Greenland Meltdown Driven by Collapse of Glaciers at Ocean Outlets [Slide Show]
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COLUMBIA GLACIER. ALASKA, U.S. July 23, 2006. In the mid-1980s ice filled this valley up to the lower edge of the dark band of vegetation. James Balog
MOUNT KILIMANJARO. TANZANIA. July 27, 2005. A fast-melting face of the Furtwängler Glacier near the summit. James Balog
SOUTH LAKE, GREENLAND ICE SHEET. GREENLAND. July 20, 2006. James Balog
STEIN GLACIER. SWITZERLAND. September 25, 2006. James Balog
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STEIN GLACIER. SWITZERLAND. September 17, 2011. James Balog
TAHUMMING GLACIER. BRITISH COLUMBIA, CANADA. August 29th 2009. The glacier has recently retreated from this cliff. James Balog
GREENLAND ICE SHEET. GREENLAND. June 7, 2010. Crevasses filled with meltwater. James Balog
NORTHERN NORTH LAKE. Greenland Ice Sheet, Greenland. July 18,2008. Lake bed, bare after the lake has drained, shows a moulin (cavity) that swallowed millions of gallons of water. James Balog
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GREENLAND ICE SHEET. GREENLAND. July 14, 2008. Bubbles of air, possibly 15,000 years old, are released as the ice sheet melts. James Balog
GREENLAND ICE SHEET. GREENLAND. July 10, 2008. Silt and soot blown from afar turn into black "cryoconite," absorb solar heat, and melt down into ice. James Balog
Future sea levels depend on how much and how quickly the massive ice sheet covering Greenland melts. Satellite-based measurements have revealed that Greenland's glaciers are melting and on the move—and the ice sheet has lost some 36 billion metric tons of ice each year in recent years from its northwestern flank. Thanks to weird weather, nearly the entire ice-covered surface of the world's largest island melted for a period this year.
Now aerial photographs reveal that this loss of ice is driven more by the accelerated breakdown of ice sheets where they reach the sea (and a subsequent speed up in outflowing ice) than the difference between snowfall and such surface melt. Danish scientists identified two periods of ice loss—1985 to 1993 and 2005 to 2010—that have been responsible for the bulk of Greenland's meltdown. The research appears in Science on August 3.
In fact, outlet glaciers have receded by more than 100 meters across the northwestern edge of the ice sheet. For example, the Sverdrup Glacier retreated by 1,000 meters between 2005 and 2010, also losing 80 meters in height. Roughly 80 percent of the ice loss seems to be attributable to this kind of loss at glacier outlets rather than the glacier as a whole. The cause may be warmer ocean temperatures, although sea-surface temperature measurements are lacking to definitely prove that hypothesis.
Aerial maps that extend the record back as far as the 1930s may help further refine scientists' understanding of this meltdown in the north—and its implications for how much the seas will rise in coming decades.