Record Greenland Ice Sheet Melting Caused by Forest Fires and Climate Change Combo

We all know that the Greenland ice sheet is melting, and could contribute significantly to sea level rise. Now, though, researchers have discovered the underlying causes behind this melting.

The Greenland ice sheet usually experiences annual melting at low elevations near the coastline. Yet surface melt on the ice sheet is rare in the dry snow region at its center. Yet in July 2012, more than 97 percent of the ice sheet experienced surface melt. This unprecedented melting was the first widespread melt that's occurred since satellite observations began.

Now, it turns out that this melting can largely be blamed on rising temperatures and ash from Northern Hemisphere forest fires. Together, these can create large-scale surface melting. This, in particular, contradicts conventional thinking that melt events like these are driven by warming alone.

The researchers analyzed six Greenland shallow ice cores from the dry snow region to confirm that the most recent melt prior to 2012 occurred in 1889. What was more interesting was that the scientists found that warm temperatures combined with black carbon sediments to cause this melting in both years.

"The widespread melting of the Greenland ice sheet required the combination of both of these effects-lowered snow albedo from ash and unusually warm temperatures-to push the ice sheet over the threshold," said Kaitlin Keegan, one of the researchers, in a news release. "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."

While the latest study didn't focus explicitly on analyzing the ash to determine the source of the fires, the researchers could make some deductions. The high concentration of ammonium concurrent with the black carbon suggests the ash's source was large boreal forest fires during the summer in Siberia and North America.

"Our Earth is a system of systems," said Mary Albert, one of the researchers, in a news release. "Improved understanding of the complexity of the linkages and feedbacks, as in this paper, is one challenge facing the next generation of engineers and scientists."

The findings are published in the journal Proceedings of the National Academy of Sciences.