Clouds spiked 2012 melt of Greenland ice sheet: new research

Low-level clouds contributed to the melt of the Greenland ice sheet in 2012, new research finds. (HANDOUT PHOTO)

If Greenland’s ice sheet were to completely melt tomorrow, global sea levels would rise by more than seven metres.

Its three million cubic kilometres of ice won’t wash into the ocean overnight.

But last summer, the melt was so large that similar events show up in ice core records only once every 150 years or so over the last 4,000 years.

In a study published in the April 4 issue of the journal Nature, researchers describe what led to the melt.

“The July 2012 event was triggered by an influx of unusually warm air, but that was only one factor,” said Dave Turner, a scientist at the National Oceanic and Atmospheric Administration, in a University of Wisconsin news release. “In our paper we show that low-level clouds were instrumental in pushing temperatures up above freezing.”

Low-level clouds typically reflect heat from the sun back into space. Snow cover also tends to bounce heat from the sun back up.

But, under some temperature conditions, clouds can be both thin enough to allow heat to pass through to the surface and thick enough to “trap” some of that heat, the researchers found.

That extra heat trapped close to the surface can push temperatures above freezing.

That is exactly what happened in July 2012 over large parts of the Greenland ice sheet, the researchers say.

They say current climate models tend to underestimate the occurrence of these clouds, common over Greenland and across the Arctic, which could spike ice melt.