Changing snowfall makes Greenland darker and warmer: study – fr

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Changing snowfall makes Greenland darker and warmer: study – fr


Washington (AFP)

Greenland is getting darker and warmer due to a weather pattern that pushes fresh snowfall away from its ice cap, a study found on Monday.

A reduction in the amount of fresh, light-colored snow leaves more old, dark snow exposed on the surface, which in turn causes the ice sheet to absorb more heat and melt faster.

“As the snow ages, even in a few hours to a few days, you get this reduction in reflectivity, and that’s why fresh snow is so important,” said Erich Osterberg, associate professor of earth sciences at Dartmouth University and co-author of the article in Geophysical Research Letters.

Osterberg and his colleagues attributed the decrease in snowfall to a weather phenomenon called “atmospheric blockage” – in which persistent high-pressure systems hover over the ice sheet for weeks at a time.

These systems, which have become more prevalent in the region since the 1990s, trap warmer air over western Greenland, reduce cloud cover blocking light, and push snowstorms north.

The result is a “triple whammy,” Osterberg said. “All of this is contributing to an increasingly rapid melting of Greenland.”

A growing body of research has linked this blocking phenomenon to human-induced climate change.

Co-author Gabriel Lewis added that it’s not just less snowfall that is causing the warming – it’s the different types of snow that remain.

“Once it falls and rests on the surface of the ice sheet in the sun, it changes shape and the snow grains get bigger over time,” he said.

It becomes more rounded and less reflective than newer crystal-shaped snow.

According to the team’s calculations, a 1% change in reflectivity across the Greenland ice sheet could result in the loss of an additional 25 gigatonnes of ice over three years.

The team traveled 2,700 miles (4,340 kilometers) through Greenland by snowmobile to conduct two sampling and survey campaigns during the summers of 2016 and 2017, in an attempt to determine the cause of the darkening, which had been observed by satellite imagery for decades.

One hypothesis was that the snow became dirtier, due to soot from air pollution.

But the researchers found only about one part per billion of impurities, dispelling this hypothesis.

According to research cited in the study, the Greenland ice sheet has warmed by about 2.7 degrees Celsius (4.85 degrees Fahrenheit) since 1982, and the continent is experiencing its highest rates of melt and runoff. for at least 450 years.

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