Cold winters linked to ebbing Arctic ice

Scientists have established a link between the cold, snowy winters in Britain and melting sea ice in the Arctic and have warned that long periods of freezing weather are likely to become more frequent.

An analysis of the ice-free regions of the Arctic Ocean has found that the higher temperatures there caused by global warming, which have melted the sea ice in the summer months, have paradoxically increased the chances of colder winters in Britain and the rest of northern Europe.

The findings are being assessed by British climate scientists, who have been asked by government ministers for advice on whether the past two cold winters are part of a wider pattern of climate change that will cause further damaging disruption to the nation's creaking transport infrastructure.

Some climate scientists believe that the dramatic retreat of the Arctic sea ice over the past 30 years has begun to change the wind patterns over much of the Northern Hemisphere, causing cold, Arctic air to be funnelled over Britain during winter, replacing the mild westerly airstream that normally dominates Britain's weather.

The study was carried out last year, before last year's harsh winter started to bite.

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.

Dr 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 was 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, 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 last year but published last month in the Journal of Geophysical Research, 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."

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," Rahmstorf said.

"The open ocean actually heats the atmosphere above because the ocean in the Arctic is about 0C, and that's much warmer than the atmosphere about it. This is a massive change compared with an ice-covered ocean, where the ice operates like a lid. You don't get that heating from below."

The scientists emphasised the climate was complex and there were other factors at play. It was too early to be sure if the past two cold winters are the result of the ice-free Arctic.

"The last winter of 2009-10 turned out to be fitting that pattern very well, and perhaps this winter as well, so that is three data points," Rahmstorf said.

"If you look ahead 40 or 50 years, these cold winters will be getting warmer because, even though you are getting an inflow of cold polar air, that air mass is getting warmer because of the greenhouse effect.

"So it's a transient phenomenon. In the long run, global warming wins out."

- Independent