Extreme melting on Greenland ice sheet can occur without record heat

The Greenland ice sheet can experience extreme melting even when temperatures don’t hit record highs, a US researcher says.

Dr Marco Tedesco, assistant professor in the Department of Earth and Atmospheric Sciences at The City College of New York says that glaciers could undergo a self-amplifying cycle of melting and warming that would be difficult to halt.

“We are finding that even if you don’t have record-breaking highs, as long as warm temperatures persist you can get record-breaking melting because of positive feedback mechanisms,” said Professor Tedesco, who directs CCNY’s Cryospheric Processes Laboratory and also serves on CUNY Graduate Center doctoral faculty.

Bare ice is darker and absorbs more heat than the overlying snow.

But absorbing more energy from the sun also means that darker patches warm up faster, just like the blacktop of a road in the summer. The more they warm, the faster they melt.

And a year that follows one with record high temperatures can have more dark ice just below the surface, ready to warm and melt as soon as temperatures begin to rise. This also explains why more ice sheet melting can occur even though temperatures did not break records.

Only new falling snow puts the brakes on the process, covering the darker ice in a reflective blanket, Professor Tedesco says.

The model showed that this year’s snowfall couldn’t compensate for melting in previous years.  “The process never slowed down as much as it had in the past,” he explained. “The brakes engaged only every now and again.”

The study will be presented at the American Geophysical Union Society (AGU) meeting in San Francisco.