for National Geographic News
Greenland's ice sheet is melting into the sea much faster today than it was just a few years ago, according to an analysis of satellite observations reported today in the journal Nature.
The rate of ice-mass loss from the Danish-owned island (Greenland map) increased by 250 percent during a period spanning May 2004 to April 2006 relative to the period from April 2002 to April 2004, the study concludes.
The new finding confirms an independent analysis of the same satellite data reported in the August 10 issue of the journal Science.
"Two hundred and fifty percent is huge," said Isabella Velicogna, an earth scientist at the NASA Jet Propulsion Laboratory in Pasadena, California, and study co-author.
"We're talking two times and a half more mass loss. What that tells us is we want to keep our eyes open and check what's going on with these glaciers," she added.
Ice is now being lost from the island at a rate of 59 cubic miles (248 cubic kilometers) a year, sufficient to push global sea levels up 0.02 inch (0.5 millimeter) a year, the team reports.
If all the ice on Greenland were to melt into the North Atlantic Ocean, scientists estimate that global sea levels would rise by 23 feet (7 meters).
Both the Nature and Science studies use data from the Gravity Recovery and Climate Experiment (GRACE) satellites, which measure monthly changes in Earth's gravitational field.
Liquid water is denser than ice and so has a stronger gravitational pull.
The satellites can therefore measure changes in Greenland's mass over time to determine the rate at which ice is melting.
The new study dates the start of accelerated melting to the spring of 2004 and finds the acceleration is confined to southern Greenland, Velicogna says.
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