Greenland Goes Green: Ice Sheet Melted in Four Days

Aired: 7/25/2012 | 0:07:28 | Clip
On July 8, NASA satellite imagery showed about 40 percent of Greenland's top ice layer intact. By July 12, only four days later, 97 percent of the ice had melted. Margaret Warner asks NASA's Thomas Wagner for scientific explanation of the massive thaw.

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