For lack of storms bringing their share of fresh snow, Greenland darkens.
A slight change in color which is not without consequence: less white, it reflects less sunlight, which accelerates its warming, according to a new study published on Monday.
The surface of the Greenland ice sheet has warmed by at least 2.7 ° C since 1982, causing the ice to melt very quickly, the work published in
Geophysical Research Letters
underlines in the introduction
.
And for several decades, satellite observations have shown that the proportion of light reflected by snow (called albedo) has been decreasing.
Greenland is getting darker ... and therefore warmer.
But the reason for this darkening remained mysterious: is it caused by the presence in the snow of light-absorbing particles (such as soot from the combustion of fossil fuels), or by something else?
Reinforcement of a climatic phenomenon
To answer, researchers from the University of Darmouth traveled hundreds of kilometers in Greenland to carry out two sampling and survey campaigns, during the summer of 2016 and 2017. The size of the flakes on the ground, the way they reflect the light, and the impurities present in the snow have been measured at dozens of sites.
Scientists concluded that the pollution could not be held responsible: "It is one of the cleanest snows in the world," said Gabriel Lewis, one of the main authors of the study, quoted in a statement.
According to them, the fault is to be looked elsewhere: the reinforcement of a climatic phenomenon, called atmospheric blockage, which can stagnate for up to several weeks over certain regions of Greenland, has reduced the number of snowstorms.
However, these are essential.
"Triple whammy"
“When (snow) falls and stays on the surface, in the sun, it changes shape and the flakes get bigger,” says Gabriel Lewis.
"In a few hours already, then in a few days, you get this drop in reflectivity, and that's why fresh snow is so important," adds Erich Osterberg, associate professor at Dartmouth and principal investigator for this study.
The same climatic phenomenon also results in the maintenance of warmer air over these regions, as well as a reduction in cloud cover.
As solar radiation is less filtered, the transformation of snowflakes on the ground is thus further accelerated.
“It's like a triple whammy,” concludes Erich Osterberg.
“All this contributes to Greenland melting faster and faster.
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