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    Greenland, West Antarctic Ice Caps Melting At Half The Speed Previously Predicted
    By News Staff | September 6th 2010 01:00 AM | 12 comments | Print | E-mail | Track Comments
    The Greenland and West Antarctic ice caps are melting at half the speed previously predicted, shows a team from the Jet Propulsion Laboratory, Delft University of Technology (TU Delft, The Netherlands) and SRON Netherlands Institute for Space Research in Nature Geoscience.

    The melting of the ice caps has been charted since 2002 using the measurements produced by the two GRACE satellites. From space they detect small changes in the Earth's gravitational field and these changes are related to the exact distribution of mass on Earth, including ice and water. When ice melts and lands in the sea, this therefore has an effect on the gravitational field.

    Based on this principle, previous estimates for the Greenland ice cap calculated that the ice was melting at a rate of 230 giga-tons per year (i.e. 230,000 billion kg), which would result in an average rise in global sea levels of around 0.75 mm a year.   For West Antarctica, the estimate was 132 giga-tons per year.

    However, it now turns out that these results were not properly corrected for glacial isostatic adjustment, the phenomenon that the Earth’s crust rebounds as a result of the melting of the massive ice caps from the last major Ice Age around 20,000 years ago. These movements of the Earth’s crust have to be incorporated in the calculations, since these vertical movements change the Earth’s mass distribution and therefore also have an influence on the gravitational field.

    Researchers from the Jet Propulsion Laboratory in Pasadena (US), TU Delft and SRON Netherlands Institute for Space Research have now succeeded in carrying out that correction far more accurately. They did so using combined data from the GRACE mission, GPS measurements on land and sea floor pressure measurements. These reveal that the sea floor under Greenland is falling more rapidly than was first thought. One of the researchers, Dr Bert Vermeersen of TU Delft, explains: 'The corrections for deformations of the Earth’s crust have a considerable effect on the amount of ice that is estimated to be melting each year. We have concluded that the Greenland and West Antarctica ice caps are melting at approximately half the speed originally predicted.' The average rise in sea levels as a result of the melting ice caps is also lower.

    Their Model

    "The innovative aspect of our method is that we simultaneously matched the current changes in the ice mass and glacial isostatic adjustment to the observations, instead of assuming that a particular glacial isostatic adjustment model is correct," says Dr Vermeersen. "For Greenland in particular, we have found a glacial isostatic adjustment model that deviates rather sharply from general assumptions. But at present there are too few data available to verify this independently. A more extensive network of GPS readings in combination with geological indicators for the local and regional changes in sea level changes around Greenland over the last 10,000 years, will possibly be able to provide conclusive evidence on this matter in the years to come."

    References:


    Xiaoping Wu, Michael B. Heflin, Hugo Schotman, Bert L. A. Vermeersen, Danan Dong, Richard S. Gross, Erik R. Ivins, Angelyn W. Moore&Susan E. Owen, 'Simultaneous estimation of global present-day water transport and glacial isostatic adjustment', Nature Geoscience 3, 642 - 646 (2010) Published online: 15 August 2010 | doi:10.1038/ngeo938

    David H. Bromwich, Julien P. Nicolas, 'Sea-level rise: Ice-sheet uncertainty', Nature Geoscience 3, 596 - 597 (2010) Published online: 15 August 2010 | doi:10.1038/ngeo946

    Comments

    Stellare
    This is yet another example of how confusing it must be for the general public, let alone decision makers, to know what to make out of the climate change science. At the IPY Oslo Science Conference in June 2010 we heard that particularly Greenland was melting faster (accelerating loss) than first believed. ( There were some debate about Antarctica, but generally it was also before this result believed to be more stable than Greenland. )

    Now this view is changing again. I'm not surprised, but then I happen to know more about the uncertainties related to this research than most people. I have therefore no trouble with the fact that one of the author of this result also were an author of the work presented in Oslo in June. As I have argued before, we need to start communicating the uncertainties related to climate change better. It is uncertainties that we need to manage better. Climate is changing, we just don't know how much and how it will manifest itself all that well. Particularly, we do not know well the local consequences. And this is what we need to address in a more professional way than today.

    GRACE is awesome, though! :-)

    Bente Lilja Bye is the author of Lilja - A bouquet of stories about the Earth
    Hank
    What this tells us is that science works.   One of the recommendations of the IAC in fixing the reputation of the IPCC is to no longer let working groups make statements that are assigned high confidence but for which there is little evidence and to use a probability scale to quantify the likelihood of a particular event occurring, but only when there is sufficient evidence to do so.

    The public would have a much clearer understanding of climate change had that been done all along naturally, as a matter of scientific integrity.  These guys had a projection based on data, found there was a flaw in how the data was calculated, and corrected it.   No back flipping to talk about how awesome the wrong results were and how it changes nothing - just plain honesty and a correction.

    It's darn refreshing.   Leave it to you geodesy people to rescue the reputation of climate science.  :)
    The IPCC's 2007 report explicitly excluded major contributions to sea level rise from ice melts. I'm puzzled why the IAC picked on this as a weakness when the IPCC's report understated the risk. Or do they think the IPCC is under attack for understating risks?

    It would have been helpful if you had looked at the paper itself rather than just repeated verbatim the EurekAlert press release. Since the paper is not open access the public depends on science journalists such as yourselves to provide insight into such results. Just republishing press releases is not science journalism.

    Just a suggestion.

    Hank
    Eurekalert is a press distribution service owned by AAAS, the biggest competitor to Nature, so it is unlikely they are writing anything for them.  Nature sends these out to various groups, including us and Eurekalert and 500 other places, and we get some 50-75 per day and print maybe 2.    And we're not journalists.  Journalists get paid to interpret and we instead believe people are smart and can just have facts, no framing or spin needed.  

    What insight is this lacking? They didn't account for some data and corrected it.  Science works.
    I guess I was just confused by the "News Staff" byline. And my complaint was that by just publishing the press release (the one I was looking at was on EurekAlert, issued by the Delft U press office, http://www.eurekalert.org/pub_releases/2010-09/duot-mri090610.php) you are not just presenting the facts, but repeating what some flack has written. (You would be surprised how many "journalists" do no more.) The facts are in the original article. You claim no spin but by reprinting press release you accept their spin. Don't you want to see the underlying article and see what it really says?

    The editorial that accompanied the report in Nature Geoscience implied that there was more to the story, but I couldn't figure out much from its abstract. See if you agree: http://www.nature.com/ngeo/journal/v3/n9/full/ngeo946.html.

    Keep up the good work.

    Hank
    This site is populated by knowledgeable readers and those who want to know what is happening first.   

    When you have a smart audience, it is okay to let them have anything because they are spin-resistant and knows it is just interesting.   You were able to calibrate the article mentally so what makes you think no one else can?   TU Delft wrote a synopsis which you, probably in America, read on AAAS Eurekalert, so do you need to read an entire study to know that one metric used by a group to predict ice loss was calibrated incorrectly and they corrected it?   No, they say it right up there and that sort of transparency is evident in every other branch of science and it will do a world of good if it's more evident in climate science as well.   That's what science is about.

    You see more to the story 'implied' in their abstract and I am sure most readers don't.  I certainly do not.   If it's losing a ton of ice but not as much as feared, I think that's a good thing.   If you want the ice to melt twice as fast as it has then I guess you might not like this news.
    Stellare
    I agree with you Hank. Reading those news stories gives me an overview of what is happening. When in need of more detail, I go directly to the source. I trust the press release way more than any random journalist interpretations. Not saying that journalist are useless and not interesting, but when it comes to getting the facts right it is better to go to the source. If I want to see how others relate the news in science to other news in science and society, I find journalist highly entertaining and informative.  So, thank you very much, I want both! :-)

    It is not about predicting ice loss, but understanding how much ice is melting right now or in the near past (relative expression of course). It is pure facts - the best observations of reality.

    Geodesists provide the answers to questions like: Are my models correctly representing nature? (Models can still be wrong of course, there might be several models that fit the facts)
    Bente Lilja Bye is the author of Lilja - A bouquet of stories about the Earth
    Hank
    Not everyone can get the source, even if we provide it, because as noted Nature Geo is not open access, but on things like this, where it is pretty clear, I don't see the difference.    The real issue, of course, is cultural calibration when it becomes to a political hot potato like global warming.   In a world of RealClimate (no article supporting CO2 global warming has ever been wrong!) on one side and Watts (no article supporting any global warming has ever been right!) on the other people look for a 'catch' in every article so they can run around calling each other Holocaust deniers or liberals.

    Luckily we just stick to the science and leave advocacy to others.
    Stellare
    The news in this story lies in "these results were not properly corrected for glacial isostatic adjustment"

    Glacial Isostatic Adjustment - GIA - is modeled based on some data. But these models needs to be developed to higher spatial resolutions. There are still unknowns here. What I understand from these results is that they have improved the GIA (updated it with new information/data) and then interpreted the GRACE data again.

    In order to measure changes in the Earth (shape, kinematics, gravity) you need a inertial reference frame (coordinate system). That is not straight forward as we all know the Earth doesn't lie still. :-) We actually need the help of Quasars to get the fine accuracy of our reference frames. It is rather fantastic though that we can measure changes on this planet with millimeter accuracy.

    Anyways, GIA can still get better... :-)

    I think you are right Hank, the geodesists are far more 'sober' when it comes to observing changes (climate change, and other more fast natural hazards) than any other group of scientists that I know of. Maybe because they know how difficult it is to measure changes - and that we are constantly improving our observations.
    Bente Lilja Bye is the author of Lilja - A bouquet of stories about the Earth
    rholley
    I'm a bit concerned – how does this affect Patrick?

    Don't shout too loud, in case it is picked up by D€£!ngpo£e, who has the mentality of a lawyer hired by a dictator putting on a show trial.
    Robert H. Olley / Quondam Physics Department / University of Reading / England
    My interpretation of this, is as follows. The IPCC was embarrassed, and no longer was considered credible by the general public. They want to reinvigorate climate change thinking and political impetus for carbon credits etc. There is a general understanding that no one buys global warming based on early work - conveners asking for papers that show what they are asking for. Then, zappo - a 50% correction. Half of their credibility is restored, and with more complete data and eustatic modeling, they can possibly erase all melting, if need be. They included Pleistocene changes because someone thought it was useful now to include them. No doubt there is uncertainty about current changes in the shape of the earth for loading and unloading and this knowledge is incomplete.

    Not many islands disappearing yet.

    This is all unfortunate, because it is misleading to other investigators. Take,for example, the work on the Antarctic Ozone hole. This confused analysis threw people off the track in understanding the origin of oxygen and the earth's magnetic field - all because someone wanted to stop people from using bad smelling underarm deodorant. Ozone is produced in a broad auroral ring, and so there is just a hole in the ring. Science only works if people really try. If you get paid anyway, not many people try that hard.
    It is up to the community to raise expectations.