Newly published research that includes satellite data from three separate sources shows that the seasonal melt on Greenland’s ice sheet during the summer of 2007 was a stunning 60 percent more than the previous high, set in 1998.
The new information, which differs from other studies by including information beginning in the early 1970s, is consistent with other indicators of worldwide global climate change, according to the author of the study, Thomas L. Mote, a climatologist from UGA.
“What we found was really quite remarkable,” said Mote, a professor in UGA’s department of geography and its Climatology Research Lab. “This work includes the longest satellite record anyone has for Greenland. No one piece of evidence ever tells the whole story, but when you put them together, they point in the same direction.”
Mote’s research was just published in the journal Geophysical Research Letters.
Perhaps just as dramatic as the huge increase in snow melt is that Greenland had as many as 50 more days of melt than average, and the melting season began a full month earlier than normal.
Mote has studied snow melt in Greenland for more than a decade, but even he was unprepared for the dramatic melt that occurred last summer. He compared data from three satellite sources:
• The Special Sensor Microwave/Imager (SSM/I), which provided information from 1987 to the present;
• The Scanning Multichannel Microwave Radiometer (SMMR), which supplied data from 1979 to 1987; and
• The Electrically Scanning Microwave Radiometer (ESMR), for data recorded in 1973, 1974 and 1976.
While other researchers had used data from SSM/I and SMMR, none had reexamined the older information generated from the ESMR satellite, and that longer record allowed Mote to see farther into the recent past of Greenland’s ice-sheet history.
“To be honest, there’s just not much useful satellite data prior to the 1980s,” said Mote.
There have been other warm periods in Greenland’s recent past, Mote says, most notably in the 1930s, though it’s difficult to say how much melt may have occurred then. But a dramatic change is now under way in a land that covers more than 800,000 square miles, but has a permanent population of less than 60,000.
Just why the huge increase in melt occurred in the summer of 2007 is not yet entirely clear, said Mote. Certainly, increasing surface temperatures are part of it.
Coastal meteorological stations showed higher-than-average temperatures for most of the season. But another culprit may be changes in the surface of the ice sheet itself.
Data show that the average number of melt days has been steadily increasing since 1997, and this may have allowed the ice sheet to become more susceptible to further melting. Large streams of water actually flow through chasms and cracks down to the land’s surface and cause the ice sheet to become unstable.
Another possible mechanism may be an increase in temperature of the snow or less snow accumulation in recent years, according to Mote.
He points out that the noticeable summer melt of ice in Greenland is consistent with satellite observations that have pointed to decreasing sea ice across the Northern Hemisphere since 2000.
“The most recent Intergovernmental Panel on Climate Change assessment report concludes that changes in surface melting have contributed to a loss of mass in Greenland,” said Mote, “which they report is ‘very likely’ a contributor to global sea rise level.”
Researchers will be watching Greenland’s ice sheet warily next summer to see if the trend continues.