Abstract: Greenland’s 2012 melt season started early, surpassing the 30-year average for melt-covered area in mid-May, and remaining far in excess of typical conditions for June, July, and through mid August. For the peak melt days in early July and again in early August, more than 70% of the surface of the ice sheet experienced some melt, and the peak melt event on July 10 to 11 occurred over 97% of the ... ice sheet.

The overall pattern of melt is closely related to elevation. At the edges of the ice sheet, near the coast, melt is far more frequent. With increasing elevation, up to 2,000 meters (6,300 feet) or so, the number of melt days decreases from tens of days to just a few days. Above 2,500 meters, melt is rare, and in most years a large region of central and northern Greenland (up to 3,100 meters above sea level, or approximately 10,000 feet) sees almost no surface melt.

During 2012, a significant increase in melting days was seen at higher elevations as well, causing surface melting to percolate into older snow below and refreeze. Runoff of water from the ice sheet was intense. In one case, bridges and other structures adjacent or crossing a usually small melt-fed river, the Watson River near Kangerlugssuaq, were destroyed in mid July.

Credit: National Snow and Ice Data Center :: Advancing knowledge of Earth's frozen regions