prepared to accept that my opinion could be wrong. I have been wrong in the past, and will, undoubtedly, be wrong in the future. But my opinion is irrelevant. The only thing that matters is the empirical data I present; or the lack of empirical data that I point to. If you want to criticise what I write, which I welcome, may I request that you concentrate on the empirical data, not the opinion I express.

  • David Wojick

    Most of the supposedly off topic comments are very much on topic and there should be a separate URL link to them as putting them after the approved comments makes them inaccessible. Some of these censored comments make the point that none of the three panelists is a skeptic. Others question the framing of the topic as biased. Many present well known skeptical scientific arguments that the panelists do not mention. As it is CD is simply not properly representing skepticism as the mandate requires. If this pattern continues CD will be a failure, merely presenting the internal range of AGW opinion. Skepticism is different.

  • Rob Dekker

    Jim Cripwell,
    You continue to reference your “catastrophic” AGW (CAGW) term, but fail to notice that the word “Catastrophic” is inherently an opinion, and thus does not have any place in any scientific discussion about Anthropogenic Global Warming (AGW).
    In fact, there is not a single scientific paper that defines the term CAGW, and it would be nice if you would identify who first used that term, and in which apparently non-scientific context.

  • ClimateDialogue: Exploring different views on climate change

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  • What I’m Reading, Sunday, November 18, 2012 | Rationally Thinking Out Loud

    [...] One has to wonder just how ignorant, no let call it stupid, global warming denialists can get. Eli cites a great example of this thermonuclear level stupidity: Rabett Run: Climate Dialogue Hits the Big Time: Dr Inferno of Denial Depot has commented there on the proper mix of experts Dr Inferno 2012-11-17 00:55:42 [...]

  • Future of Arctic enterprise | Climate Etc.

    [...] a complement to the discussion on Arctic sea ice decline at Climate Dialogue, lets take a look at the outlook for the development of existing and new economic activity in the [...]

  • Jim Cripwell

    Rob Dekker, you write “and it would be nice if you would identify who first used that term, and in which apparently non-scientific context.”

    I have no idea who first used the term. I have defined what I, and most other skeptics, mean by it, on many occasions. I know all about the science of GHGs, and there is no doubt in my mind, that when you add CO2 to the atmopshere, it will cause global temperatures to rise. So AGW is real, and I accept that AGW is real. However, the issue is how much do temperatures rise as a result of adding CO2 to the atmosphere. If the rise is negligible, and cannot be measured with the inherent noise in the system, as the empirical data strongly implies, then adding CO2 to the atmosphere is a good thing to do, not a bad thing. It is only if the addition of CO2 to the atmosphere has really detrimental effects that we need to bother. So, in discussing this on many blogs, as I have, I use the term CAGW (C being catastrophic), which means we need to restrict the production of CO2, rather than AGW, which is real, but almost certainly of no practical concern.

  • HarryWiggs

    To try to keep this to the topic as originally posted, please show the peer-reviewed “empirical data” you continue to reference, that robustly supports that the loss of the arctic’s ice in 2012 is *not* at all a result of anthropogenic forcings. Also, and to repeat Rob Dekker’s point, your continuing to use the improper term, “CAGW,” tends to lend credence to the idea that no matter how much scientific, refereed data any of us can show you, you might just reject it. to complete this post, let me again say that “CAGW” is *strictly* a construct of those who reject, out of hand, any data that supports the *proper” term, AGW.

    I await your reference list, as asked for.

  • Jim Cripwell

    Harry Wiggs, It is my understanding that Marcel intends to introduce a thread on Climate Sensitivity. I suggest that it would make sense to wait until this thread is introduced, and then we can discuss the details you want, on topic, instead of off topic. Please note that the empirical data on global temperatures that is reported on a daily, weekly, monthly and yearly basis is NEVER peer reviewed or refereed.

  • David Wojick

    Regarding the term CAGW I have used it for many years so may or may not have introduced it. The distinction between AGW and CAGW is that between the past and the future impacts, so it is scientific. AGW means human activity has caused at least a major fraction of global warming (and related changes). CAGW means continued human activity will cause dangerous levels of change, many of which have been conjecturally described in the literature. There is in fact an extensive scientific literature on the possible negative impacts to come. As Jim Cripwell points out it is CAGW that matters but CAGW is based on AGW. If AGW is false then CAGW falls, hence AGW is of great interest. But we are all here because of the CAGW speculation. I hope this helps resolve the confusion.

  • Paul Vincelli

    I think this is an excellent initiative. However, it is only an important and novel contribution insofar as genuine experts are invited. My impression of Dr. Curry is that she is a premiere example of an expert who voices some skeptical arguments concerning aspects of anthropogenic global warming Her arguments are thoughtful, evidence-based, and grounded in peer-reviewed, published science. I will quickly lose interest in this site if “experts” are invited who do not have a sustained and relatively recent record of publishing peer-reviewed papers in geophysics and climate science. The mere possession of a Ph.D.–and even the title of “Professor”–does not constitute scientific expertise.

    Please maintain well-accepted professional standards of scientific expertise in selecting experts to invite.

  • Jim Cripwell

    Charles

    Having thought about this, I think I was premature to introduce this data at this time. It will be far more relevant when we discuss climate sensitivity. For the record I include the CET graph, not because it is global, which it isn’t, but because it is the longest continuous record of directly measured temperatures, going back the the mid-17th century. So, it reinforces the global data. The second graph starts around 1850, and is the longest record of directly measured global temperatures which is available.

  • Jim Cripwell

    Paul Vincelli you write “However, it is only an important and novel contribution insofar as genuine experts.”

    Richard Feynman famously remarked “Science is the belief in the ignorance of experts”. On a personal basis, I only trust empirical data. If there is a paper written by anyone, which is backed up by a wealth of empirical data, I really dont care if the author is an expert or not. If the data is good, and the science presented is equally good, then I find the paper to be good science. If the paper is written by the best experts in the field, and the results are based on the output of non-validated models, as is so often the case with CAGW, then, IMHO, the paper is not worth the powder to blow it to hell. I have far more faith in the recordings of daily temperature readings from the AMSU satellite, than I have in the IPCC reports, such as the TAR and AR4. But then, that’s what makes the ball game.

  • Roger Knights

    When will we be allowed to employ avatars? They’re helpful.
    [CD: they are now implemented]

  • Eli Rabett

    Just a minor suggestion. Would it be possible for the editors to insert links at comments by the hoi polli to answers by the experts when given and visa versa?

  • Everette L. Wampler

    In my last post, I expressed Modern Man’s ability to solve problems.
    Perhaps I should elucidate what I meant by Modern Man’s unusual talents.
    And, that is the ability to think in terms of:
    “ Abstruse Abstract Thought. “

    My dictionary describes abstruse as meaning: “ Remote from ordinary minds, difficult to be comprehended or understand, profound, recondite. . Hidden from mental perception by ordinary mentality. “ And I add: “ Combining broad and detailed analysis of abstract objects to elicit new concepts without reference to existing concepts. The concept of ideas for bringing order from nothingness. “ Conceiving something new not having a pedigree.

    My dictionary describes abstract as meaning: “ Considered or thought of in itself; treated apart from any particular object. ” And, I add: “ A mental process using symbolic objects to arrive at meaningful conclusions. The mental processes where complex ideas are represented by symbolic objects manipulated within the mind to give real world meaning to a process or relationship. “

    I am sure you have other thoughts on this concept.

    Thank you,

    Everette L. Wampler

  • Jim Cripwell

    Rob Dekker, you write “Jim Cripwell,
    As I asked before, who are these “warmists” that you are talking about, and where is your definition of your theory of “CAGW” that you keep on mentioning ?
    Could you please give at least ONE link to a scientific paper that sustains your opinions ?”

    “Warmists” includes anyone who believes CAGW is real proven science, and not an unproven hypothesis. I, and David Woijk, have explained what CAGW is already. You just dont bother to read what is written. We agree AGW is real. The question is, how much do global temperatures rise as the concentration of CO2 in the atmopshere increases? If, as the empirical data from the 20th and 21st centuries strongly indicates, the effect of adding CO2 is negligible, and the climate sensitivity of CO2 is indistinguishable from zero, then AGW is real but not a problem. But the warmists keep insisting that global temperatures are going to rise catastrophically before the end of this century. So we have to distinguish between AGW, whose effect is negligiible and some hypothetical case where adding CO2 to the atmnosphere supposedly causes an unmitigated increase in global temperatures. I call this hypothesis CAGW. If you dont like the term, please invent one you do like, tell me what it is, and I will, in futute in discussions with you, use your term..

    As to scientific publications, I refer almost exclusively to emiprical data. As Eli Rabbit has so clearly demonstrated, if the method of obtaining the data has been peer reviewed, then the data itself does not need peer review, and is not published in any scientific paper. The data is what it is, and must be accepted as a scientific fact. There are hundreds, even tens of thousands, of sites on the internet which report empirical data of all sorts. I could not even attempt to list them all. I am familiar with some of these, and view them on a routine basis. It appears you are not au fait with this wealth of information. I suggest you go to Anthony Watts WUWT, and scroll down to the places where he references a number of these sites which are relevant to a discussion of CAGW. These are the sorts of sites I use for my data. But there are many that Anthony does not list. So, I am sorry if you are not familiar with all this data. If you want to ask me where I get any specific information, I would be delighted to give you the URL. But I am not going to list the URLs every time I refer to them on Climate Dialogue.

  • HarryWiggs

    Jim Cripwell, allow me to be blunt: Until such time as you drop the clearly-partisan terms “warmist” (though I’m happy to wear the tag, inasmuch as it is WARMING) and the utterly inaccurate and non-scientific term “CAGW,” which is NEVER used outside the disinformation camps. nothing you say can be taken as anything but a diatribe borne not of scientific rigor, but of partisan and frankly, unsubstantiated claptrap. It does not become the style of an honest broker, not of a true skeptic.

  • Jim Cripwell

    Harry Wiggs, Fair enough. As I have explained before I am perfectly willing to use any terms that anyone finds acceptable. If you will let me know what you would use as a substitute for “warmist”, and “CAGW”, I would be delighted to use them. With respect to “CAGW”, “AGW” does not describe what I am talking about. AGW exists, but it’s effect, from what little empirical data we have, is negligible. I agree that AGW is real, but I do not accept that what I call “CAGW” is real.

  • Jim Cripwell

    Climate Dialogue is Dead On Arrival.

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  • Joe Prins

    As Neven knows, I am not a climate scientist but instead am self emplyed business person. However, I am a bit of a history buff. So a couple of comments.
    1) As previously pointed out, dealing with the arctic only to explain anything is a bit of a fools game. The arctic and antarctic operate on the same “forcings” albeit some are opposites.
    2) Beside a lot of ice on both poles, what do these areas have in common: North and South Magnetic poles.
    3) Since 2001 what has happened to the Magnetic North Pole (NMP)? The yearly movement towards Siberia has accelerated, the SMP has moved some, but not much.see: http://www.bing.com/images/search?q=Magnetic+Pole+Location+2011&FORM=RESTAB#view=detail&id=1149347CEA9A07CD49F54832AB5074C45CE57FF6&selectedIndex=51
    4) As a matter of interest, the NMP is now not too far from where it was when the LIA started.
    5) It only seems logical that the location of the Polar front would be influenced by the NMP movement.
    Therefore, any discussion that does not include the North and South Magnetic pole movement would be, IMHO, to be somewhat lacking in completeness.

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