1. A planetary catastrophe to be averted
We are starting our first post on this blog by presenting what we consider the overwhelming scientific evidence of a planetary emergency arising from a combination of: (i) the warming of the Arctic, (ii) the rapid melting away of Arctic sea ice, (iii) the releasing into the atmosphere of ever larger quantities of the potent greenhouse gas, methane, from thawing structures, and (iv) positive feedback between these three processes.
|Figure 1. The huge temperature rise in the Arctic (latitudes 60 North to North Pole), compared to temperatures at lower latitudes (surface air temperatures as nine-year running means relative to the 1880–1890 mean).|
|Figure 2. Yearly Minimum Arctic Icve Volume Data from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), at the Polar Science Center, with trend (in red) added by Wipneus.|
|Figure 3. The striking rise of methane in the Arctic (click on image to enlarge)|
|Figure 4. Global emissions cause warming, especially in the Arctic, where warming is further accelerated by feedbacks, in particular sea ice loss and methane releases, threatening to lead to runaway global warming.|
We argue that the response to this emergency should be concerted international action, taking measures to cool the Arctic which would include geoengineering of a kind known as “solar radiation management” (SRM) . These measures should be taken as quickly as conceivably possible in order to reduce the risk of passing a point of no return – a point beyond which the whole climate system would tip, inevitably, irreversibly and inexorably, into such a hot state as to threaten the survival of civilisation.
This is the situation in a nutshell:
- the Arctic is warming rapidly – much faster than global warming;
- the sea ice volume is plummeting;
- a collapse in sea ice extent is likely by 2015;
- a collapse in sea ice means loss of habitat and biodiversity, risking the breakdown of an important marine food chain;
- a collapse in sea ice also means faster warming of the Arctic, creating more climate disruption and weather extremes in the Northern Hemisphere.
- methane’s potency as a greenhouse gas is about 105x that of CO2 over 20 years, weight for weight ;
- there’s a vast quantity of methane frozen into Arctic seabed ;
- loss of sea ice cover allows storms to mix the warmed surface water with colder water beneath, causing shallow seabed to warm, thawing out methane-holding structures;
- because of warming and instabilities in the seabed, large quantities of methane could be released quite rapidly – enough to drastically exacerbate global warming ;
- methane bubbles have now been observed in huge plumes, over 1km across, in shallow sea , suggesting an escalation of methane emissions could be happening already, even without further warming of the Arctic;
- Arctic methane may be contributing to rising global levels of methane in the atmosphere .
The only way to prevent a chain of events which could lead to such a runaway cycle is to cool the Arctic, save the sea ice and dampen methane emissions. To minimise risk, we need to use all possible means.
AMEG chair, John Nissen, writes:
This PIOMAS graph (see Figure 2 above) is the most terrifying graph that I have ever seen. It is what keeps me awake at night. It heralds the nightmare scenario. I really prefer not to think about it. But I do think about it – and console myself that there is a solution. Surely people will see there must be a solution. There must be something we can DO. Homo sapiens cannot be so stupid. Why are people so against geoengineering?References:
From PIOMAS it is quite obvious that the sea ice volume trend line is plunging towards the zero line, and will cross it within a few years. If the volume falls like that, the sea ice extent is bound to crash, long before the volume reaches zero, unless they go together. It’s not just the September volume that is plunging, but all the summer and autumn months. Within a few years we will lose most of the reflective capacity of the sea ice. People should realise that the sea ice is an essential part of a mechanism which has kept this planet as a ‘goldilocks planet’, hospitable to humans for the best part of 2.5 million years – not to hot and not too cold. Without the sea ice, the Arctic will continue to warm, the Greenland ice sheet will melt away, and so will the permafrost that covers a quarter of land in the Northern Hemisphere and extends under the sea of the Arctic Ocean. This melting away of the Arctic ice cap will be accelerated by the release of methane. The Arctic warming to date is already implicated in unusual weather described as “global weirding”. I expect to see the effects increased weather disruption producing more weather-related disasters, widespread crop failures and a severe food shortage in my lifetime, and I am seventy.
Why can’t so many of my scientist friends see the danger? I see them turn away when I mention the Arctic sea ice and the methane. And they don’t want to talk about solutions. Scientists never seem to talk about solutions. Scientists observe. Scientists do not want to be involved in policy. That is up to politicians. Present them the facts, and the politicians can decide.
The collapse of the sea ice is like the beginning of the end, as Churchill would say during the war to cheer us up. But it could be the beginning of a fight back, where mankind takes control of the situation, and uses collective wisdom to find ways and means to cool the Arctic quickly to save the Arctic sea ice and prevent a fatal escalation of methane emissions.
Losing the sea ice, for even just one day in the year, puts us into the unknown as far as the climate system is concerned. It also means the end of the polar bears that rely on sea ice for survival. In summer they will be swimming on and on, in a vain attempt to reach the sea ice. It is a very sad thought. But there is a solution. There must be a solution for saving the sea ice.
Going back to the PIOMAS graph, we need the sea ice volume to increase again. What we have to do is to turn that trend line round – to make a U-turn. It is foolish to imagine that this will happen of its own accord. It would be like waiting for magic – a magical beast to produce a U-turn – a Unicorn! But producing a U-turn by geoengineering is a tall order. It is a tremendous challenge. It is going to take a war effort, but I am sure it can be done if we are determined and do not delay any longer.
 Wikipedia on SRM (Solar Radiation Management)
 D.T. Shindell et al., "Improved Attribution of Climate Forcing to Emissions". Science vol 326: pp. 716-718 (30 October 2009)
 "Accumulated methane potential of the ESAS: 1) C-org in permafrost ~500 Gt; 2) Methane accumulation in hydrate deposits (GHSZ=100m) ~1000 Gt; 3) Free gas beneath the GHSZ ~700 Gt”, by Dr. Natalia Shakhova et al. in: Presentation at Symposium, November 30, 2010
 “We consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time.” Dr. Nalaia Shakhova, Geophysical Research Abstracts, Vol. 10, EGU2008-A-01526, 2008. SRef-ID: 1607-7962/gra/EGU2008-A-01526. EGU General Assembly 2008
 Vast methane 'plumes' seen in Arctic ocean as sea ice retreats,
by Steve Conner in The Independent, December 13, 2011
 Global Distribution of Atmospheric Methane, National Oceanic and Atmospheric Administration
Most geoscientists like to separate policy from science - so they will state what is happening to the Earth System but not suggest the kind of interventions that could prevent the situation from gradually deteriorating. Especially the subject of the deliberate intervention known as geoengineering has been taboo until very recently, and it is still treated with great suspicion. However this ‘gradualist’ situation, where the timescale is over decades, has totally changed with the discovery of both the extraordinarily rapid decline of sea ice and the possibility of sudden discharge of gigatons of the potent greenhouse gas, methane, from the Arctic Ocean.
AMEG was formed from a group of scientists, engineers and communicators, to alert the world to the dangers that have to be faced, and the need for extremely rapid action this year to reduce the risk of passing a point of no return with the sea ice – a point after which the Arctic Ocean would become free of sea ice for more of the year without any possibility of restorative intervention. Following such a decline of sea ice, the Arctic would continue warming but at a much greater rate than hitherto, causing or exacerbating an escalation of methane emissions from both marine and terrestrial sources and risking runaway global warming.
Passing such a point of no return would be catastrophic for the whole of humanity, as, inexorably, global temperatures would spiral upwards and food production downwards.
Therefore we consider our present situation is extremely dangerous and warrants the designation of "planetary emergency."
We see only one way to avoid passing this point of no return, which is to intervene by cooling the Arctic using geoengineering techniques. (Note that even this may not be enough to dampen methane emissions, so further measures may be needed to deal with an escalation of the methane emissions.)
The discovery of rapid decline of sea ice has taken the scientific community by surprise. Hitherto attention has been focussed on sea ice extent, but recent evidence and modelling of sea ice volume (see PIOMAS sea ice volume, figure 2 above) shows a collapse in extent is likely to by 2015, with even a possibility this summer. (By ‘collapse’ we mean a decline to bring the minimum extent to less than half the 2011 minimum.) Following a collapse in extent, the climate forcing from the “albedo effect” could more than double. And if the Arctic Ocean were to become ice free for six months or more, the climate forcing could double again. The possibility of sea ice collapse any summer soon is why we urge your help for the planning, development and deployment of a combination of geoengineering techniques as soon as conceivably possible. so as to avoid the risk of needing more drastic measures later on which might fail.
While the sea ice has been retreating, there have been growing signs of critical instability of undersea methane in the Arctic Ocean, especially in the East Siberian Arctic Shelf area where vast plumes of methane have been seen bubbling to the surface. Research in this area has been limited, but it appears that emissions have risen dramatically over the past few years, and it is thought that this could be as a result of the water above the seabed reaching a temperature threshold. The exact mechanism for this accelerated methane release is not understood (and not allowed in some models), however we have to act according to best evidence in a precautionary manner, and take a continued escalation of methane emissions as a matter for extreme concern.
Such an escalation of methane emissions may lead to very rapid global warming in the short term. Even if it does not we believe in the short term it will put the climate system out of any control for climate change mitigation with catastrophic consequences sooner or later.
We bring your attention to the facts: that there is no likelihood of even a reduction in global emissions of CO2 in the foreseeable future; that both emissions and concentration of CO2 are increasing at record rates; and that the atmospheric methane level has been rising since 2007 after a decade of little change.
Note that AMEG considers that the cooling of the Arctic should be seen one of many efforts to bring the atmosphere and oceans back towards their pre-industrial state, especially since such efforts reduce both immediate and longer-term risks arising from Arctic warming, sea ice retreat and methane release. AMEG is fully supportive of these efforts.
But above all, geoengineering must be accepted as an indispensable part of an emergency plan of action to cool the Arctic, save the sea ice and prevent methane feedback, before it is too late. We have weeks and months rather than years and decades. Measures to cool the Arctic cannot be brought in quickly enough.
Even a small chance of total ice loss this year is nonetheless a small chance we are already too late. This genie won't go back in the bottle. Without emergency action, we are certainly committing all humanity to planetary catastrophe - possibly to be experienced within our own lifetimes.
AMEG formally presented evidence for this situation, and argument for action, to the UK Environment Audit Committee of MPs, for their inquiry on protecting the Arctic . Our submission received a formal response from the Met Office (Hadley Centre) flatly rejecting both our evidence of a planetary emergency and our argument for emergency action to cool the Arctic. Peter Wadhams, a founder member of AMEG, has formally rebutted this rejection . We include this rebuttal in our blog, see below, so that it is open to comment from the scientific community.
The Hadley Centre, set up by Margaret Thatcher to advise the government on climate change issues, is considered in high regard by the majority of the climate science community, and much research is based on models produced by the centre. Their predictions of climate change are used as a basis for government policy.
If the Hadley Centre predictions are extremely optimistic about the future climate on this planet, it should be of great concern to everybody on this planet.
While it is accepted that anthropogenic CO2 emissions have led to climate change, much of the international response has centred on reductions in those emissions over a period of decades to limit global warming. By contrast, AMEG is demanding immediate action to cool the Arctic because there is strong evidence that the tipping point on sea ice has already been reached. It is too late for CO2 emissions reductions to have any appreciable effect on reducing temperatures there.
The Hadley Centre is in denial of the seriousness of the situation and the need for emergency action.
References and additional material
This was written by Professor Peter Wadhams in response to information provided recently by Professor Julia Slingo OBE, Chief Scientist, Meteorological Office, firstly in the report 'Possibility and Impact of Rapid Climate Change in the Arctic' to the Environmental Audit Committee and subsequently in answering questions from the Committee on Wednesday 14 March 2012. In the responses, the Meteorological Office refers to an earlier presentation to the Committee by Peter Wadhams, made on 21 February 2012.
The following comments are based on the uncorrected transcript of Professor Slingo’s presentation to the EAC, 14 March 2012 session, as at:
Speed of ice loss
In response to questions from the Chair, Prof. Slingo ruled out an ice-free summer by as early as 2015. Furthermore, Prof. Slingo rejected data which shows a decline in Arctic sea ice volume of 75% and also rejected the possibility that further decreases may cause an immediate collapse of ice cover.
The data that Prof. Slingo rejected are part of PIOMAS, which is held in high regard, not only by me, but also by many experts in the field. From my position of somebody who has studied the Arctic for many years and has been actively participating in submarine measurements of the Arctic ice thickness since 1976, it seems extraordinary to me that for Prof. Slingo can effectively rule out these PIOMAS data in her consideration of the evidence for decreasing ice volume, when one considers the vast effort and diligence that has been invested over such an extended period in collecting data under the ice by both British and US scientists. Prof. Slingo offers no reason whatsoever for dismissing this extremely pertinent set of measurements and their associated interpretation, arguing that "the observational estimates are still very uncertain". This is not the case. I expand on this in an Appendix to my letter.
It has to be said that it is very poor scientific practice to reject in such a cavalier fashion any source of data that has been gathered according to accepted high scientific standards and published in numerous papers in high-profile journals such as Nature and Journal of Geophysical Research, the more so when the sole reason for this rejection appears to be perceived uncertainty. If other data are in conflict with one’s own data, then caution should be given to the validity of one’s own data, while this should immediately set in train further research and measurement in efforts to resolve possible conflicts. In this case, however, the crucial point is that there is currently no rival set of data to compare with the scale and comprehensiveness of the PIOMAS data; Prof. Slingo sets against the clear observational database only the Met. Office’s models. These models (and in fact all the models used by IPCC) have already shown themselves to be inadequate in that they failed to predict the rapid decline in sea ice area which has occurred in recent years. It is absurd in such a case to prefer the predictions of failed models to an obvious near-term extrapolation based on observed and measured trends.
Regarding the possibility of an imminent collapse of sea ice, Prof. Slingo ignores a point raised earlier by herself, i.e. that, apart from melting, strong winds can also influence sea ice extent, as happened in 2007 when much ice was driven across the Arctic Ocean by southerly winds (not northerly, as she stated). The fact that this occurred can only lead us to conclude that this could happen again. Natural variability offers no reason to rule out such a collapse, since natural variability works both ways, it could bring about such a collapse either earlier or later than models indicate.
In fact, the thinner the sea ice gets, the more likely an early collapse is to occur. It is accepted science that global warming will increase the intensity of extreme weather events, so more heavy winds and more intense storms can be expected to increasingly break up the remaining ice, both mechanically and by enhancing ocean heat transfer to the under-ice surface.
The concluding observation I have to make on this first point is that Prof. Slingo has not provided any justification for ignoring the measurements that we have of ice volume changes and the clear trend towards imminent ice-free summers that they indicate.
Methane – potential emissions and escalation
My second point of contention is Prof. Slingo’s position on the possibility of imminent large releases of methane in the Arctic, which is consistent with her sanguine attitude to the rate of loss of ice cover. She states "Our estimates of those (large releases of methane) are that we are not looking at catastrophic releases of methane." Prof Slingo suggests that there was "a lack of clarity in thinking about how that heating at the upper level of the ocean can get down, and how rapidly it can get down into the deeper layers of the ocean". This appears to show a lack of understanding of the well-known process of ocean mixing. As Prof. Slingo earlier brought up herself, strong winds can cause mixing of the vertical water column, bringing heat down to the seabed, especially so in the shallow waters of the East Siberian Arctic Shelf. A recent paper shows that "data obtained in the ESAS during the drilling expedition of 2011 showed no frozen sediments at all within the 53 m long drilling core" (Dr. Natalia Shakhova et al. in: EGU General Assembly 2012; http://meetingorganizer.copernicus.org/EGU2012/EGU2012-3877-1.pdf).
The East Siberian Arctic Shelf (ESAS), where the intensive seabed methane emissions have been recorded, is only about 50 m deep. Throughout the world ocean, the Mixed Layer (the near-surface layer where wind-induced mixing of water occurs) is typically 100-200 m deep. It is shallower only in areas where the water is extremely calm. This used to be the case for the Arctic Ocean because of its ice cover, but it is no longer the case, because of the large-scale summer sea ice retreat which has created a wide-open Beaufort Sea where storms can create waves as high as in any other ocean, which exert their full mixing effect on the waters. It is certain that a 50 m deep open shelf sea is mixed to the bottom, so I am at a loss to understand Prof. Slingo’s remarks, unless she is thinking of the deep ocean or deeper shelves elsewhere than the East Siberian Sea.
Furthermore, Prof. Slingo states that "where there is methane coming out of the continental shelf there it is not reaching the surface either, because again the methane is oxidised during its passage through the sea water and none of those plumes made it to the surface. So there is a general consensus that only a small fraction of methane, when it is released through this gradual process of warming of the continental shelf, actually reaches the surface." This statement is also incomprehensible as far as the East Siberian Arctic Shelf is concerned. With such a shallow water depth the methane plume reaches the surface within a few seconds of release, giving little opportunity for oxidation on the way up. She may be confusing this situation with that of the much deeper waters off Svalbard where methane plumes are indeed observed to peter out before reaching the surface, due to oxidation within the water column.
To illustrate the reality of this warming of ESAS shelf water, I reproduce (fig. 1) a satellite sea surface temperature data (SST) map from September 2011, provided by Dr James Overland of Pacific Marine Environmental Laboratory (PMEL), Seattle. This shows that in summer 2011 the surface water temperature in the open part of the Beaufort and Chukchi seas reached a massive 6-7°C over most of the region and up to 9°C along the Arctic coast of Alaska. This is warmer than the temperature of the North Sea at Scarborough yesterday. This extraordinary warming is due to absorption of solar radiation by the open water. These are not the temperatures of a very thin skin as suggested by Prof. Slingo. The NOAA data apply to the uppermost 7 m of the ocean, while PMEL has backup data from Wave Gliders (automatic vehicles that run oceanographic surveys at pre-programmed depths) to show that this warming extends to at least 20 m. We can conclude from fig.1 that an extraordinary seabed warming is taking place, certainly sufficient to cause rapid melt of offshore permafrost, and this must cause serious concern with respect to the danger of a large methane outbreak.
The choice of pursuing geo-engineering or not
Finally, I would like to address Prof. Slingo’s closing remarks on geo-engineering.
Both Professor Slingo and Professor Lenton repeat a point made by many critics of geo-engineering that once you start geoengineering you have to continue. On this point, I like to draw attention to evidence earlier provided to the Environmental Audit Committee by Professor Stephen Salter, as can be found at
Prof. Salter responds: "I must disagree. You have to continue only until emissions have fallen sufficiently or CO2 removal methods have proved effective or there is a collective world view that abrupt global warming is a good thing after all. No action by the geo-engineering community is impeding these. Indeed everyone working in the field hopes that geoengineering will never be needed but fears that it might be needed with the greatest urgency. This is like the view of people who hope and pray that houses will not catch fire and cars will not crash but still want emergency services to be well trained and well equipped with ambulances and fires engines." Basically he is talking about the precautionary principle.
I fully agree with Prof. Salter on this point, and I also fully share with Prof. Salter the anxieties of the Arctic Methane Emergency Group. A highly proactive geo-engineering research programme aimed at mitigating global warming is more rational than expecting the worst but not taking any action to avert it.
Professor of Ocean Physics,
Department of Applied Mathematics and Theoretical Physics (DAMTP),
University of Cambridge
Member of Arctic Methane Emergency Group; Review Editor for Intergovernmental Panel on Climate Change 5th Assessment (chapter 1)
Appendix: The scientific database for sea ice loss
On a previous occasion (21 February) I testified to the Committee and showed them the results of submarine measurements of ice thickness combined with satellite observations of ice retreat. When these two datasets are combined, they demonstrate beyond doubt that the volume of sea ice in the Arctic has seriously diminished over the past 40 years, by about 75% in the case of the late summer volume. If this decline is extrapolated, then without the need for models (which have demonstrably failed to predict the rapid retreat of sea ice in the last few years) it can be easily seen that the summer sea ice will disappear by about 2016 (plus or minus about 3 years). It might be useful to summarise the history of research in this subject.
In her testimony Prof Slingo placed her faith in model predictions and in future data to come from satellites on thickness (presumably Cryosat-2, which has not yet produced any usable data on ice thickness). Yet since the 1950s US and British submarines have been regularly sailing to the Arctic (I have been doing it since 1976) and accurately measuring ice thickness in transects across that ocean. Her statement that "we do not know the ice thickness in the Arctic" is false. In 1990 I published the first evidence of ice thinning in the Arctic in Nature (Wadhams, 1990). At that stage it was a 15% thinning over the Eurasian Basin. Incorporating later data my group was able to demonstrate a 43% thinning by the late 1990s (Wadhams and Davis, 2000, 2001), and this was in exact agreement with observations made by Dr Drew Rothrock of the University of Washington, who has had the main responsibility for analyzing data from US submarines (Rothrock et al., 1999, 2003; Kwok and Rothrock, 2009) and who examined all the other sectors of the Arctic Ocean. In fact in his 2003 paper Rothrock showed that in every sector of the Arctic Ocean a substantial thickness loss had occurred in the preceding 20 years. Further thinning has since been demonstrated, e.g. see my latest paper on this (Wadhams et al., 2011). Among the foremost US researchers at present active on sea ice volume decline are Dr Ron Kwok of the NASA Jet Propulsion Laboratory and Dr Axel Schweiger of University of Washington (leader of the PIOMAS project), and these have both been moved to write to Prof Slingo expressing their surprise at her remarks deriding the scientific database.
Even if we only consider a 43% loss of mean thickness (which was documented as occurring up to 1999), the accompanying loss of area (30-40%) gives a volume loss of some 75%. Summer melt measurements made in 2007 in the Beaufort Sea by Perovich et al. (2008) showed 2 m of bottom melt. If these enhanced melt rates are applied to ice which is mainly first-year and which has itself suffered thinning through global warming, then it is clear that very soon we will be facing a collapse of the ice cover through summer melt being greater than winter growth. These observations do not just come from me but also from the PIOMAS project at the University of Washington (a programme to map volume change of sea ice led by Dr Rothrock himself and Dr Schweiger), the satellite-based work of Ron Kwok, and the high-resolution modelling work of Dr Wieslaw Maslowski at the Naval Postgraduate School, Monterey (e.g. Maslowski et al 2011).
Kwok, R., and D. A. Rothrock ( 2009 ), Decline in Arctic sea ice thickness from submarine and ICESat records: 1958- 2008, Geophys. Res. Lett ., 36, L15501.
Maslowsky, W., J. Haynes, R. Osinski, W Shaw (2011). The importance of oceanic forcing on Arctic sea ice melting. European Geophysical Union congress paper XY556. See also Proceedings, State of the Arctic 2010, NSIDC.
Perovich, D.K., J.A. Richter-Menge, K.F. Jones, and B. Light (2008). Sunlight, water, ice: Extreme Arctic sea ice melt during the summer of 2007. Geophysical Research Letters 35: L11501. doi: 10.1029/2008GL034007.
Rothrock, D.A., Y. Yu, and G.A. Maykut. (1999). Thinning of the Arctic sea-ice cover. Geophysical Research Letters 26: 3469–3472.
Rothrock, D.A., J. Zhang, and Y. Yu. (2003). The arctic ice thickness anomaly of the 1990s: A consistent view from observations and models. Journal of Geophysical Research 108: 3083. doi: 10.1029/2001JC001208.
Shakhova, N. and I. Semiletov (2012). Methane release from the East-Siberian Arctic Shelf and its connection with permafrost and hydrate destabilization: First results and potential future development. Geophys. Res., Vol. 14, EGU2012-3877-1.
Wadhams, P. (1990). Evidence for thinning of the Arctic ice cover north of Greenland. Nature 345: 795–797.
Wadhams, P., and N.R. Davis. (2000). Further evidence of ice thinning in the Arctic Ocean. Geophysical Research Letters 27: 3973–3975.
Wadhams, P., and N.R. Davis (2001). Arctic sea-ice morphological characteristics in summer 1996. Annals of Glaciology 33: 165–170.
Wadhams, P., N Hughes and J Rodrigues (2011). Arctic sea ice thickness characteristics in winter 2004 and 2007 from submarine sonar transects. J. Geophys. Res., 116, C00E02.
5. The threat from Arctic methane
IMMINENT COLLAPSE OF ARCTIC SEA ICE DRIVES DANGER OF ACCELERATED METHANE THAW
This is rebuttal by Peter Wadhams to the Archer article on RealClimate entitled “Much ado about methane” .
In a January 4th post on "Real Climate", David Archer addressed those who are raising concerns about the speed of ice loss in the Arctic and the resultant potential for warming water temperatures to thaw frozen methane and release it as gas to the atmosphere. In essence, he dismissed such concern as a form of unfounded alarmism making "much ado about nothing". In this rebuttal, I would like to respectfully challenge this dismissive stance and assert that severe dangers are arising in the Arctic which call for the full attention of humanity.
The present thinning and retreat of Arctic sea ice is one of the most serious geophysical consequences of global warming and is causing a major change to the face of our planet. A challenging characteristic of the behaviour is that both the rate of retreat (especially in summer) and the rate of thinning in all seasons have greatly exceeded the predictions of climatic models. The sea ice cover of the Arctic Ocean, particularly in summer, has been in retreat since the 1950s at a rate of about 4% per decade which has recently increased to 10% per decade. More seriously, the thickness of the ice has diminished.
Satellites can track ice area, but ice thickness distribution is most accurately measured by sonar from underneath the ice. Since 1971, I have been going to the Arctic in UK nuclear submarines, mapping the ice thickness using upward-looking sonar along the vessel's track. U.S. submarines have also allowed such availability. Opening these submarines to scientific work has been a marvellous service to climate research. It was thanks to submarines that I was able to show for the first time that the ice in the Arctic is thinning (in a 1990 paper in Nature , showing a 15% thickness loss in 11 years), and recent work from UK and US submarines now shows a loss of more than 43% in thickness between the 1970s and 2000s, averaged over the ocean as a whole . This is an enormous loss - nearly half of the ice thickness - and has changed the whole appearance of the ice cover. Most of the ice is now first-year rather than the formidable multi-year ice which used to prevail.
The thinning is caused by a mixture of reduced growth in winter (because of warmer temperatures and more heat in the underlying water column) and greater melt in summer. A change in the direction and speed of ice motion has also played a role, with the ice departing quicker from the Arctic Basin through Fram Strait rather than circulating many times inside the Arctic.
The summer (September) area of sea ice reached a record low in 2007, almost matched in 2011, but what is most serious is that the thinning continues. It is inevitable that very soon there will be a downward collapse of the summer area because the ice will just melt away. Already in 2007, measurements indicated that during the summer there were 2 metres of melt off the bottom of ice floes in the Beaufort Sea, while the neighbouring first-year floes had only reached 1.8 metres during winter - so all first-year ice was disappearing. This effect will become more important and will spread throughout the Arctic Basin.
There is currently disagreement about when the summer Arctic will become completely ice-free. It depends on which model is being employed. My own view is based on purely empirical grounds, that is, matching the observations of area from satellites with observations from submarines (combined with some modelling) of thickness to give us ice volume. If we think in volume terms instead of area terms, the downward trend is more than linear, in fact it is exponential, and if extrapolated it gives us an ice-free summer Arctic as early as 2015 or 2016.
Others have talked of later dates, like 2030-2040, but I do not see how the trend of summer ice volume can possibly permit this. Those who agree include W Maslowski, a leading ice modeller (Naval Postgraduate School, Monterey), and the PIOMAS project at University of Washington which generated the data shown below .
The figure shows the minimum volume of Arctic sea ice in midsummer, based on areas observed from satellites and thickness trends inferred from submarine observations. Extrapolation leads to a zero volume in 2015. It must be pointed out that this perspective stands in direct contradiction to very complacent statements about the Arctic sea ice from the IPCC in the AR4 report of April 2007 saying the sea ice was very likely to last beyond the end of the century.
The ice retreat is having major impact on the planet. The Arctic is the most rapidly warming region on earth (warming at 3-4 times the rate of low latitudes). It has become widely accepted that Arctic amplification of global warming is due to the albedo effect of sea ice retreat. The increased open water reduces the albedo (fraction of solar radiation reflected into space) and causes warming at high northern latitudes to be much faster than the tropics, with enormous implications for climatic instability. Secondly, the summer retreat of the ice from the wide Arctic continental shelves (particularly the East Siberian Sea) allows the shallow surface layer to warm up, bringing temperatures of up to 5 degrees C right down to the seabed.
Quantification of this effect has only very recently been attempted, in a paper to the 2011 AGU by Hudson . The startling conclusion is that the rate of warming of the Arctic from the sea ice albedo effect could double or worse, once the Arctic Ocean is ice-free in September. And it could double again, once the ocean is ice-free for half the year. But the timescale makes this all the more worrying.
The scientific community has drawn attention to the risk of dangerous climate change if the world does not reduce greenhouse gas emissions - a worthy and critical objective. However, I wish to point toward a much more immediate problem that does not seem to be recognised among the climate change community at large: This is the problem of rapid retreat of Arctic sea ice, and likely consequence of catastrophic methane feedback.
These rapidly warming temperatures are accelerating the melt of offshore permafrost, releasing methane, trapped either as methane hydrates or as free gas beneath the permafrost, and causing large plumes of methane to appear all over the summer Arctic shelves (observed for the last 2-3 summers by Semiletov and colleagues on joint University of Alaska - Far Eastern Research Institute cruises). Methane levels in the Arctic atmosphere have started to rise (measured by Dr Leonid Yurganov, Johns Hopkins University) after being stable for some years. As methane is a very powerful, if short lived, greenhouse gas (as much as 105 times as powerful per as unit weight of CO2 over a 10 year time horizon, though only lasting about 8 to 12 years in the atmosphere), this will give a strong upward kick to global warming.
According to research crew leader Igor Semiletov, "We carried out checks at about 115 stationary points and discovered methane fields of a fantastic scale - I think on a scale not seen before.... This is the first time we've found continuous, powerful and impressive seeping structures more than 1,000 meters in diameter."  He has also described how warmer temperatures are making their way down to the bottom of the shallow sea in the Arctic continental shelf areas: "When ice has gone, there are stronger winds and waves and a deeper mixing of water which causes the comparatively warm upper layer to mix with water at deeper levels. There are already studies which confirm that in some areas, bottom temperature in summer is 2 to 3 degrees above zero Celsius (freezing). As this warming spreads to a larger area, the more that shelf-based permafrost will thaw."  There have been warnings that a major methane outbreak may be imminent.
In a piece Archer co-authored in 2009 , he acknowledged both the significant warming power of methane and the fragile and "intrinsically vulnerable" nature of hydrates: "There are concerns that climate change could trigger significant methane releases from hydrates and thus could lead to strong positive carbon-climate feedbacks. .... Methane hydrate seems intrinsically vulnerable on Earth; nowhere at the Earth's surface is it stable to melting and release of the methane." In this same piece, Archer affirms another key factor: "Rapid warming well above the global average makes the Arctic hydrates particularly vulnerable to climate change."
Archer clearly acknowledges the vulnerability of methane hydrates to thawing in response to rising Arctic temperatures. Accelerating ice loss can only accelerate that temperature rise through the albedo effect, so we should be regarding the potential loss as an imminent and urgent crisis. Ira Leifer, from the Marine Science Institute at UCSB, describes the mechanics of a "runaway" methane feedback: "A runaway feedback effect would be where methane comes out of the ocean into the atmosphere leading to warming, leading to warmer oceans and more methane coming out, causing an accelerated rate of warming in what one could describe as a runaway train." 
Given that this "train" would be one way and feed upon itself in a way that might well be unstoppable by humanity, it would seem to be a classic case where the precautionary principle should be invoked as a justification for action.
 RealClimate: Much ado about methane
(The link “worked up” refers to Gary’s piece:
 Wadhams: 1990 Evidence for thinning of the Arctic ice cover north of Greenland. Nature, London, volume 345, 795-797
 Wadhams: Arctic Sea Ice Thickness: Past, Present & Future
 PIOMAS graph link: http://neven1.typepad.com/.a/6a0133f03a1e37970b0153920ddd12970b-pi
 UK Independent, Dec.13, 2011
 Documentary interview with Semiletov:
 Archer, co-author: Gas hydrates: entrance to a methane age or climate threat
 Documentary interview with Leifer:
The author: Peter Wadhams Sc.D. is Professor of Ocean Physics at the University of Cambridge in the UK. He is an oceanographer and glaciologist involved in polar oceanographic and sea ice research and concerned with climate change processes in the polar regions.
6. Further evidence of escalating methane emissions
Steven Chu, Secretary for Energy and Nobel Laureate, is one of the most eminent people to point out the danger of methane from the Arctic getting out of control, in a vicious spiral of greenhouse warming from the methane causing greater methane emissions. Could an escalation of methane emissions already be happening, as the sea ice retreats?
The Russian scientists, Natalia Shakhova and Igor Semiletov, have spent many years studying the East Siberian Arctic Shelf. They were recently interviewed by members of the AMEG team at the EGU meeting in Vienna. They remain deeply concerned about the methane they have observed bubbling up from the seabed of the East Siberian Arctic Shelf (ESAS).
The concern of AMEG has been heightened by recent measurements of an excess of methane in the atmosphere over the ESAS, as shown in the image produced from AIRS NASA data, see Sam Carana's blogpost .
The methane excess over the shallow sea of the ESAS and over Yakutia is a novel development. By late winter, or early spring, March and April, the region has been cleared of all previous year's melting seasons' methane by the global winds when the grounds have remained frozen during the winter season. However, in 2012 this region has had an unusually persistent level of methane almost 100 ppb above regional average.
The methane excess over ESAS is extraordinary because one would expect the area to be covered in thick ice at this time of year. However the methane must be coming up through cracks in the ice or through existing polynias. In methane monitoring by HIPPO, in another part of the Arctic, the methane only appears over ice where there are cracks (called leads) or partial cover .
It is known from the last melting season that vast increases of methane venting occurred in ESAS. We consider that the most likely explanation of the extra methane in the atmosphere is that the methane emitted from ESAS seabed, as observed by Shakhova and Semiletov in 2011, has built up under the ice in winter and then escaped into the atmosphere in March and April, either through leads in the ice or through cracks formed by the methane itself.
There has been a contrary suggestion that the methane might be formed by microbes in the sea, but no such activity has been observed, and the sea is already supersaturated with the methane that has risen from the seabed according to Shakhova.
Sam Carana also has a blogpost on recent greenhouse gas levels . You can see that large whiffs of methane, up to 2500 ppb, have been detected at Barrow, one of only three measuring stations in the Arctic. The mean annual level there, now over 1900 ppb, is well above global average. Compare it with the lower latitude measurements at Mauna Loa, Hawaii, where the mean annual level was stable around 1780 ppb for a decade but since 2007 has risen to 1820 ppb. The rise in methane could be coming from the Arctic, but this has been difficult to confirm. However the signs are consistent with an escalation in methane emissions from the ESAS seabed.
7. A choice for society
This is not just a matter of a spat between scientists. On the one hand there are those who consider that the future of the planet is at stake – whether mankind undertakes a fire-fighting exercise to cool the Arctic, or whether mankind allows the sea ice to melt away and the emissions of methane to escalate with a risk of causing runaway global warming. On the other hand there are those who deny the seriousness of the situation, those who would do nothing until more certainty has been established, those who believe that the fire-fighting equipment is more dangerous than the fire to be put out, those who believe that the Arctic sea ice will recover on its own accord, those who deny the mortal danger arising from the situation in the Arctic, even considering it “much ado about nothing.”
AMEG sees that society has a choice: to risk oblivion or strive to survive. As Jared Diamond wrote in his book “Collapse, how societies choose to fail or survive” , there can be a failure of the perception of danger. The Met Office evidence shows it is failing to perceive the danger, as if living under a dam about to burst . If governments around the world do not heed the danger, society has chosen to fail.