Greenland’s white snow is getting darker. Scientists have generally attributed that darkening to larger, slightly less white snow grains caused by warmer temperatures. But researchers have found a new source of darkening taking hold: impurities in the snow.
“It can increase the speed of melting,” says Marie Dumont, a remote sensing scientist at Météo France in Grenoble, who publishes today with her colleagues in Nature Geoscience.
Scientists have known for years that Greenland’s snow is getting darker, based on satellite observations that have revealed lower albedos, or reflectivity. That’s a problem because the darker the snow is, the more sunlight it absorbs, and the faster it melts. Greenland’s melting ice sheets are already predicted to raise sea levels by 20 centimeters by 2100.
But Dumont and her colleagues have found that, since 2009, there has been a darkening that cannot be explained by larger snow grain size alone. Using satellite observations, they found lower albedos at elevations and at times of the year that are too cold for larger snow grains to form.