West Antarctic ice sheet not in jeopardy
December 1, 1998
By Environmental News Network staff
The ice sheet is the largest grounded repository of ice on the planet and some scientists caught up in the debate over global warming have argued that the melting of this ice sheet would lead to a dramatic rise in sea levels.
The international team of scientists, who reported their findings in the journal Science, analyzed five years of satellite radar measurements covering a large part of the Antarctic ice sheet in an effort to determine if there is any direct evidence of the ice sheet melting.
While the scientists generally agree that global warming is occurring, their study suggests that it is not having an effect on the Antarctic ice sheet.
"Based on our short, five-year period of observation of the interior of Antarctica, we do not seem to detect that the ice is melting more than one centimeter per year," said explained C.K. Shum, an associate professor of civil and environmental engineering and geodetic science at Ohio State University.
"That would mean that the interior Antarctic ice sheet does not seem to be contributing to sea level rise more than 1 millimeter per year."
A one-centimeter decrease in Antarctic ice sheet volume roughly converts into a one-millimeter rise in global sea level.
Shum and his colleagues from University College in London and the Delft University of Technology in the Netherlands, analyzed radar data retrieved from two European Space Agency remote sensing satellites -- ESA-1 and ESA-2 -- used to measure ice altitudes from 1992 through 1996.
The orbits of the satellites reached far enough North to allow them to regularly monitor at least 60 percent of the continent's grounded ice.
The majority of the West Antarctic ice sheet sits atop dry land while the east Antarctic ice sheet is grounded below sea level. Changes in the East Antarctic sheet would have little effect on sea level since the ice displaces sea water. But a complete melt of west Antarctic ice would pour new water into the oceans, raising sea levels.
"We assume that global warming is under way now," said Shum, "and it may be enhanced by human activities but, until now, its effect on ice loss in Greenland and the Antarctic has been mostly speculation. We wanted to look at ice sheets to see how they contribute to sea level rise."
While the researchers had to devise new algorithms to decipher the raw, ice sheet data and correct for several variables such as radar penetration below the ice surface and snow accumulation, they say the study represents the longest time series for which data is available.
The National Aeronautics and Space Administration is planning a new mission for the year 2001 called ICESAT. It would position a new satellite in a near-polar orbit, increasing the amount of ice sheet coverage, and use a more accurate laser altimeter to take measurements.
These, combined with the radar data, would give a much better assessment of mass balance changes, if any, in the Antarctic ice sheets.
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