MercoPress. South Atlantic News Agency

Accelerated depletion rate of Greenland's ice sheet

The Greenland ice sheet - which holds 70 percent of the world's fresh water - is shedding ice at an accelerating pace, according to a study released this week.

From 2004 to 2006, the rate of loss more than doubled compared with the prior two-year period, according to an analysis of satellite data by two researchers at the University of Colorado at Boulder.

"Nature is doing something we didn't expect," said Isabella Velicogna, a researcher in the CU physics department. The accelerated depletion rate ? 250% - suggests that the ice sheet responds quickly to changes in climate, the paper said.

"This raises the question of a much larger loss of the ice sheet in this century than we previously thought," Velicogna said.

The Greenland sheet is the second-largest ice mass on Earth - surpassed by Antarctica. It lost the equivalent of 164 million cubic miles of ice from April 2004 to April 2006 - more than enough water to fill Lake Erie.

The paper by Velicogna and John Wahr appears in this week's edition of the journal Nature. The loss of ice appears to be linked to climate change and a 4.4 degree increase in recorded Greenland temperatures in the past 20 years, Velicogna said.

There are two forces working to reduce the ice shelf, she explained. First, there is melting ice, which not only directly reduces the sheet's size but runs beneath the glacier and acts as a lubricant to move ice toward the ocean.

The second is the "discharge" of ice as it breaks from the sheet and slides into the sea.

"Once the discharge starts, it doesn't stop quickly, even if the temperature falls," Velicogna said. "It's like a car rolling downhill."

The CU study follows research done by the University of Texas at Austin showing Greenland lost 57 cubic miles of ice annually from 2002 to 2005.

Both studies used Gravity Recovery and Climate Experiment (GRACE) satellites that the National Aeronautics and Space Administration and Germany launched in 2002.