Winter sea ice in the Arctic has failed to reform fully for the third year in a row. Scientists said yesterday that the area of ocean covered by Arctic ice at the end of the winter months was lower only in March 2006.

Researchers fear that the floating sea ice is now on a downward spiral of shrinkage that cannot recover fully even during winter because of warmer temperatures. Walt Meier of the US National Snow and Ice Data Centre in Boulder, Colorado, which released the satellite data yesterday, said: "We're seeing near-record lows and higher-than-normal temperatures. We expect the downward trend to continue in future years."

Computer models predict that the summer sea ice will be totally gone by the end of the century. Some scientists, however, believe that this could occur as early as 2040. If the sea ice of the Arctic disappears completely in summer, regional temperatures could increase faster than in the past. Some scientists also believe that the change in the regional climate could have far-reaching impacts on other parts of the northern hemisphere, perhaps by altering ocean currents such as the Gulf Stream.