The increasingly rapid rate of ice loss from Greenland
http://www.sciencemag.org/news/2017/02/great-greenland-meltdown
In Greenland, the great melt is on. The decline of Greenland's ice sheet is a familiar story, but until recently, massive calving glaciers that carry ice from the interior and crumble into the sea got most of the attention. Between 2000 and 2008, such "dynamic" changes accounted for about as much mass loss as surface melting and shifts in snowfall. But the balance tipped dramatically between 2011 and 2014, when satellite data and modeling suggested that 70% of the annual 269 billion tons of snow and ice shed by Greenland was lost through surface melt, not calving.
The accelerating surface melt has doubled Greenland's contribution to global sea level rise since 1992–2011, to 0.74 mm per year. "Nobody expected the ice sheet to lose so much mass so quickly," says geophysicist Isabella Velicogna of the University of California, Irvine. "Things are happening a lot faster than we expected."
Although the Arctic is warming twice as fast as the rest of the world, high temperatures alone can't explain the precipitous erosion of Greenland's ice.
Unseasonably warm summers appear to be abetted by microbes and algae that grow on the increasingly wet surface of the ice sheet, producing pigments that boost the ice's absorption of solar energy. Soot and dust that blow from lower latitudes and darken the ice also appear to be playing a role, as are changes in weather patterns that increasingly steer warm, moist air over the vulnerable ice.
2012 melting showed it wasn't sun falling on darkened snow that drove the melt—in fact, the skies were pretty cloudy over much of the island during the two melting events. Instead, it
was warm temperatures and rainfall, provided by big "blocking" high-pressure systems that kept the mild weather in place. As the Arctic warms, such melt episodes are likely to "occur much more frequently in the future," says Dirk van As of the Geological Survey of Denmark and Greenland in Copenhagen. Earlier this year, climate scientist Marco Tedesco of Columbia University
published data supporting an earlier proposal that the retreat of Arctic sea ice has disrupted the polar jet stream, causing weather systems to meander more slowly from west to east.
