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Black soot from forest fires may accelerate Greenland ice cap melting

The Greenland ice sheet is a gigantic ice cap covering 85 percent of the island’s total land area. The ice sheet has covered large parts of Greenland for the last 2 to 3 million years, and at its edge can be up to 100,000 years old, a “permanent historical monument from the last ice age.”

The ice sheet, which is only a few yards thick at the ice fringe, compared with more than 10,500 feet thick at its highest point. There, the thick, heavy ice creates enormous, slow-moving glaciers, which under the influence of the force of gravity are forced out towards the coasts, where they break off and form icebergs. These active glaciers and constant melting have meant that the ice has been recycled many times.

A recent study led by Kaitlin Keegan of Dartmouth College, examined climate data and cores of Greenland’s ice during the country’s two biggest recorded thaws, in 1889 and 2012. According to Science News, the researchers found that those years had experienced relatively warm temperatures as well as heavy blankets of black carbon, which combined to cause rare snow-surface melting on up to 97 percent of the ice sheet.

Dark particles of carbon soot, coming from wildfires, volcanoes or human sources, affect the albedo of the snow resting on top of the ice sheet. Albedo is a measure of how much light that hits a surface is reflected without being absorbed. Darker surfaces absorb more of the sun’s energy than lighter ones, so the dark particles of carbon can raise the surface temperature of snow.

Thus black carbon could speed the ice sheet’s thaw by melting snow atop the ice sheet, the Science News article said. That resulting meltwater then trickles into the ice sheet’s frozen core, causing more melting below the surface.

The findings appeared in the Proceedings of the National Academy of Sciences.