During a normal Greenland summer, about half of the ice sheet undergoes thawing at or near its surface. At higher elevations, most of the melt water quickly refreezes, while closer to the coast some is retained by the ice sheet and the rest flows to the sea.
But for several days this month, nearly all of Greenland’s ice sheet showed signs of surface thawing – from the thin ice near the coast to the 2-mile thick ice located in the island’s interior. Moreover, melting advanced from normal to an extent not seen in 30 years of satellite observation in a matter of days.
On July 8, satellite data showed normal melting across about 40% of the surface. But by July 12, the same satellites showed melting over an estimated 97% of the entire ice sheet.
The extreme melt coincided with an unusually strong ridge of warm air, or a heat dome, over Greenland. The ridge was one of a series, each stronger than the one that preceded it, that has dominated Greenland’s weather since the end of May.
The latest heat dome began to move over Greenland on July 8, parking itself over the ice sheet about three days later. By July 16, it had begun to dissipate.
Melting near the highest point of the central ice sheet was confirmed by ground observations at Summit Station, where air temperatures hovered near or above freezing for several hours on July 11 and 12.
“Ice cores from Summit show that melting events of this type occur about once every 150 years on average. With the last one happening in 1889, this event is right on time,” says Lora Koenig, a Goddard glaciologist and a member of the research team analyzing the satellite data. “But if we continue to observe melting events like this in upcoming years, it will be worrisome.”
“The Greenland ice sheet is a vast area with a varied history of change. This event, combined with other natural but uncommon phenomena, such as the large calving event last week on Petermann Glacier, are part of a complex story,” said Tom Wagner, NASA’s cryosphere program manager in Washington.
What, if any, affect this month’s dramatic melt might have on the summer’s ice loss or sea level rise is at this time unknown.
Image Above: Thawing at or near the surface of Greenland’s ice sheet based upon data from three satellites on July 8 (left) and July 12. Areas indicated as “melt” (dark pink) correspond to sites where two or three satellites detected surface melting. Areas shown as “probable melt” (light pink) correspond to sites where at least one satellite detected surface melting. Each of the satellites measure different physical properties at different scales and are passing over Greenland at different times. Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory
