Arctic ice grows darker and less reflective

Arctic ice is losing its reflective sheen. It's common knowledge that each summer, more and more of the ice melts leaving the dark waters of the ocean uncovered – a process that accelerates global warming by reducing the amount of solar radiation reflected back into space. Now it turns out that the surviving sea ice is also becoming darker and less reflective.

For the first time, a detailed analysis of 30 years of satellite data for the Arctic Ocean has quantified how much the albedo, or reflectivity, of Arctic ice is diminishing. Aku Riihela of the Finnish Meteorological Institute told New Scientist he estimates that darker ice means the Arctic Ocean's albedo at the end of the summer is of the order of 15 per cent weaker today than it was 30 years ago

The cause of the darkening, says Riihela, is partly due to thinning ice 

 and the formation of open water fissures, and partly because in the warmer air, ponds of liquid water form on the surface of the ice. The shallow ponds on the ice can dramatically reduce reflectivity and increase the amount of solar radiation that the ice absorbs. "This shows that the increasing melt affects the inner Arctic sea ice, too," said Riihela.

Earlier this year, Marcel Nicolaus of the Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany, reported a trans-polar study aboard a German icebreaker, which found that "more than 50 per cent of the ice cover now consists of thin one-year ice on which the meltwater is particularly widespread".