Tuesday, October 25, 2011

Greenland melting in 2011 well above average with near-record mass loss

Professor Marco Tedesco from the City College of New York reports that extreme melting continues from the Greenland Ice sheet this year with close-to-record simulated surface mass balance, bare ice exposure, albedo and runoff anomalies. He warned that glaciers could undergo a self-amplifying cycle of melting and warming that would be difficult to halt.

Related: Record summer melting in 2010 | Greenland sets a new melt record in 2010 - sea levels to rise

"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.

This year was the 6th in terms of melting index which compares the number of melting days during the summer season, estimated from satellite based microwave observations. The surface mass balance loss this year was comparable to 2010. "The loss in 2011 and 2010 was much higher than the mass gain from snow accumulation." the report says.

"The 2010 season was largely driven by a longer season and therefore captured by microwave data, where the 2011 season was characterized by a relatively short but intense melting season, with the albedo feedback mechanism playing a major role (as in 2010) and large bare ice areas subject to melting." summarises the report on 2011 melting in Greenland

Professor Tedesco lead a 4 week expedition to the Jakobshavn Isbræ glacier in western Greenland this year to gather data at close range, including air temperatures, wind speed, exposed ice and its movement, the emergence of streams and lakes of melt water on the surface, and the water’s eventual draining away beneath the glacier.

According to modelling of the ice melt process, melting between June and August was well above the average for 1979 to 2010. As melting occurrs, dark water forms lakes and pools on the glacier and darker bare ice is exposed leading to more warming through the albedo feedback mechanism. New snow would increase the albedo or surface reflectivity reducing warming. But Professor Tedesco said in a media release "The process never slowed down as much as it had in the past," he explained. "The brakes engaged only every now and again."

The team concluded from their observations and satellite measurements that melting is a large-scale effect across much of Greenland. "It's a sign that not only do albedo and other variables play a role in acceleration of melting, but that this acceleration is happening in many places all over Greenland," Tedesco cautioned. "We are currently trying to understand if this is a trend or will become one. This will help us to improve models projecting future melting scenarios and predict how they might evolve."