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Notes from The Gathering #5: Arctic sea ice: is it tipped yet?

Filed under: — david @ 13 December 2007

The summer of 2007 was apocalyptic for Arctic sea ice. The coverage and thickness of sea ice in the Arctic has been declining steadily over the past few decades, but this year the ice lost an area about the size of Texas, reaching its minimum on about the 16th of September. Arctic sea ice seems to me the best and more imminent example of a tipping point in the climate system. A series of talks aimed to explain the reason for the meltdown.

Sea surface temperatures were warmer this past summer also; I forget how many standard deviations the temperature was off the trend, but it was definitely anomalous. The region of the meltback is just inside the Bering Strait, where warm water flows in from the Pacific, but in the analysis of Steele et al. this inflow of comparatively warm water was not particularly anomalous in 2007 relative to other years. It could be that the exposure of the sea surface to the atmosphere by the melting ice could have an impact, although the meltback is so late in the solar heating season (September) that this effect seems of limited explanatory value also. Bit of a chicken and egg problem here.

Melting ice can be seen from space, I believe as puddles sensed by the QuickSCAT satellite. The puddles are most abundant in mid-summer when the sunlight is strongest, and by mid-September when the ice meltback was the strongest, the melting season was largely over. Apparently the reason for the disappearance was an anomalous weather system which generated a strong jet of surface winds blowing straight over the pole southward toward the Atlantic ocean, a “Polar Express”. A research ship frozen into the ice in 2006 crossed the Arctic in about a year, about three times faster than the transit time of the Fram in the 1890’s. To summarize, the ice cubes in the freezer tray didn’t melt because the freezer is broken exactly, but because the ice cube tray fell out of the freezer onto the warm floor.

The disappearance of the ice was set up by warming surface waters and loss of the thicker multi-year ice in favor of thinner single-year ice. But the collapse of ice coverage this year was also something of a random event. This change was much more abrupt than the averaged results of the multiple IPCC AR4 models, but if you look at individual model runs, you can find sudden decreases in ice cover such as this. In the particular model run which looks most like 2007, the ice subsequently recovered somewhat, although never regaining the coverage before the meltback event.

So what is the implication of the meltback, the prognosis for the future? Has the tipping point tipped yet? When ice melts, it allows the surface ocean to begin absorbing sunlight, potentially locking in the ice-free condition. Instead of making his own prognosis, Overland allowed the audience to vote on it. The options were

  • A The meltback is permanent
  • B Ice coverage will partially recover but continue to decrease
  • C The ice would recover to 1980’s levels but then continue to decline over the coming century

Options A and B had significant audience support, while only one brave soul voted for the most conservative option C. No one remarked that the “skeptic” possibility, that Arctic sea ice is not melting back at all, was not even offered or asked for. Climate scientists have moved beyond that.


202 Responses to “Notes from The Gathering #5: Arctic sea ice: is it tipped yet?”

  1. 1
    stuart says:

    Of course if it is B, as the models might seem to somewhat suggest (and wouldnt be too surprising as just an effect of variability), then no doubt next year the contrarians will start telling everyone how the arctic melt has reversed, in the same way that 1998 has been touted as the ‘end of global warming’ in some corners.

  2. 2
    Nick Barnes says:

    This is a little confusing. There’s no need to explain anything particular about September this year. The sea ice was at a record low level before we even got to September. September was more-or-less routine: we lost ice as we do in every September, but not a remarkable amount. The really exceptional time for sea ice loss this year was the second half of June.

    Check the tale of the tape: http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/sea.ice.anomaly.timeseries.jpg, or the last 12 months: http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.365.jpg

    [Response: Yeah... hmm. The speaker's statements seemed to make sense to me at the time, but your point now seems like a good one. I could choose excuse A This is not my speciality, I'm only trying to report stuff that seems interesting, or B This meeting is exhausting. Good thing I don't have to operate any heavy machinery. David]

  3. 3

    A recurring problem with public perceptions of excursions in weather and climate is a widespread innumeracy, notably (a) an insufficient appreciation for what it means to have random excursions from a strong trend, and (b) inappropriate assessments of risk, even sizeable ones. The latter really came through in the conclusion of Professor Lonnie Thompson’s talk yesterday. I’ve heard the same from others, that until dead bodies start being carted away from the intersection, noone’s going to think about putting up traffic controls. Unfortunately, here we are talking about numbers of dead much greater than the Shoah, and much greater than the numbers lost in all of World War II. And the powers that are in charge of these things are playing it like a poker game.

    It is just so damn sad.

  4. 4
    paul m says:

    Will the melting of the Ice Sheets have an effect on the orbit of the earth around the sun?

    For that matter does a rising/falling sea level have an effect on the earth’s orbit (5ft-50ft-200ft-tides)?

    Is the suns radiation still increasing over what it was in the past and do the climate models take this into account?

  5. 5
    AndrewM says:

    Interesting sea ice maps on http://www.arctic-warming.com , when another arctic warming started about 90 years ago.

  6. 6
    Ray Ladbury says:

    paul m,
    Earth’s orbit will not be affected, as Earth’s mass will remain constant. The rate of rotation may be slightly affected as mass shifts from pole toward the Equator and changes (slightly) the moment of Inertia.

  7. 7
    Brett says:

    Is there some percentage of ice coverage at which point the ice doesn’t recover much in the winter enough to stop complete melting the next time summer comes around?

  8. 8
    Hank Roberts says:

    Paul M asked about the solar trend, assuming it’s going up. Check your assumption for significance, Paul:

    Measured at +0.05 percent (one twentieth of one percent, or five-one-hundredths-of-one-percent — per ten years. Awfully close to zero, eh, compared to the rate of change of fossil fuel use, and temperature.

    >http://www.nasa.gov/centers/goddard/news/topstory/2003/0313irradiance.html

    “The accurate long-term dataset, therefore, shows a significant positive trend (.05 percent per decade) in TSI between the solar minima of solar cycles 21 to 23 (1978 to present). This major finding may help climatologists to distinguish between solar and man-made influences on climate….”

  9. 9
    Russell says:

    I went golfing one day and started the day by shooting 2 birdies in a row. Well I immediatly extrapolated this to the 18 holes, and concluded that a 54 was in order, due to the results from my limited data set. Unfortunately, I learned the error of my way, and my score returned to the mean.
    The history of the Arctic Ocean, is a blank slate. Any attempt to draw conclusions from the limited amount of data available, is destined to fail. If you can’t tell me what it was like 200, 600, 1000, 4000, 10000, etc. years ago, you can’t tell me where it will be in the future.

    [Response: I rolled a sphere down an inclined plane twice, measured the time it took and calculated the acceleration. I predicted that the for the next 16 rolls the acceleration would be constant. Lo and behold, I was able to predict how long it took the 18th time. See the difference? - gavin]

  10. 10

    Well, I agree that A and B are correct. “The meltback is permanent” and it “will continue to decrease” at the same rate until it has gone completely!

  11. 11
    Dr. J says:

    It is obvious none of you listened to this presentation at AGU on Monday morning: “PP11A-0203
    Ice free Arctic Ocean, an Early Holocene analogue.”
    Yes, the Arctic Ocean has been ice free many times in the past and that state has lasted many hundreds of years [edit]

  12. 12
    Gary says:

    A study relating to this – “Our study confirms many changes seen in upper Arctic Ocean circulation in the 1990s were mostly decadal in nature, rather than trends caused by global warming,” said Morison.

    http://www.nasa.gov/vision/earth/lookingatearth/ipy-20071113.html

    [Response: Note that this has very little to do with the ice melt. - gavin]

  13. 13

    Paul writes:

    [[Will the melting of the Ice Sheets have an effect on the orbit of the earth around the sun?]]

    Not enough to measure, no.

    [[For that matter does a rising/falling sea level have an effect on the earth’s orbit (5ft-50ft-200ft-tides)?]]

    Again, not enough to measure.

    [[Is the suns radiation still increasing over what it was in the past and do the climate models take this into account?]]

    The Solar constant has shown no trend up or down since about 1950.

  14. 14
    Paul says:

    Gavin’s response to Russell’s comment about golf is a terrible analogy. I would equate the changing climate to a game of golf long before I would equate it to rolling a ball down an incline. There is very little variability in rolling a ball down an incline. There are innumerable factors that affect climate just as there are in a game of golf. Gavin is suggesting that a linear relationship can be extrapolated out of limited climate data, when it obviously can’t be.

    [Response: No I wasn't. I was using the analogy of predictability of a system where you have a good idea of the physics vs. an empirical statistical model based on a low number of past occurrences. Physics is extrapolatable, statistics (in this specific case), is not. - gavin]

  15. 15
    Patrick M. says:

    Re 8:

    Go ahead, Gavin, and predict the extent of arctic sea ice for the next 5 years. I hope that sphere you were rolling is crystal, cause you’re gonna need it…

    [Response: I go with option B. - gavin]

  16. 16
    B Buckner says:

    It is not obvious to me that an ice free north pole is necessarily a positive feedback. The conventional thinking is that the albedo of the ice is much higher than open water, therefore the sunlight will warm the arctic water rather than being reflected back into space. I have never seen the ice free heat exchange condition quantified and compared to the ice cap condition. Please direct me to a reference if handy.

    The upper layer of the ocean is heated by direct sunlight, mostly in the tropics. On average, the ocean surface is warmer than the atmosphere, and that is certainly the case near the north pole. The ocean is cooled by net back (ir) radiation, conduction on contact with the cooler atmosphere, and heat loss due to evaporation.

    So with the ice cap in place, there is no direct solar heating of the arctic water. Without the ice cap, there is only limited solar heating because of the low angle of the sun, 11 degrees above the horizon on average during the six months of sunlight at the pole. At this angle, the albedo of water is about 0.3 or an order of magnitude higher than in the tropics. With the albedo of older snow and ice at about 0.6, the open ocean will absorb more heat than the ice capped ocean.

    With the ice cap in place there is essentially no cooling of the arctic ocean. The ice effectively blocks net back radiation, eliminates contact with the atmosphere and therefore conduction, and blocks evaporation. So the question is, is the small increase in direct solar heating of the arctic water larger than the cooling that occurs when the warm arctic water is left exposed? Qualitatively, it appears obvious that the arctic ocean will net cool. With the sun continuing to heat the ocean water at the tropical latitudes regardless of ice cap conditions up north, it would seem that the presence of an ice cap would result in a warmer ocean over the long term, with the converse also being true. Perhaps this is why there are long term warm/cold climatic cycles, rather than runaway heat or cold. At the peak of each cycle, the oceans are acting counter to temperature trends.

  17. 17
    Ian says:

    Re “There is very little variability in rolling a ball down an incline”

    This is true only if you’re measuring in the sorts of units that match our unaided senses – watching the ball roll and counting full seconds to yourself, for example. Use an oscillator to time the ball and you’ll find all sorts of variability, measured in small fractions of a second, in the ball’s travel. The important point is that despite this variability, we can predict adequately well for many purposes, because we understand something about the basic physics. Similar argument for climate…

  18. 18
    Mitchell says:

    There is hope:
    Arctic Sea Ice Re-Freezing at Record Pace
    After Record Summer Melt, Recovery Still Lags
    http://www.thedailygreen.com/environmental-news/latest/arctic-sea-ice-47121205

  19. 19
    John Ransley says:

    Umm, it seems someone can’t count or I’m missing something. Dispatch #4 is the same as dispatch #3. cheers

  20. 20
    Patrick M. says:

    Re 13:

    Option B? That’s lame. Draw a graph of the next 5 years. It’s physics right? It should be similar to predicting an eclipse or rolling a ball down an incline.

  21. 21
    J.C.H. says:

    Isn’t Option B is too easy? If ice of any sort comes back by a sliver for a moment in time, it’s a partial recovery?

    I think the question should be posed in terms of perennial ice, and a recovery should have to exceed 5% to be make it count.

    If slightly more annual ice survives the melt season, is that really significant?

  22. 22
    Chuck Booth says:

    RE #3 Paul m’s question about melting glaciers and Ray’s response (#5):”The rate of rotation may be slightly affected as mass shifts from pole toward the Equator and changes (slightly) the moment of Inertia.”

    An interesting point in light of a report several years ago in Science suggesting that the extensive damming of rivers in the northern hemisphere has altered the earth’ moment of intertia, hence, its rotational velocity (increasing it, if I’m not mistaken). Unfortunately, I couldn’t track down the article. But, the following articles do deal with the effects of melting glaciers and rising sea level on the earth’s rotation (not its orbit, of course):

    Global Sea Level and Earth Rotation
    W. R. PELTIER
    Science 13 May 1988:
    Vol. 240. no. 4854, pp. 895 – 9011
    Recent analyses of long time scale secular variations of sea level, based on tide gauge observations, have established that sea level is apparently rising at a globally averaged rate somewhat in excess of 1 millimeter per year. It has been suggested that the nonsteric component of this secular rate might be explicable in terms of ongoing mass loss from the small ice sheets and glaciers of the world. Satellite laser ranging and very long baseline interferometry data may be used to deliver strong constraints on this important scenario because of the information that these systems provide on variations of the length of day and of the position of the rotation pole with respect to the earth’s surface geography. These data demonstrate that the hypothesis of mass loss is plausible if the Barents Sea was covered by a substantial ice sheet at the last maximum of the current ice age 18,000 years ago.

    Oceanic Effects on Earth’s Rotation Rate
    Clark R. Wilson
    Science 11 September 1998:
    Vol. 281. no. 5383, pp. 1623 – 1624

    Changes in the mass distribution of water in Earth’s oceans in turn leads to variations in its angular momentum. In his Perspective, Wilson discusses results presented in the same issue by Marcus et al. in which techniques of radio astronomy were used to measure changes in Earth’s angular momentum. The variations were observed by measuring changes in the length of day, and therefore Earth’s rotation rate. Measurements such as these may serve as an indicator of oceanic behavior, much as other indices are used to keep track of atmospheric climate.

  23. 23
    harkness says:

    Aren’t a lot of scientific bodies now predicting total loss of Arctic ice during the summer in just a few years? How could that square with even partial recovery of perennial ice? Shouldn’t we expect regular loss of ice every year? Haven’t the models been wildly optimistic about this until quite recently?

  24. 24
    harkness says:

    Sorry, more questions: Is there a possibility that all that fresh water from the melting Arctic ice will find its way into the northern Atlantic, decrease the salinity there, and slow or stall the thermohaline circulation?

    And once the entire Arctic Ocean is ice free, won’t that mean the whole thing will be sucking up solar energy 24/7 during midsummer? Won’t that lead to a super-heated body of water? Will that accelerate the melting of the tundra in Siberia and Alaska, releasing ever more massive volumes of methane?

    Could the Arctic Ocean heat enough in these circumstances to melt the clathrates locked underwater along the continental shelves releasing even more massive amounts of methane? What are we looking at here?

    As I recall from high school chemistry, melting of ice is an endothermic reaction–it cools the water and air around it as it melts. With no more ice melting to cool the water, will we see even higher levels of solar heating?

    Sorry for so many questions, but these have been on my mind for a while.

  25. 25
    Greg says:

    I know my city isn’t the one causing all this American pollution:

    http://www.efficientenergy.org/Top-Ten-Green-Cities-in-the-United-States

    this article shows who is and who isn’t. I also too the carbon calculator at http://www.earthlab.com and I can see that I am not the one who is polluting, you guys should take it too to reaffirm that you aren’t either (I could be preaching to the congregation here)

  26. 26
    Andrew says:

    Re “Go ahead, Gavin, and predict the extent of arctic sea ice for the next 5 years. I hope that sphere you were rolling is crystal, cause you’re gonna need it…”

    Well this was from my brother. I am very happy to see it here because he is always elbowing me about how http://www.realclimate.com doesn’t post his comments. So presumably now we will not have to cover that ground any more.

    I have not read the original post yet so I won’t comment further until I have.

  27. 27
    Andrew says:

    Re: “Option B? That’s lame.”

    Did you want the correct answer or to be “impressed” with something false?

    What is YOUR prediction for arctic ice extent over the next five years? If we’re going to call people out for forecasting skill, then by all means let’s have some superior forecasting skill.

  28. 28
    Dale Butler says:

    Preferential warming at the poles due to CO2 dominance in a dry environment.

    1. It is certainly true that water vapour has a huge and overpowering greenhouse effect.

    2. It is also true that in the polar latitudes there is very little water vapour in the atmosphere. It is mostly locked up as ice or snow or has been simply precipitated out.

    3. Co2 will diffuse throughout the entire atmosphere in accordance with the gas laws.

    4. As the CO2 content at the poles increases it will have the effect of increasing the polar temperatures slightly, particularly during the polar summers. (The effect of Increased CO2 on the tropical latitudes will tend to be swamped by the
    high humidity).

    5.Thus the effect of increasing CO2 since c.1900 will differentially tend to heat the polar regions.

    6. This rise in temperature will allow the water vapour to penetrate further into the polar region before it gets turned into ice

    7. This in turn increases the “greenhouse effect” due to both water vapour and CO2, remember that the effect is circumferential and thus a small linear change is multiplied by piXr2XH(H= atmospheric depth). Presumably there is a vapour diffusion zone centred upon some latitude.

    8. Add in Albedo effects due to ice melt and you possibly have a recipe for rapid change

    This is the sort of feedback mechanism that concerns me.
    Dale Butler

  29. 29

    The Earth has already experienced a globally averaged 0.7 or 0.8 degree C warming,over the past century, and it may be 3or 4 times that in some regional polar areas.

    Anyone who accepts that sunlight falling on ice free waters which has less reflectivity than sunlight falling on a large ice mass covering those waters and also accepts that this reduction in albedo has a positive feedback effect,leading to further warming, can’t help but opt for A or B, it seems to me.

    The initial warming, over the past century, has caused a condition at the North Pole, that will only add to this warming, which will lead to further melting, which will lead to a further temperature increase. We may well have arrived on the slippery slope as far as the North Polar region is concerned.

  30. 30

    Who has examined the impact of an ice-free summer Arctic and warmer Arctic waters with release of tundra and Siberian ghg sinks? This looks like a place where feedbacks could multiply.

  31. 31
    Alex J says:

    AndrewM, while your site says past warming in the Arctic was “largely ignored by alarmist scientists”, it has actually been acknowledged by those concerned about the current, ongoing and global trend. Not only on this site, but on NASA’s, where they point out that regional warming through the early 30′s was much slower. Even at this point (and clearly it ain’t done yet), the current trend is broader in scope.

  32. 32
    Andrew says:

    Don’t know a thing about what may or may not be in the IPCC models.
    However, what seems obvious is that it’s not that the freezer is
    completely broken as much as it is that the ice cubes have fallen out.

    In other words, what we are seeing is a dramatically more fluid artic.
    (at least during the summer and fall)
    The increased fluidity is allowing the sea ice to flow out of the artic
    at an unprecedented rate.

    Perhaps some have noticed that the record minimum sea ice extent when
    expressed as a millions-km2 from normal actually occured in October.
    This was well after sun set, but at a time before enough freezing took
    place to lock everthing into place.

  33. 33
    B Buckner says:

    The difference in albedo between open ocean and ice/snow in the polar region is small due to the low sun angle. An ice-capped ocean cannot cool because the ice blocks outgoing ir radiation, conductance with the atmosphere and evaporation, all potent cooling effects. Net result, arctic ocean cools without ice cap, warms with it, therefore negative feedback.

  34. 34
    Bruce Tabor says:

    A curious difference between the measurement of loss of ice from the Greenland ice cap and loss of Artic sea ice is the different ways these are measured.

    Greenland ice loss is measured by volume (or equivalently, mass), which makes sense in terms of the implications for sea level rise. Arctic ice loss is measured by loss of area (extent). Yes, sea level rise is not an issue, and ice thickness is difficult to measure.

    Physically arctic sea ice area is important due to it’s influence on albedo, but in terms of melting rate, surely ice volume is more important for the physics?

    I’ve had trouble finding estimates of loss of ice thickness, but it is clear that arctic sea ice has thinned considerably. It is quite possible that we are well past half-way – maybe at 75% in terms of loss of arctic sea ice mass.

  35. 35
    John Monro says:

    I hope Santa is reading this, because it won’t be long before he’ll be needing a boat. He needs to start cracking now, so rather than his little helpers packing Christmas presents, he needs to be making some long term investments in timber and nails for a sustainable infrastructure……hmmmm, perhaps that’s what we should all be doing. I can imagine some future artist showing Santa careering through the skys in his boat, the sledge being redundent, with the reindeer, now extinct, replaced by dolphins.

    I think your options are a bit vague. Do options “A” and “B” for instance allow even a small recovery?

    What about then option “A”, rapid meltdown of ice until summer free by or before 2013, option “B” no summer ice by 2030, and option “C” summer ice gone by 2080. My option is for “A”, and indeed I think the ice will be gone by 2010.

    We will then have the open Arctic Ocean absorbing, from my understanding, about a third more solar energy each summer due to the difference in albedo between Arctic sea ice and open water. This will dramatically accelerate temperature rises in the northern hemisphere, melt the Greenland ice cap, and for a while we are going to have a planet of two halves – a rapidly warming northern hemisphere and a much more modestly increasing temperature in the southern. I am no climate scientist but what would be the estimate of the maximum difference in temperature rises in the two hemispheres and how long is this state of affairs likely to continue?

    Merry Christmas everone.

  36. 36
    Steve Bloom says:

    RC authors: #4 is link spam from our naval-warfare-caused-warming friend. IMHO it should be removed, but at a minimum the live link should be killed.

    On the general subject of the early 20th century Arctic warming, scientists inspired by Jim Hansen’s ideas had a look and this was the result:

    20th-Century Industrial Black Carbon Emissions Altered Arctic Climate Forcing

    Abstract: Black carbon (BC) from biomass and fossil fuel combustion alters chemical and physical properties of the atmosphere and snow albedo, yet little is known about its emission or deposition histories. Measurements of BC, vanillic acid, and non–sea-salt sulfur in ice cores indicate that sources and concentrations of BC in Greenland precipitation varied greatly since 1788 as a result of boreal forest fires and industrial activities. Beginning about 1850, industrial emissions resulted in a sevenfold increase in ice-core BC concentrations, with most change occurring in winter. BC concentrations after about 1951 were lower but increasing. At its maximum from 1906 to 1910, estimated surface climate forcing in early summer from BC in Arctic snow was about 3 watts per square meter, which is eight times the typical preindustrial forcing value.

    To see the full paper, go here and scroll down to the publication list.

  37. 37
    Alex J says:

    John,

    I heard a rumor that “Santa” is firing the elves and moving the operation to a coal-powered factory in China. Say it isn’t so.

  38. 38
    Hank Roberts says:

    John, David reported the choices presented by the speaker, they’re not David’s choices to argue with — David reported what the audience heard and voted on. I was puzzled too, since we know there’s been some refreezing. David, can you clarify what option A meant as presented in the meeting?

    I’d guess that looking at the chart, A might mean what seems to be happening now, if the ice doesn’t recover quite a bit in the next couple of weeks. Comparing the last couple of weeks of December for all the years on the chart record, the line did drop about as low last year and then recover as it dropped the last few days. But look back at where it’s been at the end of December in past years.

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/sea.ice.anomaly.timeseries.jpg

    [Response: There wasn't really any more presented than what I wrote, but I assumed the issue is whether the summer minimum in 2008 will match that of 2007, or whether it would recover somewhat. David]

  39. 39

    Bruce Tabor (#31) wrote:

    I’ve had trouble finding estimates of loss of ice thickness, but it is clear that arctic sea ice has thinned considerably. It is quite possible that we are well past half-way – maybe at 75% in terms of loss of arctic sea ice mass.

    The NASA satellite data is coming, apparently. But for a some previews…

    Greenland’s ice sheet melted nearly 19 billion tons more than the previous high mark, and the volume of Arctic sea ice at summer’s end was half what it was just four years ago, according to new NASA satellite data obtained by the Associated Press (AP).

    Arctic Sea Ice Gone in Summer Within Five Years?
    Seth Borenstein in Washington
    Associated Press
    December 12, 2007
    http://news.nationalgeographic.com/news/2007/12/071212-AP-arctic-melt.html

  40. 40

    I thought I had seen the year 2013 mentioned somewhere before…

    According to Cryosphere Today, we were below 3 million km sea-ice area on Tuesday, more than 25% below the previous all-time low of 4 million set in 2005. I’d would try and relax: at this rate we have another five years of summer sea-ice. 2013.

    30 August 2007 at 5:14 PM
    Comment 299 of Arctic sea ice watch

  41. 41
    Bruce Tabor says:

    Arctic sea ice thickness:

    In 1999 Rothrock et al published a paper showing research from sonar data collected by US Navy submarines that showed arctic ice thickness had declined over large areas of the artic from an average of 3.1 metres to 1.8 metres (about 40%) from 1958-76 to 1993-97.
    http://psc.apl.washington.edu/thinning/thinning.html

    The following site projected the Rothrock data to predict the arctic sea ice would be virtually all gone by this year, 2007.
    http://www.daviesand.com/Choices/Precautionary_Planning/Arctic_Ice/

    Not surprisingly there is evidence that this projection is slightly wrong ;-)

    The following site states German researchers from the Alfred-Wegener-Institute for Polar and Marine Research found that mean ice thickness in September 2007 is 1 metre, down by half from 2001.
    http://news.mongabay.com/2007/0914-sea_ice.html

    I wont pretend this is a thorough literature review, but it suggests to me that ice thickness is more important than ice extent in determining when the arctic will be sea-ice free in summer, and that we have less than a decade until this occurs – it may be as early as September 2012.

    On the plus side, it will be extremely difficult for sceptics to argue against AGW after this “tipping point”. You could always invite them to take an expedition to the north pole by foot, sled, all-terrain vehicle etc.

  42. 42
    B. Waterhouse says:

    If #32, last para., is correct, what effect would a warming northern hemisphere and relatively cooler southern hemisphere have on ocean currents and weather patterns?

  43. 43
    barry says:

    Sea ice coverage in the Antarctic has been larger this summer than last, and shows an opposite trend to the Arctic coverage since the 1970s.

    http://www.gsfc.nasa.gov/topstory/20020820southseaice.html

    If I were a contrarian saying that, I would be answered “you shouldn’t invest your understanding in just one geographical location – you have to see the whole,” but the same criticism can be applied to the post at the top of this thread.

    In the interests of robustness, wouldn’t it be worthwhile acknowledging that qualification and responding to it?

  44. 44
    Lawrence Coleman says:

    I’ll put my money on B, but it’s closer to A than you like to admit. The sea ice will continue to accellerate it’s decline until it’s gone- (house of cards scenario) for the short term only during summer, for the medium term until it’s permantly gone, year round. As mentioned by nasa, the apocalyptic ice melt this year preconditions the region for an even more drastic melt the following year (positive feedback at it’s most apparant and stark!) No-one has mentioned the fate of polar bears yet, do we just wash our hands of this species or do we try to relocate as many as possible to sactuaries and zoos?. Canada is a poor option since it will also be largely swamped as sea levels inevitably rise as the greenland melt intensifies. What do you guys think?

  45. 45
    CobblyWorlds says:

    #40 Barry,
    The point about the Antarctic is that it’s trend is not considered statistically significant.

    Here’s the Arctic – significant.
    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.jpg

    Here’s the Antarctic – not significant.
    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.south.jpg

    Furthermore there are changes in the Arctic that add to the significance – widespread thinning – see below.

    #38 Bruce Tabor,
    I agree. There’s good reason to suppose ice thickness is the major factor.

    1) It takes as much energy to melt an amount of ice as it takes to warm that same amount from 0degC to 80degC.

    2) Thin ice is less mechnically strong than thick. Leads can more easily open in winter allowing ocean to atmosphere heat transfer.

    3) In terms of conductive heat loss through the ice, the thickness is the denominator term.
    i.e. Q = Ki(To-Tf)/h,
    where Ki is a constant, To-Tf is the temperature difference between surface and underside, and crucially the heat flux is Q, h is thickness. So flux is proportional to the inverse of the thickness.

    4) By definition the thicker “perennial” ice takes more than one season to re-grow. So natural variation will have a time-lag on ice growth that does not apply to ice loss. Once thinning has occurred this time-domain asymetricality can “take advantage” of weather events.

    I see sea-ice thickness as a key factor in limiting the impact of summer melt under ice-albedo feedback. A thin sheet of ice will respond all the more quickly in the melt-season thank will a thick. It’s useful to try to qualitatively visualise the differences between the “old” regime as shown in the first link above, and where we seem to be headed.

  46. 46
    pete best says:

    We are talking about it being gone in the Summer only as it is not possible for it to be gone in the winter I presume due to the sunless nature of the arctic but I guess that energy from the summer air and water can reduce the extent of sea ice recovery. Is this what we are seeing?

    Due to Antarticas nature of not being surrounded by continents and being a continent its melting potential is different but what is the reality there.

    I know that the arctic is warming quicker than antartica but surely the implications of the antartic warming reach further than the arctics warming due to its continental nature a 2 mile thick ice sheets.

    The bernard convection cells that are expanding at the tropics are down to the arctic shrinking. Is the same true for the southern hemisphere?

  47. 47
    Chris Colose says:

    What is very worrysome here is that arctic sea ice is now being lost faster than thought, and that so little is understood about accelerated glacier flow. Not sure I agree with gavin’s “rolling ball” analogy here. What worries me, in terms of these “tipping points” is that when decadal variability (ex. the positive “natural” AO was mentioned from Morrison) is superimposed on a rising trend in the nonlinear world of sea ice, the system can be pushed across a critical threshold and is unable to return to the initial cyclic state. So if the arctic crosses some point like this, even if we could magically bring conditions back to pre-industrial, the ice may still be like today or worse (and could easily get option “A”). Then you have anthropogenic effects on AO; nearly all scenarios have the AO rising (though not as fast as the ’90s swing).

    Unfortunately, the world of ice is a doom and gloom situation (see Lonnie Thompson’s presentation at AGU). Very alarming, but as Ray Pierrehumbert mentioned in the “latest dispatch” this probably doesn’t mean much when we talk about “tipping point or not” because in any case, there are problems. In either case, emissions need to be lowered.

  48. 48
    Bruce Tabor says:

    Re. 36 and 37. Timothy Chase.
    Thanks Timothy,
    I can see that my line of thinking has been put before – in the National Geographic article you cite and on Real Climate:
    http://www.realclimate.org/index.php/archives/2007/08/arctic-sea-ice-watch
    I notice (in that thread) Walt Bennett even made the prediction of all permanent arctic sea ice gone in 5 years (2012) and Chris Dillion puts it at 2011. (I posted @38 before seeing your posts.) neither would surprise me, but at this stage I would be surprised if it WASN’T all gone by 2017.

    In line with others’ observations, I suspect the reason we get surprised by sudden reductions in the extent of arctic sea ice is that we don’t have a good handle on what matters – the regional distribution and change in ice thickness.

    Also I loved Chris Gillon’s suggestion for the name of the new geological epoch: the Ohshitocene – my god what have wwe done!

  49. 49
    Fernando Magyar says:

    Re 32,
    “I can imagine some future artist showing Santa careering through the skys in his boat, the sledge being redundent with the reindeer, now extinct, replaced by dolphins.”

    We’ve been doing this for a while where I live in Florida.

    BTW some of us celebrate alternative holidays around this time of year:

    Some call it Squidmas, or Octonoël,
    To some, it’s Kopffüßerweihnachten as well
    In Spain they will wish you “Feliz Nautilidad”
    And think nothing of it–it isn’t that odd.
    There are similar phrases in Greek and Etruscan
    Expressing a good celebration molluscan
    From ocean to ocean, the banner’s unfurled:
    It’s Cephalopodmas all over the world!

    Posted by: Cuttlefish | November 25, 2007 1:15 PM

    http://scienceblogs.com/pharyngula/2007/11/squidmas_is_coming.php

  50. 50
    dhogaza says:

    Sea ice coverage in the Antarctic has been larger this summer than last, and shows an opposite trend to the Arctic coverage since the 1970s.

    http://www.gsfc.nasa.gov/topstory/20020820southseaice.html

    If I were a contrarian saying that, I would be answered “you shouldn’t invest your understanding in just one geographical location – you have to see the whole,”

    Naw, we might point out that the second half of your statement is based on a study published five years ago, and ask why didn’t you say “as of five years ago”, rather than imply that your link shows the trend continues today.


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