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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. 401
    Larry N says:

    Has anybody done an in depth analysis, of seasonal lag (statistical warmest day based on climate records after maximun solar insolation).

    Here in Halifax, August 1 is the warmest day (from a climate perspective). In the arctic (ie. Resolute, it appear to occured over a week ago), so I assume that seasonal lag is less with increasing latitude.

    However, large bodies of water, appear to lengthen season lag, as it has a dampening effect.

    In the past several years, the rate of ice melt has not slowed down in August, as in the past, and I wonder if this has more to do with seasonal lag, than the condtion (thickness and structure) of the ice.

  2. 402
    Mark says:

    Max, I read it.

    Given it starts with the unscientific and emotion-laden “Hysteria” didn’t give it a good start. Making a strawman in the first sentence wasn’t auguring well either. Jumps into another one in the next sentence but one. It’s not looking good, is it. Continues with something that is not disputed on either side of the debate (YEC’s probably don’t think it has happened for millions of years, for example). And then goes on about how when the situation in the past was different (no New York with millions of people living in it for a start…) that the climate was also differnt adds nothing to the sum of human knowledge.

    And we haven’t even gotten through the first PARAGRAPH yet.

    The first paragraph ends on a common denialist note:

    “Frankly, we don’t fully understand either the advance or the retreat.”

    Either

    a) So? Doesn’t mean we don’t understand anything about it
    or
    b) YOU may not understand, but you aren’t the world. Others may understand what you do not

    All I’ve learned is that that bloke is cuckoo.

    And Sir Isaac Newton was a quite bright fellow.

    Look at what he did later on:

    http://www.alchemylab.com/isaac_newton.htm

  3. 403
    manacker says:

    Hi Mark

    Looks like you read it (402), but still did not learn anything new, because you apparently feel you already know all there is to know (and are therefore more qualified than Prof. Lindzen to talk about climate).

    Hats off to a either (a) a very smart fellow or (b) a very conceited fellow.

    Max

    [Response: You’ve obviously never met Lindzen. – gavin]

  4. 404
    Hank Roberts says:

    BobFJ, #5, one last attempt at giving you a clue, not that I think you’re reading the science, but for any youngster who comes along and is wondering, well, what _do_ we know from before the satellite record started — the answer is
    http://scholar.google.com/scholar?hl=en&scoring=r&q=ANDRILL&as_ylo=2009

  5. 405

    re: #391

    Dear Gavin,

    If it would not be too much trouble, could you please point me in the direction of published material concerning this (in particular, the bit about where glacier retreat has exceeded 1000 yr levels):

    “There is plenty of evidence that glacier retreat on Greenland has exceeded levels earlier in the century (Jacobshavn, Liverpool land etc.). In fact, there is evidence that it has exceeded 1000 yr levels in places.”

    [Response: Try here or possibly here. – gavin]

  6. 406
    Rod B says:

    Mark (399), well said. I was almost 40 years past any real calculus when I started messing with tides. The fun part comes from treating the earth as a solid (with the moon still treated as a point mass to ease it a bit). The gravitational force goes from moon center to a delta_mass [which will get changed to (rho)*(delta_volume)] somewhere (anywhere) within the solid sphere, relating that line of force geometrically to a line between actual centers, which becomes kinda the independent variable, throwing in the earth’s centripetal/centrifugal force for flavor, then integrating the (rho)*(delta_volume)’s throughout the solid sphere. There still are a pile of simplifying assumptions; none-the-less the integration gets very messy very fast.

  7. 407
    manacker says:

    Gavin

    A quickie question for you.

    When I pointed out to Mark that Prof. Lindzen was probably more qwualified than Mark to discuss our planet’s climate you wrote (403):
    [Response: You’ve obviously never met Lindzen. – gavin]

    Can you explain what that sentence is supposed to mean?

    Thanks.

    Max

    [Response: It was a reference to conceit and arrogance. – gavin]

  8. 408
    Susan Anderson says:

    Thanks again to all. I will reiterate one point because I think it bears keeping in mind, which is that to the lay mind, it is not too complex to understand there is some association (not to be oversimplified), between northern melt and occasional and all too short-term cooler/wetter conditions further south.

    Though most of the scientific discussion here is well above my head there are many kernels of wisdom to absorb and I appreciate it.

    For the pseudo-skeptics, it is important to note that science is a process that continuously asks questions, which is quite different from spending all your time trying to disassemble the partial answers using a narrow spectrum of sources that tend to slant information by various means in service of an agenda. For every time a Pielke or Lindzen (and I have considerable respect for the latter despite the strangeness of some of his recent material) promotes controversy, there are hundreds doing real work on real data and making their best efforts at making sense of it.

    Last but not least, a neat article from Sharon Begley in this week’s Newsweek (8/3/08) which I include verbatim here. I don’t know whether to suggest one enjoy it for its truth or wring one’s hands about it.

    Climate-Change Calculus: Why it’s even worse than we feared.
    By Sharon Begley | NEWSWEEK

    Among the phrases you really, really do not want to hear from climate scientists are: “that really shocked us,” “we had no idea how bad it
    was,” and “reality is well ahead of the climate models.” Yet in speaking to researchers who focus on the Arctic, you hear comments like these so regularly they begin to sound like the thumping refrain from Jaws: annoying harbingers of something that you really, really wish would go away.

    Let me deconstruct the phrases above. The “shock” came when the International Polar Year, a global consortium studying the Arctic, froze a small vessel into the sea ice off eastern Siberia in September 2006. Norwegian explorer Fridtjof Nansen had done the same thing a century before, and his Fram, carried by the drifting ice, emerged off eastern Greenland 34 months later. IPY scientists thought their Tara would take 24 to 36 months. But it reached Greenland in just 14 months, stark evidence that the sea ice found a more open, ice-free, and thus faster path westward thanks to Arctic melting.

    The loss of Arctic sea ice “is well ahead of” what the Intergovernmental Panel on Climate Change forecast, largely because emissions of carbon dioxide have topped what the panel—which foolishly expected nations to care enough about global warming to do something about it—projected. “The models just aren’t keeping up” with the reality of CO2 emissions, says the IPY’s David Carlson. Although policymakers hoped climate models would prove to be alarmist, the opposite is true, particularly in the Arctic.

    The IPCC may also have been too cautious on Greenland, assuming that the melting of its glaciers would contribute little to sea-level rise. Some studies found that Greenland’s glacial streams were surging and surface ice was morphing into liquid lakes, but others made a strong case that those surges and melts were aberrations, not long-term trends. It seemed to be a standoff. More reliable data, however, such as satellite measurements of Greenland’s mass, show that it is losing about 52 cubic miles per year and that the melting is accelerating. So while the IPCC projected that sea level would rise 16 inches this century, “now a more likely figure is one meter [39 inches] at the least,” says Carlson. “Chest high instead of knee high, with half to two thirds of that due to Greenland.” Hence the “no idea how bad it was.”

    The frozen north had another surprise in store. Scientists have long known that permafrost, if it melted, would release carbon, exacerbating global warming, which would melt more permafrost, which would add more to global warming, on and on in a feedback loop. But estimates of how much carbon is locked into Arctic permafrost were, it turns out, woefully off. “It’s about three times as much as was thought, about 1.6 trillion metric tons, which has surprised a lot of people,” says Edward Schuur of the University of Florida. “It means the potential for positive feedbacks is greatly increased.” That 1.6 trillion tons is about twice the amount now in the atmosphere. And Schuur’s measurements of how quickly CO2 can come out of permafrost, reported in May, were also a surprise: 1 billion to 2 billion tons per year. Cars and light trucks in the U.S. emit about 300 million tons per year.

    In an insightful observation in The Guardian this month, Jim Watson of the University of Sussex wrote that “a new breed of climate sceptic is becoming more common”: someone who doubts not the science but the policy response. Given the pathetic (non)action on global warming at the G8 summit, and the fact that the energy/climate bill passed by the House of Representatives is so full of holes and escape hatches that it has barely a prayer of averting dangerous climate change, skepticism that the world will get its act together seems appropriate. For instance, the G8, led by Europe, has vowed to take steps to keep global warming below 2 degrees Celsius by reducing CO2 emissions. We’re now at 0.8 degree. But the amount of CO2 in the atmosphere is already enough to raise the mercury 2 degrees. The only reason it hasn’t is that the atmosphere is full of crap (dust and aerosols that contribute to asthma, emphysema, and other diseases) that acts as a global coolant. As that pollution is reduced for health reasons, we’re going to blast right through 2 degrees, which is enough to ex-acerbate droughts and storms, wreak havoc on agriculture, and produce a planet warmer than it’s been in millions of years. The 2-degree promise is a mirage.

    The test of whether the nations of the world care enough to act will come in December, when 192 countries meet in Copenhagen to hammer out a climate treaty. Carlson vows that IPY will finish its Arctic assessment in time for the meeting, and one conclusion is already clear. “A consensus has developed during IPY that the Greenland ice sheet will disappear,” he says. Cue the Jaws music.
    http://www.newsweek.com/id/208164

  9. 409

    #400. Manacker , Mark and others here understand Climate better than Lindzen… Because they understand AGW while Lindzen pretends he doesn’t. In this long article not one explanation about the current Arctic ice situation. No wonder because he has an agenda along with ax to grind against others which disagree.

    “Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. During the latter, alpine glaciers advanced to the chagrin of overrun villages. Since the beginning of the 19th Century these glaciers have been retreating. Frankly, we don’t fully understand either the advance or the retreat.”

    LIndzen, is the Pope of the contrarians, just like the Catholic Pope has a throne . He sits on a met chair at MIT, flaunting infallibility from his arm chair, in his background, the failed “Iris effect”. Which basically guarantees a stable climate.
    It is hard to see where the “Iris effect” fits in the varying climate he cited. Ancient alligator remnants found in the Arctic were from geological ages rich in CO2, millions of years ago. GCM’s not being perfect is a non-secutor, we all know they are flawed, but some point towards the right temperature anomaly direction, within a very close margin of error. A remarkable achievement. Neglected by Lindzen, he knows himself, again. weather computer forecasts from models are incredible, achieve weather forecasts unheard of 40 years ago.

    “for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present”

    I am sure that he has looked at Milancovich cycles, which essentially made these warmer temperatures possible, a first year met student would know more than he claims. And thus his insincerity is shown, driven by a weird mix of science and agenda, proving the majority of his colleagues wrong , a fixation muddling his objectivity.

    This entire article that he wrote requires debunking, riddled as usual with errors, and also political attacks nothing much a do with his credentials…

    Furthermore, he likes to claim that things will cool down within a few years , as he did a few years ago, inevitably, without a doubt, then June 2009 was second warmest in history… Some cooling! What good credentials when the intelligence used to achieve them is not used. So be warned, not all scientists are objective., he sadly again is one of them.

  10. 410
    Mark says:

    “Looks like you read it (402), but still did not learn anything new,”

    All that was read there was the sort of tripe you get in a “Sunday Sport” in the UK.

    What in the first paragraph has anything new?

    Not.
    One.
    Thing.

    I do not have to eat a dog-turd sandwitch to know I won’t like the taste.

    What do YOU consider “new and interesting” in there?

  11. 411
    Mark says:

    “(and are therefore more qualified than Prof. Lindzen to talk about climate).”

    As Gavin says, this is not difficult.

    However, in that tripe you posted there wasn’t anything new at all.

    Ergo *from what you asked me to read* there was nothing to learn.

    Now it could be that Lindzen knows much more than me about climate, however, that wasn’t evident in that rant.

  12. 412
    Mark says:

    RodB: “The fun part comes from treating the earth as a solid (with the moon still treated as a point mass to ease it a bit).”

    As I said, if I’m recalling what they said they did, it wasn’t the earth as a solid body, it was the earth and the tides as THREE bodies.

    I don’t know if they worked out how or why the bulges weren’t on a direct line to the moon (mind you, since the moon is some distance away, the tide is 2.6 seconds behind the moon as far as the moon is concerned, so maybe that is where the difference comes from: is it 18 miles off the right line?) or whether they just had the offset angle and used it I don’t know. But they took the three bodies of the earth/tide as fixed in relation to each other.

    And that gave them a figure for the retreat of the moon. It was cm but whether it was 1, less than 1 or about 5 I have NO CLUE.

    I have trained my brain cells to be faster using the “Norm’s theory of drinking makes you smarter” method. Those neurons may have had to sacrifice themselves for the good of the “herd”.

  13. 413
    sidd says:

    Ms. Anderson: Thanx for the article. The assertion that the Greenland Ice Sheet will disappear is new to me. I thought some of it had survived in the Eemian.

    I think there was some speculation that our fossil carbon release would suppress not the just the next glacial stage but the one after that as well, but I do not recall the citation.

    sidd

    [Response: You are correct – complete disappearance is unlikely. Berger and Loutre (2002) is the reference you are thinking of. – gavin]

  14. 414

    Lindzen’s essay was pathetic. Even I, a non-scientist, could deconstruct it easily if I had a few hours to spare (waste).

    Obviously, he completely went off the rails this time, and one can only speculate as to his motivations for doing so, but his line of blathering is so similar to that of the fossil-fuel industry-paid denial junk science, that we need not search too far.

    Follow the money.

  15. 415
    BobFJ says:

    Gavin, Reur response on 366

    [Response: Remarkable: No information apparently implies extensive melt and happy greenlanders. (But check out the position of the Jacobshavn glacier just for fun). – gavin]

    Thankyou for that, and I agree that the image of Jacobshavn is fun. I was particularly amused by the pronounced lack of linearity in retreat between 2001 and 2006.…almost stationary the latter years!
    Nice photo in 1851 too.
    Any photos of the massive melt ponds prior to 1979?

    Manacker (a Swiss), better than me, may be able to help you understand that the mechanisms of advance and retreat of glaciers are not well understood. (and not all that logical compared with some temperature data.)

    [Response: Hey, where’d those goalposts go? – gavin]

  16. 416
    BobFJ says:

    Gavin, Reur response on my 414:

    Response: Hey, where’d those goalposts go? – gavin]

    Dunno! You brought up the topic of Jacobshavn glacier, not me.
    I’m more interested in all those photos of those massive melt ponds and moulins prior to 1979, especially say 1930 -1940’s.

    [Response: Ummm… perhaps you failed to notice that Jacobshavn was much further out in the 1930s than it is now i.e. the retreat was less then. Of course, if you insist that it couldn’t possibly have been colder then, carry on looking for evidence that doesn’t exist. – gavin]

  17. 417
    Rod B says:

    Mark (411), the three-body method strikes me as being more accurate and considerably more difficult — interesting. The simple answer why a bulge is not on the centerline (in an idealized problem) is that there are no tidal forces that would cause it. The only tidal force that causes flow and hence bulges is the tangential component (not the radial component) which is exactly zero on the centerline. [To be picky there is a radial component force; it just doesn’t cause a bulge/tide.]

    Norm’s theory makes the world look better, too!

  18. 418
    BobFJ says:

    Brian Dodge Reur 376, & Rod B Reur 377
    Thankyou for your thoughtful and interesting posts.
    They deserve a thoughtful response which I’ll try and do soon.

  19. 419

    Gavin, thanks for the links!

  20. 420

    Over time, looking at graphics that appear to represent sea surface temperatures, it seems that there is a lot of melt water flowing out of Greenland. This seems to occur in pulses. Has anyone done studies on the SSTs around Greenland and how they change (on a daily basis)?

  21. 421
    Brian Dodge says:

    Permit me to improve Dr Lindzen’s hysterical editorial

    “We have had ice ages and warmer periods when alligators were found in Spitzbergen, such as the Paleocene-Eocene Thermal Maximum [55 million years ago (Ma)], which was accompanied by a number of environmental perturbations, including mass extinction of benthic foraminifera. ”

    “More recently, we have had the medieval warm period and the little ice age. During the latter, alpine glaciers advanced to the chagrin of overrun villages. Since the beginning of the 19th Century these glaciers have been retreating. Frankly, we don’t fully understand either the advance or the retreat, but there is no conclusive proof that the cause isn’t cosmic rays.”

    “Recent work (McLean et al, 2009), suggests that this variability is enough to account for all climate change since the 19th Century, assuming mathematical manipulations which remove trends are performed.”

    “This contradiction is rendered more acute by the fact that there has been no statistically significant net global warming for the last fourteen years; it is widely believed by leading climatologists that the precipitous decline and collapse in sea and shelf ice is either due to internal variability, cosmic rays, or the fact that when an iris closes over one area, it opens over another.”

    “However, a recent paper (Ramanathan, 2007) points out that aerosols can warm as well as cool, and will do whichever is necessary to refute global warming.”

    “Given that we are in a relatively warm period,( the last ten years were warmer than the previous ten years, the last twenty years were warmer than the previous twenty years, and so on) this is not surprising, but it says nothing about trends.”

    “Polar bears, arctic summer sea ice, regional droughts and floods, coral bleaching, hurricanes, alpine glaciers, malaria, etc. etc. all depend not on some global average of surface temperature anomaly, but on a huge number of regional variables including temperature, humidity, cloud cover, precipitation, and direction and magnitude of wind. The odds of any specific catastrophe or prerequisite variable actually occurring are almost zero, and when multiplied together are so vanishingly small that they cannot possibly occur. The state of the ocean is also often crucial. Our ability to forecast any of these over periods beyond a few days is minimal (a leading modeler, Lord Monckton, refers to it as essentially guesswork). Yet, each catastrophic forecast depends on each of these being in a specific range, a mathematically ludicrous proposition.”

    “The interests of the environmental movement in acquiring more power, influence, donations, and the profits resulting from the hard work and transparent accounting of energy companies are reasonably clear.”

    “It is probably no accident that Gore, himself, is associated with such activities, unlike my entirely coincidental relation with the Western Fuels Association.”

    “The forty billion possibilities for corruption are immense.”

  22. 422
    BobFJ says:

    Martin Vermeer, Reur 398:

    Fortunately most denialists are not very smart, and BobFJ’s combination of cock-sure assertions using lots of difficult words combined with elementary errors immediately got my neck-hairs up.
    I wonder if he finally understood the silliness of using pictures that had solar limb darkening digitally removed in trying to prove it doesn’t exist… I sure hope the readership here got the message.

    Well for a start, I did not say darkening does not exist but that it was a trivial consideration in what I was trying to demonstrate, which incidentally Patrick 027 (who mentioned limb darkening before you), understood OK. The analogy of the sun, whilst hugely different to a terrestrial surface, is a thought grabbing (if imperfect) demonstration, that a flat surface radiates EMR equally in all directions hemispherically. (probably a surprise to most people)
    I repeat that in my experience, if you look at the sun with eye protection, it appears to be a flat disc of uniform brightness. (In my case I’ve used an arc-welding mask…. BTW ditto with mask through various cloud densities.)
    To me, it looks similar to the SOHO MDI image except a hotter colour. http://sohowww.nascom.nasa.gov/data/realtime/mdi_igr/512/
    If you look at this image carefully (try the larger 659 KB version on 400% zoom) you will see that there is indeed some limb darkening, but it is slight.
    This is what the site says of this image:
    The MDI (Michelson Doppler Imager) images shown here are taken in the continuum near the Ni I 6768 Angstrom line. The most prominent features are the sunspots. This is very much how the Sun looks like in the visible range of the spectrum (for example, looking at it using special ‘eclipse’ glasses: Remember, do not ever look directly at the Sun!).
    I still feel that your two other referenced images are exaggerated by mathematically/digitally adding a limb darkening theory effect.

  23. 423
    Mark says:

    “The simple answer why a bulge is not on the centerline (in an idealized problem) is that there are no tidal forces that would cause it.”

    That doesn’t make sense.

    the centreline is the line between the centre of the earth and the centre of the moon, extending towards and away from the moon indefinitely.

    That centreline is the line of lowest geopotential deviation by the two masses and therefore the tides tend toward that line and create two bulges: one at the moon side and one away from the moon.

    This is only the case when both bodies are stationary.

    Ergo there IS a force to create a bulge on the centreline. Gravity.

    In a rotating system (necessary to stop the earth and moon colliding) the bulge doesn’t appear in the same place. One reason is that the gravitational well created by the moon travels at the speed of light and therefore is 1.3 seconds behind the moon. And the gravitational pull of that tidal bulge on the moon is 1.3 seconds even further behind.

    It will also be mass inertia of the water causing more lag (it has to keep up). Viscous flow causing more lag again. And surface friction moving over the seabed (where the sea is shallow/nonexistent at low tide) can cause more tide (note: this is what I considered to be the “friction” in “does tidal friction cause the earth to slow down?”).

    Whether they are bigger effects than the 18km lag from speed of light, or ignorable I do not know.

  24. 424
    manacker says:

    Bob_FJ

    You have been discussing early 20th century developments in Arctic sea ice. I cited a study on this subject earlier.
    ftp://ftp.whoi.edu/pub/users/mtimmermans/ArcticSymposiumTalks/Smolyanitsky.pdf

    The study compares the “Variability of the summary ice extent in Greenland, Barents, Kara Seas and Laptev, Eastern Siberian and Chukchi Seas in August for period 1900 –2008”.

    Source of data is stated to be:
    Ice extent data for Eurasian Arctic Sea are developed by the AARI for period 1900-2008. 1940-2008-based on a regular aerial and satellite observations.
    1924-1939-assessed by the well-known polar explorer V.Vieseby summarizing all available by that time shipborne and aerial observations.
    1900-1923-either reconstructed on a basis of publications containing descriptions of arctic navigation during that period or calculated using physical statistical model taking into account mean monthly atmospheric pressure (r ~ 0.72).
    After 1966, satellite data are used.(visual and later IR and SAR)

    Sources cited are:
    Sources for sea ice mapping in Eurasian Arctic (from “Observed Sea Ice Extent in the Russian Arctic, 1933-2006” by Andrew R. Mahoney, Roger Barry, Vasily Smolyanitsky and Florence Fetterer. JGR, 113, C11005, 2008)

    Citing a report by Mahoney et al. mean winter, spring, summer and autumn temperatures from 1930 to today are compared. This comparison shows an overall sinking trend of winter temperature (1930-1965) from -15°C to -25°C, reversing to a rising trend up to around -12°C today. The post-1965 warming was more pronounced in the Russian Arctic than in the North American Arctic. The same trend is shown, but is much less pronounced in the average summer temperatures.

    Overall temperatures and sea ice extent are compared. There appears to be a correlation between the two, with both showing a cyclical trend and two distinct warming/shrinking periods from 1910-1945 and 1976 to today. The 6th degree polynomial trend line reflects these cycles; it also shows that the latest warming/shrinking cycle has begun to reverse – but how this will really continue is anyone’s guess.

    The study takes the best data available and concludes that the warming/shrinking periods do correlate, and that these are cyclical in nature, somehow tied to solar activity with an overall cycle of around 60 years. The sea ice data prior to satellite measurements are obviously less accurate than those made since the 1970s, but temperature data should be fairly good for the entire period.

    Based on this 60-year cycle and projected cooling from 2007 to around 2035 the study projects some possible future variations in sea ice. This is based on the rather doubtful assumption that the observed historical 60-year warming/shrinking and cooling/expanding cycle will continue into the future, instead of continued warming/shrinking resulting from continued GH warming.

    The postulation of a 60-year solar driven cycle may be dubious, but to write this study off as insignificant (as Mark has done) because the earlier pre-satellite sea ice data are not as accurate as the later data is a simple form of denial.

    Max

  25. 425
    Mark says:

    “I repeat that in my experience, if you look at the sun with eye protection, it appears to be a flat disc of uniform brightness.”

    If it does, your eyes are lying to you.

    Limb darkening exists.

    You even say you admit such a phenomenon exists. Then you go and ignore it again.

  26. 426
    Mark says:

    “The postulation of a 60-year solar driven cycle may be dubious, but to write this study off as insignificant (as Mark has done) because the earlier pre-satellite sea ice data are not as accurate as the later data is a simple form of denial.

    Max”

    But it IS insignificant.

    If it were significant, then our temperature average last year would be the same as the temperature average for the year of 1948.

    It isn’t.

    Not even close.

    Ergo, insignificant.

  27. 427
    sidd says:

    Re: Smolyanitski study from 1900 to 2008

    “sixth degree polynomial trend line” ?!
    “60 yr trend” deduced from 108 yrs of data ?!!

    This is cargo cult mathematics.
    Or rather, cargo cult numerology.

  28. 428

    #421 Brian, its not only hysterical, but planned lunacy, a diversion from reality,

    “We have had ice ages and warmer periods when alligators were found in Spitzbergen, such as the Paleocene-Eocene Thermal Maximum [55 million years ago (Ma)]”

    vs recent

    “Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years,”

    Quite a deceiver, on purpose, since the latest was written by himself. Its something worthy of a US Senator in deep denial. A political ploy, not science,
    even though scientists may dable in politics, made easier now a days, since lies are so numerous in that practice.

    Now back to the ice, it looks more and more like 1997, ie the precursor year to 1998, in every way:

    http://www.osdpd.noaa.gov/PSB/EPS/SST/climo&hot.html

    except Arctic Ocean waters are amazingly warm. So my latest prediction of Arctic Ocean ice shaving the extent of 2007 seems more plausible. Again , despite extensive Arctic cloud coverage, which if factored means that the Arctic is warmer then ever, in every way, from ocean to air. I am on sched for the NE passage to open at month end:

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

    No doubt the NW passage will be open for business mid August, Canadian ice doesn’t have a chance amidst the heat onslaught. In particular, and of interest is the Arctic Ocean melt morphing, from year to year, different occurring in very distant locations. Fram Strait now is loaded with ice, as flows are not slowed down by that 2007 old ice bridge. This simply means that the melt is greatly linked with weather conditions and predisposed settings depending on the severity of Arctic winter. The accurate time to make a melt prediction should be at summer solstice, when cloud coverage has been observed. Arctic clouds in May-June 2009 have spared a melt catastrophe, or delayed it, by at least one year.

  29. 429
    Rod B says:

    Mark, in a nutshell, if you break the gravitational force into a tangential (to the earth’s surface) and a radial (perpendicular to the surface), it’s true that at the centerline the tangential is zero and the radial is maximum. But to form a bulge the radial force has to expand (or compress) the water. Water does not expand nor compress easily (hardly at all). So it’s the tangential force that pulls on the water along (and under) the surface and will cause a flow to occur and pile up the water (which is completely different from expansion). The tangential component is zero at the centerline and zero at the poles (actually 89.5+ degrees) and reaches a maximum at about 45 degrees (actually about 44.4+ degrees). The inertia and friction of the water flow limits the build interval and effects the position of the peak tidal bulge which will fall somewhere between 25 and 44 degrees. But, even though the total tidal force is a maximum on the centerline, it is all radial and the tidal bulge will be zero.

    Actually a large nutshell. Sorry.

  30. 430
    Hank Roberts says:

    Max (manacker) continues to be a consistently reliable source–for cherries.

    Give his claims the same scrutiny you’d give any claim about a science paper; look it up. Don’t trust guys on blogs claiming to be informative.

    Look the source up; check what’s claimed; look the author’s name up in Google Scholar, and check for newer work, and read the citing papers.

    Just as an example of that exercise:

    Observed sea ice extent in the Russian Arctic, 1933–2006
    http://www.agu.org/pubs/crossref/2008/2008JC004830.shtml

    “… For the Russian Arctic as a whole in summer, there have been two periods of retreat separated by a partial recovery between the mid-1950s and mid-1980s. The AARI charts, combined with air temperature records, suggest that the retreat in recent decades is pan-Arctic and year-round in some regions, whereas the early twentieth century retreat was only observed in summer in the Russian Arctic.”

    published 5 November 2008.

    Mahoney, A.R., R.G. Barry, V. Smolyanitsky, and F. Fetterer (2008), Observed sea ice extent in the Russian Arctic, 1933–2006, J. Geophys. Res., 113, C11005
    http://doi:10.1029/2008JC004830

  31. 431
    Mark says:

    “But to form a bulge the radial force has to expand (or compress) the water.”

    Rod, you’re all over the place now.

    No, it doesn’t have to compress the water.

    What happens is that the water at a higher geopotential with a nearby lower geopotential available and not occupied by water will, guess…

    Run to the lower geopotential. Same as when it runs downhill: it is moving to a lower geopotential.

    This isn’t compressing anything.

    Draw the lines of equipotential around a sphere of mass and you get lines that are themselves spherical.

    Now add in a mass at distance.

    Redraw the lines of equipotential.

    They are not spherical.

    They are not bulged toward the new mass (which would be the layman view of what’s happening: one bulge where the water is “running” toward the moon).

    The water pressure doesn’t change because of the bulge. The bulge is the water next to the bulge being able to lose energy by drifting toward the side where the geopotential heights are further away from the earth.

    It’s EXACTLY the same reason why you have lagrange points. The L1 position is the only one you’d get if you considered gravitational forces, but the other L points result from considering EQUIPOTENTIALS.

  32. 432

    408 413 Greenland Ice Sheet. Completely? Can we take it that even if not all Greenland is to go, that whatever is happening in/to Greenland will be mirrored in the Antarctic too over a similar timeframe?

  33. 433

    Re #432

    It does not make sense to me to argue that because some Greenland ice survived the last Eemian inter-glacial then we can be sure it will also survive what we are throwing at it. CO2 is now far higher than during any interglacial in the past, and more likely to rise than fall in the future.

    But hopefully the East Antarctic ice will survive. It is at a higher altitude and higher latitude than Greenland and Arctic sea ice. However, the Antarctic Peninsula is at a lower latitude, closer to that of Greenland, and the Antarctic ice shelves are at very low altitudes, so it seem very possible that they too will follow the fate of the Antarctic Peninsula, and Greenland ice shelves.

    I foresee the 7 m rise from Greenland melt being matched by another 7 m from parts of Antarctica.

    And that is with CO2 at current levels. Let is rise so global temperatures get to +2C, and we may not die of heat stroke but we will be drowned. (or at least all our major city ports and much of our arable land. Don’t forget, food does not grow well on hillsides.)

    Cheers, Alastair.

  34. 434
    Susan Anderson says:

    sidd and Dr. Schmidt, thanks for the factual response on Greenland complete melt. I sloppily ignored that final sentence. I was surprised and a little disappointed as I like Sharon Begley and the placement of this quote makes it easy to attack the overall sense, which I consider right on point. Always more to learn, I’m glad to see the truth comes first. I think the idea that in the next couple of hundred years there will be some unexpected developments that most of our descendants won’t have a chance to observe is realistic, but perhaps the feedbacks and those mountain ranges are too big a hurdle.

    Speaking of which, does anyone know of a good source for a medium-scale map of Greenland’s topography underneath all that ice?

  35. 435
    Susan Anderson says:

    Had a change to see Paul Ehrlich this year, and he was trenchant about agriculture. A good idea to remember that settlement follows convenience and the damage to lowlands etc. is going to make things fierce not only practically but in terms of inducing conflict.

  36. 436
    BobFJ says:

    Gavin, Reur response on my 416:

    [Response: Ummm… perhaps you failed to notice that Jacobshavn was much further out in the 1930s than it is now i.e. the retreat was less then. Of course, if you insist that it couldn’t possibly have been colder then, carry on looking for evidence that doesn’t exist. – gavin]

    I think those photos from space of the Jacobshavn glacier back in 1851 through to 2006 are great, and it makes good sense that there is a crudely progressive retreat over that period of coming out of the little ice age up until now. (and yes, the 1930-40’s would be expected to be further out than today)
    However, you appear to see more in it than I do, and since you made some assertions and asked me about it,here are some thoughts, re your image here:
    http://www-nsidc.colorado.edu/sotc/images/jakobshavn_retreat.jpg
    In that shot from space in 1851; that area to the left of the 1851 line is apparently the largest of all retreats? Is that for just one year, or what do you know? (BTW, the main topic link would be handy)
    Notice that the 14 intervals between 1851 and 2006 are a bit ragged, being in year-count intervals of: 24/8/19/11/16/2/22/11/37/1/1/1/1/ and 1 respectively.
    Notice that the retreat 1929 to 1931 is very similar in surface area to that of 2004 to 2006, (whilst the hypothesis is that it was thicker in the 1930‘s…. implying a greater mass melt back then than recently). Oh, but unfortunately, the 1931 to 1953 interval is not so helpful in its longer duration.
    Notice that the yearly progression 2001 through 2006 is way-way non-linear, and begs the question: why the big slow-down in 2005/2006?

    I would also suspect some further complications in predicting retreat rates of glaciers under a significant sustained warming regime, particularly the geological. (somewhat allied to my field of engineering)
    Firstly, we are talking about a very large “thermal mass” in which a significant lag in response to air temperature changes could be anticipated. However, even if the warming regime were CONSTANT, since 1851, the response should accelerate over time, as the mass of ice is progressively reduced.
    Secondly, the precipitation of snow during such a regime may have unknown variation. (insulation/mass building effects)
    Thirdly, as glaciers retreat inland, typically the gravitational gradient increases, (but probably not uniformly) which should result in further acceleration of retreat over time, in a warming regime.
    Fourthly, I would think that moraine grinding (smoothing) will have had greater predominance over the millennia, upstream and higher up the glacier, resulting in freer flow, from creep and sliding, the further the glacier retreats.
    Fifthly, it has even been posited that if the termination shortens, such as in the break-up of ice shelves, that the flow-rate increases.

    Then of course there are some glaciers that are reportedly advancing such as in Alaska and New Zealand, and there are some that terminate abruptly where there is no retention in precipitous terrain, and they hardly change in extent.

    Like I said; (I repeat), I’d prefer to see photos from space of the massive melt ponds and moulins in Greenland prior to 1979, and especially in the 1930-1940’s where thermometer records indicate significant warmth.
    This would be far more relevant to assessing regional warming in the Arctic than assuming an understanding on the complexities of Greenland glaciers. (that logically should accelerate in retreat even if the warming regime were constant over the past 150 years or so)

    [Response: Does it really take me to point out that there weren’t any ‘shots from space’ in 1851? The photo was taken in 2004 and the lines for the historical extent are drawn on using observed data. – gavin]

  37. 437
    Eric says:

    Gavin: Your comment in reply to a question about the effects of sea floor volcanoes was “no-one seems to know…” I’m an engineer and diver interested in this area and have been searching out related research papers for several years only to find what appears to be a particularly neglected subject. Several projects are now beginning to look at measuring a few such net effects in a limited way – and the Argo data will soon (over the next decade), begin to refine part of the sub-surface picture, but there appears to be little interest in or attention to sea floor hydrothermal dynamics in general. The standard geological presentation cites heat balance averages derived from bore samples that are about 80% from land masses… while just a few years ago, there was “found” a 14,000 foot high undersea mountain (near a hot-spot), spewing forth a 4-mile-wide river of superheated water. A natural question is “How many of these are there and what’s the net ocean-heating effect?”. We don’t know. What’s the net heating effect of all the hydrothermal venting along mid-ocean ridges? No one seems to know and few are trying to find out (current work on the Eastern Pacific Rise and in the Arctic are welcome exceptions). West Antarctica sits above an active zone containing one of the world’s three lava lakes… known to significantly heat at least local waters (reports of cruise-ships stopping to let people swim in warm water along Antarctic shores), yet there’s almost no discussion of whether there’s a net contribution to regional or ocean warming. A few recent studies provide an implied conclusion that sea floor hydrothermal activity is far more widespread and operating on a larger scale than is generally appreciated, but it still seems largely ignored. This at a time when ocean temperature dynamics are raising critical questions related to climate variability and possible sources and sinks yet undefined. Is there a plan that you’re aware of for more research attention to this area, or is it still considered too insignificant to be a focus of serious study?.

  38. 438
    Rod B says:

    Mark, if there is a kg of water exactly on the centerline the only tidal force is straight up toward the moon. Given the geometry, the only way a rising bulge of that kg can form is if the moon’s gravitational pull is sufficient to expand that kg. Expanding water is the mirror image of compression — with water it ain’t going to happen. Using your example it would be like the water on the top of the hill flowing (further) uphill. There is no tidal bulge on the centerline. (using the simple moon-earth example, of course)

    [to be inanely precise there in fact is a bulge from the radial tidal force, but it is infinitesimal and realized only in math.]

  39. 439
    sidd says:

    Ms. Anderson:
    Re: Greenland topo
    http://membrane.com/sidd/greenland.html

  40. 440
    wili says:

    Which brings us back to the life-and-death issue again:

    What are the likely effects of a total or even near total melt of the Arctic Ocean going to be on agriculture and other crucial systems?

    Is this somehow off topic? Is it too uncertain to discuss? Or too scary to discuss?

    Such discussion is what the world needs from sites like this, rather than troll feeding and lunar speculations. We are not just fascinated at watching the Arctic melt because it is abstractly and scientifically interesting. We are riveted to charts on Cryosphere Today and other sources because we are watching our earth change into a different kind of planet, and we can’t be sure what this mean for us and our children.

    I would still like any clear and accurate information (or even well-informed speculation) that the good folks here could provide. I have read many of the books on the subject for the general public, but I do find some climatological jargon in published papers a bit hard to follow.

    Sorry to keep harping on this. If most don’t find this subject interesting/important enough to discuss in more depth, I’ll stop pestering.

  41. 441
    sidd says:

    Mr. McDonald:
    Re: GIS/WAIS survivability

    Stipulate that GIS/WAIS will not survive. The crucial question is: what is the timescale ?

    If Hansen and Bindschadler are right and the upper limit on GIS/WAIS disintegration is 1KYr, then we are in grave danger in this century. If 1KYr is a lower limit, then we have some breathing room, perhaps, for the long retreat from the coasts.

  42. 442

    Hi 438 Wili and 439 sidd!

    Based on the best and latest info I can find as a layman, and what I would describe as a prudent reserve, these are my ‘prove me wrong’ estimates of how much by when.

    This shows the whole journey through Business as Usual – until something stops us burning coal – through to your GIS/WAIS disintergration – plus eventually the rest of Antarctica as well:-
    http://4.bp.blogspot.com/_hpUJPjLjGlc/SlPWzfmu1LI/AAAAAAAAAE8/oM8no9qLt9s/s1600-h/SLR+5m2100-5000.png

    And assuming MIT’s recent +5 degrees K by 2100 estimate the next few decades look like:-
    http://4.bp.blogspot.com/_hpUJPjLjGlc/SlPUHXUdjeI/AAAAAAAAAE0/cVRS5UxE3bc/s1600-h/SLR+5m.png

    This may be a bit more pushy than a real climate scientist would admit to, but as an ordinary bloke these curves are to my mind a fair representation of how bad it could get, and thus how urgently we should:-

    A) Do what we reasonably can avoid it,

    and simultaneously

    B) prepare our respective communities to live with it, just in case we don’t achieve anything effective with A.

    Nigel

  43. 443
    Mark says:

    “Mark, if there is a kg of water exactly on the centerline the only tidal force is straight up toward the moon”

    Then please explain why there are two tides.

    After all the opposite side of the earth has a tidal bulge (two tides, remember) where the water is going AWAY from the moon to do so.

  44. 444
    Mark says:

    “Using your example it would be like the water on the top of the hill flowing (further) uphill”

    What if the crown of the hill had a neutron star sitting on it?

    In a accreting binary system, some of the gas from the atmosphere from the larger star falls UP from that star and then gets taken in by the other star in the system.

  45. 445
    Martin Vermeer says:

    #422 BobFJ: sigh…

  46. 446
    manacker says:

    Mark

    Your logic (426) is flawed.

    There is an underlying warming and shrinking trend which is reported in the paper I cited. Nowhere did the authors claim that today’s temperature is the same as that in 1948 (as you state). They simply observed that the warming/cooling and shrinking/expanding of those portions of the Arctic sea ice which they studied occurred in a 60-year cyclical nature.

    Look, Mark, there are lots of studies out there. This is just one of many. But to write it off as “insignificant” because it happens to present a postulation with which you happen to disagree is denial on your part. That’s all.

    Max

  47. 447
    manacker says:

    Hank Roberts (430)

    You spent a lot of time talking about cherries but saying essentially nothing.

    The study I cited was limited to a large portion of the Arctic Sea Ice (but not all), as was clearly stated.

    The study showed that over that large portion of the total there was an observed cyclical warming/shrinking and cooling/expanding trend that appears to occur in 60-year cycles (remember that the Russian Arctic is a tad larger than that of North America, and they included Greenland as well).

    Max

  48. 448

    Re #439

    sidd,

    You can move all the Bangaldeshi to the Tibetan Plateau, but what are they going to live on? The point I am trying to make is that much of the good agricultural land is the flat coastal areas created during the the Eemian, when sea levels were 4 – 6 m higher. You can’t move people from there to the vast cold dry Siberian wilderness and expect them to produce the same amount of food as they can in the warm wet tropics. The higher land in the topics is too steep to farm.

    You are correct that whether the GIS/WAIS survive is not the most urgent problem for us. It is the rate of melt from which we will be affected. In other words, even if only half the GIS eventually melts, if that happens over the next 100 years then we are talking about a 10 foot rise in London, New Orleans and New York. Can they cope?

    The problem is that scientists don’t really understand feedback, especially positive feedback which is non-linear. For, instance they persist in drawing straight trend lines through the arctic sea ice extent, and seem to be incapable of grasping that, since these trend lines steepen as time goes, the melt is accelerating. It is driven by the ice albedo positive feedback.

    But there is also a positive feedback affecting the Greenland ice sheet. As the surface melts, its altitude is lowered. Lower altitudes mean warmer air and more melting. So once the ice sheet starts melting, the melt will accelerate until it has all gone. Greenland is an anomaly. It is only snow covered at such a low latitude because it is covered with two miles of ice. Remove that ice and it would be a green land just like Sweden or Alaska which are at the same latitude.

    Remove the Arctic sea ice, which keeps the Arctic cold and the Greenland ice sheet is doomed!

    Cheers, Alastair.

  49. 449

    Rod B writes:

    Mark, if there is a kg of water exactly on the centerline the only tidal force is straight up toward the moon. Given the geometry, the only way a rising bulge of that kg can form is if the moon’s gravitational pull is sufficient to expand that kg. Expanding water is the mirror image of compression — with water it ain’t going to happen. Using your example it would be like the water on the top of the hill flowing (further) uphill. There is no tidal bulge on the centerline. (using the simple moon-earth example, of course)

    [to be inanely precise there in fact is a bulge from the radial tidal force, but it is infinitesimal and realized only in math.]

    The moon tugs the nearby water more than the Earth, and the Earth more than the water on the other side, thus forming two tidal bulges. No compression or expansion of water required. Just flow. Gravitationally-induced motion.

  50. 450
    Mark says:

    “Look, Mark, there are lots of studies out there. This is just one of many.”

    One of many wrong ones.


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