A new scientific study published Monday at Nature Climate Change concludes that more melt water from Greenland may be running off into the ocean than previously calculated. That, of course, means the eventual impact the melting ice sheet of the world’s largest island has on rising sea levels could happen sooner than expected.
For several years, the international team of scientists led by Horst Machguth of the Geological Survey of Denmark and Greenland have been studying “firn.” This is porous snow resting just under the surface atop dense glacier ice. Because of its porosity, firn contains spaces that hold meltwater. Over time, this firn-held meltwater descends into the glacer where it freezes hard, which keeps it from running off. The study evaluated whether climate change has affected firn’s capacity for holding meltwater. According to the scientists, it has:
Our observations frame the recent exceptional melt summers in 2010 and 2012 (refs 5,6), revealing significant changes in firn structure at different elevations caused by successive intensive melt events. In the upper regions (more than ∼1,900 m[eters] above sea level), firn has undergone substantial densification, while at lower elevations, where melt is most abundant, porous firn has lost most of its capability to retain meltwater. Here, the formation of near-surface ice layers renders deep pore space difficult to access, forcing meltwater to enter an efficient surface discharge system and intensifying ice sheet mass loss earlier than previously suggested.
One of the scientists conducting the study, York University Professor William Colgan, said, “The study looked at very recent climate change on the ice sheet, how the last couple of years of melt have really altered the structure of the ice sheet firn and made it behave differently to future melt.”
Chelsea Harvey reports:
Until recently, many scientists have assumed that most of Greenland’s firn space is still available for trapping meltwater. But the new research shows that this is likely no longer the case. Through on-the-ground observations, the scientists have shown that the recent formation of dense ice layers near the ice sheet’s surface are making it more difficult for liquid water to percolate into the firn — meaning it’s forced to run off instead.
“If you look at some of the other studies which have been arguing that you have unlimited capacity for retention of water in the firn, this study shows that that is not the case,” said Kurt Kjaer, a curator and researcher at the Natural History Museum of Denmark, who has studied glacier dynamics on the Greenland ice sheet but was not involved in the study.
Scientists aren’t just worried about the direct impact of the potential for increased run-off but the fact that the run-off can cut channels into the ice, boosting run-off to the sea even more. It also creates slushy areas that reduce the ice’s reflectivity—its albedo—which means it will absorb more heat from the sun and further increase the pace of melting.
That’s not all.
Colgan said that other of the world’s ice caps are covered in firn, too. “Evidence is emerging to show Canadian Arctic firn is also capping off.”