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Surface-melt water rushes along the surface of the Greenland Ice Sheet through a supra-glacial stream channel. Polar ice sheets are melting three times faster than in the '90s.
Ian Joughin/ASSOCIATED PRESS
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Date published: 11/30/2012
"The more energy there is in a wave, the further the water can get inland," Ivins said.
Globally, the world's oceans rose about half a foot on average in the 20th Century. Melting ice sheets accounts for about one-fifth of sea level rise. Warmer water expands, contributing to the rise along with water from melting glaciers outside the polar regions.
In 2007, the Intergovernmental Panel on Climate Change did not include ice sheet melt in its calculations of future sea level rise because numbers were so uncertain.
It's an important factor because if all the polar ice sheets somehow melted--something that would take centuries--global sea levels would jump by more than 200 feet, said Pennsylvania State University ice scientist Richard Alley, who wasn't part of the research.
Some past studies showed melting on the polar ice sheets, while others said that the Antarctic ice sheet was growing and offsetting melting in Greenland. The new work by 47 scientists around the world combines three methods and measurements from 10 satellites to come to a scientific consensus on what's happening to the polar ice sheets.
In the 1990s, the two ice sheets combined on average lost 110 billion tons of ice each year to melting, the researchers reported. That increased and by 2005 to 2010, they were losing three times as much--379 billion tons yearly. The numbers don't include the summer of 2012 when Greenland experienced a melt that hadn't been seen in more than a century, researchers said.
NASA chief scientist Waleed Abdalati, one of the few top ice researchers who wasn't part of the study, praised the work.
"Understanding how and why the ice sheets are changing today better equips us for understanding and predicting how much and in what ways they will change in the future," he said.