Rapid Changes in Ice Discharge from Greenland Outlet Glaciers

So says Howat et al. in Science (why hasn’t this made it into the blogosphere before? Or did I miss it?). Interestingly, though the most recent change is a decrease: Using satellite-derived surface elevation and velocity data, we find major short-term variations in recent ice discharge and mass-loss at two of Greenland’s largest outlet glaciers. Their combined rate of mass-loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates, likely due to fast re-equilibration of calving front geometry following retreat. Total mass-loss is a fraction of concurrent gravity-derived estimates, pointing to an alternative source of loss and the need for high-resolution observations of outlet dynamics and glacier geometry for sea-level rise predictions. This is the first evidence I’ve seen that some of the recent increases in glacier flow may just be fluctuations, though it was always a possibility.

And there appear to be some issues in resolving this with GRACE, or perhaps rather suggestions that these glaciers weren’t producing the loss GRACE saw: Other GRACE observations suggest a 450 Gt ice-loss from south Greenland between May 2004 and April 2006 that the authors mostly attribute to increased discharge from HH and KL (20). While the timing of the increased loss agrees well with the KL/HH acceleration, our results suggest that the combined loss from these glaciers over this period can only account for 13% of this loss. Absent an extensive, but unobserved, acceleration elsewhere, measurements for other south Greenland glaciers suggest a 2000 to 2005 loss increase of roughly 23 Gt/yr (1). This suggests that despite large dynamic changes, much of the 2004-2006 loss estimated from GRACE may be related to surface balance anomalies or other causes.

Incidentally… although the title is fair enough, I wondered if it was interesting that it was titled “changes” rather than “decreases”. But then I discover that the Rignot article on increases last year was titled “Changes in the Velocity Structure of the Greenland Ice Sheet” so its fair enough.

[Update: thanks to MW for ref to http://tierneylab.blogs.nytimes.com/2007/02/08/greenlands-glaciers-take-a-breather/ -W]

14 thoughts on “Rapid Changes in Ice Discharge from Greenland Outlet Glaciers”

  1. If you read Swedish blogs 😉

    I asked this on the RC forum a while ago,
    This is the wrong topic I know, but was curious about this article: http://www.sciencemag.org/cgi/content/abstract/1138478v1
    Since I can’t read Science I’m a bit curious to know what impact this have on the dynamic part of the modelling on glaciers. A step back to around 2001 or is there still evidence that the melting goes faster?

    And got this answer from Hank Roberts
    Magnus, the Howat article is extensively blogged over at the NYT, here:
    February 8, 2007 — Greenland�s Glaciers Take a Breather –By John Tierney
    I hoped to find a science journalist in the comments; none yet. I added links to a full text related 2005 paper from the same author, and one from Lamont-Doherty from 2006.


  2. Chuckle. This is why I’ve been asking about meltwater under glaciers in the older thread about doing science in the Antarctic (water flows, the rapid formation of a drumlin observed there, and so on).

    “… an alternative source of loss and the need for high-resolution observations of outlet dynamics and glacier geometry …”


  3. I don’t have a Science sub but did find an earlier paper online (link is in the second of the Tierney glacier threads linked above).

    Near as I can tell, in this paper “Mass loss” doesn’t mean “loss of mass” (the GRACE gravity info would be the better measure of total mass of the glaciers).

    As I read what I found, that term describes “loss of massive chunks” or “mass wasting” or “calving” — so that’s why they point out the need to look at outlet geometry, to find the, er, missing mass.

    Tierney’s got a ways to go to be considered a science blogger, seems to me. I think he’s trying to entertain, not edify.


  4. Someone mentioned this a while ago- can’t remember who. But I know I was curious enough to read the paper. One sentence summary:

    Glacial discharge is only a fraction of GRACE mass loss.


  5. If you haven’t heard, after an essay of mine was published in Lidove noviny newspapers, there have been big exchanges between me and the only Czech climate scientist, as he introduces himself, whose name is Ladislav Metelka. The latest article is mine


    If you want to help this fellow-believer, you should write a text that confirms his main points, namely:

    The difference between weather in climate is not in the timescale.

    Meteorologists never use statistical methods in their work.

    Climate science can never become a hard science.

    There exist no problems with the climate models and no unjustified assumptions.

    The hockey stick graph is doing very well.

    The climate models don’t predict any warming in Greenland and Antarctica.

    Aerosols explain all cooling that was ever observed in the 20th century.

    NASA has only sent 5 missions or probes to Mars, not 20+.

    There has never been any pressure against skeptical scientists.

    0.07 Celsius, equal to the impact of the Kyoto protocol by 2050, is a negligible temperature change.

    I hope that there’s a full consensus among the real climate scientists and you will help him to defend his prayer – article, in fact. Good luck! 😉

    [Hi Lubos – I fear that I had not heard of your no doubt fascinating essay. You seem to be going over the same old tendentious talking points, so I don’t suppose there was anything new to say. If there was, do let me know! Its all helpfully explained on RC or wiki, if you’re in doubt -W]


  6. A subtle problem is that it is me, not your alarmist Czech colleague, who agrees with the points on RC and uses them, for example in the context of aerosols. 😉


  7. Lubos, all I could do is get a Babelfish translation of that forum — not likely to help someone like me who doesn’t read the language understand who’s who.

    But if that’s a bunch of non-scientists, arguing by distortion and misattribution and misrepresentation, with one or two claiming they’re relying on RC for support — heck, to participate in that’s just recreational typewriting.

    If the guy claiming RC is his source posts real cites, people can check them; if not, new readers ought to be able to figure out to check the claims, eh?

    You wouldn’t want WC to get sucked into a tar pit like that.


  8. Oops. Lubos, I misread — you’re saying that you are the one pointing to RC as a source for the good science points, in arguing with some wacko? Or have I missed a level or two of irony here?

    Meanwhile — National Public Radio right now, Ira Flatow’s Science Friday program — he is talking with scientists about the new International Polar Year and melting — just got the Greenland “two miles thick at the center …. if it all were to melt …. contribute substantially to sea level rise” quote.

    A caller is suggesting maybe a nuclear submarine be parked under the North Pole to pump water into a spray mist that would freeze out as snow, to reinforce the Arctic polar ice. Hmm, but cooling the reactor heats the ocean. Nah.


  9. Dear Hank, I don’t think that RC is nonsense from the beginning to the end. RC also contains legitimate results that are supported by research, and that’s what I quoted.

    You can always be dissatisfied with a debate like that – before you actually have any idea what is in it 😉 – but it is the best possible level of a climate debate you can get in the Czech Republic, and I think that it is higher than what you get on this blog and a few other blogs, too.



  10. Here’s rapid sea level rise again:

    “…. as Greenland and West Antarctic ice is softened and lubricated by melt-water and as buttressing ice shelves disappear because of a warming ocean, the balance will tip to rapid ice loss, bringing multiple positive feedbacks into play and causing cataclysmic ice sheet disintegration. The earth’s history suggests that with warming of 2° to 3°C, the new equilibrium sea level will include not only most of the ice from Greenland and West Antarctica, but a portion of East Antarctica, raising sea level of the order of 25 meters (80 feet).

    “Contrary to lethargic ice sheet models, real world data suggest substantial ice sheet and sea level change in centuries, not millennia ….”

    Social Research: An International Quarterly of Social Sciences
    Issue: Volume 73, Number 3 / Fall 2006
    Pages: 949 – 974

    Special Issue:
    Published Online: 17 October 2006

    Can We Still Avoid Dangerous Human-Made Climate Change?
    James E. Hansen


  11. And again:

    “… four major glaciers in East and West Antarctica were shown to be retreating in unison, raising concerns that global sea level could rapidly rise if the oceans continue to warm.

    “Dr. Andrew Shepherd, at the University of Edinburgh’s School of GeoSciences, said: “Our assessment confirms that just one type of glacier in Antarctica is retreating today – those that are seated in deep submarine basins and flow directly into the oceans. These glaciers are vulnerable to small changes in ocean temperature, such as those that have occurred over the 20th century, and those predicted for the 21st century. A rise of less than 0.5 ºC could have triggered the present imbalance.”

    “Professor Duncan Wingham, at University College London, insists that the success of the research lies in the satellite instrumentation from which it is derived: “The extreme precision with which we can now make measurements of the Earth’s surface allows us to see the increasingly subtle changes within the ice sheets that will govern their future sea level contribution.”


  12. New publication (same paper? not sure) by Howat, among others:
    Originally published in Science Express on 8 February 2007
    Science 16 March 2007:
    Vol. 315. no. 5818, pp. 1559 – 1561
    DOI: 10.1126/science.1138478

    Rapid Changes in Ice Discharge from Greenland Outlet Glaciers
    Ian M. Howat,1,2* Ian Joughin,1 Ted A. Scambos2

    Using satellite-derived surface elevation and velocity data, we found major short-term variations in recent ice discharge and mass loss at two of Greenland’s largest outlet glaciers. Their combined rate of mass loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates, likely as a result of fast re-equilibration of calving-front geometry after retreat. Total mass loss is a fraction of concurrent gravity-derived estimates, pointing to an alternative source of loss and the need for high-resolution observations of outlet dynamics and glacier geometry for sea-level rise predictions.


    Science 16 March 2007:
    Vol. 315. no. 5818, pp. 1508 – 1510
    DOI: 10.1126/science.1140469
    Rethinking Ice Sheet Time Scales
    Martin Truffer1 and Mark Fahnestock2

    Satellite data show that ice sheets can change much faster than commonly appreciated, with potentially worrying implications for their stability.




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