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NASA SCIENTISTS DETECT RAPID THINNING OF GREENLAND'S COASTAL ICE

David E. Steitz
Headquarters, Washington, DC                  July 20, 2000
(Phone:  202/358-1730)

Lynn Chandler
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/614-5562)

RELEASE:  00-112

NASA SCIENTISTS DETECT RAPID THINNING 
OF GREENLAND'S COASTAL ICE 

     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.  

     Further information on the Greenland mapping project, 
including the technology behind the science, is available at: 

                http://aol.wff.nasa.gov/aoltm.html

Imagery supporting this story is available at:

          http://svs.gsfc.nasa.gov/imagewall/greenland.html

     More information about the Office of Earth Sciences can be 
found at:

http://www.earth.nasa.gov

                                 -end-


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