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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. 51
    Doug Bostrom says:

    cougar_w 17 Jul 2009 at 6:29 pm

    “Maybe it’s something that is just learning how to grow that far north. Maybe it was there all along as mats and the changes in currents have pushed it into a place where it can be observed. Or maybe it was bound in/under/on ice and is free for the first time. However you cut it, strange goo circulating in the Arctic cannot be a good thing.”

    A big, sticky, icky glob of bad karma? ;-)

  2. 52
    MS says:

    AMSR-E sea ice concentrations calculated daily in near real time are shown here:
    Daily AMSR-E sea ice maps

  3. 53
    Anne van der Bom says:

    Knut Witberg
    17 Jul 2009 at 9:17 am

    Can it be that the black carbon soot from […], coal power stations in China, […]

    Not singling you out Knut, but I’ve seen this more often. As soon as the subject is coal power, people just can’t resist to mention China. As if there isn’t any significant coal power in the rest of the world.

  4. 54
    tamino says:

    Re: #32 (MJ Strong)

    You need to read the documentation more carefully.

    Important Note: The “extent” column includes the area near the pole not imaged by the sensor. It is assumed to be entirely ice covered with at least 15% concentration. However, the “area” column excludes the area not imaged by the sensor. This area is 1.19 million square kilometers for SMMR (from the beginning of the series through June 1987) and 0.31 million square kilometers for SSM/I (from July 1987 to present). Therefore, there is a discontinuity in the “area” data values in this file at the June/July 1987 boundary.

  5. 55
    Peter Dawe says:


    How is the gyre pump action of the freeze-melt cycle of Artic ice affected by the change in sea ice coverage?

    Is the net ice melting helping the gyre?

    Will the eventual stabilisation of a smaller cycle affect the gyre, and particularly the Gulf stream/north Atlantic drift? (I live in UK!)

  6. 56
    truth says:

    Why are Real Climate and the rest of the AGW proponents completely ignoring the research of NASA’s Drew Shindell—and NASA’s own reports on the role of black carbon in Arctic warming?
    In the light of that research, what is the use of predictions that don’t factor in the black carbon that’s clearly visible in all photographs of Arctic ice.
    Or is black carbon factored in—and if so, how are the forward projections of black carbon calculated , when they’re dependent on accurate predictions of China’s future industrial growth,[ which can even change over a year, as seen in the present circumstances] and the energy mix involved in that for the foreseeable future—as well as the ability of the world to persuade countries like Brazil, Indonesia, PNG and India to change their habits ?
    If the output of a driver of Arctic warming that is shown by NASA research to be responsible for almost half of the warming, [ namely black carbon ] is not precisely known [ or nearly so] for the future——then how can models that predict ice cover possibly be taken seriously?
    Why are climate scientists not telling governments that getting the black carbon problem mitigated is a more important goal than disrupting already damaged economies with their almost complete concentration on CO2 and emissions trading schemes —schemes that will cause even more unemployment , inflation , loss of national income and ongoing disruption and dislocation , that will harm your country and mine for many years to come?
    Surely Obama would defer his climate legislation, and exhort other leaders to do the same, if AGW scientists told him at the Copenhagen conference, that almost half of the Arctic warming was from black carbon, and that mitigation of that would have a much more immediate effect on warming than the economy-destroying CO2 emissions legislation ?
    Why is the AGW side so desperate to have all the focus on CO2?

  7. 57
    Neven says:

    SEARCH has just released the July Report for the September Sea Ice Outlook:

    “Most estimates for September sea ice extent are in a narrow range of 4.4 to 5.2 million square kilometers, as were last month’s (based on May data). However, two new responses come in at 4.0 and 4.2 million square kilometers, which would represent a new record minimum. As the submitted uncertainty standard deviations are about 0.4 million square kilometers, most of the Outlook estimates overlap”

  8. 58

    Re: comment #40

    Dear Steve L,

    These topics are all covered somewhere, yes. Just dig through the recent literature or go to the NSIDC website for the monthly reviews of sea ice conditions. Lots of explanatory material there.

  9. 59
    Ron Crouch says:

    Perhaps of greater interest will be how the increase in fresh water content of the Arctic Ocean will eventually play out.

  10. 60
    Dean says:

    Regarding googling this issue, when I search on “global sea ice trend” a WUWT post is first on the list. NSIDC came in second. Their main graph does show a slight increasing trend for the Antarctic, but nothing like the decrease in the Arctic.

  11. 61
    Jerome Chappellaz says:

    Gavin, I wonder if there is not something like “garbage in, garbage out” in the forecasts based on physical modelling. You may pay attention for instance to the work conducted by Jerome Weiss and his colleagues at LGGE (Grenoble, France), on the mechanical behaviour of sea ice. It turns out that at the scale of the Arctic basin, sea ice has a fragile mechanical behaviour instead of a visco-plastic one, as “wrongly” assumed in current models. With his PhD student Pierre Rampal, Jerome also observed that the summer and winter sea-ice drift speeds have significantly increased between 1979 and 2007, as well as internal deformation (work published in JGR of 14 May 2009). Combined with the fragile mechanical behaviour, this could contribute to explain, at least partly, what happens since two years. It also seems that the drift speed in winter bears some predictive potential regarding summer sea ice evolution.

    [Response: Hi Jerome, I wouldn’t go as far as your first statement. There is certainly more to learn about sea ice continuum rheologies – and people like Bruno Tremblay and others are working on that. A bigger issue may well be the scale issue between the global models used to make projections and the much higher resolution Arctic-only models that do a very good job in hindcasts. Observational links between drift speed and ice extent would be perhaps a profitable way to assess their fidelity, but it’s not obvious that rheology is the biggest problem – I’d probably say that Arctic cloud feedbacks are a bigger uncertainty. – gavin]

  12. 62
    dhogaza says:

    “I think it points out that the atmosphere is more complex than the computer models currently simulate,” says Dr. Roy Spencer

    Thank you, Dr. Obvious :)

  13. 63
    Martin Vermeer says:

    Fred #11, are you telling us that you tried to fit a 322-year sine wave to a time series running from 1977 to today? Really?

    There’s a guy called Tamino that might want to have a chat with you…

  14. 64
    RichardC says:

    4 Wayne said, “if El-Nino persists grows and vanishes mid spring 2010, sailing will be possible from Bering strait to Spitzbergen via the Pole come September 2010.”

    Look at the bluing of the ice in the SOTC concentration view. Pretend it’s your bucket of beer. How many years until your bucket loses all its ice? You might be dodging growlers and chunks, but I bet that given the right conditions, we could have our first trans-sailing in 2010.

    And why did you add “vanishes” to your list of El-Ninoactivities?

  15. 65

    #55 Ron, That is easy, after the great melt of 2007, the ice extent maximum following, March 2008 was very high. Old Arctic Ocean multi year ice is nearly as pure as distilled water, a great deal of it has melted in the summer of 2007. By inference Antarctica greater yearly maximum ice extent should be from glacier ice melting a great deal more. The way to prove this is by ship, a lowering of salinity around Antarctica should be noticed.

    And what do you know:

    That is it, so contrarians bragging about the greater antarctica Sea Ice extent
    should be aware of their ignorance…

  16. 66
    tamino says:

    Re: #63 (Martin Vermeer)

    Fred #11, are you telling us that you tried to fit a 322-year sine wave to a time series running from 1977 to today? Really?

    There’s a guy called Tamino that might want to have a chat with you…

    No. Sometimes you have to acknowledge a lost cause.

  17. 67
    Marcus says:

    Truth: A number of fallacies in your post:
    1) “the black carbon that’s clearly visible in all photographs of Arctic”: Actually, my understanding is that black carbon on Arctic ice is usually not visible to the naked eye. The dirty snow photos that are often shown are actually areas that are near dust sources.
    2) Neither RealClimate nor the majority of AGW proponents are ignoring black carbon: heck, Hansen was one of the first people to make an issue of it. However, even if BC has contributed to half of the warming of the Arctic to date, it is a flow pollutant not a stock pollutant, which means that as time goes on it will be a smaller and smaller percentage of the total (eg, if you emit a constant amount of CO2 concentrations keep rising, if you emit a constant amount of BC, concentrations stay constant). Politically, there are efforts to reduce BC by the Arctic Council and other international fora in which the US is actively participating. And domestically, the US and Europe _have_ reduced BC emissions significantly, mostly due to controls on diesel engines.
    3) Blaming Chinese coal: while some papers (Rypdal et al 2009, for example) show a significant contribution to BC in the Arctic from China, updated modeling work seems to suggest that that was an overestimate. As would make sense, a priori, emissions from the northernmost latitudes are very important: Russian springtime agricultural burning, northern US and European diesel and agricultural emissions, etc. Fingerprinting work from a couple of Arctic campaigns shows that the majority of the soot is biomass derived, so coal is likely not a large source.

  18. 68
    Hank Roberts says:

    Shortened “truth” question:

    > Why…ignoring…..predictions…don’t factor…black carbon…factored in—and if so, how…accurate predictions…change over a year…energy mix…foreseeable future—…habits…not precisely known [or nearly so]…future… models… predict…possibly be taken seriously…not telling…black carbon…disrupting…damaged economies…CO2… emissions trading schemes —schemes…unemployment, inflation…income…disruption…dislocation…harm…country…Obama …defer…exhort…black carbon…mitigation…economy-destroying CO2 emissions legislation…AGW side…desperate…focus on CO2?

    Short answer: atmospheric residence time of CO2

  19. 69
    CM says:

    truth (#56) asks:

    Why are Real Climate and the rest of the AGW proponents completely ignoring the research of NASA’s Drew Shindell

    For crying out loud, “truth”, Drew Shindell had a guest post here in April. Go study.

    [Response: …and if you look at Drew’s and my publication records, you’ll see over 20 co-authored papers (and more to come). Hardly surprising since his office is two doors from mine. – gavin]

  20. 70
    CM says:

    Marcus (#67), if you have some references handy for the modeling / fingerprinting work you mention in your point (3) above, could you share them please?

  21. 71
    Steve L says:

    Thanks Tenney @ 58, but I commented here because I haven’t found good coverage of those topics elsewhere. Here’s something a bit different, too — tidal forces.
    “How a moon that hangs in the frigid depths of the solar system could keep water in a liquid state is not much of a mystery. Too small to have a molten core and too far from the sun to feel even a flicker of its heat, Enceladus does have other moons — principally outlying Tethys and Dione — orbiting nearby. Each time those moons pass, they give Enceladus a gravitational tug, which causes it to flex slightly. Do that enough times — and the 4 billion years the solar system has been around is more than enough — and the pulsing moon heats up in much the way a wire hanger does if you bend it repeatedly back and forth. That explains both why the water stays liquid and why it’s repeatedly squeezed up through cracks and into space, where it flash-freezes into icy mist.”
    I have wondered what effect the Moon getting further from Earth has had over the ages. It may also have a short term effect on things like sea ice?

  22. 72

    #64 Richard, Great link! We are looking at a repeat of 1997-98. 2006-07 ENSOs
    when El-Nino lasted the winter and turned to a strong La-Nina come spring/summer.
    In brief, EL-Nino = cloudy Arctic, La-Nina= cloud free to a greater extent. It was like that in 06-07. The great melt component: the higher solstice sun, didn’t happen this year… If La-Nina thrieves in June…. bye bye ice…

  23. 73
    Ike Solem says:

    For a good earlier perspective:

    Johannessen et al. 2004 “Arctic climate change: observed and modelled
    temperature and sea-ice variability”

    On historical uncertainties:

    However, it remains open to debate whether the warming in recent decades is an enhanced greenhouse-warming signal or natural decadal and multidecadal variability (Polyakov and Johnson, 2000; Polyakov et al., 2002), e.g. as possibly expressed by the arctic warming observed in the 1920s and 1930s followed by cooling until the 1960s (e.g. Kelly et al., 1982).

    The uncertainties are exacerbated by a lack of homogeneous, century-scale instrumental data sets needed to resolve the inherent timescales of variability in the Arctic (Venegas and Mysak, 2000), a region characterized by high variability.

    Notice that physics-based projections of short-term future trends also are hampered by that same lack of data, leading to a reliance on synoptic-type forecasting approaches, which seem little more than informed guesses.

    On the use of models to compare early 20th century Arctic warming to the present trend (note that all models predict that anthropogenic forcing results in amplified Arctic warming, 2X the global mean over the next 50 years at current rates):

    A recent modelling study (Delworth and Knutson, 2000) has suggested that the 1920s–1930s warming anomaly was due to natural processes, insofar as models are capable of simulating such anomalies due to internal chaotic processes of the climate system….

    In contrast, no comprehensive numerical-model integrations have produced the present global warm anomaly (Fig. 1a) without including observed anthropogenic forcing.

    And the central questions?

    From these concerns, two overarching questions are as follows. (1) To what degree are the gradually changing atmosphere–ice–ocean conditions in the Arctic a consequence of natural climate processes and/or external factors such as anthropogenic greenhouse gas (GHG) forcing? (2) To what degree may anthropogenic forcing induce the arctic sea-ice cover to decrease or even disappear in this century?

    Can we now answer those questions? Ice has continued to decrease in thickness and extent – see the images from 2004 and 2008 from NASA JPL:

    Claims about modern warming in the Arctic being an amplification of unforced natural variability are no longer plausible, for one thing – 2002 was also a ‘record low’. Nor does melting ice fit a ‘cooling trend’ – if there was such a trend, ice would be thickening.

    This has not kept people from claiming that “intersecting modes of variability” are responsible for the current Arctic warming, or denying the existence of the trend altogether, but such claims have no evidence to back them up and are only promoted by fossil fuel-linked lobbyists and the like.

  24. 74
    Eli Rabett says:

    Black Carbon fanboys might like to get behind Eli Rabett’s Simple Plan to Save the World Supplement

    India and China and many other developing countries should reduce their emissions of black carbon by 90% or more in the next decade. This will not only significantly reduce warming of the climate, it will make a major contribution to the health of their people. Simple and economical methods of doing this are available.

    which of course, supplements Eli Rabett’s Simple Plan to Save the World

    Nations wishing to make major progress on decreasing greenhouse gas emissions should introduce emission taxes on all products. These taxes should be levied on imports as well as domestic goods at the point of sale, and should displace other taxes, such as VAT, sales taxes, and payroll (e.g. social security, health care) in such a way that tax revenues are constant, and distributed equitably.

    but somehow, the bunny brain trust thinks they are more interested in the problem than the solution. The fact is that everyone and ever nation has to do their part, but that the most effective parts may be different at this point in time.

  25. 75

    Truth asks:”Why is the AGW side so desperate to have all the focus on CO2?”

    Burning fossil fuels(and their accompanying CO2 emissions)have consequences the world over,not just in the polar regions.

  26. 76
    Anne van der Bom says:

    truth, don’t be such an alarmist:

    economy-destroying CO2 emissions legislation

  27. 77
    Jacob Mack says:

    no one group of experts can discuss all the research findings. Neither is each expert an expert in all aspects of climate. Climate science is just too vast, (albeit young) requiring more epxerts than RC has. It is true NASA has many peer reviewed research papers and findings discussed at conferences which asks more questions than there are answers for, and even casts doubts on both GCM’s and satellites as being as reliable as the RC mods may tend to represent at times. Then again this is their blog and though it is full of accurate information, no blog can stay uo to date or discuss at great length the disrepancies of findings. For example, GCM’S overstimated water vapor feedback, but ice loss has been faster than predicted. Also paleoclimate data is only a rough science, albeit a legitimate one, it is difficult to know how the climate really functiond in totality 1550 years ago and so forth. Since long term trends are really necessary (even 30 years is oftentimes inadequate) only approximations of how it has been and why it is the way it is now, and where climate/weather is going can be ascertained.Ocean and atmospheric coupling is covered well at AOS and Harvard’s site; the site eluedes me at the moment, but I will find it for you, if you cannot do so. Best of luck!

  28. 78
    Jacob Mack says:

    LOL, Gavin and Drew, I saw your response to Truth after my post; still there are so many papers out there discussing what Truth is aking about.

  29. 79

    OT, but amusing in an appalling sort of way (not the story, the comments!)

  30. 80
    Hank Roberts says:

    Best way to find current information: look at prior publications and follow citations forward. Best source of advice: your local reference librarian.

    Best bet without leaving your chair or this site, is the Search box and the topic list in the right sidebar; pick a relevant recent topic in previous years on what interests you; read the cited papers.

    Then find them online, and follow “cited by” links to read papers citing them published more recently. That’s how science works.
    which will lead, by following cites forward, to much of interest that’s recent.


    Following the papers cited there forward in time finds pretty much everything on the subject you might want to read.

    Record of a Mid-Pleistocene depositional anomaly in West Antarctic continental margin sediments: an indicator for ice-sheet collapse?

    Author(s): Hillenbrand CD (Hillenbrand, C. -D.), Kuhn G (Kuhn, G.), Frederichs T (Frederichs, T.)
    Volume: 28 Issue: 13-14 Pages: 1147-1159 Published: JUN 2009

    “… Abstract: Modern global warming is likely to cause future melting of Earth’s polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5-6 m…. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr…. A prominent depositional anomaly spans MIS 15-MIS 13 (621-478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15-MIS 13 was the most likely time period….”

  31. 81
    Thomas says:

    71: The retreat of the moon is currently only a couple of cm per year, so the rate of change of the tides should not be relevant for the time periods in which paleoclimate data is reasonable. IIRC tidal drag drops off at a pretty rapid expnent of the distance. Total current dissapation on the earth is a few terawatts -mostly in shallow seas, which is several orders of magnitude lower than solar insolation. I do wonder if tidal dissapation might possibly be a solution to the weak young sun problem, whereby the early sun is too weak to keep the early earth from freezing -even with high concentrations of greenhouse gases.

  32. 82
    Doug Bostrom says:

    truth 18 Jul 2009 at 8:57 am

    That handle you’ve chosen, it causes me problems. Does it refer to accuracy, or precision? Are you a source of truth? Are you a darkly humorous and ironic presence? Is this a lack of humility we’re witnessing? What enlightenment can you offer?

    Surely a real name or at least something more innocuous would be less distracting, whatever it is you’re trying to convey. I see “truth” and I just get stuck, the more so when you take a prat within a handful of words.

  33. 83
    jcbmack says:

    Hank Roberts,
    you are always a gem for references and referencing lessons. Thank you, you tireless veteran.

  34. 84

    Re: comment #71

    Dear Steve L,

    I am going to have to fall back on the wise response of Tamino at #66.

  35. 85
    J. Bob says:

    #17 – MJ Strong – Your right
    Global sea ice still running about normal, no mass meltdown:

    If the Antarctic sea ice is at almost recorded highs, why would the interior be any different. You don’t normally see melted ice cream in the middle of a freezer, when all else is froze.

    #29 Tamino-you know that analysis I did on the Central England data set (1659-2008) you said was “bungled”. Check out my post on WUWT UAH global Temp Anomaly post 7/7/09;

    You might be enlightened on use of cross checking analysis methods.

  36. 86
    Hank Roberts says:

    jcbmack: I do nothing but point out a few examples of how good citations — and a good reference librarian — help people learn.

  37. 87
    Mark says:

    “That handle you’ve chosen, it causes me problems”

    Doug, it’s Son of Mulder (the truth is out there) and “the truth” before that.

    Same ol’, same ol’.

  38. 88

    #85 Firstly, “Mass” is closer to volume than to ice extent, Mass wise there is a significant meltdown, by Northern Hemisphere multi year ice on the verge of extinction. Secondly, the two poles are not easily comparable, for obvious reasons, ice extent around the same latitudes in the North and South, Barents, Greenland and North Atlantic seas between 70 and 65 North may be something to study, but still not comparable with Antarctica still. Combining hemisphere ice extent jointly is not a good way to explain world wide ice conditions with respect to climate. It is rather used to avoid explaining present climate conditions.

  39. 89
    Steve L says:

    Tenney, I’m no lost cause. Don’t be [edit]. The first point of my first comment was that minimum ice extent was too ‘knife-edge’ a thing to forecast well and somewhat unimportant in the grand scheme, anyway. My last comment was about an effect that, if I understand correctly, could affect something as fickle as the Arctic sea ice minimum: if stormy weather can cause a considerable proportion of the ice to break up and/or leave the Arctic Ocean, then the timing of a strong tide (relative to other conditions) and the currents it causes could also have an important effect on a given year’s minimum. Right? Tides are more predictable than weather (obviously) and yet they aren’t discussed as a potential part of a model. I wonder if that’s an oversight. You can insult me, ignore me, or provide a thoughtful comment/rebuttal — your choice.

    To someone other than Tenney: David reviewed “Revenge of Gaia” here ( and describes the solution to increasing solar forcing (over geological time) as reducing atmospheric CO2. The Moon’s orbit is also increasing over time, reducing tidal effects (I presume). The link in comment 70 is to a Time magazine piece that implies an orbiting moon can warm a planet over geological time. I have never read about this idea in reference to cooling the Earth over time, or in reference to the Earth’s climate more generally. Have you? Sorry about being off-topic, but I wanted to mention it in the context of supporting the idea that the Moon has climatological effects (and so it’s not totally crazy to examine it with respect to even short-term phenomena like seasonal sea ice).

  40. 90
    Martin Vermeer says:

    Marcus #67, I was going to suggest in reponse to your pointing out the fallacies in “truth”‘s comment, that it would be more parsimonious to list the things he does not get wrong… but then I noticed that there aren’t any.

    Taken literally that would mean that the best would be not to comment at all, and now I see that tamino in #66 already covered that base…

    It’s clairvoyance I tell ya.

  41. 91

    Oddly, eyeballing the graph J. Bob posted (7/16, 9 AM) certainly makes me think there is a downward trend WRT global sea ice extent, which seems to be the opposite of his conclusion. (And I’m guessing he may have missed Tamino’s comment about the discontinuity in the numbers.) But eyeballing, as we know, is not the ultimate arbiter. So I looked to see what I could find, and came up with this, from 2008 (data current to 2006):

    “. . .the trends in ice extent and area in the Arctic are now slightly more negative at −3.4 ± 0.2 and −4.0 ± 0.2% per decade, respectively, while the corresponding trends in the Antarctic remains slight but positive at 0.9 ± 0.2 and 1.7 ± 0.3% per decade.”

    Still not “global.” So, resorting to the metaphorical back of the envelope, NSIDC gives average maximum areal extent as about 15 million km2 for the Arctic, and 18 million for the Antarctic. (Baseline minima are ca. 7 million and 4 million respectively–yes, quite different from current numbers.) If you assume that the maxima are the most applicable numbers for assessing which trend dominates the global trend–minima are clearly less favorable to J. Bob’s case–you’ll conclude the balance is downward. (For instance, you could reason that since the Antarctic maximum is about 15% larger, that trend should be weighted by a like amount: .9% x 1.15 = 1.035%–not nearly enough to counterbalance the Arctic ice loss.)

    (Of course, this will change with time one way or another: if the separate trends persist, the Antarctic growth will come to dominate over time, since Antarctic sea ice will come to be a larger and larger portion of the total. Conversely, the Arctic and Antarctic minima are presently tending to converge. On the other hand, there is good reason to think that it won’t play out that way: as planetary warming continues, the growth trend in the Antarctic sea ice will surely reverse.)

    Naturally, a proper analysis would be much more complicated and comprehensive than this (and you’d need a better analyst than I.) You’d have to make sure that everything was “orthogonal” and “homogenous”–that is, that you were applying the correct trends to the correct data, and not, for example, the June trend to the yearly mean anomaly–or at least applying appropriate correction factors as needed. (That’s if I’m understanding those terms correctly.)

    Lastly, one reason that the aggregated data is so hard to find is surely that the Arctic and Antarctic cases are so different–nobody seems to think that studying both “at once” is very productive. For a nice summary of the many differences, see:

    (BTW, I strongly suspect I didn’t achieve proper “orthogonality & homogeneity” in the “back of envelope” stuff above. For one thing, the abstract I quoted doesn’t explicitly say that the trends discussed are WRT annual means–that’s just my guess. If so, I presumably should have done my weighting with annual mean extents, too. But that would have been too much data crunching than I could stomach for a brief (and nominally casual) post.) Frankly, I was hoping just to find the data used to generate the graph, and then run the numbers for trend–but no dice.)

  42. 92
    Steve L says:

    Thomas, 81 — thanks. I didn’t see your reply prior to what I just posted (assuming it survives moderation).

  43. 93
    Michael Sweet says:

    J. Bob #85

    Are you suggesting that the uiuc graph you linked to shows ice running about normal? Fit a line to the data. It is obvious even from a cursory examination that the ice has declined in the past thirty years according to the linked graph. Looks like you bungled it again.

  44. 94

    The public certainly keys on the Arctic Sea ice and I mention it on air rather frequently. They do have trouble understanding the difference between Antarctica and the Arctic. Perhaps half do not even realize that one is Ocean and the other is continent.

    Make no mistake though, for good or bad, the disappearing ice in the North is more than just a scientific metric, it’s the poster child for our changing planet.

    Hank: Kudos from me too, but you can lead a horse to water….

  45. 95
    Mark says:

    “Global sea ice still running about normal, no mass meltdown:”

    Yet the link says:


    Uh, mass is density times volume.

    Not density times area.

    Still, I wouldn’t expect you to know that. It’s science.

  46. 96
    Mark says:

    “If the Antarctic sea ice is at almost recorded highs”

    It’s because it’s passing to its winter.

    Where there is exactly as much no sun as there has always been.

    Even the best coffee flask lets the coffee get cold after four months…

  47. 97
    Michael Stefan says:

    J. Bob – Have you even considered why Antarctic sea ice is so high (increasing) even though the Southern Hemisphere oceans were the warmest on record for June? A good explanation of the increase in Antarctic sea ice can be found at Skeptical Science; and no, that doesn’t mean that land ice isn’t melting, which it is. Antarctica has also been rather warm lately based on various maps (e.g.).

    Also, I think it is obvious that something is “up” with UAH if they disagree so much with surface temperatures (especially considering the ocean temps):

  48. 98
    NeilT says:

    #85 J. Bob,

    I was going to post on this over the weekend but ran out of time.

    I have studied the same chart you are looking at. But I seem to see different figures. You seem to be looking at the peak. I’m looking at the span of time at high ice concentration. You wil note that at the beginning of the chart there was a solid period of months where the Global Ice was high. Now and for years, there has been a spiked drop off smack in the middle of high ice time. Which means the duration of high ice levels has dropped significantly.

    If you only look at the spike then, yes, the drop has been somewhat insignificant.

    If you look at the amount of time we now have high ice concentrations it would appear to me, without reference material, that it has dropped by some 20%-30%

    Which is what the scientists are saying.

    So pointing at the same charts, reading them incorrectly and then boldly stating that the published results are wrong; doesn’t seem to be a good way of putting your argument forward.

  49. 99
    Jacob Mack says:

    Hank Roberts: This is in dire need, what you provide, and do not belittle what you do in helping others learn. Your efforts are still, as always greatly appreciated.

  50. 100
    Hank Roberts says:

    “All instruction is but a finger pointing to the moon; and those whose gaze is fixed upon the pointer will never see beyond. Even let him catch sight of the moon, and still he cannot see its beauty.”
    (April 1888)

    How difficult it is to see the Earth!