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Arctic sea ice... take 2

Posted on 25 August 2010 by gpwayne

NOTE: Last Monday, I must have had a senior moment - I meant to post the new Basic version of the "Arctic sea ice has recovered" argument but somehow ended up copying and pasting the Intermediate version. I'll take this as a cautionary tale not to rush a blog post just before going to sleep. In the meantime, here is the actual Basic version written by Graham Wayne:

Discussions about the amount of sea ice in the Arctic often confuse two very different measures of how much ice there is. One measure is sea-ice extent which, as the name implies, is a measure of coverage of the ocean where ice covers 15% or more of the surface. It is a two-dimensional measurement; extent does not tell us how thick the ice is. The other measure of Arctic ice, using all three dimensions, is volume, the measure of how much ice there really is.

Sea-ice consists of first-year ice, which is thin, and older ice which has accumulated volume, called multi-year ice. Multi-year ice is very important because it comprises most of the volume of ice at the North Pole. Volume is also the important measure when it comes to climate change, because it is the volume of the ice – the sheer amount of the stuff – that science is concerned about, rather than how much of the sea is covered in a thin layer of ice*.

Over time, sea ice reflects the fast-changing circumstances of weather. It is driven principally by changes in surface temperature, forming and melting according to the seasons, the winds, cloud cover and ocean currents. In 2010, for example, sea ice extent recovered dramatically in March, only to melt again by May.

Sea-ice is subject to powerful short-term effects so while we can't conclude anything about the health of the ice from just a few years' data, an obvious trend emerges over the space of a decade or more, showing a decrease of about 5% of average sea-ice cover per decade.


Source: Rayner et.al, 2004, updated

Where has the thick ice gone?

When we consider the multi-year ice and look at the various measurements of it, we see a steep decline in this thick ice. As you might imagine, thick ice takes a lot more heat to melt, so the fact that it is disappearing so fast is of great concern.

Source: Polar Science Centre, University of Washington

It is clear from the various data sets, terrestrial and satellite, that both the sea ice extent and multi-year ice volume are reducing. Sea ice extent recovered slightly during the Arctic winters of 2008-09, but the full extent of annual ice reduction or gain is seen in September of each year, at the end of the Arctic summer. The volume of multi-year ice has not recovered at all, and is showing a steeply negative trend.

* Footnote: Although a thin layer of ice doesn’t tell us much about the overall state of ice loss at the Arctic, it does tell us a great deal about Albedo, the property of ice to reflect heat back into space. When the sea ice diminishes, more heat passes into the oceans. That heat melts the thick ice and speeds up the melting of thinner sea ice, which in turns allows more heat to accumulate in the oceans. This is an example of a positive feedback.

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Comments

Comments 1 to 45:

  1. Is the data available to take the volume chart back to 1950? Would be interesting to see data for the same period for both extent and volume.
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  2. No the data is not available back to then for volume from the polar science center unfortunately.
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  3. I really hate the idea of trying to fit a linear trend line to a curve which is certainly not linear! Early in the 20th century the minimum ice extent was fairly constant, but it has accelerated downwards in recent decades. The way things are going, the ice will completely disappear much sooner than the straight line would suggest.
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  4. In that context, fitting a quadratic trend to either the sea ice extent or sea ice volume since 1979 produces a much better fit - ie the losses are accelerating through time, rather than simply declining linearly. Those trends reach zero (in September) for extent around 2030, and volume before 2020.
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  5. I thought albedeo was primarily a measure of reflection of visible light, since that is where most of the energy is from sunlight. Dark water absorbs more of this energy than white ice. The energy absorbed by the water leads to heating, and some of the absorbed energy is then re-radiated as heat radiation (IR).
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  6. Mikemcc, yes, you're right -- "albedo" is the average reflectance across either the visible spectrum or the visible & near-infrared range (say, 0.4 to 0.7 or 1.0 or 1.3 micrometers) depending how one wants do define it. The albedo of a surface determines what fraction of the incident light from the sun is reflected. The portion that isn't reflected is, of course, absorbed, raising the temperature of the surface.
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  7. pikaia is right. The curve would not be linear, as the albedo effect of more dark ocean each year would act as a catalyst. Hence, curving the relationship between ice volume and time. (However, adding another difficult variable to an otherwise simple concept could prove troublesome for politician simpletons and John Q public.)
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  8. Again the PIOMAS isn't measured data but modelled data, an important distinction. That's why it can be, and sometimes is, wrong.
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  9. HumanityRules at 00:35 AM on 26 August, 2010 Again the PIOMAS isn't measured data but modelled data, an important distinction. That's why it can be, and sometimes is, wrong. = = = = = = = = = = = = = = = = = = It is a model derived from measurements like almost every other metric used on a similar scale (100-1000 square kms). Even the isobars on an MSLP chart are effectively models.
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  10. HumanityRules, you may be right, however, the graph shows a drastic acceleration in the decrease in ice volume, are you saying it is drastically wrong? If it is even 10% or 20% wrong, the decline is alarming. Furthermore, are you saying the declining trend it shows is wrong? Even if the apparent acceleration in decline in ice volume is exaggerated, that is small consolation, as the straight line itself is quite steep. Even if, as you say, the model is sometimes wrong, it is still very useful to see the problem we are facing. Unless it is always wrong? Is that what you are saying, that it is useless?
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  11. See the article about John Cook at The Guardian. BTW, do not ask people there to donate to John's site because your comment will be removed. I wonder how I know this....? :)
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  12. 10.Gordon What I'm saying is that for the past two seasons the PIOMAS model has under-estimated the extent. In 2008 it estimated extent would be lower than 2007. This year it has a fairly low estimate of extent which looks like again being an under-estimate. There are some actual measurements of ice thickness. Here's one that's fairly easy to follow (http://epic.awi.de/Publications/Haa2010b.pdf). It's conclusion is that in 2009 there was very little difference in ice thickness compared to 2007. This is the first line from their conclusion "We conclude that older sea ice in much of the Arctic Ocean was of similar or even slightly larger thickness in April 2009 relative to conditions in 2007, but within the expected range of interannual variability." You might argue that this covers only a small fraction of the arctic but unfortunately this is probably as good as it gets. If ice thickness is roughly the same, maybe slightly higher and if the extent and concentration are both greater than 2007 then where does the recent dramatic fall seen by POIMAS come from? The PIOMAS authors in a 2008 paper highlight the fact that the 2007 conditions are weighing heavily on their 2008 predictions, my guess is it is still doing so. I think that this is an over-estimation of the influence that 2007 ice conditions is having on model outputs moving forward. I do think in general the past decade or two have shown a decline in arctic sea ice. It's worth concidering though how long this obsession with trend has been going on. The arctic ice and weather conditions have long been known to have high levels of natural variability. Comment on the arctic seems to blind itself from this variability to focus wholy on the recent downward trend, which is extrapolated forward indefinately as you seem to do. I think it's worth considering the recent conditions in relation to those long term natural variations.
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  13. 12. HumanityRules Thanks for your response. We'll see very clearly within a few years who's right about arctic ice volume. It will be interesting. I don't think people are 'obsessed' with this trend. Using the term slights people who disagree with you, implying they are not critical thinkers. The stakes are high, and therefore intense interest is justified. No one is unaware of past variability in arctic ice and weather conditions. People are not blindly extrapolating this trend indefinitely. Offhand, I can't think of any trend I've seen that continues indefinitely. Certainly, if the PIOMAS graph above is accurate, it will go horizontal in the not too distant future. Flatlining, so to speak. Let's hope the trend reverses before that. I'm all for that, I just see no sign of it now.
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  14. 13.Gordon "obsessed" is the wrong word to use but the intention was to show that the recent trend seems to have overtaken the long term variability of the arctic in many peoples minds. And certainly in the discussion of arctic and AGW. I was looking further into this idea and came across the website of Igor Polyakov , an arctic researcher. He seems to have published plenty on the subject and his website has some interesting short, but detailed write-ups. There are some extraordinary lines on the website and in some of his publications such as this. "If long-term trends are accepted as a valid measure of climate change, then the SAT and ice data do not support the proposed polar amplification of global warming. Intrinsic arctic variability obscures long-term changes, limiting our ability to identify complex feedbacks in the arctic climate system." From GRL, VOL. 29, NO. 18, 1878, doi:10.1029/2001GL011111, 2002 I know nothing about this guy except that he doesn't seem to be a perpherial figure in the science.
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  15. http://www.gi.alaska.edu/~bhatt/publications/polyakovetal_2010.pdf A more upto date paper about trends versus natural ossilations in the north atlantic. The indroduction is worth reading just to get the sense of how the author seems to think there is still much to argue for on the subject.
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  16. HR, Polyakov has an interesting take on the Arctic, including this from his 2002 paper: " Extending our SAT time series by 25 years back to 1875 (years associated with an extended and cold negative LFO (phase) leads to a two-fold increase of the arctic trend compared with the Northern Hemispheric trend (Table 1,Figure 3). While this appears consistent with polar amplification, we believe it is more appropriately described as a statistical artefact resulting from biased sampling of the LFO." "In an analysis of long-term air temperature changes Vinnikov et al. [1980] used gridded northern-hemispheric SAT for 1891–1978, the first half of which was dominated by the negative, cold LFO phase prior to the 1920s, and the second by the positive, warm LFO phase of the 1930–40s. Averaging these data within zonal bands they also found a two-fold polar amplification of SAT trends (Table 1)." Of course much has happened in the Arctic since 2002.
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  17. HR, there is obviously a vast difference between PIOMAS predictions of minimum ice extent made months in advance and PIOMAS estimates of ice volume made after the fact. There is no evidence of significant discrepancy in those volume calculations. Indeed, they were very close to the measurements yielded by IceSat until it went offline... if anything they slightly UNDER-stated the decline in ice volume. Cryosat II data should be coming out some time in the next couple of months. From the available evidence it seems likely to me that data will be in close agreement with the PIOMAS results. Your citation of the Haas paper is interesting... as you cut it off right before; "However, the volume of older ice may have been less overall due to a lower areal coverage, and because our surveys were still spatially limited."
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  18. 16.Dappledwater My understanding is that both your quotes relate to the idea that due to the natural variability wherever you start and end your data set will determine the trend. It's a different way of saying we should look beyond the recent arctic ice trend to the bigger picture. 17.CBDunkerson "There is no evidence of significant discrepancy in those volume calculations." I've shown you evidence! While PIOMAS is in it's own death spiral in 2009 scientists have been out in planes with radars showing that the ice is slightly thicker than it was in 2009. Planes with radars I mentioned in the post there is no good spatial coverage of ice thickness in the arctic. To turn things around where is the evidence that the post-2007 drops in PIOMAS do match reality? I've genuinely looked for them and can't find them. The Haas paper is probably the best actual measure of arctic ice thickness post-2007. I agree Cryosat II will be a big step forward. It should be noted Haas and his radar are part of the consortium generating thickness data in order to calibrate the satellite.
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  19. HumanityRules at 09:43 AM on 27 August, 2010 There are some more post 2007 articles in Arctic ice, a reality check. I have a small amount of even more recent information, but will try to collate this. There are however multiple smaller scale studies for ice thickness, using all sorts of methods, but difficult to draw arctic wide conclusions as thickness and melt rate are not uniform over the sea ice area.
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  20. HumanityRules at 09:43 AM on 27 August, 2010 There is also an update (to April 2010) of the Maslanik and Fowler 2007 "age of ice" animation which these guys kindly did for me in the second article on Arctic sea ice. As older ice is generally thicker, this is pertinent.
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  21. HR @18 - that's not what those passages suggest, however who knows?, it's not discussed in the paper. Pete Hogarth - the multi year ice ain't what it's cracked up to be either
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  22. HR, ummm... yes, and I quoted the part of that 'scientists in planes' paper where they said the volume of older ice may have decreased. You're trying to use a small area study to advance a conclusion that the study itself contradicts based on insufficient data.
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  23. I realize that this is a basic post, but it makes no mention of ice area. Ice extent is a fundamentally flawed measure of ice because loose ice is subject to being moved around by wind and currents, and shows suppressed variability because thicker ice spreads out as the ice that restrains it disappears. The only reason it is used is because it has value for navigation, and hence a longer historical record. Ice area, on the other hand, tells you how much of the ocean surface is actually covered with ice, and so is a much better measure of the albedo and the potential feedback effects it implies. Extent tells you where there are chunks of ice floating around. Volume and area tell you how much ice there is and how much of the planet's surface it covers.
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  24. CBW, I think that NSIDC and other scientists prefer to use ice extent because the errors in measuring it are lower. The sensors have difficulty telling apart melt ponds on top of ice and open ocean so that adds to the error of area measurements. They prefer to use extent data dealing with the public because they are more sure of those numbers. see this link: http://nsidc.org/arcticseaicenews/faq.html#area_extent In any case, all of the measures of ice are going down. It is just a question of how fast they are going down. Once the new ice volume satellite comes on line that data will be much more useful. That should be sometime this fall.
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  25. CBW writes: The only reason it is used is because it has value for navigation, and hence a longer historical record. Yes, for most physical processes ice area is probably more relevant than ice extent. But estimates of ice extent tend to be more reliable than ice area, at least in the non-winter months. For those of us who are just casual observers and aren't using sea ice data in actual quantitative models, the main thing is just to be consistent. The folks over at WUWT have shown a tendency to shift back and forth among different data sets (extent, area, NSIDC, JAXA, CT, PIPS, etc.) depending on which one is more exciting to them at any given time. That's a recipe for self-deception, IMHO. Pick one metric that you like to track, and stick with it.
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  26. Oops, Michael Sweet beat me to it...
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  27. I agree that it is important to understand the strengths and limitations of whatever data set you are using. And any of the measures has the potential to mislead if the limitations are not understood. The issues in measuring area in times of surface melt are also strengths: if the area of surface melt is increasing, that tells you something. And melt ponds have a lower albedo than snow covered ice, so they are contributing to the feedback effect in the same way (if to a lesser extent) than open water. But extent doesn't account for open water until it reaches 85%, so it underestimates this effect. And since ice tends to spread out across the surface of water, extent is likely concealing the the degree to which the ice is depleted as solid ice thins and breaks up. But, as you say, any way you slice it, all three measures are in decline and this year will be no exception. Area and extent are headed for the second or third lowest of all time, and volume will almost certainly be the lowest ever.
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  28. Actually, based on PIOMAS, volume is ALREADY the lowest ever and has been since some time in the first half of August. The previous record (from last September) was 5,800 km^3, but if I'm reading the graphs right this year may hit 4,000 km^3.
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  29. Whenever sea ice in the Arctic is discussed, I see only one aspect of the ice sheet mentioned: the property of reflecting incoming heat, from the sun, back out into space. The albedo of ice and snow is certainly much higher than that of open, dark, water. But another aspect is that even a relatively thin ice sheet serves to keep the heat of the water locked in. How much heat is radiated from an open ocean surface at, say, 274 degrees Kelvin at night, compared to that from an ocean surface covered by arctic ice? I have no answer, but I would like to see the subject discussed. Maybe the increased radiation during the darker hours, compensates for the absorption of energy when the sun is up? It sounds, to me, like an important negative feedback. "Dark water absorbs more of this energy than white ice." Sure, but how much energy are we talking about here? The same amount of sunlight that hits a square meter, or slightly more, in the tropics, is spread out over more than five square meters at a latitude of 80 degrees north (or south). In addition to this dilution, the same sunlight also has to pass through five times as much atmosphere on its way down to the surface. Even less energy is thus left to possibly pass into the water. But then we have one more factor: much of (most of?) the radiation that hits the water at an angle of 10 degrees, is reflected like from a mirror. Those who lament the absence of ice in the Arctic seem to forget (or pretend to forget) that the amount of solar energy per area unit that actually passes into the Arctic ocean through the surface, is at most a few percent (my guess) of what passes into tropic oceans. So how important is this effect? I do not know, but I would certainly like to learn more from somebody who does.
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  30. Do the numbers on reduced albedo Argus (repeating what researchers have not forgotten to do) and you'll be treated to some staggeringly large figures. Increasing solar heating of the Arctic Ocean and adjacent seas, 1979-2005: Attribution and role in the ice-albedo feedback Follow the references in the paper above and you can see why it's fallacy to believe the people studying this are as naive as you imply. "I doubt it" sure becomes boringly repetitious after N+... iterations.
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  31. For those keeping track; Arctic sea ice extent is now at about 5.25 million km^2... placing it below several of the ARCUS predictions for this year and on track to likely wind up somewhere in the middle of the pack. That said, the ARCUS predictions are for the September average rather than the absolute minimum and thus the rate of re-freeze in the latter part of September will be a significant factor. Still, it seems clear that this year will have a lower extent (both absolute and September average) than 2009. It probably won't beat the 2008 (or 2007) minimums and thus will likely be the third lowest extent on record. As noted above, Arctic ice volume is already at a new record low and still dropping.
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  32. doug_bostrom, First, I think you ought to be more careful with how you quote people. Where did I say "I doubt it"? The answer is nowhere. You made it up, just as you invented the N+ iterations. And what is so "boringly repetitious"? I have never before raised these matters about arctic ice. Instead of answering at least one of my questions yourself, you claim that I am implying that "the people studying this" are naive. I have read through the report you recommended, and I cannot find that they adressed the function of heat radiation from a dark ocean anywhere at all. The only things they talked about were ice albedo and solar heat input. But where there is input there is also output, and it is obvious that a warm black body radiates a lot more than an icy white cold body. So most of my thoughts from #29 remain unanswered.
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  33. Argus dance around your words all you like but their meaning was fairly clear. You doubt what's reported, or perhaps more specifically you want to create an impression of doubt. "Dark water absorbs more of this energy than white ice." Sure, but how much energy are we talking about here? You go on to specify various parameters affecting absorption of solar energy in sea water at high latitudes. You "wonder" while projecting a rhetorical stance: Those who lament the absence of ice in the Arctic seem to forget (or pretend to forget) that the amount of solar energy per area unit that actually passes into the Arctic ocean through the surface, is at most a few percent (my guess) of what passes into tropic oceans. So how important is this effect? Duly answered. Nobody has forgotten the parameters you mention, but apparently you're not really interested in improved understanding, your mission or preferred perspective seems more about doubt. So in your next comment you focus on your earlier question about the difference in radiative properties of ice versus water: I have no answer, but I would like to see the subject discussed. Maybe the increased radiation during the darker hours, compensates for the absorption of energy when the sun is up? It sounds, to me, like an important negative feedback. You could have a stab at that question yourself, you could provide a constructive comment here with your result, but you appear to prefer leaving the question hanging in the air, conveying doubt. I'm done playing the game with you but here are clues to your answer: ice conducts heat about 4 times better than water, water and ice are similarly good radiators with water being a little better than ice with more emissivity particularly at longer wavelengths. Don't forget to extend your experiment into the atmosphere so as to get a net effect.
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  34. doug_bostrom, After a long series of insinuations and subjective guesswork on your side, about the real "meaning" of my words, you finally approach at least one of the topics I wanted to have a discussion around. That's good. But was all your arrogant language necessary? If I bring up facts not covered in the top post, does that imply that I "want to create an impression of doubt"? Would you thus like to exclude everyone who doesn't agree with you or the post author, from asking questions? Is it wrong to "wonder"? Do I also have to provide all the answers to be allowed to write comments? I certainly am "interested in improved understanding", why else would I bring up matters not discussed yet, and ask questions not answered yet? What is wrong with "leaving the question hanging in the air"? Again, do I have to have the answer as well, before I comment? And I still wonder why your revered Arctic report adresses only heat input, and not heat output.
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  35. From the main essay:
    As you might imagine, thick ice takes a lot more heat to melt, so the fact that it is disappearing so fast is of great concern.
    I just wanted to check... I presume the big reason for this would be that it is denser -- more compact as the air has been squeezed out of it. Another reason would be that through previous summer seasons the saltwater has been drained out of it -- as saltwater has a lower freezing temperature -- leaving rotten ice -- which with cycles of being compacted and drained each summer after perhaps two or three years will be pure enough that you can drink the melt water -- implying a higher freezing point.
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  36. Peter Hogarth, What an impressive video!!! It is like watching a dying beast gasping for breath, and flailing around to hang on to some life. Very emotional and unscientific, of course.
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  37. Timothy Chase, My guess is that the author means thick ice takes a lot more heat to melt - simply because it is thick. In other words, we are talking about the heat needed to melt ice per square meter (surface), not per cubic meter (volume). As for salt and saltwater in the ice, there is almost no salt in sea ice once it is frozen.
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  38. There is some updated information, consistent with the PIOMAS results in the article, on Arctic sea ice age from the NSIDC; "At the end of the summer 2010, under 15% of the ice remaining the Arctic was more than two years old, compared to 50 to 60% during the 1980s. There is virtually none of the oldest (at least five years old) ice remaining in the Arctic (less than 60,000 square kilometers [23,000 square miles] compared to 2 million square kilometers [722,000 square miles] during the 1980s)."
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  39. So, we'll see the final, really wild seasonal variations when/if that 1-2 year old ice is gone. What's interesting is that it's held fairly steady overall during the period shown, but was nearly obliterated in the famous '07 slice. I suppose that feature may show as an early harbinger once the data is extended, an early wiggle toward the final outcome. I must say, Serreze's prognostications look to be right on track.
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  40. If 2011 sees the summer development of the Arctic DiPole, strong possibility of open water at the pole by melt season's end. Had there been favorable weather in July it could have happened this year. Hope the pole cams float. Maslowski's looking pretty good, too. The Yooper
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  41. PIOMAS also updated... September 2010 average ice volume of 4,000 km^3. Which is way down from the previous record low of 5,800 km^3 in September 2009. Obviously if that rate continued the ice would all be gone within three years. Even the average rate over the past ten years has been -1000 km^3 per year, so four more years at that rate. So yeah, Maslowski's projection (2016 +/- 3 years to nearly ice free) is looking pretty good. Indeed, these numbers suggest it was conservative. However, NSIDC is still saying 20 to 30 years... presumably based on the extent trend, which is much less pronounced than the volume trend. We'll know within a couple of years which is going to be the ultimate determinant. My money is on volume. Doug, actually as I read the chart the 2+ year ice percentage increased slightly in 2007. The first sharp dip shown is for Sept 2008, then a smaller one for Sept 2009, and now a third even smaller dip for Sept 2010. This is consistent with ice volume having declined since 2007 while extent increased slightly. The fact that these are percentages also changes how we should look at them somewhat... 55% of the 4.3 September 2007 extent is still more than 15% of the 4.8 September 2010 extent, but not as much more as the percentages alone suggest.
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  42. CBD, I was looking at the bit of the graph where the 1-2YO (blue slice) ice nearly vanished; I think I didn't make myself clear. What I find striking is how nearly constant that constituent has been over the time span of the graph, only to go through the sharp drop in '07 leading to '08. Smacks of something changing a lot, quickly.
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  43. CBDunkerson, 2+ years old ice is the green area and it's still decreasing after 2007. What strikes me is the huge amount of >2 years ice that melted away this summer, continuing the decrease started in 2007. And, according to NSIDC, the oldest sea ice virtually disappeared.
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  44. CBD, thanks for the numbers update. That '07 'increase' probably reflects the winter levels transitioning from '06 to '07. We know what the summer of '07 did. For all practical purposes, the last chance of a 'recovery' ended that year. We are left with the prospect of being one bad (for the MultiYear ice) summer away from a late-summer/early-fall-navigable Arctic Ocean. With its attendant habitat loss for the walrus, seal and polar bear (the Arctic Fox is the poster-child for the forgotten species, but will probably endure best). Keep an eye on the MY ice advection out the Fram this winter. That, plus a strong dipole next year, will officially mark the dawn of a new era in international commerce...and species loss in the Arctic. As Doug & Riccardo delineate, the times they are a-changin'. Now. On our Watch. The Yooper
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  45. A "Johnny-come-lately" comment, but I really do dislike the PIOMAS graph in this article, almost as much as the NSIDC "percentage multi-year ice" graph posted above at #38. Neither graph allows the observer to assess the significance of these measurements of ice loss. The data used to make the PIOMAS anomaly graph shows summer 2010 volumes dropping below 4,000 km3 with an annual average loss running at 900 km3 over recent years. The NSIDC graph ignores the 30% reduction in summer ice extent. With the reducing extent factored onto the graph, the conclusion looks far more stark - 700,000 km2 of old ice with an annual drop of 300,000 km2 over recent years.
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