Arctic ice hits 'tipping point'

Dwindling Arctic sea ice may have reached a 'tipping point' that could make British winters even wetter, according to researchers.

Arctic sea ice levels naturally ebb and flow throughout the year and are always lowest in September. But September 2005 marked their lowest level in 50 years and satellite data show average September sea ice extent down by 8.6 per cent per decade and accelerating.

Some computer models even predict an ice-free Arctic Ocean in September by 2050.

The loss of Arctic sea ice is most often tied to harmful effects to wildlife and increasing erosion of coastlines. But today, scientists at the University of Colorado warn in the journal Science of a link between Arctic sea ice loss and changes in atmospheric patterns. These patterns could result in reduced rainfall in the American West and increased precipitation over western and southern Europe.

Dr Mark Serreze, of the university's National Snow and Ice Data Centre, who led the study, said the Arctic sea-ice extent trend has been negative in every month since 1979 and is linked to both rising concentrations of greenhouse gases and strong natural variability in Arctic sea ice.

"When the ice thins to a vulnerable state, the bottom will drop out and we may quickly move into a new, seasonally ice-free state of the Arctic," Dr Serreze said.

"I think there is some evidence that we may have reached that tipping point, and the impacts will not be confined to the Arctic region." The wider impact on temperate regions such as Europe is discussed by Dr Serreze and Julienne Stroeve of the centre and Marika Holland of the National Centre for Atmospheric Research.

The decline in Arctic sea ice could affect western American states by lessening the severity of Arctic cold fronts and reducing snowfall, affecting the ski industry and agriculture, he said. "Just how things will pan out is unclear, but the bottom line is that Arctic sea ice matters globally."

The changes could also cause increased rainfall in western and southern Europe in winter. He told The Daily Telegraph: "The basic issue is that the Arctic acts as the Northern Hemisphere 'refrigerator' of the climate system. Change the nature of the refrigerator, and the rest of the climate system will respond."

Because Arctic temperatures have risen from 2F (-17C) to 7F (-14C) in recent decades, there is no end in sight to the decline in sea ice extent, said Dr Serreze.

"While the Arctic is losing a great deal of ice in the summer months, it now seems that it also is regenerating less ice in the winter," he said. "With this increasing vulnerability, a kick to the system just from natural climate fluctuations could send it into a tailspin."

The potential for such rapid ice loss was highlighted in a December 2006 study co-written by Dr Holland in Geophysical Research Letters. In one climate model simulation, the Arctic Ocean became nearly ice-free in September between 2040 and 2050.

"Given the growing agreement between models and observations, a transition to a seasonally ice-free Arctic Ocean as the system warms seems increasingly certain," the researchers write today in Science.

Another study in Science, by Kathy Law at IPSL-CNRS in Paris, France, and Andreas Stohl at Université Pierre et Marie Curie in Paris, warns that if large portions of sea ice melt, more pollution and stronger climate effects are predicted because of the resulting increase in shipping and Arctic oil drilling.

In a study of the other pole, University of Edinburgh scientists identified four Antarctic glaciers that pose a threat to future sea levels. Working with University College London, they determined the effect melting ice in Antarctica and Greenland has on global sea level and concluded they were responsible for a rise of 0.35 millimetres a year over the past decade - about 12 per cent of the global trend.