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Antarctic ice shelf half the size of Scotland on verge of collapse

  1. Apr 4, 2009 #1
    http://www.guardian.co.uk/world/2009/apr/05/ice-shelf-wilkins-antarctic" [Broken]

     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Apr 5, 2009 #2
    Here is a video showing the Wilkins ice shelf

    https://www.youtube.com/watch?v=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/poKX6OnehTc&hl=en&fs=1"></param><param [Broken] name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/poKX6OnehTc&hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>
     
    Last edited by a moderator: May 4, 2017
  4. Apr 5, 2009 #3

    Xnn

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    http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=376


    JIM ELLIOT, BRITISH ANTARCTIC SURVEY:


    There are about 1,500,000 km^2 of ice shelves in Antarctica.
    Wilken is about 16,000 km^2 of that or about the size of Connecticut or Jamaica.

    Good news is that when they breakup they do not contribute much to a rise in sea level. However, the rate of breakup is such that there won't be many left in another 100 years or so.

    The Arctic used to have ice shelves too. However, they are mostly gone now. Once ice shelves are gone, the warming begins to work on land based ice and that melting does contribute directly to a rise in sea level. No need to immediately sell ocean front property, but long term this will be an issue.




    http://news.bbc.co.uk/2/hi/science/nature/3132074.stm

     
    Last edited by a moderator: Apr 24, 2017
  5. Apr 5, 2009 #4
    An enormous amount of fresh water goes to waste. 16,000 km^2 and a thickness of 100 meters, that's about 1400 km^3 of water. People can live quite well with 100 liters per day, so this would be enough for the entire world for 6 years.
     
  6. Apr 6, 2009 #5

    Gokul43201

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    Yet, we know that, on the whole, the Antarctic (and nearby SH) regions have, if anything, only been gaining ice coverage over the last few decades.

    s_plot_tmb.png
    http://nsidc.org/data/seaice_index/

    So then, are there other regions of the Antartic shelf that are experiencing unprecedented cooling? Or if not, is the region of warming small compared to the regions of cooling? And if that is the case, what makes this significant?


    Looks like the Antarctic gains more fresh water every year than it loses. I think if you're worried about losing fresh water, you would be better served looking at Arctic sea ice coverage (not that anyone is very likely to bankroll a start-up that chips off ice from Greenland and ships it to refugee camps in Rwanda).
     
  7. Apr 6, 2009 #6

    mgb_phys

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    That could make sense, warming oceans = more water vapour in the air = more precipitation.
     
  8. Apr 6, 2009 #7

    Xnn

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    Gokul;

    The most current peer reviewed paper on the subject has found that there is robust warming across Antactica:

    http://www.nature.com/nature/journal/v457/n7228/abs/nature07669.html

    Sea ice comes from more than just freezing temperatures. With the breakup of such massive ice shelves, it's not too surprising that sea ice extent has trended upward. These ice shelves are initially hundred of meters thick. After they float out to sea, they eventually breakup into smaller pieces and then cover surface areas much larger than they did originally.

    The Arctic on the other hand has almost no ice shelves left. This is why there is never any news about them and also why sea ice extent in the North has been trending downward. However, both polar regions are warming.
     
  9. Apr 6, 2009 #8

    Gokul43201

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    But that's only part way through an explanation. You'd then have to connect precipitation to ice coverage, but more importantly, show that it is the dominant source of ice formation. And even then, this may be a bit of an oversimplification. After all, the Arctic has indeed been losing ice a lot more rapidly than the Antarctic has been gaining it. And that's been going on for at least a few decades now. But yes, I recognize that it could make sense (i.e., be reconciled by an argument based on even somewhat elementary principles, though I'm skeptical, because I think there are more factors involved such as wind patterns, ocean currents, deep water migration and other such complexities)... but that part of it was not really what I was questioning here.

    I haven't read the paper yet, but "most of West Antarctica" still sounds like less than half the continent.

    I can't say I fundamentally understand this argument, but nevertheless, an explanation of this kind is essential to making some kind of logical connection between "global warming" and one particular ice shelf breaking up (and I didn't find any attempt at such an explanation in any of the articles posted) . After all, I think it is undisputed that warming over the SH is significantly weaker than over the NH. So when averaging over entire hemispheres give such an easily detectable divergence from the mean trend, I see very little usefulness in suggesting a correlation between the value of some chosen proxy integrated over such a small region as a particular section of Antarctica and a global trend. And I say "suggesting" because that is really all I see in the articles linked so far; there seems to be more innuendo and suggestion than any real attempt at explanation.
     
    Last edited: Apr 6, 2009
  10. Apr 6, 2009 #9

    sylas

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    Um, what? I may be reading you wrong, but that looks a very odd comment.

    Do you have other ideas for how an ice cap builds up? The whole basis of deuterium temperatures obtained in paleoclimate studies from ice cores is based on the fact that an ice cap is built up by precipitation.

    Cheers -- Sylas
     
  11. Apr 6, 2009 #10

    mgb_phys

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    I just meant that "more snow != global warming is false"
    I don't know if thse ice shelves are the result of recent local snow fall or they are ancient ice that moved in glaciers from further inland. Which would also mean the recent increase in ice coverage in the graph is irrelevant.

    ps. why the size of Scotland? The standard unit for size is "Wales". And at 20,000km^2 is a lot closer to the size of this event than Scotland (at 75-80,000km^2) anyway
     
  12. Apr 6, 2009 #11

    Gokul43201

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    No, I think you read me right. But I didn't do a good job of saying what I meant. I guess I should have used a word like 'accumulation' rather than 'formation.' I may still be completely wrong here, since I know very little about this stuff, but nevertheless, I was trying to say that trends in ice coverage need not correlate very strongly with trends in precipitation.

    This (like a lot of other things in this field) is something I didn't know about. But in any case, my intent was not simply on the rate of ice formation, but on the net rate of ice growth (formation rate - removal rate, I guess), since that is what shows up in the ice coverage trends.
     
  13. Apr 6, 2009 #12

    Gokul43201

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    I hope I didn't give the impression that I was arguing that more snow => global warming is false. I was not making that argument. I was merely making the observation that given the overall ice coverage trends for the Antarctic, unprecedented loss of ice in some regions would seem to be more than made up for by significantly large gains of ice in other regions. More specifically, I was objecting to the suggestions that, in general, observations of unprecedented loss of ice in some small region X support the assertion that global warming is true.
     
  14. Apr 6, 2009 #13

    sylas

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    I'm at fault here for not following carefully.

    The context of the remark, as I understand it, is from your [post=2149205]msg #5[/post], where you noted that there is increasing ice in the southern hemisphere. You were referring to sea ice cover; and I was thinking of the ice cap.

    Yes, sea ice cover doesn't have much at all to do with precipitation. The biggest variations are, of course, between summer and winter, and relate to temperature. Differences from year to year are much smaller, and there are all kinds of effects that can have an impact on this. Ocean currents are important, especially around the Antarctic. I agree with you that changes in precipitation are unlikely to be much of a factor.

    (Addendum added in edit: although it might. I'm reading a bit of background, and it seems that precipitation could be a factor after all.)

    Cheers -- Sylas
     
    Last edited: Apr 6, 2009
  15. Apr 7, 2009 #14

    Xnn

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    Here's an peer reviewed science journal article on increasing Antarctic sea ice. Although I'm not entirely comfortable with it, the suggestion is that decreasing salinity leads to a staginating ocean surface near that Antarctic. From this, less heat from the depths is available to melt the sea ice.

    http://psc.apl.washington.edu/zhang/Pubs/Zhang_Antarctic_20-11-2515.pdf

     
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