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Sea ice minimum forecasts

Filed under: — gavin @ 17 July 2009

One of the interesting things about being a scientist is seeing how unexpected observations can galvanize the community into looking at a problem in a different way than before. A good example of this is the unexpectedly low Arctic sea ice minimum in 2007 and the near-repeat in 2008. What was unexpected was not the long term decline of summer ice (this has long been a robust prediction), but the size of 2007 and 2008 decreases which were much larger than any model had hinted at. This model-data mismatch raises a number of obvious questions – were the data reliable? are the models missing some key physics? is the comparison being done appropriately? – and some less obvious ones – to what extent is the summer sea ice minimum even predictable? what is the role of pre-conditioning from the previous year vs. the stochastic nature of the weather patterns in any particular summer?

The concentration of polar expertise on the last couple of questions has increased enormously in the last couple of years, and the summer minimum of 2009 will be a good test of some of the ideas that are being discussed. The point is that whether 2009 is or is not a record-setting or near-record setting minimum, the science behind what happens is going to be a lot more interesting than the September headline.

In the wake of the 2007 minimum, a lot of energy went in to discussing what this meant for 2008. Had the Arctic moved into a different regime where such minima would become normal or was this an outlier caused by exceptional weather patterns? Actually this is a bit of false dichotomy since they aren’t exclusive. Exceptional patterns of winds are always going to be the proximate cause of any extreme ice extent, but the regime provides a background upon which those patterns act. For instance, in the paper by Nghiem et al, they showed the influence of wind patterns in moving a lot of thick ice out of the Arctic in early 2007, but also showed that similar patterns had not had the same impact in other years with higher background amounts of ice.

This ‘background’ influence implies that there might indeed be the possibility of forecasting the sea ice minimum a few months ahead of time. And anytime there is the potential to make and test predictions in seasonal forecasting, scientists usually jump at the chance. So it proved for 2008.

Some forecasting efforts were organised through the SEARCH group of polar researchers, and I am aware of at least two informal betting pools that were set up. Another group of forecasts can be found from the Arctic ice forecasting center at the University of Colorado. I personally don’t think that the intrinsic worth of a successful prediction of overall sea ice extent or area is that societally relevant – interest in open shipping lanes that might be commercially important need much more fine-grained information for instance – but I think the predictions are interesting for improving understanding of Arctic processes themselves (and hopefully that improved understanding will eventually feed into the models and provide better tests and targets for their simulations).

What was particularly interesting about last years forecasts was the vast range of forecasting strategies. Some were just expert guestimates, some people used linear regression on past data, some were simply based on persistence, or persistence of the trend. In more mature forecasting endeavours, the methods tend to be more clustered around one or two proven strategies, but in this case the background work is still underway.

Estimates made in June 2008 for the September minimum extent showed a wide range – from around 2.9 to 5.6 M km2. One of the lowest estimates assumed that the key criteria was the survivability of first year ice. If one took that to be a fixed percentage based on past behaviour, then because there was so much first year ice around in early 2008, the minimum would be very low (see also Drobot et al, 2008). This turned out not to be a great approach – much more first year ice survived than was predicted by this method. The key difference was the much greater amount of first year ice there was near the pole. Some of the higher values assumed a simple reversion to trend (i.e. extrapolation forward from the long-term trend to 2008).

Only a couple of the forecasts used physics-based models to make the prediction (for instance, Zhang et al, 2008). This is somewhat surprising until one realises how much work is needed to do this properly. You need real time data to initialise the models, you need to do multiple realisations to average over any sensitivity to the weather, and even then you might not get a range of values that was tight enough to provide useful information.

So how did people do? The actual 2008 September minimum was 4.7 M km2, which was close to the median of the June forecasts (4.4 M km2) – and remember that the 2007 minimum was 4.3 M km2. However, the spread was quite wide. The best estimates used both numerical models and statistical predictors (for instance the amount of ice thicker than 1m). But have these approaches matured this time around?

In this year’s June outlook, there is significantly more clustering around the median, and a smaller spread (3.2 to 5.0 M km2) than last year. As with last year, the lowest forecast is based on a low survivability criteria for first year ice and I expect that this (as with last year) will not pan out – things have changed too much for previous decades’ statistical fits on this metric to be applicable. However, the group with the low forecast have put in a ‘less aggressive’ forecast (4.7 M km2) which is right at the median. That would be equal to last year’s minimum, but not a new record. It would still be well below the sea ice trend expected by the IPCC AR4 models (Stroeve et al, 2008).

There is an obvious excitement related to how this will pan out, but it’s important that the thrill of getting a prediction right doesn’t translate into actually wanting the situation to get worse. Arctic ice cover is not just a number, but rather a metric of a profound and disruptive change in an important ecosystem and element of the climate. While it doesn’t look at all likely, the best outcome would be for all the estimates to be too low.

858 Responses to “Sea ice minimum forecasts”

  1. 651
    manacker says:

    [edit]

    [Response: Basta. From now on, all posts simply repeating points made a dozen times before get deleted. – gavin]

  2. 652

    Barton asks, rhetorically, in response to manacker: “Nobody’s ever observed that. . . melting bright ice leaves dark land under it?”

    Well, the albedo observations have been quite a bit more detailed than that. I cited this paper upthread, but M obviously didn’t realize that this was an instance of the “empirical observations” that he thinks don’t exist.

    Hanesiak et al, 2001:

    http://www.agu.org/pubs/crossref/2001/1999JC000068.shtml (abstract)
    http://www.umanitoba.ca/ceos/files/publications_pdf/042.pdf (pdf)

  3. 653
    manacker says:

    Barton Paul Levenson (650)

    Atmospheric water vapor content and temperature do, indeed, correlate to some extent. But it would be foolish to assume that relative humidity will remain constant with increased temperature. (Minschwaner + Dessler have shown based on observations in the tropics that RH actually decreases with warming).

    Surface albedo depends on a lot more than just Arctic sea ice extent. There is also Antarctic sea ice extent (growing) and northern hemisphere snow cover (no change since the 1980s). I do not question the premise that snow cover and sea ice should theoretically shrink with a warming planet, but the empirical data so far have not demonstrated much change in overall surface albedo to date.

    As to the solar impact on 20th century warming, there have been several studies by solar experts, which have concluded that roughly half of the observed 20th century warming can be attributed to the unusually high level of solar activity (highest in several thousand years). These studies have concluded that the solar impact on early 20th century warming was greater than on the warming which occurred after 1970, but the overall average for the entire century was around half of the warming or 0.35C

    If you would like the reference to these studies so you can check them yourself, please let me know.

    Max

  4. 654
    manacker says:

    Gavin,

    A question:

    When someone repeats the “accepted consensus opinion” on AGW, will you also censor this out as repetitive?

    Max

    [Response: If all they do is repeat the same thing over and again, yes (and I do). The point of these threads is not to keep repeating the same thing until everyone gets bored and goes home. Either contribute to a discussion – which actually involves engaging in points that others make – or go somewhere else where they don’t care. Dozens of people have engaged with you, so reciprocate. – gavin]

  5. 655

    #604 Rod B… Yes Hadley has a problem, as their ice animation projection errs so is their GT calculations (to measure or calculate melt). Hadley apparently does not incorporate a great chunk Arctic temperatures which appears to warm the most. The very area where the melt is occurring, their GT’s are not true GT’s like GISS or NOAA but rather GT-(arctic area) and are valid for a great swat of the world… If they get their ice extent projections right they might reconsider or discover more model algorithm related errors.

  6. 656
    Larry N says:

    They finally uploaded the last week worth of images from the nort pole webcam (currently around 86 degrees north 2 west).

    I no longer see any melt ponds (or very few) compared to last year. The camera has tipped over on its side however. Has the melt ponds drained?

    North Pole webcam

  7. 657
    CTG says:

    Re 654 Max

    We all know that you and BobFJ are desperately trying to earn the “Banned from RealClimate” badge, so that you can go whine to your friends about how nasty the scientists are. Diddums.

    This is probably why you have lately dropped all pretence of real arguments, and resorted to flame-bait material such as “it has been cooling since 2001”.

    Come on, at least make it interesting and pretend to have a real argument. Tell us why Arctic ice melting faster than ever before is really a sign of global cooling, or something like that. Go on, please?

  8. 658

    BobFJ @ 613:

    There is no question that Ray Pierrehumbert (a highly respected professor of climate science here) agrees something along the lines of what Max says. In fact he refers to and discusses“a pause in warming“, and the debate is not about whether there is a pause, but what is causing it. Notice too, in the title: “Warming, interrupted”

    (please ignore the discussions of authorship since that’s in question …)

    As an aside, the only people who’ve gotten climate predictions correct since 1998 or so are people who know what “The Gore Minimum” means. If someone is out there taking money, I’ll put mine on 2010 having more summer ice than 2007.

    More on-topic, the fact that 2007 was a record for a minimum on a trend line where the minimum is declining about 50,000 km^2 / yr is far less interesting than noticing that no one is freaking out that there was surplus ice in 1996. What “previously not understood” physics is responsible for what appears to be an atypical recovery?

  9. 659
    Brian Dodge says:

    I have some questions that perhaps someone reading this can model/answer. I’m a native of Daytona Beach, FL, and there is a weather phenomenon that occurs at the beach during periods of clear sky and calm winds as frequently occur when a high is over the area. During the day, the land heat faster than the ocean; this creates updrafts inland, and cooler, denser, moist air flows inland from the ocean, where its heated by the warmer land, rises, often creates afternoon thunderstorms, creating a localized “Hadley” convection cell. At night, the land cools faster (once the clouds have dissipated) and the circulation reverses. This has the side effect of blowing mosquitoes and no-see-ums to the beach at night from freshwater swamps near the coast.

    Will the presence of open water now occurring in the arctic create relatively stable offshore winds in the fall and early winter before freeze up – a seasonal rather than daily sea breeze? Could the winds drive offshore surface currents and upwelling of relatively warmer deep water, making the process self sustaining? Might there be enough energy transport to create offshore precipitation & latent heat release, and onshore/inland downwelling of dry air & no snow? Can we name these seasonal cells “Dodge cells”? &:>)

  10. 660
    Hank Roberts says:

    > If you would like the reference to these studies so you can check
    > them yourself, please let me know.

    Yes, post the cites, and the page of the second- or third-hand website where you’re reading this spin, since you’re not quoting from the primary source.

    You know you’re posting a distortion of the research, each time you do this. You persist in repeating twisted and bent notions and claiming they’re facts.

    Do it again, as long as Gavin lets you.

  11. 661
    Hank Roberts says:

    Melt ponds are visible. Where are you looking?
    There are a handful of days in August, the camera’s been erratic.
    http://www.arctic.noaa.gov/npole/index.php?year=2009

    When they’re backlit they reflect; otherwise they look dark.

    http://www.arctic.noaa.gov/npole/2009/images/tmp/noaa1-2009-0805-051110.jpg.tmp
    http://www.arctic.noaa.gov/npole/2009/images/tmp/noaa1-2009-0802-041020.jpg.tmp

  12. 662
    Hank Roberts says:

    Paste Manacker’s first 3 lines above into Google, that turns up him going on at great length here on the same stuff he’s paraphrasing above:

    most recently here:
    wattsupwiththat.com/2008/08/21/rueters-world-meteorological-organization-says-this-year-so-far-coolest-for-at-least-5-years/

    and here:
    http://ccgi.newbery1.plus.com/blog/?p=63&cp=9#comment-2224

    But it’s the same nonsense as he’s been posting before, over and over
    — cooling, negative cloud feedback, IPCC must revise, blahblahblah.

    It’s like seeing someone with a peculiar talent in archery, can hit from anywhere downrange at worst to perhaps the outside ring of the target at best, but never, ever, ever near the bullseye. Dancing around and around.

  13. 663

    Data out of context is just as bad as thoughts out of context. Your thoughts are misleading you because you don’t have enough context, STILL.

    You state M+D have shown RH decreases with warming, IN THE TROPICS. When discussing global climate it is IMPORTANT to look at the ENTIRE PLANET (not cherry pick unless you have relevant context (and you don’t)). And still, last I heard, RH is hanging in around 80% while the planet is warming and we are getting more moisture in the atmosphere as expected as oceans increase in temperature.

    As to your comment regarding surface albedo that “empirical data so far have not demonstrated much change”. You don’t understand Arctic (polar) amplification effect.

    http://www.arctic.noaa.gov/essay_serreze.html
    https://www.realclimate.org/index.php/archives/2006/01/polar-amplification/

    As to solar attributing to half the warming: if you have the cites please provide them when you make the statement. Things go faster that way. Yes, please provide the cites and links to the papers if available.

  14. 664
    Phil. Felton says:

    Re #656

    Larry N says:
    8 August 2009 at 10:10 AM
    They finally uploaded the last week worth of images from the nort pole webcam (currently around 86 degrees north 2 west).

    I no longer see any melt ponds (or very few) compared to last year. The camera has tipped over on its side however. Has the melt ponds drained?

    That’s my interpretation, the ice has got very thin there if you look at the associated data from the station, I wonder if it will make the Fram strait, they usually recover the camera in October, I think they’ll need a ship this time.

  15. 665
    Jim Bouldin says:

    CTG says (657)”This is probably why you have lately dropped all pretence of real arguments, and resorted to flame-bait material

    He dropped all such pretense as soon as he showed up here, with his assertions (wait no they were proofs–he used actual numbers and math as I recall) about the maximum possible levels of atmospheric CO2 (there is NO carbon in the ocean or terrestrial biosphere to feedback on fossil fuel additions), and about how we can burn all fossil fuels with very little temperature increase, because even at 700-1000 ppm there’s negligible temperature sensitivity.

    The guy’s a major league troll. He has no desire to learn anything here, it’s obvious. As with all trolls, best policy is to ignore after a couple honest attempts to help. He’s gotten way more than a couple.

  16. 666

    My #660 is of course to manacker #653

  17. 667
    Hank Roberts says:

    Decline in Arctic sea ice thickness from submarine and ICESat records: 1958–2008
    http://www.agu.org/pubs/crossref/2009/2009GL039035.shtml

    R. Kwok, D. A. Rothrock

    The decline of sea ice thickness in the Arctic Ocean …
    … a much stronger and richer data set. Within the data release area (DRA) of declassified submarine sonar measurements (covering ∼38% of the Arctic Ocean), the overall mean winter thickness of 3.64 m in 1980 can be compared to a 1.89 m mean during the last winter of the ICESat record—an astonishing decrease of 1.75 m in thickness. … Prior to 1997, ice extent in the DRA was >90% during the summer minimum. This can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to <55% during the record setting minimum in 2007. This combined analysis shows a long-term trend of sea ice thinning over submarine and ICESat records that span five decades.

    published 6 August 2009.

    Citation: Kwok, R., and D. A. Rothrock (2009), Decline in Arctic sea ice thickness from submarine and ICESat records: 1958–2008, Geophys. Res. Lett., 36, L15501, doi:10.1029/2009GL039035.

  18. 668
    Doug Bostrom says:

    Hank Roberts 8 August 2009 at 12:56 AM

    “When some guy is posting bad information, make sure the guy’s name or pseudonym is posted along with the refutation, each time, and point to good information that people can read for themselves to see that he’s wrong.

    Answer them all, and let Google sort them out.”

    More meta-discussion!

    Yes, the “body of literature” is useful indeed. In manacker’s case, a search on Max Anacker or manacker reveals a remarkable history, a puzzling picture. On some sites he presents as a raving loon, yelling about scientific conspiracies and governmental cabals. In other places he seems more reasonable, though if you read carefully you’ll realize that many if not most of his posts include some subtle nugget of misdirection or misinformation going beyond the immediate topic under discussion. Thus, for instance, the crafty introduction of Antarctic ice in a thread on Arctic ice, requiring the inception of yet another stream of futile attempts at correction/clarification. This appears to happen as any given particular avenue of wrongness is about to force manacker into retreat.

    If forced to choose, I would conclude that here on RC manacker is not so much concerned with pursuing arguments about climate with an eye to improving understanding as much as he’s writing for a silent audience, either as performance for acquaintances made elsewhere or to pollute other people’s minds with degenerate perspectives. With regard to the latter case he often appears superficially to demonstrate that many aspects of climate science are so unsettled as to be wide open in making conclusions; for the casual observer manacker is an intellectual trap, only to be eluded by devoting an unwarranted amount of time picking apart his claims.

    Examined as a phenotype manacker is rather interesting and instructive.

  19. 669
    dave p says:

    Re melting v 2008 http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.365.jpg

    Melting is lagging last year.

  20. 670
    Rod B says:

    Gavin re your response to (621) re authorship: I never knew that. That’s helpful to understand the process here on RC.

  21. 671

    #670, 669 dave, not for long! The ice appears to do a 2008, whereas its melting late in the season, from overall thinness, there is a lot broken ice everywhere, hard to make an overall extent measurement… Fram melt is particularly fast. , despite the lack of High sun. The Northwest Passage is just about to open via Peel Sound, a magical mystical place for tourists, Where the beaches are pink. in the past the gateway to China.
    Its been warm up there (+5 to +10 C more than enough to clear the passage) so for the second year running, both passages will be open for ordinary ships.

  22. 672
    Jacob Mack says:

    Hank # 660, indeed, primary sources are of utmost importance, hence my avoidance as a rule of wikis and other secondary sources.

  23. 673
    Hank Roberts says:

    “dave p” claims Arctic “melting is lagging last year” and points to the anomaly chart, which may differ by about a pixel, if it’s accurate.

    Well, how could we learn any more than looking at a chart?
    Ah, yes, look at the data.

    Well, I don’t see it easily at NSIDC, let’s look at Stoat’s favorite:

    http://www.ijis.iarc.uaf.edu/seaice/extent/AMSRE_Sea_Ice_Extent.png

    The latest value : 6,610,000 km2 (August 7, 2009)

    Their data is downloadable; this is last year’s:

    08,06,2008,6579844
    08,07,2008,6485625
    08,08,2008,6485000
    08,09,2008,6417656
    08,10,2008,6343906
    08,11,2008,6291563

    Let’s see, 6610000 minus 6485625 —
    dave p?

  24. 674
    Hank Roberts says:

    Oops, that wasn’t meant as a trick question; what matters is not the raw number but the rate and the accuracy; here’s what you find at NSIDC as of today, using the PgDn key:

    “Averaged for the month, July 2009 saw a decline rate in ice extent of 106,000 square kilometers (41,000 square miles) per day. For comparison, the rate of decline for July 2007 was 107,000 square kilometers (41,000 square miles) per day and the July 2008 rate of decline was 94,000 square kilometers (36,000 square miles) per day….”

    Note the gray band: http://nsidc.org/images/arcticseaicenews/20090804_Figure2.png

  25. 675
    BobFJ says:

    Barton Paul Levenson, Reur 649, in part:

    “…if there has been a “net” warming of 1.6 W/m^2, and there has been cooling of 1.6 W/m^2, it means the gross warming must have been 3.2 W/m^2….”

    Could you run that by again please. I don’t understand how you mean it in relation to the table on page 4 of the relevant link
    http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf
    Isn’t Max simply saying that the SPECIFIC anthro-forcing of 1.66 from CO2 is roughly the same as the NET forcing of 1.6? Also, the reason for that is that a whole bunch of lesser SPECIFIC positive and negative forcings all NET out to roughly zero? (and in context in that discussion, those lesser forcings, a NET of 0.06 can almost be ignored)

  26. 676
    Paul Klemencic says:

    Actually this year is very close to 2008 at this point. Last year was a leap year, so there is an extra day of melt in last year’s data. We should be comparing August 6th from last year with August 7th this year, which puts the two within about 30,000 km2, which is well within the accuracy for measuring sea ice extent.

    dave p was actually looking at NSIDC’s Ice Area graph, which has a likely measurement error even larger than ice extent measurement (according to NSIDC personnel). In either case, there simply is very little difference for comparable days into the melt season.

    But the pattern of the melt seems very different, with the Siberian side of the Arctic showing more rapid melt, and melt in the Beaufort Sea side lagging last year’s melt. The melt seems to be following a very different process than last year.

  27. 677

    #673 Hank, From the numbers you presented you can see that data acquisition is not exactly perfect, and requires some ulterior thinking as to really get a grasp of a melting. 08,07,2008 and 08,08,2008 had basically very little melt compared to other days, this is inconsistency should be presenting an error factor within the measurement itself. When the ice compresses it is easier, so the real numbers depend on winds, or consolidation by sudden freezing right after sea ice minima…

    Special thanks as always to all your efforts, truly commendable but especially informative…

  28. 678
    BobFJ says:

    Wayne Davidson 639, following on from your 591:

    2001 when your [Max] claim it has been cooling ever since; Really?? Sea ice utterly denies your reasoning….

    I pointed out to you Wayne that sea-ice melt is not simply a matter of air temperature, to which Max was referring.

    You do not make it clear if you read 543, as recommended, but if so, did you notice for example this statement from NASA?
    “The winds causing this trend in ice reduction were set up by an unusual pattern of atmospheric pressure that began at the beginning of this century,” Nghiem said.

    To elaborate; sea-ice melt is affected by at least winds, air temperature, thermohaline circulation, water temperature, precipitation, cloud cover, solar variations, black carbon, dust….. will that do?

    You can speculate as much as you like as to how significant these things are, but it is highly assumptive of you to assert any factuals. The real facts are that air temperature is only one of the drivers of sea ice concentration, and sea ice is fragile compared to say ice shelves and glaciers.

    Perhaps compare another complexity:
    If you have been following the discussion on retreat of the more robust Jakobshavn glacier, you may have learnt that the popular intuitive cause of retreat as a consequence of air temperature, is clearly NOT the primary cause of retreat.

  29. 679

    max writes:

    Atmospheric water vapor content and temperature do, indeed, correlate to some extent. But it would be foolish to assume that relative humidity will remain constant with increased temperature. (Minschwaner + Dessler have shown based on observations in the tropics that RH actually decreases with warming).

    Not enough. Water vapor feedback is positive. Here are four recent studies which reach that conclusion from empirical evidence:

    Brown, S., Desai, S., Keihm, S., and C. Ruf, 2007. “Ocean water vapor and cloud burden trends derived from the topex microwave radiometer.” Geoscience and Remote Sensing Symposium. Barcelona, Spain: IGARSS 2007, pp. 886-889.

    Dessler AE, Zhang Z, Yang P 2008. “Water-Vapor Climate Feedback Inferred from Climate Variations.” Geophys. Res. Lett. 35, L20704.

    Philipona, R., B. Dürr, A. Ohmura, and C. Ruckstuhl 2005. “Anthropogenic greenhouse forcing and strong water vapor feedback increase temperature in Europe.” Geophys. Res. Lett., 32, L19809.

    Santer, B. D, C. Mears, F. J. Wentz, K. E. Taylor, P. J. Gleckler, T. M. L. Wigley, T. P. Barnett, J. S. Boyle, W. Bruggemann, N. P. Gillett, S. A. Klein, G. A. Meehl, T. Nozawa, D. W. Pierce, P. A. Stott, W. M. Washington, M. F. Wehner, 2007. “Identification of human-induced changes in atmospheric moisture content.” Proc. Natl. Acad. Sci., 104, 15248-15253.

    As to the solar impact on 20th century warming, there have been several studies by solar experts, which have concluded that roughly half of the observed 20th century warming can be attributed to the unusually high level of solar activity (highest in several thousand years). These studies have concluded that the solar impact on early 20th century warming was greater than on the warming which occurred after 1970, but the overall average for the entire century was around half of the warming or 0.35C

    If you would like the reference to these studies so you can check them yourself, please let me know.

    Just read this:

    http://BartonPaulLevenson.com/Sun.html

    When I do the math, I don’t find ANY significant solar influence from 1880 to 2007. I’ve tried it with four different measures of solar activity — TSI (solar constant), sunspot number, years since minimum, and years since maximum. It’s just not there.

  30. 680
    Ron Taylor says:

    BobFJ, what makes you think that the only effect of global warming in the Arctic is the local surface temperature increase? Global warming impacts atmospheric pressure distributions, clouds, winds and ocean currents. The atmosphere and oceans are dynamic systems that respond to the energy being added to them.

  31. 681

    #678 Bob, Is clear, you extrapolate one wind event, and claim all years are wind events… Amazingly incorrect!!!
    Please keep showing your misinterpretations as to inform us all of your climate ignorance, and soon you will have to use another nick name.

  32. 682

    #678 Bob , Might as well help you, Winds are never the same , year by year, patterns vary always, week by week… There is dominant winds at one point or another, but no specific pattern being always persistent. Perhaps after a while, you will understand…

  33. 683
  34. 684
    Hank Roberts says:

    Well, BobFJ: “These require summing asymmetric uncertainty estimates from the component terms, and cannot be obtained by simple addition.”

  35. 685
    Hank Roberts says:

    > “primary cause”

    http://www.ingentaconnect.com/content/igsoc/jog/2008/00000054/00000187/art00008?crawler=true

    “… We examine seasonal and interannual changes in ice-front position, surface elevation and flow speed for 32 glaciers along the southeastern coast between 2000 and 2006…. Many retreats began with an increase in thinning rates near the front in the summer of 2003, a year of record high coastal-air and sea-surface temperatures….”

  36. 686
  37. 687
    Hank Roberts says:

    “… the science marches on. On July 7, the American Geophysical Union put out a press release on a paper appearing in the Journal of Geophysical Research—Oceans. ‘Scientists have evaluated for the first time how much the thickness and volume of Arctic sea ice, not just the ice’s surface area, have shrunk since 2004 across the Arctic Ocean basin. Even where the sea ice cover persists despite climate change in the region, a vast portion of the remaining ice layer has become thinner than it used to be, the new study finds.'”
    http://pubs.acs.org/cen/editor/87/8730editor.html

  38. 688
    Mark says:

    An example of a wind being dominant is the trade winds.

    Reliable enough to build a seafaring empire with but with lots of variation.

  39. 689
    Ike Solem says:

    <a href="http://www.boston.com/news/world/canada/articles/2009/08/09/vast_expanses_of_arctic_ice_melt_in_summer_heat”Vast expanses of Arctic ice melt in summer heat, Charles J. Hanley, AP Special Correspondent, August 9, 2009

    “TUKTOYAKTUK, Northwest Territories—The Arctic Ocean has given up tens of thousands more square miles (square kilometers) of ice in a relentless summer of melt, with scientists watching through satellite eyes for a possible record low polar ice cap.

    From the barren Arctic shore of this village in Canada’s far northwest, 1,500 miles (2,414 kilometers) north of Seattle, veteran observer Eddie Gruben has seen the summer ice retreating more each decade as the world has warmed. By this weekend the ice edge lay some 80 miles (128 kilometers) at sea.

    As far as realistic future climate projections, the minimal reliable period for predictions appears to be about a decade, doesn’t it? On shorter timescales, natural variability can dominate the trend.

    The same thing happens on with cyclic seasonal trends – short warm periods between winter storms do not indicate the onset of an early spring. Likewise, periods of rapid warming are interspersed with periods of small-scale equilibration.

    As the ice melts and more ocean is exposed, the polar ocean will cool more rapidly in the fall (thus warming the atmosphere, leading to prolonged fall warmth, as observed). Since ocean temperatures play a role in sea ice thickness and extent, this is a kind of negative feedback – but it is only a short term effect, as warmer summer water in the North Pacific continues to infiltrate in the fall. Thus, the actual warming trend ends up looking more like a jagged staircase than a smooth slope, with steps as broad as a decade, as various positive and negative feedbacks kick in.

    For example, see:

    http://www.whoi.edu/beaufortgyre/pdfs/shimada_seaice_grl2006.pdf

    Shimida et al. April 2006 GRL “Pacific Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean”

    The basic issue is this:

    In the Canada Basin the primary oceanic heat source to the sea-ice cover and atmosphere is not the Atlantic Water which lies beneath the halocline but, instead, the Pacific Summer Water that occupies the upper portion of the halocline…

    They also describe the complex interplay between wind, water and ice in the region, and how ocean warming may affect that:

    However, if sea-ice cover is reduced along the coast, then the momentum of wind is more efficiently transferred to the ice and underlying waters. Therefore the delayed development of sea-ice cover in winter enhances the retroflexion (westward turning) of PSW, just as the warmest pulse of PSW arrives on the Beaufort Slope. This anomalous heat flux into the western Canada Basin retards sea-ice formation during winter which, in turn, causes an imbalance between ice growth in winter and ice melt in summer, further accelerating sea ice reduction.

    That enforces the point that amplified Arctic warming but is due to increased equator-to-pole heat transport as much as to other local factors (aerosols & albedo).

    The authors also point out that:

    The potential of shifting from no-slip to free-slip boundary conditions constraining sea-ice motion implies that thresholds are established that, once crossed by an initial reduction in sea-ice, result in catastrophic change.

    If you look at current sea ice images you can see that this is the region with greatest ice melt:

    http://nsidc.org/data/seaice_index/images/daily_images/N_daily_extent_hires.png

  40. 690
    dave p says:

    funny why the ice area figures differ so much. It seems this year will be similar to 2008 give or take 100,000 sq km.

  41. 691

    #689, Ike, its truly complex, but there are a few main simple features which make a greater or lesser melt.

    1- High sun during the summer solstice
    2- Few clouds allowing the high sun to do its thing
    3- A cloudy Arctic winter preceding a sunny summer
    4- Higher than usual temperatures
    5- Salinity (the elephant frequently not discussed about)

    Educating Bob a bit more, lets look at his “wind” obsession…

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/ARCHIVE/19790808.png

    1979 Chuckchi sea open water

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/ARCHIVE/19890808.png

    1989 Chuckchi sea??? Open water. Barents sea open..

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/ARCHIVE/19990808.png

    1999 Chuckchi sea open water. Barents sea Open

    http://arctic.atmos.uiuc.edu/cryosphere/NEWIMAGES/arctic.seaice.color.000.png

    2009 Chuckchi sea open water. Barents sea Open

    Winds:

    http://www.cdc.noaa.gov/map/images/rnl/sfcwnd_90b.rnl.gif

    In 2009 Must be Bob’s winds!!! He appears to be right in the Chuckchi However wrong in the Barents… With stronger than usual winds going towards Scandinavia.

    Lets look at the melt progress from 1982 with respect to 2008

    http://maps.grida.no/go/graphic/arctic-sea-ice-minimum-extent-in-september-1982-and-2008

    Even with a great melt there is a pattern, so most RC readers know the reason for this pattern, I will leave Bob explain to us his demonstrably impressive grasp on this subject…

  42. 692

    #590, Dave, really liked Paul’s Leap year comment in #676, simple factors are often underestimated. Its not at all like 2008, I am a bit perplexed by NSIDC verifiable MODIS claims of more sun over the Beaufort, yet more ice. As I wrote earlier, I didn’t see the sun hitting that area alot during the solstice period. So I preclude MODIS 3 month analysis, just as a matter to think about what happened, I come up with a cloud “imprint” , but the ice should be very thin, and will melt quite easily given present warmer temperatures.

  43. 693
    Hank Roberts says:

    > funny why the ice area figures differ so much

    dave p — did you read the explanation on the site?
    It’s less confusing if you read the explanations at

    http://nsidc.org/arcticseaicenews/

    Click where you see “Learn about” and “Read about”
    under the daily update.

    “Learn about update delays ….
    Read about the data.”

    Look at the pictures; sometimes there are clouds.
    Anything interfering with a good picture is noise; it affects daily results.
    They explain how they clean up the noise, for more accurate monthly results.

  44. 694
    BobFJ says:

    Barton Paul Levenson, Reur 650, in part:

    Nobody’s ever observed that there’s more water vapor pressure when it’s hotter?

    I think everyone agrees that there must be a positive feedback from increased water vapour with global warming. (e.g. Dessler, Zhang, & Yang, GRL, 35; 2008). However, what do you speculate WRT side effects such as possible changes in cloud cover and species? Might there be increased precipitation, with higher albedo fresh snow somewhere? If there is more water vapour, might you speculate that there will be increased evaporation? (which according to NOAA and others is already the greatest HEAT loss process from the surface, see links).
    http://education.gsfc.nasa.gov/ess/Units/Unit2/u2L5aimage.jpg
    http://en.wikipedia.org/wiki/Earth’s_energy_budget

  45. 695
    Jacob Mack says:

    # 694:there will be some evaporative cooling from increased water vapor cooling too, (cloud formations, higher-lower optical densities in conjunction with CCN, more/less rain and so forth)and LW heat loss to space, however, there will be net warming effects approaching equilibrium in conjunction with natural weather and climate processes.(conduction, convection, advection, wind magnitude changes, adiabatic processes and lapse rates)If there was not huge evaporative heat losses then AGW would be far more severe than it currently is. I am out of time, so I am brief, but I look forward to other poster responses as we use greater specificity.

  46. 696
    Jeff says:

    BobFJ (comment 694),
    Evaporation is not the greatest heat loss process from the surface. Longwave surface radiation amounts to almost five times the energy output that evapotranspiration provides. Check out Fig 1. in this link, which gives more recent data than that in Trenberth (1997).

  47. 697
    Hank Roberts says:

    Sure, BobFJ, you could, well, scientists could write several hundred papers
    http://scholar.google.com/scholar?cites=14448914297137877150&hl=en
    or even a book about it.
    http://scholar.google.com/scholar?cluster=9611808599973159357&hl=en
    Google Scholar could be your friend.

  48. 698
    Hank Roberts says:

    PS, BobFJ, if you want to read just one paper, start here:
    http://courses.eas.ualberta.ca/eas570/h2o_cycle_global_warming.pdf

  49. 699
    Hank Roberts says:

    Oh, and BobFJ, if you don’t want to read one, at least read a bit from the conclusion section. Like this, which gets across a point related to some science Gavin’s mentioned to me several times over the years, in reply to some of my dumber questions, and that I’m finally getting a glimmering of:

    7. Conclusions
    A number of important aspects of the hydrological
    response to warming are a direct consequence of the
    increase in lower-tropospheric water vapor. Because
    the increase in strength of the global hydrological cycle
    is constrained by the relatively small changes in radia-
    tive fluxes, it cannot keep up with the rapid increase in
    lower tropospheric vapor. …. In many popular,
    and in some scientific, discussions of global warming, it
    is implicitly assumed that the atmosphere will, in some
    sense, become more energetic as it warms. By the fun-
    damental measure provided by the average vertical ex-
    change of mass between the boundary layer and the
    free troposphere, the atmospheric circulation must, in
    fact, slow down….

  50. 700
    BobFJ says:

    Re my 650, Please ignore previous, that link also failed, second try
    The second link is broken… This one should be OK:
    It contains three energy diagrams.

    Earth’s_energy_budget

    If this one is also broken, please paste the following line into Google:
    Earth’s energy budget – Wikipedia