Clouds melting Greenland ice sheet rapidly: study

Cloudy skies are raising the temperature of Greenland Ice Sheet by 2 to 3 degrees, accounting for as much as 30 per cent of the ice sheet melt, a new study has found.
Researchers showed that clouds are playing a larger role than previously believed in melting the second largest ice sheet in the world which is likely driving almost a third of global sea level rise.
"Over the next 80 years, we could be dealing with another foot of sea level rise around the world," said Tristan L'Ecuyer from the University of Wisconsin-Madison in US.
"With climate change at the back of our minds, and the disastrous consequences of a global sea level rise, we need to understand these processes to make more reliable projections for the future. Clouds are more important for that purpose than we used to think," said Kristof Van Tricht from University of Leuven in Belgium.

When it comes to heat, clouds essentially behave in two ways - they either cool the Earth's surface by reflecting sunlight back into space, or, like a thick blanket, they trap heat at the surface - the greenhouse effect of clouds, researchers said.
On Greenland, which is covered in bright, light-reflecting snow, clouds primarily act to trap heat.

Using two satellites - CloudSat and CALIPSO - researchers were able to take 'X-ray images' of Greenland's clouds from space between 2007 and 2010 and determine their structure, how high they were in the atmosphere, their vertical thickness, and their composition (ice or liquid).

The researchers combined this data with ground-based observations, snow model simulations and climate model data to map the net effect of clouds.
They learned that cloud cover prevents the ice that melts in the sunlight of day from refreezing at 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," said Tricht.
"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, Tricht added.

The findings were published in the journal Nature Communications.