In the most comprehensive survey ever undertaken of the massive ice sheets covering both Greenland and Antarctica, NASA scientists confirm climate warming is changing how much water remains locked in Earth's largest storehouse of ice and snow.Other recent studies have shown increasing losses of ice in parts of these ice sheets. This new survey is the first to inventory the losses of ice and the addition of new snow on both continents in a consistent way throughout an entire decade.
The survey shows that there was a net loss of ice from the combined polar ice sheets between 1992 and 2002 and a corresponding rise in sea level. The survey documents for the first time extensive thinning of the West Antarctic ice shelves and an increase in snowfall in the interior of Greenland, as well as thinning at the edges. All are signs of a warming climate predicted by computer models.
The survey, published in the Journal of Glaciology, combines new satellite mapping of the height of the ice sheets from two European Space Agency satellites. It also used previous NASA airborne mapping of the edges of the Greenland ice sheets to determine how fast the thickness is changing.
In Greenland, the survey saw large ice losses along the southeastern coast and a large increase in ice thickness at higher elevations in the interior due to relatively high rates of snowfall. This study suggests there was a slight gain in the total mass of frozen water in the ice sheet over the decade studied, contrary to previous assessments.
This situation may have changed in just the past few years, according to lead author Jay Zwally of NASA's Goddard Space Flight Center, Greenbelt, Md. Last month NASA scientists at the Jet Propulsion Laboratory, Pasadena, Calif., reported a speed up of ice flow into the sea from several Greenland glaciers. That study included observations through 2005; Zwally's survey concluded with 2002 data.
When the scientists added up the overall gains and loses of ice from the Greenland and Antarctic ice sheets, there was a net loss of ice to the sea. The amount of water added to the oceans (20 billion tons) is equivalent to the total amount of freshwater used in homes, businesses and farming in New York, New Jersey and Virginia each year.
"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 two percent of the recent increase of nearly three millimeters a year," says Zwally. "Continuing research using NASA satellites and other data will narrow the uncertainties in this important issue."
NASA is continuing to monitor the polar ice sheets with the Ice, Cloud and land Elevation Satellite (ICESat), launched in January 2003. ICESat uses a laser beam to measure the elevation of ice sheets with unprecedented accuracy three times a year. The first comprehensive ice sheet survey conducted by ICESat is expected early next year, said Zwally, who is the mission's project scientist.