One US climate scientist has warned that if the Gulf stream was turned off, Britain and Ireland would experience temperatures familiar on the Arctic island of Spitsbergen. Temperatures in Britain would drop about 5C and Norway would suffer a 10C fall. The Gulf stream flows north from the Caribbean, keeping Britain at least 5C warmer than expected at its latitude. Britain's chief scientist, Sir Robert May, once calculated that it delivered 27,000 times the warmth that all Britain's power stations could supply. It merges with the north Atlantic current and the encounter of this giant, warm surface river with the Arctic winter ice is a powerful part of the convection machine which keeps the ocean swirling.
Ice is fresh water - so the sea that remains is increasingly cold, salty and dense.
But the Arctic ice cover is in retreat - shrinking by an area the size of the Netherlands every year. It is also thinning, from more than three metres thick to less than two metres in 30 years. What worried Dr Wadhams and his Arctic colleagues meeting in Cambridge yesterday was the failure, once again, of the huge Greenland ice tongue. It was a powerful agent in the ocean mixing system - and there were signs that the ocean circulation had begun to flag. When these both turn off, which will happen within the next 30 years, then the result will be a much slower transport of heat by the ocean from the tropics to our latitudes.