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  • The Big Thaw
    Posted by Frank Morring, Jr. 8:29 PM on Feb 09, 2012

    Greenland is melting. So is Antarctica, and most of the 200,000 glaciers elsewhere in the world.

    blog post photo
    Greenland Tourism

    Overall, some 4.3 trillion tons of ice melted between 2003 and 2010.

    That figure was calculated from data generated by the twin Gravity Recovery and Climate Experiment (Grace) satellites. Launched in 2002, the U.S-German mission maps Earth's lumpy gravity by measuring the distance between the two satellites, which varies with the density of the surface below their tandem orbit.

    Over time, changes in the density where there is ice show how much of it has melted as Earth's climate warms.

    blog post photo
    NASA/JPL-Caltech/University of Colorado

    When frozen, the melted ice would have formed a cube 1,000 miles on a side, according to the calculations. In liquid form, it added about a half inch to the global sea level.

    "Earth is losing a huge amount of ice to the ocean annually, and these new results will help us answer important questions in terms of both sea rise and how the planet's cold regions are responding to global change," says John Wahr, a physics professor at the University of Colorado, Boulder, who helped lead the study of Grace data that produced the map, and this video representation of the data.

    From its orbital perch, the Grace satellites can take a much broader view of ice melt than is possible with ground-based studies. Before the Grace findings were published Wednesday in the journal Nature, the best data on ice melt in the high mountains of Central Asia -- the Himalaya, Pamir and Tien Shan -- came from projections from ground measurements. Those estimates ranged as high as 50 billion tons of ice melt per year in the region.

    But the Grace data map reproduced below shows that figure was high. Instead of 50 billion tons, the three ranges lose about 4 billion tons a year.

    blog post photo
    NASA/JPL-Caltech/University of Colorado

    In the map, the black dots represent glaciers. Blue denotes mass loss, while red shows gains in ice mass. Most of the mass loss in the region can be attributed to ground water depletion in the plains south of the mountains.

    "The Grace results in this region really were a surprise," says Wahr, suggesting that that the higher estimates didn't take into account glaciers at very high altitudes that are hard to reach.

    "Unlike the lower glaciers, most of the high glaciers are located in very cold environments and require greater amounts of atmospheric warming before local temperatures rise enough to cause significant melting," Wahr says.

    Tags: os99

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