Greenland Ice Sheet May Melt More Due to One Uncalculated Force: Clouds

First Posted: Jan 12, 2016 11:42 AM EST

It turns out that clouds play a much larger role in the melting of the Greenland ice sheet than previously thought.  Scientists have found that compared to clear skies, clouds enhance the meltwater runoff by a third.

The Greenland Ice Sheet is the second largest ice mass in the world with the largest in Antarctica. The ice sheet is losing mass at a high speed, and increasingly contributes to the sea level rise on our planet. The role of clouds, though, has never been calculated before.

"Clouds always have several effects," said Kristof Van Tricht, one of the researchers, in a news release. "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. That works both ways. Clouds block the sunlight, which lowers the temperature. At the same time, they form a blanket that keeps the surface warm, especially at night. In this study, we examine the net result of these two indirect effects on the entire Greenland ice sheet."

In this latest study, the researchers used satellite observations to detect clouds over the Greenland ice sheet from 2007 to 2010. They compared the results with ground-based observations. The researchers combined these observations with snow model simulations and climate model data to map the net effect of clouds.

"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 Van Tricht. "Contrary to what you would expect, this effect is not so much 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."

The study highlights the need for more accurate cloud representation to make more accurate climate models.

The findings are published in the journal Nature Communications.

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