Rising temperatures and ash from Northern Hemisphere forest fires combined to cause large-scale surface melting of the Greenland ice sheet in 2012, an echo of a similar event that occurred in 1889, a new study finds.
The massive Greenland ice sheet — the second largest ice body in the world after the Antarctic ice sheet — experiences annual melting at low elevations near the coastline, but surface melt is rare in the dry snow region in its center. In July 2012, however, satellites observed for the first time surface melt across more than 97 percent of the ice sheet, generating reports that the event was almost exclusively the result of climate change.
These NASA maps show how, within the space of four days in the summer of 2012, Greenland’s vast ice sheet faced a degree of melting not seen in three decades of satellite observations. The image at left shows the ice sheet on July 8, 2012, with a large part of it experiencing no melting (shown in white) in summer, as is typical. By July 12, 2012, the surface of virtually the entire ice sheet was melting (shown in red). (Image credit: NASA)
In the new report, published in the journal Proceedings of the National Academy of Sciences, researchers analyzed an ice core from the dry snow region of the ice sheet. Their findings indicate that in both 2012 and 1889 exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires to darken the surface of the ice sheet to a critical albedo threshold, causing the large-scale melting events. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, large-scale melt events on the Greenland ice sheet may begin to occur almost annually by the end of century, the researchers say.