New 'benchmark' for loss of reflectivity
Another wild card is the loss of the albedo of the ice, or its surface reflectivity. As the ice thins and once-white areas turn to dark open waters, solar energy is absorbed rather than reflected back into space. This, in turn, can spur further ice melt.
The study released yesterday in Nature Climate Change breaks new ground by putting definitive numbers on the albedo effect, using satellite data. It confirmed that the mean albedo, or surface reflectivity, of the Arctic ice zone in late summer declined over an almost three-decade period, between 1982 and 2009. The average sea ice zone albedo for August was approximately 15 percent smaller in 2009 than it was in 1982, Aku Riihelä, a remote sensing scientist at Finnish Meteorological Institute and lead author of the study, said in an email.
The fact that reflectivity decreased in areas with dark water was not surprising, but there also was a decrease in reflectivity with remaining sea ice.
This "means that the average surface conditions are changing. There are more open water leads within the ice, and the surface melt of the sea ice is more intensive than before. The thinning and retreat of the sea ice thus seem to affect not only the marginal oceans of the Arctic, but also the inner parts," Riihelä added.
Mark Flanner, an assistant professor at the University of Michigan who did not participate in the research, said that several factors could reduce albedo of existing ice, including earlier snowmelt and melt ponds on top of the ice. Snow is very reflective, and its disappearance earlier in the year allows absorption of more solar energy. Those things, along with thinner ice that allows light to reach dark water, can help reduce albedo overall, he said.
The scientific community had an understanding that overall albedo decreases with declining ice, but the new study is distinctive for putting a number on the decline. That could help with projections of climate models and hypotheses of broader changes to the rest of the ecosystem.
"It will provide a benchmark," he said.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500