Goddard Space Flight Center, Greenbelt, MD
Scientists who want to monitor the state of our global climate may have to look no farther than the coastal ice that surrounds the Earth's largest island.
A NASA study of Greenland's ice sheet reveals that it is rapidly thinning. In an article published in the July 21 issue of Science, Bill Krabill, project scientist at the NASA Goddard Space Flight Center's Wallops Flight Facility, Wallops Island, VA, reports that the frozen area around Greenland is thinning, in some places, at a rate of more than three feet per year. Any change is important since a smaller ice sheet could result in higher sea levels.
"A conservative estimate, based on our data, indicates a net loss of approximately 51 cubic kilometers of ice per year from the entire ice sheet, sufficient to raise global sea level by 0.005 inches per year, or approximately seven percent of the observed rise," Krabill said.
"This amount of sea level rise does not threaten coastal regions, but these results provide evidence that the margins of the ice sheet are in a process of change," Krabill said. "The thinning cannot be accounted for by increased melting alone. It appears that ice must be flowing more quickly into the sea through glaciers."
Greenland covers 840,000 square miles and 85 percent of the island is covered by ice, some of which is up to two miles thick. With its southern tip protruding into temperate latitudes, monitoring this portion of the ice sheet may be one of the best ways to measure changes in our climate, at least in the Northern Hemisphere.
The ice mapping was completed by NASA, which has been surveying the Greenland ice sheet for nearly seven years. In 1993 and 1994, NASA researchers surveyed the ice sheet using an airborne laser altimeter and precision global positioning satellite receivers. Those same areas were surveyed again in 1998 and 1999.
Now, for the first time, portions of the entire ice sheet covering Greenland have been mapped with sufficient accuracy to detect significant changes in elevation.
Krabill noted that while some internal areas of Greenland show slight ice thickening, most areas along the coast show significant thinning. "Why the ice margins are thinning so rapidly warrants additional study," according to Krabill. "It may indicate that the coastal margins of ice sheets are capable of responding more rapidly than we thought to external changes, such as a warming climate."
"For the first time, we are seeing evidence that one of the two great ice bodies on the Earth (the other is the Antarctic ice sheet) is contributing, in a modest fashion, to observed sea level rise," said Dr. Ghassem Asrar, Associate Administrator for NASA's Office of Earth Science. "NASA's ICESat spacecraft, which is scheduled for launch in 2001, will allow us to make similar measurements routinely and keep an eye on both Antarctica and Greenland."
The Office of Earth Science, NASA Headquarters, Washington, DC sponsors the Greenland ice mapping project. NASA's Office of Earth Sciences studies long-term climate trends to learn how human-induced and natural changes affect our global environment.
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