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Human activity is driving retreat of Arctic sea ice

What the science says...

Select a level... Basic Intermediate

Arctic sea ice has been retreating over the past 30 years. The rate of retreat is accelerating and in fact is exceeding most models' forecasts.

Climate Myth...

Arctic icemelt is a natural cycle

"In 2007, the Northern Hemisphere reached a record low in ice coverage and the Northwest Passage was opened. At that point, we were told melting was occurring faster than expected. What you were not told was that the data that triggered this record is only available back to the late 1970s. We know the Northwest Passage had been open before." (Matt Rogers)

Global warming affects Arctic sea ice in various ways. Warming air temperatures have been observed over the past 3 decades by drifting buoys and radiometer satellites (Rigor et al. 2000, Comiso 2003). Downward longwave radiation has increased, as expected when air temperature, water vapor and cloudiness increases (Francis & Hunter 2006). More ocean heat is being transported into Arctic waters (Shimada et al. 2006).

As sea ice melts, positive feedbacks enhance the rate of sea ice loss. Positive ice-albedo feedback has become a dominant factor since the mid-to-late 1990s (Perovich et al. 2007). Older perennial ice is thicker and more likely to survive the summer melt season. It reflects more sunlight and transmits less solar radiation to the ocean. Satellite measurements have found over the past 3 decades, the amount of perennial sea ice has been steadily declining (Nghiem et al. 2007). Consequently, the mean thickness of ice over the Arctic Ocean has thinned from 2.6 meters in March 1987 to 2.0 meters in 2007 (Stroeve et al. 2008).

Global warming has a clearly observed, long term effect on Arctic sea ice. In fact, although climate models predict that Arctic sea ice will decline in response to greenhouse gas increases, the current pace of retreat at the end of the melt season is exceeding the models’ forecasts by around a factor of 3 (Stroeve et al. 2007).

Figure 1: September Arctic Sea Ice Extent (thin, light blue) with long term trend (thick, dark blue). Sea ice extent is defined as the surface area enclosed by the sea ice edge (where sea ice concentration falls below 15%).

What caused the dramatic ice loss in 2007?

The sudden drop in sea ice extent in 2007 exceeded most expectations. The summer sea ice extent was 40% below 1980's levels and 20% below the previous record minimum set in 2005. The major factor in the 2007 melt was anomalous weather conditions.

An anticyclonic pattern formed in early June 2007 over the central Arctic Ocean, persisting for 3 months (Gascard et al. 2008). This was coupled with low pressures over central and western Siberia. Persistent southerly winds between the high and low pressure centers gave rise to warmer air temperatures north of Siberia that promoted melt. The wind also transported ice away from the Siberian coast.

In addition, skies under the anticyclone were predominantly clear. The reduced cloudiness meant more than usual sunlight reached the sea ice, fostering strong sea ice melt (Kay et al. 2008).

Both the wind patterns and reduced cloudliness were anomalies but not unprecedented. Similar patterns occurred in 1987 and 1977. However, past occurences didn't have the same dramatic effect as in 2007. The reason for the severe ice loss in 2007 was because the ice pack had suffered two decades of thinning and area reduction, making the sea ice more vulnerable to current weather conditions (Nghiem et al. 2007).

Other Studies on the Cause of the Sea Ice Decline

Vinnikov et al. (1999) estimated the probability that the Arctic sea ice decline could simply be natural.  The authors used very long control runs of both the Geophysical Fluid Dynamics Laboratory (GFDL) and Hadley Centre climate models (5,000 years for the GFDL model) to assess the probability that the observed and model-predicted trends in Arctic sea ice extent occur by chance as the result of natural climate variability.  They found that large trends in sea ice extent only appeared over short time intervals in the control run, due to natural variability alone.  This suggests that natural variability will not cause large long-term Arctic sea ice trends.

Updating this analysis using observational data through 2011 (not even including the 2012 record low sea ice extent), the 32-year trend (1979-2011) is -530 thousand square km per decade, and the 20-year trend is -700 thousand square km per decade.  Using the Vinnikov et al. results, these trends both correspond to probabilities of well under 0.1% of being due solely to natural variability.

Day et al. (2012) used five climate models to try and quantify the contribution of natural variations in Arctic sea ice changes.  They found that between 5% and 30% of the Arctic sea ice decline from 1979 to 2010 could be attributed to the natural cycles of the Atlantic Multidecadal Oscillation (AMO) and Arctic Oscillation (AO), and even less can be attributed to natural cycles since 1953, since these natural cycles tend to average out over longer timeframes (as Vinnikov et al. also found).

"despite increased observational uncertainty in the pre-satellite era, the trend in [Arctic sea ice extent] over this longer period [1953–2010] is more likely to be representative of the anthropogenically forced component."

Stroeve et al. (2011) noted that in 2009-2010, the AO was in a state which should have resulted in a large sea ice extent; the fact that 2010 was a year of relatively low sea ice extent is indicative long-term human-caused sea ice decline.

"Based on relationships established in previous studies, the extreme negative phase of the Arctic Oscillation (AO) that characterized winter of 2009/2010 should have favored retention of Arctic sea ice through the 2010 summer melt season. The September 2010 sea ice extent nevertheless ended up as third lowest in the satellite record, behind 2007 and barely above 2008, reinforcing the long-term downward trend."

Notz and Marotzke (2012) also found very poor correlation between the AO and Pacific Decadal Oscillation (PDO) and Arctic sea ice extent (yellow and green in Figure 2), concluding:

"the available observations are sufficient to virtually exclude internal variability and self-acceleration as an explanation for the observed long-term trend, clustering, and magnitude of recent sea-ice minima. Instead, the recent retreat is well described by the superposition of an externally forced linear trend and internal variability. For the externally forced trend, we find a physically plausible strong correlation only with increasing atmospheric CO2 concentration. Our results hence show that the observed evolution of Arctic sea-ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in Arctic sea ice already today."

notz fig 4

Figure 2: Correlation between September sea ice extent and CO2 forcing (red), solar forcing (blue), PDO index (green), and AO index (yellow).  Figure 4 from Notz and Marotzke (2012).


Recent discussion about ocean cycles have focused on how internal variability can slow down global warming. The 2007 and 2012 Arctic melts are a sobering example of the impact when internal variability enhances the long term global warming trend.  Overall, the scientific literature is quite clear that natural variability alone cannot account for the long-term Arctic sea ice decline, which is mainly due to human-caused global warming.

This rebuttal was updated by Judith Matz on September 13, 2021 to replace broken links. The updates are a result of our call for help published in May 2021.

Last updated on 15 October 2016 by dana1981. View Archives

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Further viewing

The following animation shows how the oldest thickest sea ice has been progressively flushed from the Arctic Ocean over the last two decades. The colours are an indication of the age of the sea ice. Lighter colours are older sea ice - white is 10 years old.


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Comments 1 to 25 out of 79:

  1. So the sudden drop in sea ice in 2007 was due to weather conditions, not climate change ( excepting weather is the end product of the climate process). How many times do we need to remind ourselves "one swallow does not a summer make"? Sea ice is a part of the negative feedback system that keeps climate (reasonably) stable. Melting requires heat (334J/gm if I remember rightly)and this mostly affects local sea temperature. It also keeps plankton et al very happy and bloomimg nicely, (they like it cool)which is good because they lock up a bit more CO2 and the food chain speeds up.
  2. John Well written. I like this one much better than the original.
  3. This whole piece is somewhat humorous. To even use arctic ice as evidence of a global warming trend as caused by CO2 over merely 3 decades of evidence is utterly ridiculous. Anthropogenic GW advocates will cite that the Northwest Passage has opened the for the first time since records began in 1978. Since records began. Sorry, but if a norweigan sailor by the name of Roald Amundsen could navigate the passage in 1906, then you're going to have to accumulate another century of evidence of so-called Anthropogenic Global Warming before the case is made. Remember people, satellite data is only available after satellites were invented...
  4. What jecht8 either doesn't know or acknowledge is that it took Amundsen 3 years to make the trip because only bits opened up at a time. Also, he took an extremely shallow water route sticking close to the mainland shore. When we speak of the NW passage opening now, we're talking about being able to go pretty much full speed, just steering around a few bergs - and it's the more northern, deep water route.
  5. Two recent Arctic Ice updates: Beginning in early January 2009, sensor drift caused an underestimation of ice that grew until the error was finally caught in the mid-February. Internet visitors who look to the NSIDC for data sent emails to the center and, it became clear that there was a significant problem—sea-ice-covered regions were showing up as open ocean. (See NSIDC) MORE . . . (May 4, 2009) Ice in the Arctic is often twice as thick as expected, report surprised scientists who returned last week from a major scientific expedition. The scientists - a 20-member contingent from Canada, the U.S., Germany, and Italy - spent one month exploring the North Pole as well as never-before measured regions of the Arctic. Among their findings: Rather than finding newly formed ice to be two metres thick, "we measured ice thickness up to four metres," stated a spokesperson for the Alfred Wegener Institute for Polar and Marine Research of the Helmholtz Association, Germany's largest scientific organization. More info to come from Polar 5.
  6. The Arctic seems to be warming up. Reports from fishermen, seal hunters and explorers … all point to a radical change in climate conditions, and hitherto unheard-of high temperatures in that part of the earth's surface. … Ice conditions were exceptional. In fact so little ice has never before been noted. The expedition all but established a record, sailing as far north as 81 degrees 29 minutes in ice-free water. … Many old landmarks are so changed as to be unrecognizable. Where formerly great masses of ice have been were found, there are now often moraines... At many points where glaciers formerly extended far into the sea, they have entirely disappeared. - - - The above alarming excerpts were taken from an October report to the US Weather Bureau. October 1922, that is, not 2009. So it has happened before, and will happen again. We should not think that everything is so special for our time: the contents of this site strike me as very centered around here and now. It is 10 years this, 30 years that, highest since record began in 1978, and so on. That is a very short time perspective. Somehow the lack of perspective in the climate discussions remind me of the 2000+ year old quote attributed to Socrates that most people would place in our time frame: "The children now love luxury; they have bad manners, contempt for authority; they show disrespect for elders and love chatter in place of exercise. Children are now tyrants, not the servants of their households. They no longer rise when elders enter the room. They contradict their parents, chatter before company, gobble up dainties at the table, cross their legs, and tyrannize their teachers." It is presumptuous to think that mankind rules the earth's climate. There are other, more powerful, forces in play. But we think we can raise or lower the average temperature of the earth at will! 0.33 degrees up, or why not 4 degrees. Or raise the oceans, 38 centimeters up, or why not 6 meters, or whatever ! Invent a figure, and people will bow to you in awe. Ridiculous. Anything could happen, and probably will, but we are not in control.
  7. Argus, yes, you can claim whatever you wish untill you look at the data. Which tell a different story. By the way, in the '20s the arctic was already warming.
  8. Well Riccardo, who was warming it so much then, when human CO2 emissions were only a fraction (less than 1/10) of what it is now? The cows and their methane outlets? What explanation do you have in your 'data'?
  9. Argus, it should come as no surprise that climate has changed before. Indeed, one has to look at how climate works, i.e. that there are several possible forcings other than CO2. In particular, in the first half of last century there has been a reduced volcanic activity (grey line) concomitant to an increase of total solar irradiance (top panel). The result is an increase in temperature till about 1950, overall and in the Arctic as well.
  10. Thank you very much for acknowledging that there are other forcings than CO2, and that climate changes similar to what we are experiencing now, have occurred before. It seems to me that 99% of what is presented here is focussed on CO2 only, as if there were no other explanation to anything at all happening on this planet. Also, thanks for the links! I am continually reading up on more facts presentations and connected debates within this great site (and some others). I am slowly learning, and by now I know a lot more than the average person in the street, but I also recognize how little I know compared to those who have studied this field seriously for years.
  11. Argus, I'm glad you now realize that we all think that there's not just CO2. It's an important point to make clear as did our host writing a post on it. It is only by looking at all the important factors that scientists can be so confident on the causes of recent and past climate variations. Please keep reading and asking, it won't take that much time :)
  12. Argus, a good overview is cce's The Global Warming Debate. It will give you a good base from which you can more efficiently and effectively pursue particular topics here.
  13. Is the graph from Stroeve 2007? I find it quite hard to read a graph that I don't know the source from.
  14. The Prince of Cherries is at it again. the ice itself is about to set a record high for the date in the DMI database (emphasis added). BTW, that database includes the years 2005-2010. We are about to set a record high for a specific date in a statistically insignificant 6 year period. Huzzah! With just 3 more years, we draw a different conclusion: Note that the annual rebound of new ice is always steeper than the melt. And yes, even with globally increasing temperatures, there will still be winter in the Arctic.
  15. Heh. "Prince of Cherries". Meanwhile the ice volume remained far below previous record lows through the end of September. Ice volume is now only about 20% of what it was in 1979 while extent is about 60%. However, the two factors ultimately ARE linked... if volume hits 0% extent perforce will as well. Unless the volume trend suddenly levels off for some reason Goddard only has a few more years (at best) of being able to play games with extent data.
  16. Response to NQuest from the ice age thread> You're missing the point. None of those examples suggest that the changes will be monotonic year-after-year. When discussing global warming we are referring inherently to long term trends. Given the degree of annual variation, you need about 15 years to establish statistical significance. A 2-3 year trend means little to nothing with regard to the long term trends being discussed. This is a common misunderstanding among many skeptics and this same discussion has played out many many times on this site. It is in no way new or "sudden". The natural variation referred to is of the inter-annual short-term variety. If you take a look at the graph provided in this post, you can see clearly that there has been a clear downward trend extending from about 1970. You may also notice that there are many 2-3 year "recoveries" amidst this trend. It is because of this variability in the signal that you must look at 10+ years of data to make any claims about whether the ice is melting or growing over the long term.
  17. e (16) - Could you please explain to me why is it that the glacialist, when discussing the expansion of the glacier made the statement, "We're not sure why this happens".
  18. @NQoA: because they're not certain about the particular characteristics of that glacier that make it resist the global trend towards glacier retreat. Again, no one said all glaciers would recede at the same time, or at the same rate. Given the number of glaciers on the world, some are bound to react differently. The fact remains, however, that an overwhelming majority of glaciers are retreating.
  19. NQuest @17: Perhaps without realizing that the discussion was to be moved to this thread, muoncounter provided you an explanation on the 'ice age' thread. Please note that he cites directly from the link you provided. The article's own tone seems to be in opposition to the use to which you wish to put it, a behaviour which seems lamentably common among contrarians who visit this site. The article suggests that this glacier is certainly anomalous, but since the rest of the world's ice (as documented in this very post or handily summarized with this search of SkS) continues to decline, I hardly see how it can present a major challenge to the science supporting AGW. Certainly I would conjecture that one factor in the Perito Monero glacier's stability would be an increase in precipitation (specifically, snowfall at the glacier's source), which follows from an increase in atmospheric water vapour, which follows from (wait for it...) warming temperatures. Sooner or later, though, if temperatures continue to rise, Perito Monero will follow its fellow glaciers into decline. At any rate, it seems to me that bringing up Argentine glaciers is a complete non sequitur - perhaps even a red herring - when it comes to discussions specifically focused on Arctic sea ice decline.
  20. @Argus: no one said CO2 was the only forcing. To claim otherwise would be a type of strawman fallacy. The point you're apparently missing is that, no, the climate change we are currently experiencing is not like what has happened before. We have a pretty good idea of why climate changed in the past, and none of the various circumstances that provoked past change is at play today What *is* different, of course, is that this time we're pouring gigatons of CO2 in the atmosphere, and that CO2 is causing temperatures to rise. Just to make things clear, though: are you in fact disagree with NQoA? Because the latter seems to think there is no warming, while you claim the warming is natural. Aren't going to argue with NQoA as well? After all, he's also disagreeing with you. I'd love to see some "skeptics" break the unspoken rule once in a while, but I don't think this is going to happen here...
  21. Re: NQuestofApollo (17) Perhaps if you had read Dr. Rivera's extended comments in the longer version of the article here:
    "One hypothesis for the 3-mile-wide (5 kilometer-wide) Perito Moreno's advance is the glacier's apparent insensitivity to changes in what glaciologists call the equilibrium line on glaciers, Rivera said. Roughly equivalent to the snow line, the equilibrium line is the elevation above which the glacier is growing, due to snow accumulation, and below which the glacier is melting. When this line moves higher up a hill or a mountain due to rising temperatures, for example, more of the glacier is situated in the melting zone, and the glacier retreats. But because Argentina's Perito Moreno glacier is so steep in the area where the equilibrium line falls, climate shifts don't impact the line's movement much, at least as it relates to the height of the mountain, Rivera noted. As a result, the amount of of ice lost or gained is minimal. It could also be that Perito Moreno simply hasn't got all that much to lose. The lake where Perito Moreno ends—Lago Argentino—is shallower than the bodies of water at the ends of most glaciers. Most glaciers calve, or release ice, in deep water, but not Perito Moreno, where the calving rates are higher than on other Patagonian glaciers. That means less of the glacier is in the melting zone below the equilibrium line. As heavy snowfall above the equilibrium line pushes the glacier downhill, the glacier breaks up when it hits the lake, Rivera explained. Such impacts kept the glacier from growing longer when the climate was cooler, and thus more likely to expand, he said. If Perito Moreno had extended into a deep lake area, it would have become a longer glacier, and Earth's recent warming trend would be causing the glacier to melt and its ice to retreat more easily, Richard Alley, a glaciologist at Pennsylvania State University in University Park, said in an email. "Instead, we have a shorter glacier, with less [of a] zone where the warming can cause melting, but a large high-elevation [snow and ice] accumulation zone," Alley added."
    Forming an opinion based on an incomplete news article on one glacier that happens to be advancing at a time when glaciers worldwide are in retreat is cherry-picking. No one said glacial retreat would be linear and uniform. Perito Moreno, for the reasons surmised, is one of the exceptions to the overall trend. Noise in the data. For more on glacial changes, go to Mauri Pelto's blog. The Yooper
  22. Natural cycle? Really? Not this year: Observations from the ground in the Eastern Arctic, ... and views taken by satellites at 500 kilometres above the earth’s surface showed ArcticNet participants that ice formation in 2010 is abnormally slow. ... “We have dramatic changes taking place,” with the Arctic becoming a place of rain instead of snow ...
  23. muoncounter, thanks for the AO link, but I already look at that almost every day since it affects my own weather (an aside: AO predictions this year have been less accurate than usual). That site has the long term trends here and we're still in strongly negative territory. As I said on the other thread, AGW is responsible for ice loss. AO is also a factor and negative AO should bring a recovery in ice. Another factor is last year's El Nino and a decline in ice. This year should see a continued recovery due to negative AO if that theory holds (paper linked on other thread). That still leaves the question on the other thread of the effects of AGW on AO according to models.
  24. #23: "we're still in strongly negative territory" What you're looking at is the three month running mean, which is strongly negative, but that's a hindcast. The daily record and the forward looks are here: -- replaces the auto-updating graph. Sure looks like it bottomed in mid December.
  25. Muoncounter, you are looking at short term fluctuations. Last year AO also looked like it bottomed in December but then hit an all-time low (since 1954) in February.

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