Market News

 January 13, 2016
Greenland ice sheet melts up to a third faster under cloudy skies

 As Greenland's ice sheet continues to melt, researchers are looking to the clouds.

Results from a new study have found that the melting of the ice sheet can increase by one-third when the skies are cloudy.

The second largest ice mass in the world, after Antarctica, Greenland's ice sheet is melting at increasing speeds and making a big contribution to the planet's rising sea levels.

The findings, by KU Leuven and published in the journal Nature Communications, mark the first that suggest clouds have a bigger role in the melting process than previously thought.

"Clouds always have several effects," lead author Kristof Van Tricht from the Department of Earth and Environmental Sciences said.

"On the one hand, they help add mass to the ice sheet when it snows. On the other, they have an indirect effect on the ice sheet as well: they have an impact on the temperature, and snow and ice react to these changes by melting and refreezing."

The process works both ways, Mr Van Tricht said.

The temperature drops as clouds block the sunlight, while, at the same time, clouds form a blanket that maintain heat on the surface, particularly at night.

"In this study, we examine the net result of these two indirect effects on the entire Greenland ice sheet."

From 2007 to 2010 the researchers used satellite observations to locate clouds over the ice sheet and mapped the net effect of clouds by combining snow model simulations and climate model data.

"Over the entire Greenland ice sheet, clouds raise the temperature, which triggers additional meltwater runoff: 56 billion tons per year -- a third more than clear skies," said Mr Van Tricht.

Surprisingly, he said the effect is not as visible during the daytime melting process, but rather during the following night.

"A snowpack is like a frozen sponge that melts during the day. At night, clear skies make a large amount of meltwater in the sponge refreeze. When the sky is overcast, by contrast, the temperature remains too high and only some of the water refreezes. As a result, the sponge is saturated more quickly and excess meltwater drains away."