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Sea ice minimum forecasts

Filed under: — gavin @ July 17th, 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. 201
    Phil. Felton says:

    Re #188
    I’ll stick with what the document says;
    Cavalieri et al. (1992) summarizes several of these studies. In general, accuracy of total sea ice concentration is within +/- 5% of the actual sea ice concentration in winter, and +/- 15% in the Arctic during summer when melt ponds are present on the sea ice.

    That’s a standard way of specifying instrumentation. That means you have about a +/- 2 million sq. km. error/uncertainty in the presented data, and the real data it somewhere in there.

    No, that’s an error in the concentration not the area/extent, the boundary of the ice is defined by a threshold concentration (usually 15%). A 10% error in concentration does not mean a 10% error in the location of the boundary (far from it), if the concentration gradient is steep, as it usually is, the error in the boundary is small.

  2. 202
    Doug Bostrom says:

    BobFJ 21 Jul 2009 at 8:13 pm

    I don’t care about your condition of being cracked or not, I’m instead still baffled by your previous blanket statement that ice shelves are unaffected by climate.

    Since you have not explained otherwise, I take it you concede that ice can be modeled with reasonable confidence as a beam (or girder, if you prefer) and that a beam composed of ice behaves similarly within its material property confines to beams composed of other materials? That is to say, a beam (or girder) of ice does not increasingly resist a deflecting force as its cross section is reduced? Presumably you also concede that ice fractures in a brittle mode? Finally, I suppose you concede that ice eventually melts when warmed above the freezing point?

    As you’ve conceded all those things, in sum that as an ice sheet is reduced in thickness by warming temperatures it is thus more susceptible to mechanical failure, how is it that you hypothesize that ice shelves can be unaffected by climate change?

  3. 203
    Thomas says:

    168: A few decades back I actually studied glaciology. A simple model for ice is a plastic material, with yield strength of about 1bar. For hydrostatic pressure of water in a crack that would be roughly a hundred meters depth. Any deeper than that, and armed with hydrostatic pressure, the water can go where it pleases. This fact is believed to be important for the stability of glacier dammed lakes.

    Regarding the errors regarding ice area (locally fraction of coverage): What effect would the errors have for ice extent (area within which coverage is estimated as >=15%? This is the much more frequently published metric -even though I will agree area and volume are more important physically. Presumably these areas are grid point by grid point, so unless there was systemic bias they should largely cancel out.

    Poor Steve L, he is interested in the possible effect of tides on the dim younf sun problem, but the climatologists are interested in recent (and near future) climate. To them deep time is 100 million years, which in the context of potential tidal forcing is nothing. I’m sure it would be an interesting subject in theoretical comparitive planetary climatology. Unfortunately we have virtually no data in this field -about all we can do with exoplanets is estimate orbit, mass and radius.

  4. 204

    I don’t quite see how your experiment helps, BobFJ.

    The container walls are elastic, unlike the ice, and there is no possibility of supercooling or even differential pressures. The only thing that is demonstrated that is parallel is the “path of least resistance,” which I discussed in my original post:

    “Presumably the pressure can preferentially act in two ways: to lift liquid water in the melt pond, or to propagate the crack downward.”

    The latter seems to be what happens, quite often. Rapid draining of large melt ponds via moulins has been scientifically observed.

    Descending to the anecdotal realm, I myself often noticed as a child how quickly water flowing on top of an ice sheet could erode a channel. None of this gives me confidence that the meltwater is very likely to freeze consistently.

  5. 205
    dhogaza says:

    I’ve told Hank of for bad arguments, Steve.

    Not to mention many others, who you’ve not bothered to understand, then after throwing them under the bus, saying “oh, well, cheers!”

    I have to admit – I don’t pay much attention to you unless you’re attacking me unfairly, or someone else trying to make a reasonable point or ask a reasonable question who you attack with hydrogen bombs.

    Your contribution here is almost entirely negative, mostly due to nuking people with friendly fire.

    You are smart enough to do better.

    But, apparently you’d rather be known as an asshole, rather than being known for being knowledgeable, having reading comprehension skills, and helpful to the cause.

    A 10% error in concentration does not mean a 10% error in the location of the boundary (far from it), if the concentration gradient is steep, as it usually is, the error in the boundary is small.

    Indeed, J Bob, the latest engineer proving the works of scientists to be wrong, assumes that errors in bits of the data analysis means that the same amount of error follows for the ice extent or area calculations.

    Good luck with that extrapolation, J Bob.

    Meanwhile, have you ever noticed how the denialsphere is never so straightforward with uncertainties?

  6. 206
    Ike Solem says:

    BobF,

    No, it’s just the typical respinning that is objectionable, perhaps not the paper itself. Again, the abstract says, first:

    (a) the Arctic amplification (ratio of the Arctic to global temperature trends) is not a constant but varies in time on a multi-decadal time scale.

    That’s plausible, but what does it mean? Could such multidecadal patterns be used for projections of future trends, is there a chaotic-type progression, or are you just looking at random fluctuations, i.e., noise in the warming trend?

    b) the Arctic warming from 1910–1940 proceeded at a significantly faster rate than the current 1970–2008 warming.

    You’d have to know a lot more about the data coverage. Were there similar changes as today in ice thickness and areal extent at that time? There are few if any such records – but there is the issue of aerosols to consider, which appear to play a large role in warming the Arctic atmosphere, not just recently as per Shindell et al. but also ever since the industrial revolution took off:

    <a href="http://www.cgd.ucar.edu/~mflanner/ppr/Mccnnl07.pdfMcConnell et al. 2007 20th-Century Industrial Black Carbon Emissions Altered Arctic Climate Forcing (pdf)

    During the 5-year period of maximum industrial BC emissions from 1906 to 1910, estimated surface forcing in the Arctic was 3.2 W m–2, which is about eight times the typical early summer forcing before industrialization.

    (c) the Arctic temperature changes are highly correlated with the Atlantic Multi-decadal Oscillation (AMO) suggesting the Atlantic Ocean thermohaline circulation is linked to the Arctic temperature variability on a multi-decadal time scale.

    The complexity of deep water formation and gyre-driven western boundary currents results in very complex water mixing in the North Atlantic, and not just at the surface. A simple thermohaline conveyor belt seems to be the wrong model, as many data-based studies indicate, for example:

    http://www.sciencedaily.com/releases/2009/05/090513130942.htm

    . . .much of this water, originating in the sea between Newfoundland and Greenland, is diverted generally eastward by the time it flows as far south as Massachusetts. From there it disburses to the depths in complex ways that are difficult to follow.

    A 50-year-old model of ocean currents had shown this southbound subsurface flow of cold water forming a continuous loop with the familiar northbound flow of warm water on the surface, called the Gulf Stream.

    If the loop is not continuous, then there is no slowing the loop via changes in salinity – there is just the continued transport of gradually warming water via the gyre-driven Gulf Stream. Britain and similar zones are thus likely to suffer most from flooding and summer heat, not from a deep freeze.

    The paper could very well be legitimate, but simply wrong, or missing important features. If one wished to ‘denigrate’ said paper, one would say it was “not even wrong.”

    Chylek does seem to have a recorded perspective on the issue:

    http://www.usatoday.com/weather/climate/2006-07-24-global-warming-skeptic_x.htm

    July 2006. . “You really cannot say for certain what is causing current climate change,” Chylek said in an interview.

    In February, when a team of U.S. scientists produced new data suggesting Greenland’s glaciers are melting more rapidly than previously thought, Chylek shot back with is own evidence. He said Greenland temperature records show the North Atlantic island was cooler in the second half of the 20th century than it was in the first half.

    In the same article, we have:

    Pielke’s father, Robert Pielke Sr., is one of those climate renegades.

    Pielke Sr. said in an interview that he thinks greenhouse gases are not the whole story behind climate change. Massive human land-use changes — for example, wholesale shifts from forest to agriculture — are also important, he said. And, global temperature data are fraught with uncertainties, he said. He also is skeptical of the computer climate simulations used to forecast future climate changes.

    That is a bit dated, but the repetitive behavior is remarkably numbing… what, do we get to talk about the radiative behavior of the atmosphere again… saturation, is it?

  7. 207
    Hank Roberts says:

    He’s just having fun with y’all.

    But for some kid reading this later, obviously science fair help needed.

    Bob, take a thin-walled 1″ PVC plumbing pipe ten feet long, wall thickness as close as you can find to matching the thickness of your little freezer containers for comparison.

    Stand it on end. Fill it with water. Let it freeze solid (you’re having unusually cold weather wherever you are, right? If not just wait til next time it gets below freezing for a few days).

    What happens?

    Now do it with as many feet of that same pipe as you can put vertical, 30 or 40 feet if you’ve got a tall house.

    Now, how deep are the cracks in the ice shelves
    – compared to your ten foot length of PVC?
    – compared to the four inch depth of your freezer containers?

    How strong are the walls of your PVC pipe, or your freezer containers, compared to ice? Rather stronger, right? You can make little bridges out of all three materials and test them for breaking strength.

    Even better, take two PVC pipes, say 3″ and 6″ diameter, nested. Fill the space between them. Freeze the water in that space. Split off the outside pipe and run a little water through the inside pipe and pull it out.

    Now you have a ten foot pipe made entirely out of solid ice.

    Stand it on end, outdoors in freezing weather.

    Pour the coldest water you can find into it, cold enough it won’t melt the ice around it.

    What happens?

  8. 208
    Hank Roberts says:

    And yes, none of this has anything to do with arctic sea ice.
    Red herring (sigh).

  9. 209
    BobFJ says:

    Doug Bostrom Reur202:
    You wrote in part:

    I don’t care about your condition of being cracked or not, I’m instead still baffled by your previous blanket statement that ice shelves are unaffected by climate… [and]
    …how is it that you hypothesize that ice shelves can be unaffected by climate change?

    Not what I said Doug. I now quote something of mine more typical:
    Re mechanical hinging failure of ice shelves:
    Thanks for so much interest but I remain unconvinced by the arguments presented that global warming has a significant effect in accelerating the process.

    Concerning your “strength of materials” theory, you should not confine it to a simplistic beam section-modulus consideration. Deflection of plates or diaphragms, especially if there is a curving hinge fracture is very complicated. Throw-in that the plate is floating in water which is heaving up and down on tides and responding to multi-directional wave impulses, gravitational effects and whatnot it gets extremely difficult to predict the nature of failure. Oh, and BTW ice creeps, I imagine more so when it is “warm”, (less fracturing), if the above were not complicated enough. It might even be that a thinner plate, more like a “flexible” diaphragm, may survive better than thick, so it all becomes rather intuitive, even to a mechanical engineer like myself.

    If you still want to make a section-modulus hypothesis, you also should keep a sense of scale for your simplistic “beam”. Ice sheets vary between about 100 and 1,000 metres thick, or 330 to 3,300 feet thick. Has that range changed much lately do you know?

    What we need is a really good rock-engineer (geologist)!

    The favourite climate effect argument that I’ve seen so far is the hypothesis of hydrostatic stressing of pre-existing mechanical failure, however again, a sense of scale of the huge “thermal mass” of ice compared to that of the melt water, which looses contact with the warm air above that created it, needs to be considered.
    The experiment described in 198 is further commentary that suggests that that hypothesis is rather weak.

  10. 210
    Mark says:

    “I have no reason (or ability) to come up with my own.”

    And that’s just defeatist. Or you’re pulling the sympathy card.

    Until you’ve tried, you don’t know how hard or easy it is, so how do you know you do or don’t have the ability?

  11. 211
    Mark says:

    “Mark @185 thinks my argument is crap. I can’t find out why from him because he’s [self-edit] and focused on personal stuff,”

    Nope, I think your argument is bad, not crap.

    There’s a difference.

    A crap argument would be “I don’t know what’s going on with the climate, so AGW is wrong”. A bad argument is also “I don’t know what’s going on with the climate, so AGW is right”, though that can be fixed with “because lots of people who study this think it’s right”.

    What’s BAD about your argument isn’t “something personal”, [edit], it’s about your explanation of what you’re asking.

    You have to have done some investigation to know that the moon wanders off. But that investigation comes with the information about WHY. Yet you didn’t know that.

    EVEN IF you’re genuine, you had to edit out what’s happening from what you read.

    And that’s a great way to get a ***bad*** argument.

    Worse, you need to be able to think for yourself and you seem to be predicated to rely on the kindness of strangers.

    Guess what? I’m a stranger.

    Am I kind?

    The very problem itself should have given you a red light to check the order-of-magnitude before asking a [edit] question. And your attitude that someone else should do it for you is a ***bad*** argument.

    After all, I’ve now told you that it doesn’t matter.

    But how do you know I’m even in the right ball park?

    That is why your position leads to a ***bad*** argument.

    But if you want to see it as a personal thing, go ahead. It is another bad argument to do so, but I can’t stop you and don’t care enough about you to worry about it.

  12. 212
  13. 213
    Mark says:

    “I would guess that the relationship is gyroscopic. ”

    The kick back that is taking the moon further away is also due to the fact that the high tides aren’t pointing directly at the moon, therefore the earth isn’t a spherical rigid system and there is a torque applied.

    The application of that torque transfers energy into the orbit of the moon and takes its energy out of the earth’s rotation.

    I didn’t do that lab experiment at university (since in astrophysics you can’t fit any appreciable volume of the universe into a lab, lab work often means “with a calculator and a pencil”) but it was on the list of things to do and someone else in the class did it.

  14. 214
    pete best says:

    http://www.thedailyshow.com/

    Quite amusing on yesterdays agenda. Steven Chu is being interviewed.

    Funny, get some people here to lighten up here slightly as a lot of verbal is going around for no good reason.

  15. 215

    Mark writes:

    “The Moon creates tides and the friction slows the Earth, non?”

    No.

    Steve is right. It’s the friction of ocean water in tidal bays that accounts for most of the slowing in the Earth’s rotation, especially in the Bay of Fundy in Canada.

    “I think this latter approach is preferable, but of course I’m ignoring that the Sun’s gravity also plays a role in tides”

    Twice the force, in fact.

    Not correct. Lunar tidal force on the Earth is more than twice solar. Mid-ocean tide height is about 30 centimeters from Lunar gravity and 14 centimeters from Solar.

    Following Webster (1925), the mean mid-ocean tide height is

    h = 0.85 M R^4 / (m r^3)

    where M is the mass of the perturbing body, m the mass of the perturbed body, R the radius of the perturbed body, and r the distance between them.

    SI figures: For the Sun on Earth, M = 1.9891e30, m = 5.9736e24, R = 6,371,010, a = 1.496e11. For the Moon on Earth, substitute M = 7.35e22 and a = 384,401,000.

  16. 216

    Re: comment #89

    Dear Steve L,

    Many people commenting here put in several hours per day over years in order to get up to speed on the various aspects affecting the ongoing situation in the Arctic Sea. If you can’t find recent articles via google, then you are not looking hard enough. I have posted more than 1,200 articles on climate change on my own blog. Go there and use the search field at the top left corner, or click on an appropriate label — you will find plenty of good information.

    As to your comment (quoted below), I would tend to agree.

    “The first point of my first comment was that minimum ice extent was too ‘knife-edge’ a thing to forecast well and somewhat unimportant in the grand scheme, anyway.”

    But leaving that aside, factors that used to have the greatest influence on the sea ice melt are having to move aside for new factors as the ice becomes thinner and thinner. Winds have a much greater influence on its behavior now. The ice is moving around much faster than it did 5 years ago (it’s in the published research, ok, I found it, so you can, too). This only makes sense.

    The cap of cold air that used to sit on top of the North Pole has weakened to the point that it is being pushed around like nobody’s business. So, it is stormier in the Arctic.

    Heat from the equatorial regions is being transported on water vapor streams up to the Arctic where it has warmed the air and the waters. You could have observed this by watching the satellite images at the time, but it is now also published in the peer-reviewed literature. I found it. It’s on my blog. Go, read, learn. These factors are much more significant than tidal effects.

    You want to know about these things, then put in the time.

  17. 217

    Re: comment #119

    Dear Nick O,

    Re: “If anyone wants to follow this up, I’ll try to dig out a few references.”

    I do try to follow the submarine melting in the Arctic. If you have good links and it would not be too much trouble, I would be very glad to have them. Thanks,

    Tenney

  18. 218
    Mark says:

    “Not correct. Lunar tidal force on the Earth is more than twice solar.”

    See, RodB.

    THAT is how you correct someone’s mistake.

    A simpler way to put it is that the square/cube relationship means that the 1/r factor is cancelled out because they both extend the same area and the only remaining factor is the relative average density of the two objects.

    I’ll need to check the bay of Fundy thing because that’s not what I was taught.

  19. 219
    Hank Roberts says:

    http://www.google.com/search?q=compare+tidal+effect+of+sun+and+moon+on+Earth

    See also: catb.org/~esr/faqs/smart-questions.html

    … How To Answer Questions in a Helpful Way
    Be gentle. …
    … There is no need of public humiliation for someone who may have made an honest mistake. A real newbie may not know how to search archives or where the FAQ is stored or posted.

    If you don’t know for sure, say so! A wrong but authoritative-sounding answer is worse than none at all. Don’t point anyone down a wrong path simply because it’s fun to sound like an expert. Be humble and honest; set a good example for both the querent and your peers.

    If you can’t help, don’t hinder. Don’t make jokes ….

    … Try to turn the bad question into a good one; remember we were all newbies once.

    While muttering RTFM is sometimes justified when replying to someone who is just a lazy slob, a pointer to documentation (even if it’s just a suggestion to google for a key phrase) is better.

    If you did research to answer the question, demonstrate your skills rather than writing as though you pulled the answer out of your butt…. teaching them research skills by example is showing them how to grow food for a lifetime.”

    —-
    The strength of the sun’s gravity is 179 times that of the moon’s but the moon is responsible for 56% of the earth’s tidal energy while the sun claims responsibility for a mere 44% …
    geography.about.com/od/physicalgeography/a/tides.htm

    The sun’s gravitational force on the earth is only 46 percent that of the moon…. http://home.hiwaay.net/~krcool/Astro/moon/moontides/

    And you’ll find quite a few more varying numbers, depending on whether you’re doing calculations from mass and distance, or from the height to which the tide is raised by the sun compared to the moon in a particular spot at a particular time or some average therefor.

    —-

    Meanwhile BobFJ continues to bleat for attention by claiming what we really need to understand how floating ice behaves is a hard-rock geologist. I’m sure he has some particular geologist in mind. There are more than a few geologists, especially the hard-rock variety, who opine as experts about climate change. Oodles of theory, belief, and opinion, but not a minute for reading up on the work actually done on the subject. It’s compelling.

    Not.

  20. 220

    A the risk of getting caught in cross-fire, it sounds to me like Barton & Mark have hold of different parts of the same problem. Surely conservation of rotational energy AND tidal friction–which presumably accounts for the “fact that the high tides aren’t pointing directly at the moon”, as Mark put it–are both involved?

  21. 221
    wili says:

    Tenney Naumer, I did go to your blog and found it very impressive.

    It looks like you have been combing through news releases and scientific papers for some time, gleaning the best and most relevant, and organizing them helpfully. Still I could not find an item that addresses a question a number of us have posed to deafening silence here (even while irrelevant lunar lunacies seem to get much attention):

    What do models say will be the most likely immediate and longer-term effects of a total loss of Arctic sea ice in late summer?

    Surely this is the great issue staring us in the face. Are there no such studies? Can you point us to any or any speculation by climatologists on this? Do none of the climatologists that frequent this site have anything to say on this crucial issue facing the earth?

    I understand that scientists are reticent about talking about things they haven’t studied, but they are in a better position than I to know what research is now going on about this. Even news that there are no models that look at this and no one is planning to look at it would be informative.

    Again, thanks for pointing us to your useful blog, and any light from you or others on the issue of what the world faces in the next few years would be most appreciated.

  22. 222
    Doug Bostrom says:

    BobFJ 22 Jul 2009 at 1:20 am

    Just so we’re clear, here is your original assertion:

    “May I point out that this phenomena and also the calving of icebergs are fundamentally mechanical fracturing failures. If you study the canyons developing in ice shelves, before break-up, they appear to run parallel to the influence of the ocean, primarily because of tidal and wave action, resulting in hinging at the sites of the canyons. As an engineer, I find it hard to see any climate change effect that would significantly accelerate this normal process.”

    So you yourself identified what you believe to be the dominant structural failure mode of an ice shelf, then immediately went on to say “I find it hard to see any climate change effect that would significantly accelerate this normal process.”

    As to your most recent remark and the handwaving therein, it was not a explanation of your assertion that ice shelves are immune to a warming climate.

    What’s more, the handwaving leads me to wonder if you fundamentally understand what a hinging failure is.

    “What we need is a really good rock-engineer (geologist)!”

    A geologist is a “rock-engineer”? How in the world did you get that impression?

    “The favourite climate effect argument that I’ve seen so far is the hypothesis of hydrostatic stressing of pre-existing mechanical failure, however again, a sense of scale of the huge “thermal mass” of ice compared to that of the melt water, which looses contact with the warm air above that created it, needs to be considered.”

    That paragraph translates into “I doubt it”. Doubt is not an argument. Unless you’re prepared to do the work to demonstrate how your idea is plausible, you’ve going to continue conveying the impression that you’re engaging in idle speculation and are not really informed about the subject you’ve chosen to discuss.

  23. 223
    Mark says:

    re 219, also remember this:

    http://catb.org/~esr/faqs/smart-questions.html

    How to ask questions the smart way.

    Web and IRC forums directed towards newbies often give the quickest response

    Don’t claim that you have found a bug (equivalent is “have they thought of…?”)

    Prune pointless queries

    How To Interpret Answers
    ++++++++++++++++++++++++

    RTFM and STFW: How To Tell You’ve Seriously Screwed Up

    Dealing with rudeness

    On Not Reacting Like A Loser
    Odds are you’ll screw up a few times on hacker community forums — in ways detailed in this article, or similar. And you’ll be told exactly how you screwed up, possibly with colourful asides. In public.

    “When this happens, the worst thing you can do is whine about the experience, claim to have been verbally assaulted, demand apologies, scream, hold your breath, threaten lawsuits, complain to people’s employers, leave the toilet seat up, etc.”

    And in “Questions not to ask”:

    Q: Can I convert an AcmeCorp document into a TeX file using the Bass-o-matic file converter?

    A: Try it and see. If you did that, you’d (a) learn the answer, and (b) stop wasting my time.

    NOTE: the site is about IT, so some leeway in interpretation on that one is required. But that one is most relevant to Steve’s post originally.

  24. 224
  25. 225
    Mark says:

    “Surely conservation of rotational energy AND tidal friction–which presumably accounts for the “fact that the high tides aren’t pointing directly at the moon”, as Mark put it–are both involved?

    Comment by Kevin McKinney ”

    Since I didn’t do the lab work about it, it could be that they work out to “the same thing”, just one was predicated by the torque but that happens to be the mechanical equivalent of “water piles up on the coast”.

    That’s why I’m going to have to take a look at the fundy thing. See if the explanations are the same thing, just “explained” differently.

  26. 226
    Mark says:

    PS isn’t that Hank and Mark? (And Steve sulking in the corner…)

  27. 227
    Hank Roberts says:

    Mark, would you look carefully at what you said above?

    “the square/cube relationship means that the 1/r factor is cancelled out because they both extend the same area and the only remaining factor is the relative average density of the two objects.”

    You’re referring to the angle subtended by the Moon and Sun in the sky (why we have such nice eclipses).

    Hold up a marble at a distance where it perfectly eclipses the Moon.

  28. 228
    Mark says:

    The difference may be that it isn’t friction either: it’s the water walloping into the ground that is working here. That’s not friction unless you have a very lax definition of friction.

    Like instead of CFIT, it’s CFFFT: Controlled Flight: Friction From Terrain.

  29. 229
    sidd says:

    Re: Tides

    One way to think about tides might be the following.

    1)the gravitational potential varies inversely as distance
    2)the gravitational force is the gradient of the potential, so it varies as the inverse square of distance
    3)the tidal force, being the difference of the gravitational forces on either side of the subject body, is given by the gradient of the gravitational force and varies as the inverse cube of distance.

    denoting the earth sun distance as R, and the earth-moon distance as r, the mass of the sun as M, and that of the moon as m

    ratio of the gravitational forces due to each is M/m*(r/R)^2 and the ratio of the tidal forces is M/m*(r/R)^3

    so the dependence is on the fractions M/m and r/R.
    M=2e30,m=7e22,R=1.5e11,r=3e8, so the fractions are 2.85e7 and 2e-3
    the ratio of the gravitational forces is 114, whereas the ratio of the tidal forces is 0.22

    the mass of the sun is about 30 million times the mass of the moon, but the sun is about 500 times further away. This latter factor overpowers the mass effect when cubed, but not when squared.

    the energy dissipation is messier, and being lazy, i shall not attempt a calculation here. I do want to to point out that the effect of the ‘land tides’ contributes to the dissipation as well as the oceans, (the land flexes quite a bit too)

    as always, check my math, and my physics.

  30. 230
    wili says:

    John, thanks for the links. But they seem to deal with general issues of the consequences of climate change beyond at various temps. I would be very interested in any link you have that specifically consider modeled effects of the Arctic sea ice collapse that seems to be upon us any year now.

    Anything that deals with this specific, imminent threat from anyone would be greatly appreciated.

  31. 231

    Riding the razors edge of OT, I found this really cool image of gravity anomalies on earth

    http://earthobservatory.nasa.gov/Features/GRACE/page3.php

  32. 232
    Nick O. says:

    re. comments on submerged relict ice e.g. #145 etc., also #217 (Tenney Naumer), for a primer, have a look at Mackay and Black (1973), in “Permafrost”, Second International Conference proceedings (N.A.S. publication). Mackay did a lot of work, going back to the 1950s some of it, and is still cited. More recently, you could probably look at research by people such as Julian Murton (University of Sussex) e.g. Murton JB (2005), Permafrost and Periglacial Processes, 16; also Chris Burn at Carleton University (Canada), but there are others as well who you could look at, just check the cited refs. Hope this helps.

    Regarding lake bed ice (i.e. lakes over ice, whether the lake floor is debris covered or not), try West and Plug (2008), JGR Earth Surface 113(F1) to start with, and references cited therein.

    The overall volumes of submerged and buried ice are quite small compared with the sea ice, of course, but even so, the extent may be many kilometres along the coastal shelf provided it’s not too deep. Could be some interesting sea bed mass movement effects as this stuff starts melting. Some of it is buried permafrost, other parts massive ice, and so on.

  33. 233

    Re:230,wili;
    This site by the British met office includes an animated projection of arctic sea ice extent out to the year 2100 for March and September.
    http://www.metoffice.gov.uk/climatechange/science/projections/

  34. 234
    Hank Roberts says:

    Wili, these (click for most recent, pick a beginning year) are helpful.

    http://scholar.google.com/scholar?sourceid=Mozilla-search&q=arctic+%22sea+ice%22+loss+consequences

    There are physical and biological changes and no one can give a complete and definite answer, but the recent International Polar Year research is only beginning to show up in the journals; keep searching, click the links that notify you when a scientific paper is cited and you can get email from the journal’s website for example, or just keep checking.

    Look at the earlier topics here as well, you’ll recognize some of the scientists’ names.

  35. 235
    Rod B says:

    It’s a nit and probably has no significant effect, but, for the record, the lunar tidal force is 2.2 times the Sun’s at 45 degrees (lat or long), pretty close to Hank’s 46% figure, which might be correct at a different lat or long. The main reason there is not a tidal budge on the centerline is that the tangential tidal force is zero there and the radial tidal force causes virtually no tidal bulge since its compressive/expansive forces have no noticeable effect on water. Another factor in slowing the Earth’s rotation is the direct torque applied by the gravitational force on the off-center tidal bulge; though this is likely even more miniscule than the tiny friction stuff. (I once grossly calculated this torque would stop the Earth’s rotation in 10^23 years — long after the Red Giant Sun burns us up (talk of your global warming!!))

    Worthless, but maybe interesting.

  36. 236
    Rod B says:

    sidd (229), another insignificant but maybe interesting nit. The tidal forces vary closely with the cube of the distance, but not exactly. It is actually very complicated and on the average varies with something between the square and the cube with a bias toward the cube side, while varying with latitude and longitude.

  37. 237
    Marcus says:

    Off topic: does anyone know of a recent published estimate for the contribution of water vapor (or water + clouds) to total greenhouse forcing, along the lines of the Water Vapor: Feedback or Forcing post from April of 2005? Thanks!

  38. 238

    #230 wili

    Unfortunately your question has a relative component. What is an ‘immanent threat’? And as has already been pointed out, defining specific outcomes with precision is quite difficult. Generally you can expect problems that are progressive in nature and accelerating in impact.

    Maybe this image will help understand the amplification effect?

    http://www.ossfoundation.us/projects/environment/global-warming/myths/images/arctic/icealbedo.jpg/image_view_fullscreen

  39. 239

    Hank, dear, you are awesome cool, and you don’t even know it.

  40. 240

    Re: comment #221

    Dear wili,

    Thanks for the compliments, I appreciate them.

    Second, you just rudely (kidding) pointed out the 10-ton elephant in the room that no one is talking about publicly.

    But, hey, if I had access to those fancy computer models and a bunch of NASA computers, I sure as hell would have already looked at that ages ago.

    And, if there is one thing I know about myself, it is this — if I think up what I think is a great idea, I have the certain knowledge that someone else has already come up with it long before I ever did.

    Let’s see, due to the radically changed albedo, the cold air that used to hang around up at the North Pole will get shoved out of the way, and the jet stream will go all wacky, and weather all over the Northern Hemisphere will change in ways we cannot even imagine, the changing patterns of wind will alter the sea-surface temperatures of the North Atlantic and North Pacific Oceans, also screwing with what we used to know as the four seasons.

    Everything we used to know will be useless.

    And, this will all probably take place within the next 5 to 10 years.

    Rising sea levels will be nothing compared to the weather whiplash we are going to be experiencing.

    Over time (100 years? 10,000 years?), some sort of equilibrium state will be realized, and things will sort of calm down into a kind of regularity again.

    Gee, I wonder why no one has published a peer-reviewed paper on this, yet? Can’t imagine why…can you?

    But, hey, let’s have some fun in the meantime!

    I am taking bets on which is going to open first — the Northwest or the Northeast Passage? Comments welcome:

    http://climatechangepsychology.blogspot.com/2009/07/northwest-passage-or-northeast-passage.html

    [N.B. Y'all have to hit the page-down key a few times to get past that list of articles and down to the post.]

    Signed,

    A card-carrying member of the Eat, Drink, and Be Merry Generation

  41. 241

    Re: comment #232

    Dear Nick,

    Thank you — I will try to google some of that and see if it is online. (I forgot to mention that I live about 500 clicks from the ocean, in the middle of nowhere, at roughly 14° 51′ 42.09″ S, 40° 49′ 58.61″ W. You are welcome to visit any time — bring lots of books, please.)

  42. 242

    Oh, yeah, wili, my apologies — I forgot to mention that explosion of methane from the melting permafrost. Factor that one in, too.

  43. 243
    Hank Roberts says:

    > water vapor
    http://geotest.tamu.edu/userfiles/216/Dessler2008b.pdf
    http://geotest.tamu.edu/userfiles/216/dessler09.pdf

    http://www.grist.org/article/Looking-for-validation

    “The problem with climate-model criticism”
    Posted 4 months, 3 weeks ago

    I have a paper [PDF] in this week’s Science discussing the water vapor feedback. It is a Perspective, meaning that it is a summary of the existing literature rather than new scientific results. In it, my co-author Steve Sherwood and I discuss the mountain of evidence in support of a strong and positive water vapor feedback.

    Interestingly, it seems that just about everybody now agrees water vapor provides a robustly strong and positive feedback. Roy Spencer even sent me email saying that he agrees.

    What I want to focus on here is model verification…..”

    ——————————
    I have a good perspective, because I often get in the hair of giants.

  44. 244

    #237 Marcus

    I don’t think it would have changed much, relatively speaking.

    http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/

    If anyone knows if the numbers have been refined, I’d love to see that too?

  45. 245
    BobFJ says:

    Doug Bostrom 222:
    Doug, you really should lighten up!
    For example, my Rock-engineer = geologist was a joke.

    As far as I’m aware, there is absolutely no dispute that break-up and calving from ice shelves is primarily from mechanical failure, from a variety of causes. However, there is an area of debate is, in which I speculated:
    As an engineer, I find it hard to see any climate change effect that would significantly accelerate this normal process.”
    For a wordsmith like you, I’m rather surprised that you distort my “[NOT] significantly accelerate this normal process” to mean an assertion that I’ve claimed there is no effect from warming. It is hardly helpful in the debate if you keep saying that I‘ve said something that I have not said. (twice here, and twice in your previous missive)

    I’ve also written that as yet, there has been nothing produced here, claiming a significant effect from warming on these mechanical failures, that is any less speculative than my offering. (as far as I can see)
    You should also take into account that a cross-disciplinary approach in scientific study is probably more fruitful than that of cliquey over-specialization.
    You might like to check this abstract out, which includes the words speculation and may:

    Larsen Ice Shelf Has Progressively Thinned
    Andrew Shepherd,1* Duncan Wingham,2 Tony Payne,3 Pedro Skvarca4
    The retreat and collapse of Antarctic Peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related. Satellite radar altimeter measurements show that between 1992 and 2001 the Larsen Ice Shelf lowered by up to 0.27 ± 0.11 meters per year. The lowering is explained by increased summer melt-water and the loss of basal ice through melting. Enhanced ocean-driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the Larsen Ice Shelf.

    However, it also provides a reference to comment more on your simplistic hypothesis of comparing an ice shelf (plate) floating in complexly heaving water, to that of a beam with a reducing section-modulus.
    If we take it from 1979, when satellite observations began, and a recent report that Larson B was about 220 metres (~730 feet) thick, and assume linearity, this suggests that 30 years ago, perhaps it was 228 metres thick. That is hardly a dramatic change, and perhaps you should consider that ice shelves have widely varying thicknesses, yet they all have mechanical failures. It is far more complicated than you seem to think.

    Now here is another profound contribution from you:
    What’s more, the handwaving leads me to wonder if you [BobFJ] fundamentally understand what a hinging failure is.
    Well actually I believe I do understand it, given that my formative tertiary education as an engineer included 5 years of study in “strength of materials” Call me a liar if you like, but that is hardly promoting sensible debate.

  46. 246
    Brian Dodge says:

    @ wili 22 Jul 2009 at 2:20pm
    http://www.cdc.noaa.gov/people/michael.alexander/Deseretal.seaicesubmit.2-09.pdf
    “The Seasonal Atmospheric Response to Projected Arctic Sea Ice Loss
    In the Late 21st Century”
    Submitted to the Journal of Climate
    January 23, 2009
    3. Results
    a. Arctic sea ice concentration and thickness
    b. Surface energy flux response
    c. Atmospheric temperature response
    d. Terrestrial snow cover and precipitation responses
    e. Heat budget
    f. Atmospheric circulation response

    So new pubs indicate that people are modeling the impacts, and you can see from the above results headings that the range of impacts is wide. I’m still wading through the paper, but my first take is that the increase in precipitation they see will have the greatest impact. It’s early days in analysing what the sea ice loss will do- this paper dates to January-, so there’s also more to be done -”Our experiments address only the direct impact of Arctic sea ice loss on the atmospheric circulation and climate, and neglect the potential role of oceanic feedbacks. In particular, warming of the Arctic Ocean due to enhanced solar heating associated with sea ice loss may provide additional forcing to the overlying atmosphere, although Singarayer et al. (2006) has shown this effect to be small. In addition, warming of the high latitude north Pacific and Atlantic Oceans due to enhanced downward turbulent energy fluxes as a result of anomalous warm air advection out of the Arctic may also alter the atmospheric circulation response through feedbacks with the midlatitude stormtracks…”

  47. 247

    Pretty much all over the Canadian Arctic, temperatures are unusually high:

    http://www.weatheroffice.gc.ca/forecast/canada/index_e.html?id=NU

    namely Iqaluit… There is no doubt the NW passage will open yet again. I am impressed by heat despite overall cloud coverage above normal. The Arctic Ice is shrinking less than 2008 at the same date, the NE passage will open end of July
    NW passage mid August I would say.

  48. 248

    I recalled from an old article by Fritz Leiber–a spin-off of the research in tidal theory he did to prepare for his novel The Wanderer–that situations such as the famous high tides of the Bay of Fundy arise from resonances formed by the tidal basin itself.

    So a quick search of “tidal resonance” and there’s this dandy image of the Bay, with brief explanation and link to the Wiki.

    http://earthobservatory.nasa.gov/IOTD/view.php?id=6650

    It’s probably more basic than what you’re looking for, but it’s a start, perhaps.

    (BTW, younger science fiction fans might want to check out the novel–it’s apparently back in print. It’s been years since I read it, but I bet it holds up.)

  49. 249
    Rod B says:

    John P. Reisman (238), I understand the albedo of ice to vary from about 0.4 to about 0.75 with an average over types and wavelength of about 0.6. Your reference showing 0.85 might be good for snow (even a bit low for some) but is too high for ice, including ice with a moderate snow cover.

  50. 250

    About 36 hours ago, I mentioned that this year’s melt seemed poised to overtake 2006 & move into second place in the all time list. Happened today, according to IJIS, by a razor-thin margin–seems the extent took a bit of a dive yesterday.

    “Second place” may not hold up long–IJIS often revises their number within the first day, and if the revision is upward, there isn’t much headroom. Still, it’s a milestone while it lasts at least, and the revision could just as well be downward.


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