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winter, replacing the mild westerly airstream that normally dominates the UK's weather.
• The study was carried out in 2009, before last year's harsh winter started to bite, and is all the more prescient because of its prediction that cold, snowy winters will be about three times more frequent in the coming years compared to previous decades.
• The researchers used computer models to assess the impact of the disappearing Arctic sea ice, particularly in the area of the Barents and Kara seas north of Scandinavia and Russia, which have experienced unprecedented losses of sea ice during summer.
• Their models found that, as the ice cap over the ocean disappeared, this allowed the heat of the relatively warm seawater to escape into the much colder atmosphere above, creating an area of high pressure surrounded by clockwise-moving winds that sweep down from the polar region over Europe and the British Isles. Vladimir Petoukhov, who carried out the study at the Potsdam Institute for Climate Impact Research in Germany, said the computer simulations showed that the disappearing sea ice is likely to have widespread and unpredictable impacts on the climate of the northern hemisphere.
• One of the principal predictions of the study was that the warming of the air over the ice-free seas is likely to bring bitterly cold air to Europe during the winter months, Dr Petoukhov said. "This is not what one would expect. Whoever thinks that the shrinking of some far away sea-ice won't bother him could be wrong. There are complex interconnections in the climate system, and in the Barents-Kara Sea we might have discovered a powerful feedback mechanism," he said.
• In the paper, submitted in November 2009 but published last month in the Journal of Geophysical Research, Dr Petoukhov and his colleague Vladimir Semenov write: "Our results imply that several recent severe winters do not conflict with the global warming picture but rather supplement it."
• Arctic sea ice has been in retreat over recent decades, with record lows recorded in September 2007. The normal recovery of the sea ice during winter has also been affected, especially in the Barents and Kara seas which have seen significant losses of ice cover over the past decade.
• Stefan Rahmstorf, professor of physics of the oceans at the Potsdam Institute, said the floating sea ice in winter insulates the relatively warm seawater from the bitterly cold temperatures of the air above it, which can be around -20C or -30C.
• "The Arctic sea ice is shrinking and at the moment it is at a record low for mid-to-late December, which provides a big heat source for the atmosphere," Professor Rahmstorf said. "The open ocean actually heats the atmosphere above because the

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