Greenland Gravity (Ice) Measurements

This figure shows the ice mass loss in Greenland as observed by Grace over the period 2002-2005 measured in cubic kilometers per year. The ice mass loss observed contributes about 0.4 millimeters (.016 inches) per year to global sea level rise. Image: NASA/JPL/U.Colorado
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...Just a few years ago, the world's climate scientists predicted that Greenland wouldn't have much impact at all on sea level in the coming decades. But recent measurements show that Greenland's ice cap is melting much faster than expected.

These new data come from the NASA/German Aerospace Center's Gravity Recovery and Climate Experiment (Grace). Launched in March 2002, the twin Grace satellites circle the globe using gravity to map changes in Earth's mass 500 kilometers (310 miles) below. They are providing a unique way to monitor and understand Earth's great ice sheets and glaciers.

Grace measurements have revealed that in just four years, from 2002 to 2006, Greenland lost between 150 and 250 cubic kilometers (36 to 60 cubic miles) of ice per year. One cubic kilometer is equal to about 264 billion gallons of water. That's enough melting ice to account for an increase in global sea level of as much as 0.5 millimeters (0.019 inches) per year, according to Isabella Velicogna and John Wahr of the University of Colorado, Boulder. They published their results in the scientific journal Nature last fall. Since global sea level has risen an average of three millimeters (0.1 inch) per year since 1993, Greenland's rapidly increasing contribution can't be overlooked.

"Before Grace, the change of Greenland's ice sheet was inferred by a combination of more regional radar and altimeter studies pieced together over many years, but Grace can measure changes in the weight of the ice directly and cover the entire ice sheet of Greenland every month," says Michael Watkins, Grace project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif...

"We have to pay attention," Velicogna adds. "These ice sheets are changing much faster than we were expecting. Observations are the most powerful tool we have to know what is going on, especially when the changes - and what's causing them - are not obvious."
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