The Arctic Ocean will probably be free of sea ice during the month of September by the end of this century, suggests an analysis of climate model projections and past observations reported online in Nature Geoscience. Most current climate models underestimate the observed deterioration rate of Arctic sea-ice cover, but a robust model-based estimate for the?twenty-first century is possible by combining known physical links between past and future evolutions of sea ice and the available observations.

By analysing a range of climate model simulations, Julien Bo? and colleagues found a close linear relationship between the simulated summer sea-ice extent in the twentieth century and the projected rate of sea-ice decline over the twenty-first century. Calibrating these projections with satellite observations of past Arctic sea-ice cover, they estimate that full loss of sea ice in September will probably occur in the Arctic Ocean by the end of this century. Using this method, the researchers have achieved a projection of future sea-ice cover, although most models significantly underestimate the observed decline in Arctic sea-ice cover.