Melting of ice sheets in Greenland could be caused by climate change, as well as a series of forest fires that radically affected the local environment.
Dartmouth College researchers conducted a detailed study of the Greenland ice sheets. They wanted to know what was responsible for losses seen there between 1889 and 2012. To study the history of Greenland's climate, investigators examined the six shallow ice cores, going back more than 100 years.
Most environmentalists believed thinning was almost exclusively caused by rising global temperatures. This study is the first to reveal additional factors resulting in the loss of ice sheet mass.
Dry snow melting on the sheets does not directly contribute to rising sea levels. The new study found that as water from the melt trickles down through lower layers of ice, it re-freezes.
But, this melting reveals darker layers of ash that were previously hidden, providing a darker surface than upper layers of snow and ice. This darker surface absorbs more light than pure snow, lowering the albedo, or amount of energy reflected back into space. This could lead to a runaway melting effect, warn researchers.
"The widespread melting of the Greenland ice sheet required the combination of both of these effects - lowered snow albedo from ash and unusually warm temperature - to push the ice sheet over the threshold. With both the frequency of forest fires and warmer temperatures predicted to increase with climate change, widespread melt events are likely to happen much more frequently in the future," Kaitlin Keegan, lead author of the study and doctoral student at Dartmouth, said.
The dry snow regions are concentrated toward the center of the island nation. Melting is rare in those regions. In the first widespread melting ever recorded in the history of satellite observations, ice reductions were seen over 97 percent of the Greenland ice sheet.
This melting was last seen in 1889, after forest fires coated large areas of the ice sheet with ash.
"The same mechanism drove two widespread melt events that occurred over 100 years apart, in 1889 and 2012. We found that black carbon from forest fires and rising temperatures combined to cause both of these events, and that continued climate change may result in nearly annual melting of the surface of the [sheet] by the year 2100," researchers wrote in the article announcing their study.
Previous research showed the hot summer of 2012 in Greenland was spurred by a layer of warm air, blanketed by thin clouds. Heated air from North America helped fuel the high temperatures.
The National Science Foundation and NASA helped to sponsor the research.
Analysis of thinning ice sheets in Greenland and contributing factors, including the forest fires, was published in the Proceedings of the National Academy of Sciences.
