Mass gains of Antarctic Ice Sheet greater than losses

Nov 3, 2015

Source: NASA/Goddard Space Flight Center

A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.

The research challenges the conclusions of other studies, including the Intergovernmental Panel on Climate Change’s (IPCC) 2013 report, which says that Antarctica is overall losing land ice.

According to the new analysis of satellite data, the Antarctic ice sheet showed a net gain of 112 billion tons of ice a year from 1992 to 2001. That net gain slowed to 82 billion tons of ice per year between 2003 and 2008.

“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic Peninsula and the Thwaites and Pine Island region of West Antarctica,” said Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, which was published on Oct. 30 in the Journal of Glaciology. “Our main disagreement is for East Antarctica and the interior of West Antarctica — there, we see an ice gain that exceeds the losses in the other areas.” Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.”


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6 comments on “Mass gains of Antarctic Ice Sheet greater than losses

  • @OP link “If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years — I don’t think there will be enough snowfall increase to offset these losses.”

    Various studies have shown the bulk of the Antarctic ice loss has been in West Antarctica.

    The study analyzed changes in the surface height of the Antarctic ice sheet measured by radar altimeters on two European Space Agency European Remote Sensing (ERS) satellites, spanning from 1992 to 2001, and by the laser altimeter on NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) from 2003 to 2008.

    This is old an obsolete technology compared to data from several more recent studies, and without related temperature readings could be misleading. Warmer moister air from global warming increases local snowfall but raises the temperature of the ice and snow by many degrees. This is why there are local increases in snowfall in limited areas in Greenland, while the overall picture is one of massive ice loss.

    Zwally said that while other scientists have assumed that the gains in elevation seen in East Antarctica are due to recent increases in snow accumulation, his team used meteorological data beginning in 1979 to show that the snowfall in East Antarctica actually decreased by 11 billion tons per year during both the ERS and ICESat periods. They also used information on snow accumulation for tens of thousands of years, derived by other scientists from ice cores, to conclude that East Antarctica has been thickening for a very long time.

    This study seems to be saying that ice in East Antarctica has been increasing in thousands of years previously but not much at present or recently!

    “At the end of the last Ice Age, the air became warmer and carried more moisture across the continent, doubling the amount of snow dropped on the ice sheet,” Zwally said.

    That is how a warming climate works. Initially there is more warmer snow from the increased humidity is a warmer atmosphere. This snow has a temperature near to melting point, as distinct from the hard-frozen ice 10 or 15 degrees colder.

    https://www.princeton.edu/main/news/archive/S43/04/11E77/index.xml?section=topstories

    During the past decade, Antarctica’s massive ice sheet lost twice the amount of ice in its western portion compared with what it accumulated in the east, according to Princeton University researchers who came to one overall conclusion — the southern continent’s ice cap is melting ever faster.

    The researchers “weighed” Antarctica’s ice sheet using gravitational satellite data and found that from 2003 to 2014, the ice sheet lost 92 billion tons of ice per year, the researchers report in the journal Earth and Planetary Science Letters. If stacked on the island of Manhattan, that amount of ice would be more than a mile high — more than five times the height of the Empire State Building.

    The vast majority of that loss was from West Antarctica, which is the smaller of the continent’s two main regions and abuts the Antarctic Peninsula that winds up toward South America. Since 2008, ice loss from West Antarctica’s unstable glaciers doubled from an average annual loss of 121 billion tons of ice to twice that by 2014, the researchers found. The ice sheet on East Antarctica, the continent’s much larger and overall more stable region, thickened during that same time, but only accumulated half the amount of ice lost from the west, the researchers reported.

    “We have a solution that is very solid, very detailed and unambiguous,” said co-author Frederik Simons, a Princeton associate professor of geosciences. “A decade of gravity analysis alone cannot force you to take a position on this ice loss being due to anthropogenic global warming. All we have done is take the balance of the ice on Antarctica and found that it is melting — there is no doubt. But with the rapidly accelerating rates at which the ice is melting, and in the light of all the other, well-publicized lines of evidence, most scientists would be hard pressed to find mechanisms that do not include human-made climate change.”



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  • http://www.nature.com/news/stable-region-of-antarctica-is-melting-1.17606

    ‘Stable’ region of Antarctica is melting 21 May 2015

    Radar data from Cryosat-2 probe show sudden ice loss on southern Antarctic Peninsula.

    New data reveal that glaciers along the southern Antarctic Peninsula suddenly surged towards the sea five years ago. The findings, published in the 22 May Science1, add to evidence that the ice blanketing West Antarctica is much less stable than previously thought.

    A radar instrument aboard the European Space Agency’s Cryosat-2 satellite, launched in 2010, captured the dramatic changes in the topography and elevation of the southern Antarctic peninsula. Researchers confirmed the loss using measurements from NASA’s twin Gravity Recovery and Climate Experiment (GRACE) probes, which capture ice-mass loss, but not ice movement.

    “There was nothing happening, and then, all of a sudden in the last five years, all of these glaciers started to send ice into the ocean,” says Bert Wouters, a glaciologist at the University of Bristol, UK, and an author of the study.



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  • This study seems to illustrate the difficulties in using altimetry to get accurate measurements. For accurate measurements of ice volume, both the ice surface and the underlying bedrock need to be measured.
    The comments below do not seem to be confirmation of the conclusions of this study, but rather are a call for better measuring techniques!

    @OP link – “The new study highlights the difficulties of measuring the small changes in ice height happening in East Antarctica,” said Ben Smith, a glaciologist with the University of Washington in Seattle who was not involved in Zwally’s study.

    “Doing altimetry accurately for very large areas is extraordinarily difficult, and there are measurements of snow accumulation that need to be done independently to understand what’s happening in these places,” Smith said.

    To help accurately measure changes in Antarctica, NASA is developing the successor to the ICESat mission, ICESat-2, which is scheduled to launch in 2018. “ICESat-2 will measure changes in the ice sheet within the thickness of a No. 2 pencil,” said Tom Neumann, a glaciologist at Goddard and deputy project scientist for ICESat-2. “It will contribute to solving the problem of Antarctica’s mass balance by providing a long-term record of elevation changes.”



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  • Roedy
    Nov 4, 2015 at 6:36 am

    Antarctica is a desert. Warmth in the oceans is sending moist air over Antarctica, which drops as snow.

    I think it is a little more complex than that. There is no doubt that there are some increases in ice volume in East Antarctica, and substantial reductions in West Antarctica, where large masses of ice can slide down slopes into the ocean, as retaining ice-shelves melt away in warmer waters.

    @OP – there, we see an ice gain that exceeds the losses in the other areas.” Zwally added that his team “measured small height changes over large areas, as well as the large changes observed over smaller areas.

    This is I think, the basis of the apparent conflict with other studies. In the very cold temperatures of East Antarctica powder snow blows around in huge dune-like drifts, so while the study claims that snowfall in the East has reduced, it claims that the thickness in some areas has increased. This could imply redistribution rather than increased deposition or reduced melting.

    @OP link – Zwally said that while other scientists have assumed that the gains in elevation seen in East Antarctica are due to recent increases in snow accumulation, his team used meteorological data beginning in 1979 to show that the snowfall in East Antarctica actually decreased by 11 billion tons per year during both the ERS and ICESat periods.

    There is also the factor that parts of Antarctica are geologically active.

    As I said earlier, some of the technology providing data from the 1990s and earlier, has been superseded by multiple forms of more advanced and more accurate satellite instruments and techniques, which give coverage of the whole continent and not just selected sample parts.



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