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Human activity is driving retreat of Arctic sea ice

What the science says...

Select a level... Basic Intermediate

Thick arctic sea ice is undergoing a rapid retreat.

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)

Arctic sea ice has aptly been termed a "canary in the global warming coal mine," a sensitive indicator of climate change; because of its importance as a diagnostic of global warming, climate change skeptics struggle to explain the decline of Arctic sea ice as a natural phenomenon. 

Satellite measurements of Arctic sea ice extent reveal a rapid decline over the past 30 years, particularly at the end of each year's annual melt season.  The downward trend and the increasing difference between seasons are in keeping with predictions of the effects of global warming. As the Arctic warms, the volume of ice in the region gradually declines, making it less likely ice will survive more than one year and thus exposing more open water at the end of each melt season.

(from National Snow and Ice Data Center )

As an explanation for the decline of Arctic sea ice, skeptics hypothesize we're seeing the effects of natural cycles causing deep, decades-long swings in Arctic ice coverage and volume. Lending observational support for such cycles is much more difficult than relying on direct observations of ice extent with contemporary instruments. Still, thanks to ocean sediment cores and some other physical clues left by past climate regimes we have reasonable insight into past Arctic sea ice extent. Combining various information about past climate behavior, we can better understand why changes in ice coverage have occurred in past times, whether those natural variations are happening today, and how those changes compare to today's sea ice trend. 

While it's true that natural variations of the climate have caused significant changes in Arctic ice extent in the past, it's important to note that such changes are not airtight arguments against anthropogenic global warming causing today's loss of ice. After all, events of the past do not describe newly identified influences by human culture on today's climate. Indeed, comparisons between past and present Arctic climate reveal different reasons for yesterday's and today's Arctic sea ice changes and strongly suggest that today's changes are largely anthropogenic (Overpeck et al. 1997).  Meanwhile, analysis of several hundred indicators of past Arctic sea ice extent tells us that recent losses appear to have no parallel in records going back many thousands of years (Polyak et al. 2010).

The past 200 years offers an example of how natural and anthropogenic influences on Arctic sea ice can be distinguished.  The Arctic appears to have undergone an unusually cool period in the early 19th century, certainly natural, with recovery to more normal conditions extending into the 20th century leading to the warming we see today. Referring to the graph above, we can see that after the earlier cool period sea ice extent in the Arctic appears to have largely stabilized, later to begin a steady decline in chorus with other emerging observations of global warming such as increasing air and ocean temperatures. This decline in ice extent is happening even though the causes for natural recovery from the unusual cold of the 19th century are no longer in play, while research strongly suggests these recent reductions in Arctic sea ice are caused by a new, anthropogenic mechanism (Johannessen et al. 2004).  

Although natural factors have always influenced the state of Arctic sea ice, research strongly suggests that today's decline is driven by the novel influence of anthropogenic CO2 we've added to the atmosphere and thus is unique in Earth's history.

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 23 June 2013 by Doug Bostrom. 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 50 out of 75:

  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.
  26. Eric @25, Actually I agree with you re #24. With that said, we have had two winters, back-to-back as it happens with incredibly low bouts of the AO, but two data points are obviously not enough to establish whether or not this marks the beginning of a long-term trend. I'm curious to see whether this is evidence of a transition to a new state or simple internal climate variability. Time will tell. The mechanisms and physics behind Arctic amplification in this case, are very well established.
  27. Re # 23, Am I missing something? A negative Arctic Oscillation allows cold Arctic air to slide south, while warmer southern air moves north. Wouldn't this effectively slow recovery of the ice during winter?
  28. True @27, Essentially, in broad terms, yes. Arctic sea ice extent in December 2010 and January 2011 have been running at or near record lows. Hudson Bay only froze over completely over a month later than average. There is still no sea ice along the Labrador coast.
  29. #27 Trueofvoice, yes, recovery is slower due to the negative AO (and negative NAO) bringing lots of very warm air into NE Canada. It's possible we could see the negative AO regime bringing us less ice in general. #26 Albatross, I agree that it is too short a time period to tell if negative AO is a trend or just a random excursion. The paradox paper in the other thread called it red noise causing episodic behavior.
  30. Muoncounter, in the Science is Settled thread you said "What is becoming apparent is that prior predictions of these 'larger changes' were conservative. That suggests the natural cycles aren't so natural any more." I agree that the local warming feedback you referred to there is probably underestimated. What you did not consider in that thread is that the (likely natural) cycle of positive AO in the first half of the 90's also contributed to ice loss. What we will need to look at next is whether the ice loss from AGW and local feedback overwhelms the recovery we should see from negative AO and La Nina. Amd as I said in my previous post we still don't know the effect of AGW and ice loss on the AO.
  31. #30:"we still don't know the effect of AGW and ice loss on the AO." Eric, It might be useful to determine whether ice loss can be modeled by a combination of AGW and AO. If that is correct, there ought to be a long term trend with residuals. See the graphs here, here and here for ideas about the trend; quadratic looks reasonable. The oscillation's timing should be tested against any periodicity in these residuals. If the magnitude of the residuals is small, it would indicate that the oscillation is relatively weak as a driver of ice loss.
  32. From here. "the ice cap extents over the last 60 years the north pole all but completly melts EVERY YEAR." Sorry, Briago, but that's just not true; the Arctic polar ice does not all but completely melt each year. The NSIDC has excellent data; see their October 2010 press release for a recent summary. One of the great things about SkS is the information here is based on research and data. In short, facts. Most of the posters also strive to substantiate their claims with evidence. If you are serious about the subject of climate change (and you should be), please put your opinions on hold for a while, look around and learn.
  33. An interesting historical record of life and Arctic Sea Ice.

    [DB] Hot-linked URL.

  34. Camburn, You need to stop posting gibberish about things you do not know. This Wikipedia article documents that the entire Northwest passage was ice filled until 10 years ago. Your assertion that it has been passable by non-icebreaking vessels for decades is simply untrue. Capt. Larsens voyage has been replicated in recent years, in only a few weeks to make the passage, it is no longer remarkable for a light icebreaker to transit the NW passage. It is remarkable that someone who posts so little data is so fast to question scientists who actually measure the Arctic ice. How can you question that work when you have no idea how they measured it?
  35. michael: Capt Larson made the voyage in 1944 through the northern route. Even last year his route was not passable. Live with it, it is history. IF you lived near the Arctic, you may know that the Canadian Coast Guard replenishes supplies on an annual basis to the northern stettlements. It has been doing this for decades. Just the way it is. During WW2, the Northest Passage was also sailed by German Warships......remember? If you don't you can look it up. Some simple history items are well known. How can I question cyrosphere? Quit easily. It is a graph posted with no supporting data prior to 1979. Sorry that my 3.5 prediction with the support of the Shindell/Schmidt paper, russtles your feathers it seems.

    [DB] Assertions without links to sources will be disregarded.  IIRC, the Komet took the NE passage, not the fabled NW passage (so even that does not help you).

    BTW, Climate4you is a blind guide: it will lead you astray.

    "How can I question cyrosphere?  Quit easily.  It is a graph posted with no supporting data prior to 1979."

    Study this link for a history of Arctic Sea Ice, how to find the data on it...and how to properly analyze it.

    Or you can email your questions to the good people at the Arctic Climate Research at the University of Illinois here:

  36. Fortuitously, Peter Sinclair has just posted this item on why the melt is so fast. Yet another reminder that air temperature and SST cannot give us the whole story.
  37. In 2007, a lightweight catamaran made the 3,200-mile Northwest Passage voyage entirely by sail. Peter Semotiuk, who runs a single-band sailor's radio network at a port in the middle of the passage, completed the voyage in 1988 and said: "This summer [2007] the passage was largely wide open. It's a very different picture to say 20 years ago, when I travelled the length of the passage." Corporal Henry Larsen's St. Roch was made from extra thick timbers of Douglas Fir, sheeted in Australian gumwood and powered by a diesel engine. University of Calgary: The Larsen Expeditions BBC: Plain sailing on the Northwest Passage
  38. The catamaran passage wasn't a freak event either. 30 recreational boats have completed the voyage in the past decade. The ease of passage through the Northwest Passage is a matter of significant political importance for Canada, the US & Russia. Parliament of Canada: The Northwest Passage and Climate Change
  39. #35, also worth reading Polyak et al and associated data links within to get a context of Arctic ice variability over the past century and also Holocene. You're embarrassing yourself by suggesting that there has been anything other than a sharp decline in Arctic ice since about the 1970s. The last time extents were as low is reasonably well-constrained by dating of wood on old shorelines and of wood trapped in ice shelves - several thousand years ago. [caused by higher Arctic insolation in the early-mid-Holocene]. As Michael Sweet and Bibliovernis have shown, there is no evidence that ice levels in the 1940s were anywhere near today's levels. Anecdotes of sailors commenting on the lack of ice have to be placed in context - a context of a very large amount of ice up there in the early part of the century. Their 'lack of ice' could easily be a great deal of ice by today's standards. A bit like a Scot thinking a day of 20C is hot, which makes sense if you live in Scottish summers, but would make no sense for somebody from Italy!
  40. DB: Note I said the NE passage when talking the Komet. Sorry, but I don't go to climate 4u. skywatcher: Where have I posted that there is not a sharp decline presently in Arctic Ice? I have posted papers that show the variability in Arctic Ice over a long time period. I will state again, for Capt Larson to have made the voyage in 1944 was a feat and a testament to the conditions that year. This also coincides with the period that Greenland had temperatures just slightly lower than present. Here is the route of the St Roch. Note that it went between Banks Island and Victoria Island. Watch the ice this summer and see if this lane is ever passable. Norther Route

    [DB] I looked up your comment:

    "During WW2, the Northest Passage was also sailed by German Warships......remember? If you don't you can look it up. Some simple history items are well known."

    Fortuitous typo?  A thinly veiled attempt at a snarky witticism?  Be it known that your narrative you are pursuing is from the Climate4you/WUWT/CA playbook and that our patience with it...grows thin.

    From time to time you show signs of being an actual skeptic and then you return to form.  So be it.

    Please support assertions with links to peer-reviewed science, construct your comments to comply with the Comments Policy and also ensure that they are on-topic in the future.

  41. This St. Roch nonsense has been done to death many times before, even on SkS. Any way of searching, so that reference can be made to the last thread that went through all this ?

    [DB] Would you care to write up and contribute a guest post on that topic?  :)

  42. With reference to DB's moderator response above, I would be prepared to try to get something written (if only for my own future reference) but I would need to be able to find all previous references to the St Roch on SkS, because I think quite a bit of relevant information is already there - it just needs to be gathered together and researched in more detail. Is there any way of gathering this information ?

    [DB] Short answer: There's no easy way to find a comprehensive listing in all the SkS comments.  A search of various terms will bring up a listing of blog posts containg the terms, but one is still forced to then hunt-and-peck through the sometimes length comment threads.

    If you are interested in doing it, it would be easiest (from a manhours perspective) to start from scratch.

    A good starting point for research:

  43. Here's a new model study, Up and/or down for the next few decades, multiple factors at play. This doesn't quite gel with previous reporting does it?

    [DB] "This doesn't quite gel with previous reporting does it?"

    I doubt that you care to elaborate on your implication here, as I'm pretty sure where you're coming from (and it won't pass the Comments Policy prohibitions).

    Needless to say, that's old news, I'm afraid.  Discussed extensively already at Neven's and RC.  Per Gavin:

    This is not particularly relevant for current behaviour though. More important is how good the aerosol forcing is, or the indirect impacts of black carbon etc. - but we don't know the real answer. - gavin

    Note the bit about "not being relevant for current behavior"...because the ice is currently disappearing in the Arctic 4 times faster than predicted by all models except Maslowski's (which is still tracking for his 2016±3 years).

  44. Schmidt's other comment is also worth repeating. " This is mostly about a quantification of the size of internal variability. By looking at multiple runs with the same forcing and looking at the variability in short trends, you can make a statement about the range. The current trend is at the edge of what the NCAR runs show, and so it is conceivable that what we are seeing has been a weaker forced trend, combined with a (stochastic) increase to the trend because of internal variability. With that assumption, one can look at the other simulations and calculate the likelihood of the stochastic component going the opposite way and slowing down the observed trend. But these likelihoods rely on the NCAR model's estimates of both the forced trend and the internal variability being correct. The former is less likely than the latter"
  45. RyanStarr, setting aside the fact that it IS a new study and thus there hasn't been time to analyze or test its accuracy yet; The study author also said that it should not be taken to mean that the Arctic ice is not retreating. Rather, when they incorporated what they believe to be the possible range of mechanical impacts on sea ice loss (a new form of analysis which they had to assign large uncertainty bands to) they found that the trend over the next 10 years could be either up or down... but that the trend over the next 20 or more years was sharply downward. The biggest problem I see with their argument that the upcoming ten years could see a significant upward trend is that there hasn't been a single previous upward trend of that duration in the satellite record. If you cherry pick very carefully you can find a couple of five year periods where the trend was slightly positive, but nothing close to statistical significance let alone a ten year duration. If they were right about mechanical effects producing a roughly 50% chance of significant 10 year upward trends then we should have seen one by now, or at least something close. Time will tell. However, it doesn't change the fact that we are currently at a record low ice volume, a record low ice area, and a near record low ice extent. The only reason the extent isn't a record low is that the average concentration of the ice pack is. Currently, only ~57% of the ice extent is actually covered in ice (e.g. ice area is 57% of ice extent). Basically, this means that the ice is more spread out than at any previous time in the satellite record. 2007 set the record low extent because winds pushed the ice into a small highly concentrated mass. 2011 currently has an only slightly higher extent despite the ice being the most spread out it has ever been. This is consistent with an example I've been using for a few years; Consider a 10' x 10' x 10' cube: Volume = 1000 cu ft, Area = 100 sq ft, Extent = 100 sq ft Now break it into 1000 1' x 1' x 1' cubes scattered in a 15% concentration: Volume = 1000 cu ft, Area = 1000 sq ft, Extent = 6667 sq ft The same volume of ice, but broken up and spread out it has 10 times the area and 66.67 times the extent. To get extent back down to 100 sq ft, 985 of the 1' x 1' x 1' cubes (98.5%) would have to melt. Obviously that is the extreme case and that kind of perfect breakup and spreading doesn't occur naturally, but it illustrates how it is possible for extent to remain largely unchanged as the ice breaks up and melts away. According to PIOMAS ice volume has set a new record low for the day, each and every day, from 12/20/2009 through 07/31/2011 (the last date data is available for currently). That's 589 consecutive days of new record lows. If the rate of volume decline seen over that time period continued then volume would hit zero in three years. As DB notes, Maslowski's volume projection is the only 'model' which has matched the rate of ice loss over the past five years or so. If that doesn't change in the next few years we'll be seeing only tiny remnants of ice in summers within this decade.
  46. @DB, not sure what you mean, the general message from the AGW supporting side of the argument has been that ice loss is accelerating and will continue to as CO2 levels rise. This study suggests otherwise, that a high degree of natural variability exists in the decadal time frame. They say 50-60 years is required to pass before warming effects become apparent. It would also suggest that any current trend is also natural, unless you want to entertain the notion of 'spurts' of AGW ice loss. This very much contradicts the view popularly expressed on this site, this thread actually. The news isn't so old, it's still August, and hasn't been discussed _here_ at all.

    [DB] For the many reasons stated earlier, the study is essentially a thought experiment not supported by actual observations and metrics.  You were pointed out why it's not applicable to what we observe and measure by myself in my earlier response to you and by CBD in his repy to you above.

    "The news isn't so old, it's still August,"

    Compared to the rate of demise of the Arctic Sea Ice, as ably denoted by muoncounter below, the study is indeed old news.  Obsolete, even.

    "and hasn't been discussed _here_ at all."

    Just because we allow occasional reinvention of the wheel does not also mean we will suffer through continual reinvention of the flat tire.

  47. @CBD, thanks or reply, I think we have to keep in mind how short the current record is, and of course there is a first for everything. With short records we can expect to see lots of 'firsts'!
  48. RyanStarr, most of what you claim this study says or suggests... it does not. Perhaps you should read it before commenting further on 'what it means'.
  49. Ryan#46: "any current trend is also natural," Prove it. Historic records, consistent with modern measurements, say different. Looks like the 'natural cycle' is flat and the recent melt is anything but natural.
  50. CBD: "... it does not." An understatement. Kay et al 2011 say just the opposite of Ryan's claim: On all timescales examined (2–50+ years), the most extreme negative observed late 20th century trends cannot be explained by modeled natural variability alone. ... In a warming world, CCSM4 shows that multi-decadal negative trends increase in frequency and magnitude, and that trend variability on 2–10 year timescales increases. --emphasis added

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