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Arctic sea ice discussions

Filed under: — group @ 20 July 2011

This is a thread to discuss issues related to the 2011 Arctic sea ice minimum. The following graphs will update every day:

JAXA Sea ice extent:



Cryosphere Today sea ice concentration:




298 Responses to “Arctic sea ice discussions”

  1. 1
    lawrence coleman says:

    Has anyone seen the uni-bremen arctic sea ice extent graph? Looks to me as though we are well on track to post another record september summer low. While the 2011 line was scraping the bottom as the lowest maximum on record it is now falling more rapidly than i have ever seen as you would expect with a rapidly warming arctic ocean under the fragile sea ice…if something miraculous doesn’t happen from now to september it looks very much as though we will smash the benchmark 2007 summer low.
    At this point i might remind you all that this is not happening in geological time..rather this disaster is happening on virtually a year by year basis. Very soon..we will have no more permament summer sea ice left and the winter ice sheet will have shrunk to a cataclysmic low. We shall see firsthand the vital importance the arctic icecap has on world climate..for all those remaining sceptics out there with their heads firmly wedged in the sand bucket of ignorance. Those graphs show to me that we have gone way beyond the tipping points regarning ice albedo..from now on and for at least the last 40 odd years we have created an environment juggernaut of unstoppable climate change that is not going to be reversable for many many centuries to come.

  2. 2
    pete best says:

    A question for everyone:

    Does/will Arctic summer ses ice melt then impact Greenland further, ie; if the summer sea ice melt accelerates (now on track possibly for a 2030-2040 Arctic summer sea being ice free. I know we have wide projections/predictions for sea level rise but 0.5-2 meters is quoted for end of the century total sea level rise but is 5 meters possible in 90 years as Hansen once tentatively suggested.

    50 cm a decade is 5 a year or 50 mm. Is it possible BAU ?

  3. 3

    Every ice reserve on the planet is decreasing. It is my simplistic contention that it is the melting of the ice reserves that is preventing runaway global warming. Sooner or later the energy sink which ice provides as it melts and sublimes will be inadequate to counter the solar input and both temperature and sea level will rapidly rise simultaneously. The only question is when this will occur.

    jadavison.wordpress.com

  4. 4
    wili says:

    Current temps are up 6-8 degrees C above normal and we are already at all time lows. Only a sudden change in conditions up there will keep us from hitting a new record. This is also being discussed over at Climate Progress, and in a rare mid-month post over at NSIDC.

    http://nsidc.org/arcticseaicenews/index.html

  5. 5
    Timothy says:

    #2 pete best

    Whilst the seasonal disappearance of Arctic sea ice would make some difference, I wouldn’t expect such a difference to be large. It’s worth reminding yourself, by looking at the NSIDC charts, that it has been usual for the sea ice around half of Greenland to disappear each year, even before the recent dramatic decline in summer Arctic sea ice extents.

    What might start to happen later in the century is that the sea-ice would retreat earlier in the season, allowing more sunlight to be absorbed by the oceans, and so more heat would be lost by the oceans in the Arctic autumn. One presumes that this could extend the melting season for Greenland, but it would also represent a relatively large source of water vapour, so perhaps more snow on the summit too.

    I know there are a lot of modelling efforts being made to look at Greenland, so hopefully there will be a lot more on this sort of thing in AR5.

  6. 6
    Hunt Janin says:

    Sorry to be so ignorant, but how much will it matter if the sea ice extent in 2011 turns out to be less than the 2007 low?

  7. 7
    Andy Revkin says:

    It’s important, while pondering a single year, to keep in mind long-term trends. There was a “regime change” in Arctic Ocean ice more than a decade ago that is still exerting an influence, as Ignatius Rigor and others have reported. More here:
    Thin Ice the Norm in Warming Arctic – http://nyti.ms/osf21G
    and here:
    http://dotearth.blogs.nytimes.com/2010/09/14/arctic-sea-ice-continues-its-summer-slide/

  8. 8
    Mark Serreze says:

    Some readers may also want to take a look at NSIDC’s Arctic Sea Ice News and Analysis” site (http://nsidc.org/arcticseaicenews/). We just posted a new piece discussing conditions through mid July. As we get towards the seasonal minimum in September, we be putting out discussion pieces on a two-week and then a weekly basis. Regarding the rapid decline in ice extent over the past few weeks, it appears that a key driver has been a strong anticyclone centered over the northern Beaufort Sea which tends to promote warm conditions and convergent ice motion. There are signs that that pattern is now starting to break down but we’ll have to wait and see. Furthermore, melt onset was quite early over much of the Arctic Ocean.

  9. 9

    Northeast passage is about to be open at any moment soon , a stunning world record, and I present on my blog, http://eh2r.blogspot.com/, wide open water North of Greenland, equally shocking.

  10. 10
    ian perrin says:

    James Hansen suggests that the portion of sea-level rise contributed by melting ice is non-linear and is best predicted by inspecting its doubling time. That he measures at 5 to 10 years. That in turn gives us a total rise of around 5m by the end of the century. But most of that comes in the last decade or two.

  11. 11
    observer says:

    James Hansen spoke from the 5 meters sea level rise only under two assumptions: We dont cut back our GHG emissions and do business as usual. This would lead to more than 600 ppm of CO2 till the end of the century. The second assumption is, that ice sheets are becoming instable and disintegrate, e.g. float faster into the oceans. If both assumptions would be true, it could be realistic that we would see such a drastic sea level rise. But if the ice sheets will become so instable is not clear at the moment, it is only a possibility. And it is also not clear, if we do business as usual. If we cut back our emissions, the sea level rise would logically be much smaller. So, the 5m is a possible worst-case scenario.

  12. 12
    arcticio says:

    Why is the overall knowledge, attention and interest about this region that low. Strangely enough same companies denying consequences of CO2 emissions prepare to get hands on the resources below a diminished ice pack.

    The Arctic presents climate change in fast forward mode every day: http://www.arctic.io/satellite

    Are we waiting for the moment the last million square miles 5cm thick disappear within one day? Who is blocking inevitable funding of Arctic research?

    What can we expect as weather on the northern hemisphere when the Arctic is ice free soon?

  13. 13
    simon evans says:

    @pete best

    2m of sea level rise by 2100 is usually considered the maximum plausible under any circumstances.

    See these links below, or indeed just search Realclimate for “sea level rise” and you’ll get the same answer.
    http://www.nature.com/climate/2010/1004/full/climate.2010.30.html
    http://www.youtube.com/watch?v=ybjg0ZN3jl0
    http://www.timesonline.co.uk/tol/news/environment/article6982299.ece
    http://www.endsreport.com/19501/sea-level-forecast-is-good-news-for-flood-planners

  14. 14
    Kevin Stanley says:

    I saw a graph recently, from Hansen I believe, of an exponential curve going to 5 meters of sea level rise by 2100. It had a slow take-off. The 50mm/year mark wouldn’t be crossed for several decades. But then, that last decade of this century would see @#$#^% INSANE rise. And assuming time doesn’t stop when the graph does, the beginning of the 2100s would see a coastline changing so fast you could practically sit at the shore and watch it advance. (that’s hyperbole, but it would be really really fast)

  15. 15
    Kevin Stanley says:

    @ Pete Best: If the rise is exponential through the rest of the century, with a slow take-off (as I believe Hansen envisioned), I believe it would be possible, but we wouldn’t see anything like 50mm/year for several decades. Near the end of the century, though, you’d practically be able to stand at the shore and watch it advance….

  16. 16
    Chris says:

    Is it just me or is there a bit of creep in the date of the lowest sea ice extent? Or is a better interpretation that the lower the minimum, the later the date of the minimum ice is?

  17. 17

    What’s the expert opinion on the graph that fits quadratic trendlines to the monthly PIOMAS data, which Neven posted back in April:
    http://neven1.typepad.com/blog/2011/05/piomas-april-2011.html
    It certainly seems a more plausible fit than the linear trends they always show on the official PIOMAS charts. But did anyone test the fit properly, and if so, do the extrapolation of these lines over the next few years have any credibility?

  18. 18
    Nick Barnes says:

    I’m an amateur in this area – my only experience is closely watching the ice over the last 5 or 6 melt seasons. I am guardedly optimistic about this year, because of the condition of the sea-ice in the central arctic, as shown on MODIS. I expect the melt rate to reduce markedly in the next few weeks, and the September minimum extent to be somewhere around that of 2008.

  19. 19
    Lou Grinzo says:

    Like most people here, I’m watching the ice situation at both poles plus Greenland with more than passing interest. Aside from the obvious warming/feedback implication, I’m interested in what the public reaction will be to hitting zero ice, even briefly, during the summer. I would like to think that it would be such a dramatic event, one that would garner so much media attention, that it would have a profound effect on the public, much as the famous photo of Earth from one of the pre-landing Apollo missions supposedly did. (And yes, today is the anniversary of Neil and Buzz strolling on the moon, while Michael took an extended joy ride.)

    Which brings me to the issue of when we might see that ice-free period. Over on Neven’s Arctic Sea Ice Blog, he posted a graph in May (http://neven1.typepad.com/blog/2011/05/piomas-april-2011.html) in which someone did a quadratic projection of the trends for each month. Just eyeballing it, the quad. approach seems to fit the existing data very well. The problem is that it yields a projection of August, September, and October being ice free in 2018. I would love to hear someone explain what’s wrong with this picture, as even those three months being essentially ice free by 2030 or 2040 is alarming. (If nothing else, I would expect to see the trend lines flatten out as the thicker ice, while still declining, will constitute a higher percentage of the total ice. That should slow down the progression somewhat, shouldn’t it?)

    Everyone here: Please feel free to use my newly reworked graphs page (http://www.grinzo.com/energy/graphs.html) which includes links to numerous energy, climate, and weather graphics. Suggestions for improvements are welcome, of course.

  20. 20
    Pierre Allemand says:

    I am surprised to note that almost all the comments are concentrated on the sea level rise more or less tied to the arctic ice extend. Can I just remind everybody that sea level is absolutely not concerned by this extend. The level of your glass does not change when the ice cube floating at the surface melts.

    [Response: Actually that isn't quite true for Arctic sea ice, the reason being that sea ice is relatively fresh (~5 psu) and it is floating on salty sea water (~34 psu). That means that the volume of water of the ice melt is slightly greater than the volume of sea water displaced, and so that when the ice melts, it does raise sea level slightly. This isn't an important factor in global sea level rise, but it's best to be accurate in these things. - gavin]

  21. 21
    Hunt Janin says:

    Could sea ice possibly be a black swan situation?

  22. 22
    todd arbetter says:

    @Chris:

    The main driver in the actual date of minimum ice extent is weather. The ice in September even in the old days was less compact than in winter. If you have wind blowing one way, it could push the ice together and lower the ice extent. If it blows another way, the ice spreads apart, increasing ice extent. The ice area (the area of water covered by ice, not including the open water) is the same, but the extent varies, at least in this thought experiment.

    It happens that the last two years, there has been an early freeze-up (1st or 2nd week of September) where the ice extent starts increasing. But this was followed by another short warm period where the ice started melting again and went below the first value in early September. This is why, for climate, it’s more important to look at the monthly average than the day-to-day values.

    The National Ice Center (NIC) in Washington DC is the government agency responsible for monitoring sea ice conditions, and they release a projection every June 1 predicting the opening and closing dates for the shipping channel between Barrow and Prudhoe Bay, Alaska, as well as tabulating past dates since the 1950s. If you look at the dates of opening, they are trending earlier. But the dates of closing are not getting later, and they can vary by 2-3 weeks from one year to the next. That suggests the opening is more determined by the state of the climate and the closing is more determined by the weather.

  23. 23
    Patrick 027 says:

    Re 3 John A. Davison – It’s great to realize that there is a latent heat of melting, but quantifying it, it’s not so large an energy sink. A period of rapid melt would reduce or concievably could temporarily reverse global warming, but I don’t think that’s happenned yet.

    These might not be the correct proportions to consider but for what it’s worth:

    3 K warming * 3000 m (rounded up from memory of what ocean depth would be if spread out over global area) * 1000 kg/m3 * ~ 4.2 kJ/(kg*K) ~=
    38 GJ/m2

    10 m sea level rise from melting * 0.7 (fraction of globe that is ocean) *
    1000 kg/m3 * 334 kJ/kg (latent heat) ~=
    2.34 GJ/m2

    Of course it may take ~ 1000 years to get the deep oceans ‘up to speed’, but there is also an equilibration delay in the ice sheets. But graphs I’ve seen of warming thus far show most additional heat going into the ocean (aside from melting ice, there’s also air heat capacity, latent heat of increasing atmopsheric water vapor, and heating of the land surface and crust (the effective depth which is affected at relevant time scale, which isn’t much).

  24. 24
    Patrick 027 says:

    “could temporarily reverse global warming”
    in terms of temperature, not heat

  25. 25
    Nagraj Adve says:

    What are the implications of an ice free Arctic in summer, for weather in the northern hemisphere and South Asia in particular?
    Could anyone suggest any reliable studies about this?
    Nagraj
    New Delhi

  26. 26
    Septic Matthew says:

    Isn’t this close to the trend line over the last 30 years, and isn’t that trend line almost perfectly linear, lacking any quadratic or higher order polynomial? It’s threatening enough if it continues a linear decline.

  27. 27
    mps says:

    While the minimum this year may end up being very low, it is worth noticing that in the IJIS data, the ranking of a year in July doesn’t seem to be a very good predictor of where it will bottom out in September. I would urge some caution before assuming that this will be a record/near record year. It would be nice to repeat this thread in September.

  28. 28
    Neven says:

    Regarding the rapid decline in ice extent over the past few weeks, it appears that a key driver has been a strong anticyclone centered over the northern Beaufort Sea which tends to promote warm conditions and convergent ice motion. There are signs that that pattern is now starting to break down but we’ll have to wait and see.

    I concur with Dr. Serreze here. Things were pretty stable and conducive to extent decrease so far, but the weather has been changing the last few days and will continue to do so. It’s not clear yet what the effect on extent decrease will be, but I’m pretty sure there will be a slowdown at first (which we have been witnessing since yesterday actually).

    I write regular updates on what’s been happening and what might happen in the short term on the Arctic Sea Ice blog, and some other stuff like animations and comparisons between this year’s melt and that of previous years. Most of the interesting stuff is in the comment sections though.

    I’m pretty confident this year’s minimum will come in lower than last year’s, but it’s too early to tell if there will be a new record. And to look a bit further ahead, it will also be interesting to see after the minimum has occurred, if we get a third NH weird winter in a row.

  29. 29

    Nick, #18

    “I am guardedly optimistic about this year,” No such “ice is getting better” thing is happening:”

    http://psc.apl.washington.edu/wordpress/wp-content/uploads/schweiger/ice_volume/BPIOMASIceVolumeAnomalyCurrentV2.png?%3C?php%20echo%20time()%20?

    volume dropping seems in free fall. You have to incorporate volume in your mental calculations.

  30. 30
    Stacey says:

    How many millions of tonnes of shipping have passed through the navigable waters of the north east and north west passges without ice breakers?

  31. 31
    dhogaza says:

    Pierre:

    I am surprised to note that almost all the comments are concentrated on the sea level rise more or less tied to the arctic ice extend.

    No, they aren’t.

    Someone asked “Does/will Arctic summer ses ice melt then impact Greenland further”, i.e. the Greenland Ice Sheet, which is on land.

    Then people started talking about possible increases in the rate of sea level rise, *in the context* of the question raised about the Greenland Ice Sheet.

    I suppose everyone could make absolutely clear whether they’re talking about sea or land ice in each post, but the average poster here is knowledgable enough that the implicit context is clear.

  32. 32
    BillS says:

    At least as important as sea ice extent are (1) the dates of minimum and maximum extent within a particular basin and (2) the type of ice that makes up a given year’s sea ice. The steady decline in the amount of multi-year ice in most, if not all, basins may be of greater long-term importance than any given years’ variations of extent.

    Regarding P. Best’s #2, there is growing evidence that the stability of Greenland’s tidewater glaciers (basically those that end in fjords) is related to the water column temperatures at the glacier/ocean interface. Many, if not most, of Greenland’s glaciers’ grounding lines are well below sea level. If a warming ocean can eat away at a glacier’s terminus, it will retreat inland into the ice sheet followed by the ocean.

    It’s a thorny problem.

  33. 33
    dhogaza says:

    septic matthew:

    Isn’t this close to the trend line over the last 30 years, and isn’t that trend line almost perfectly linear, lacking any quadratic or higher order polynomial? It’s threatening enough if it continues a linear decline.

    Here’s a post by Tamino made shortly after the NSDIC data for September 2010 was made available, using a quadratic fit. It captures the annual variance within its 95% confidence intervals except for one year which barely lay outside that range.

    He extrapolated that to come up with a prediction for the 2011 minima (using JAXA) of 4.63 +/- 0.9 million km^2. Admittedly a wide range but it’s looking pretty good for a prediction made 11 months before the upcoming minima.

    Check out the post, it’s good …

  34. 34
    R. Gates says:

    Here’s a couple of thoughts on this years melt:

    It will obviously be a race to see if 2011 can beat 2007 for the lowest summer minimum on modern satellite record…a lot of course depends more on weather. Especially of interest will be to see if a sustained dipole anomaly will set up going into August and how much this impacts ice export through the Fram strait and bringing some warmer late summer meridional winds across the arctic.

    But more to the point in comparison between 2011 and 2007: Ice extent is probably not the best metric to compare these two years, for even if 2011 nudges 2007 out of “lowest extent on record” or comes in slightly higher, 2011 still easily blows away every other year for the lowest sea ice volume on record. Simply put, there’s just a whole lot less sea ice than any other year on modern record. The variability of the weather will determine the final extent for this year, but the long-term trend of sea ice is clearly continuing to spiral down, and despite the pronouncements of some skeptics about a “recovery”, the Arctic continues strongly on target to become ice free, or virtually so, in the next few decades.

  35. 35
    SecularAnimist says:

    So, is there any plausible case where the following is NOT going to happen during this century:

    1. Rapidly warming arctic melts the sea ice.

    2. Melting sea ice exposes more and more open ocean.

    3. Open ocean absorbs more solar energy, thereby accelerating the warming and the melting, and exposing more open ocean, which absorbs even more solar energy.

    4. Steps 1-3 continue until Arctic warms sufficiently to thaw permafrost/tundra and to destabilize underwater clathrates, thereby releasing vast amounts of methane.

    5. Game over; PETM extinction looks like a picnic by comparison.

  36. 36
  37. 37
    Kevin Stanley says:

    re: #27 mps “in the IJIS data, the ranking of a year in July doesn’t seem to be a very good predictor of where it will bottom out in September.”

    I played with the IJIS data a bit, and while this also probably isn’t a great predictor, I found it entertaining:
    I took the daily changes in extent for 7/20 through 9/30 for each year from 2003 to 2010, and grafted them onto the 2011 data up to 7/19. So basically I had the answer to the question “if the same amount of ice extent is lost from this date forward as was lost in 20XX (where XX is 03-10), what would the minimum be?”

    The range I got was from a high value of 5,017,813 km2 (equivalent losses for the rest of the season to the corresponding period in 2006) to a low of 3,650,782 km2 (corresponding to losses from this date forward in 2008). Data from half the years (’04,’07,’08,’10) led to a new record minimum, data from the other four didn’t (’03, ’05, ’06 , ’09). The average of all 8 was very close to the IJIS minimum extent: 4,264,785 km2.

    Scientific? Hell no. But I found it interesting as just a rough indication of what the minimum would look like if the melt season progressed from here as recent seasons have–which it probably won’t, of course…thinner ice, earlier melt onset, so much more solar energy from those clear skies and dark waters of the last few weeks…and who knows what the weather might do….

  38. 38

    #30 Stacey

    “How many millions of tonnes of shipping have passed through the navigable waters of the north east and north west passges without ice breakers?”

    In the lore of Arctic shipping, all good captains past and present day, fear ice, so much so that the NW passage was sketched as the equivalent as death for sailors. Hence proving that the passage was never open as now a days. It is a matter of a shipping company to dissuade their good captains that the ice is gone.

  39. 39
    Lennart van der Linde says:

    Hansen and Sato argue in their latest draft paper (p.22 and on) that rapid melting of Arctic sea ice due to BAU emissions will probably cause acceleration and even disintegration of (vulnerable parts of) the Greenland and West-Antarctic ice sheets during this century:

    http://arxiv.org/ftp/arxiv/papers/1105/1105.0968.pdf

    Assuming a doubling time in melt rate of 10 years this could cause about 5 meters of sea level rise by 2100. In the last few decades of this century that would mean more than 1 and even 2 meters of sea level rise per decade.

    However, they also argue that the many and massive resulting icebergs would cause a negative feedback by cooling the ocean surface that would limit the maximum melt rate to maybe 1 meter per decade (that estimate is from their first draft; it’s not in the second). So that would maybe limit maximum sea level rise by 2100 to around 4 meters?

    After 2100 ice would keep melting and sea level rising for many centuries. If Hansen and Sato are correct in their estimate of 1 meter/decade as the maximum rate of SLR, then 14 meters of SLR in 2200 and 70 meters before the end of the millennium would be the current worst-case scenario as far as SLR is concerned.

  40. 40
    Septic Matthew says:

    33, dhogaza

    thank you

  41. 41
    PeterM says:

    Hansen said earlier this year, that temperatures as they are now, just slightly above the warmest part of the Holocene, Ice sheets become ‘unstable’. Considering we are now at the warmest part of the Holocene- and ice melt in the arctic seems to be accelerating – he is right. If we reach the lows of 2007, odds are that by 2020, we will see half of what we have this year or 2007.

  42. 42
    Hank Roberts says:

    > 30 … how many ….?

    You can start counting with this one:
    http://www.alaskadispatch.com/article/first-commercial-ship-sails-through-northwest-passage
    Sep 07, 2010

  43. 43
    Lynn Vincentnathan says:

    Sorry for being OT, but a claim came up on a blog recently — does the U.S. federal government spend $4billion per year on global warming studies? And if so, what can we compare that with……like how much it spends on the space program or wars.

  44. 44
  45. 45
    L Hamilton says:

    An alternative to linear or quadratic representations of the trend in Arctic sea ice is the asymmetrical S-shaped Gompertz curve, applied to ice extent here,
    http://neven1.typepad.com/blog/2011/04/trends-in-arctic-sea-ice-extent.html
    (2011 Sep mean prediction 4.4m km^2)
    and to ice area and volume here,
    http://neven1.typepad.com/blog/2011/04/trends-in-arctic-sea-ice-volume.html
    (volume looks like it’s crashing soon).
    Chris Randles and I have both contributed Gompertz-based guesses to the July SEARCH Sea Ice Outlook.
    http://www.arcus.org/search/seaiceoutlook/2011/july

    Although Gompertz curves are just as unphysical and naive as linear or quadratic models, they offer several appealing features:
    - fit the recent steepening decline better than linear
    - fit the gradual 1970s-1980s decline better than linear or quadratic
    - imply a rapid but ultimately asymptotic approach to zero ice.

    How well our 4.4 predictions compare with this year’s reality, or with more sophisticated models in the SEARCH SIO, we’ll see in a few months.

  46. 46
    Chris R says:

    Some context: Mid July and the ice area is typical of what could be expected for the September minimum in the 1980s.

    #35 Secular Animist,
    Add in the speed of warming of the ocean, and the speed of warming of the sea bottom sediments and we may find the clathrate issue is more ‘chronic’ than ‘catastrophic’.
    http://geosci.uchicago.edu/~archer/reprints/archer.2007.hydrate_rev.pdf
    Archer “Methane hydrate stability and anthropogenic climate change”, Biogeosciences, 2007.

    I’m not saying it’s not a problem, just disagreeing on the sort of problem it looks likely to be.

  47. 47
    Ed Davies says:

    Sort of preceding Steve Easterbrook’s question (#17) about quadratic fits to PIOMAS, I’d like to ask how much confidence it’s right to have in the PIOMAS data in the first place? As I understand it it’s essentially a model which is tweaked using the available observations. What I have no idea about is how good is that tweaking at keeping the results real.

  48. 48
    tamino says:

    I’ve posted an update to my prediction for the 2011 minimum sea ice extent.

  49. 49
    w kensit says:

    A simple soul, I cannot understand why anyone pays any attention to the sea ice extent. Counting ice-cubes/ square Km must be the least scientific measure, to the point of uselessness, of any climate warming measure. Sure, at one time it was all we had, but with the advent of satellite volume measure it’s time to relegate it to science’s trashcan.
    Danmarks Meteorologoische shows arctic warming returning to the 50 yr average since May while Washington U’s ice volume measure continues to plunge without hesitation. Perhaps the Arctic has reached the point where weather anomolies will have no effect upon the overall trends.

    [Response: The DMI temperature data is a model simulation that is being compared to another model simulation (ERA 40) and with no bias correction related to different models or input data series over time. As is, even trends within a single reanalysis are suspect, thinking that that the comparison of two re-analyses run over different time periods with different models is credible, is the height of foolishness. - gavin]

  50. 50
    Nick Barnes says:

    wayne #29,

    No such “ice is getting better” thing is happening

    I didn’t say the ice is getting better. Certainly we are going to see very low ice this year, and worse in years to come. As for PIOMAS, I am discounting it entirely because the volume numbers suggest a much larger departure in the last couple of years, compared to the previous decade, than I think we are seeing. I’m eager to see live, detailed, calibrated, Cryosat data come online. I agree that if PIOMAS is accurate, we will certainly see a dramatic new record set this year. But if the ice had been as thin as PIOMAS suggested then the solsticial clear skies this year would have left the central arctic basin in tatters. Look at a recent MODIS shot of the central arctic, like this one from yesterday:

    http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r04c03.2011200.terra.1km

    100% concentration, no significant leads. Compare to this, the same area on the same date last year:

    http://rapidfire.sci.gsfc.nasa.gov/imagery/subsets/?subset=Arctic_r04c03.2010200.terra.1km

    My sense that this year’s melt is going to bottom out at maybe 4.7 or 4.8 (Mkm^2 IJIS extent) is based largely on looking at pictures like that.


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