(Fred Pearce/New Scientist, 27 March 2012) -- The disappearance of Arctic sea ice has crossed a "tipping point" that could soon make ice-free summers a regular feature across most of the Arctic Ocean, says a British climate scientist who is setting up an early warning system for dangerous climate tipping points.

Tim Lenton at the University of Exeter has carried out a day-by-day assessment of Arctic ice-cover data collected since satellite observation began in 1979. He presented his hotly anticipated findings for the first time at the Planet Under Pressure conference in London on Monday.

Up until 2007, sea ice systematically fluctuated between extensive cover in winter and lower cover in summer. But since then, says Lenton, the difference between winter and summer ice cover has been a million square kilometres greater than it was before, as a result of unprecedented summer melting. These observations are in contrast to what models predict should have happened.

Tagged: Arctic, News, Polar research: Reports and findings