Conventional thermal models of ice sheets don’t take into account the warming action of water as it flows through the sheet, instead primarily considering heating via warmer air on the ice sheet surface. This sort of warming tends to be relatively slow, often requiring centuries to significantly warm the ice sheet.

But as ice sheets flow towards the coast, they grate on the bedrock, causing crevasses and fractures to form in the sheet’s upper 30 metres. According to the new study, as melt water flows through these openings, it can create ‘caves’ and networks of ‘pipes’ that carry water through the ice and spread warmth.

In order to quantify this phenomenon, the scientists modelled the effect on an ice sheet’s temperature of water flowing through it for eight weeks every summer – the length of a typical active-melt season. The results suggested that the presence of water flowing through an ice sheet could significantly speed up warming. ‘We are finding that once such water flow is initiated through a new section of ice sheet, it can warm rather significantly and quickly, sometimes in just ten years,’ said the study’s lead author, Thomas Philips of the University of Colorado at Boulder. 

Several factors contributed to the effect, including the fact that the water can remain in liquid form throughout the winter, which leads to a reduction in seasonal cooling.

January 2011