University of Melbourne researchers writing in Nature say melting sea ice is a major cause of warming in the Arctic. The findings challenge previous theories which  propose that warmer air transported from lower latitudes toward the pole, or changes in cloud cover, are the primary causes of enhanced Arctic warming.

Using the latest observational data from the European Center for Medium-Range Weather Forecasting, researchers were able to uncover a distinctive pattern of warming, highly consistent with the loss of sea ice.

 "The sea ice acts like a shiny lid on the Arctic Ocean. When it is heated, it reflects most of the incoming sunlight back into space. When the sea ice melts, more heat is absorbed by the water. The warmer water then heats the atmosphere above it," says James Screen of the School of Earth Sciences at the University of Melbourne.

"What we found is this feedback system has warmed the atmosphere at a faster rate than it would otherwise," Screen says.

Prior to this latest data set being available there was a lot of contrasting information and inconclusive data. "This current data has provided a fuller picture of what is happening in the region," Screen says.

Over the past 20 years the Arctic has experienced the fastest warming of any region on the planet. Researchers around the globe have been trying to find out why.

Researchers say warming has been partly caused by increasing human greenhouse gas emissions. At the same time, the Arctic sea ice has been declining dramatically. In summer 2007 the Arctic had the lowest sea ice cover on record. Since then levels have recovered a little but the long-term trend is still one of decreasing ice.

Citation: James A. Screen, Ian Simmonds, 'The central role of diminishing sea ice in recent Arctic temperature amplification', Nature 464, 1334-1337, April 2010; doi:10.1038/nature09051 Letter