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March 2006

Vol. 11, No. 13 Week of March 26, 2006

NASA: polar ice loss adds to rising sea levels

NASA study of Greenland, Antarctic ice sheets shows net loss over 10 years; not enough ice loss to account for sea level rise

Alan Bailey

Petroleum News

According to a PR Newswire report and an item on the National Aeronautics and Space Administration web site, a NASA study of the massive ice sheets covering Greenland and Antarctica has found a net loss of ice between 1992 and 2002. In the first comprehensive inventory of ice losses over a complete decade, the NASA scientists have confirmed that climate warming is releasing water locked in the ice, the reports say.

“If the trends we’re seeing continue and climate warming continues as predicted, the polar ice sheets could change dramatically,” said survey lead author Jay Zwally of NASA’s Goddard Space Flight Center, Greenbelt, Md. “The Greenland ice sheet could be facing an irreversible decline by the end of the century.”

The NASA scientists used satellite maps from two European Space Agency satellites and previous NASA airborne mapping to measure the rate at which the thickness of the Greenland ice sheet is changing. Similarly, the researchers used nine years of elevation mapping over much of Antarctica to determine changes in ice thickness there.

The results from Greenland showed that exceptionally heavy snowfalls in the interior more than counterbalanced large ice losses along the southeastern coast, thus leading to a net increase in ice. In Antarctica an outflow from the west of the continent resulted in a major loss of ice. All of this evidence is consistent with computer models predicting a warming climate, the researchers say.

Bigger loss in Antarctica than Greenland gain

Because there was more ice lost from Antarctica than gained in Greenland, a net mass of 20 billions tons of water was released from the polar ice caps to the oceans. That amount of water will have caused a rise in sea level but doesn’t fully account for the total sea-level rises that have actually been observed.

“The study indicates that the contribution of the ice sheets to recent sea-level rise during the decade studied was much smaller than expected, just 2 percent of the recent increase of nearly three millimeters a year,” Zwally said. “Continuing research using NASA satellites and other data will narrow the uncertainties in this important issue.”

And although this particular survey concluded with 2002 data, more recent NASA observations have reported a speed up of ice flow into the sea from several Greenland glaciers.

“The melting of ice at the edges of the ice sheet is also increasing, which causes the ice to flow faster,” Zwally said. “A race is going on in Greenland between these competing forces of snow build-up in the interior and ice loss on the edges. But we don’t know how long they will be approximately in balance with each other or if that balance has already tipped in favor of the recently accelerating outflow from glaciers.”

NASA is now using the ice, cloud and land elevation satellite, known as ICESat, to make highly accurate laser-based elevation measurements of the ice sheets.

The researchers have published their findings in the Journal of Glaciology at http://www.igsoc.org.






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