Clear Skies Drove the Biggest-Ever Drop in Greenland’s Ice Sheet
Clear Skies Drove the Biggest-Ever Drop in Greenland’s Ice Sheet
(Bloomberg) -- Clear skies and more sunlight over Greenland last summer resulted in the biggest drop in the ice sheet’s mass ever recorded, new research shows.
The phenomenon was linked to an exceptional high-pressure system that prevented the formation of clouds, according to a study led by Marco Tedesco from Columbia University’s Lamont-Doherty Earth Observatory. That suggests climate models that don’t incorporate atmospheric data could be underestimating future melting by about half, Tedesco said in commentary accompanying the research.
“These atmospheric conditions are becoming more and more frequent over the past few decades,” he said. “Simulations of future impacts are very likely underestimating the mass loss due to climate change.”
Scientists closely monitor the surface mass balance of Greenland’s ice sheet—that is, how much mass is lost due to melting compared with how much is gained due to snowfall and other accumulation. But when there are no clouds, there’s no snow. As a result, about 50 billion fewer tons of snowfall fell over the ice sheet than average last year. Without the fresh snow cover, the ice absorbed more heat, eventually melting down to 320 billion tons below the average mass for 1981 to 2010, the biggest drop since record-keeping began in 1948. It gained back just 50 billion tons, about 13% of the average increase between 1981 and 2010.
Such a small increase is not good news said the study’s co-author, the University of Liege’s Xavier Fettweis, in commentary on the paper. That’s in part because surface mass losses aren’t the only way glaciers shrink. Fissures also form in the ice, causing large chunks to break off into the ocean, a process known as calving. Under stable conditions, the gains in surface mass balance would be high enough to compensate for the ice that’s lost when icebergs calve off, but not under current conditions.
The same weather system caused a different damaging effect in the northern and western parts of Greenland. Warm, moist air from the lower altitudes gather there and formed clouds, but instead of bringing snowfall, these clouds trapped the heat that would normally bounce off of the ice into the atmosphere, creating a small-scale greenhouse effect.
Overall, the Greenland ice sheet lost an estimated 600 billion tons in 2019, representing a sea level rise of about 1.5 millimeters.
“You can see the mass balance in Greenland as your bank account,” Tedesco said. “In some periods you spend more, and in some periods you earn more. If you spend too much you go negative. This is what happened to Greenland.”
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