Modeling the resilience of Greenland's ice

Michael Marshall in New Scientist: Greenland's vast ice sheets are proving surprisingly resilient. That means the glaciers will melt only slowly as the climate warms, provided it does so steadily. However, wild changes in the weather could make them melt much faster.

Greenland's ice sheets are shrinking already as the climate warms, and some glaciologists fear that they could accelerate their own destruction. If they all melted, they would raise global sea levels by 6.5 metres – though even in a world 8 °C warmer than now this might take 1000 years. The feared self-destruct device is water. As a glacier melts, water runs down to its base. In theory, this lubrication should accelerate the glacier's slide downhill and melt it sooner.

But this positive feedback is "limited", says Christian Schoof of the University of British Columbia in Vancouver, Canada, who has built a new model of glaciers that simulates how they respond to meltwater. He says glaciers can get rid of excess water because of the way their internal structure changes.

….Schoof's model could help explain what is happening to Greenland's glaciers, says glaciologist Roderik van de Wal of Utrecht University in the Netherlands, who has found no sign of the feared feedback effect. "The melt has been increasing but glacier velocities have not," he says. "This is a physical explanation."

But there is one fly in this otherwise comforting ointment. Changeable weather can cause short-term spikes in water supply, adding more water than the glacier's drainage can cope with and temporarily speeding it up. "The variability of the weather is key," Schoof says….

A glacier in Greenland somewhere west of Tasiilaq, shot by Ville Miettinen, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license