
The dramatic finding comes from a study of ocean circulation in the North Atlantic, which found a 30% reduction in the warm currents that carry water north from the Gulf Stream.
The slow-down, which has long been predicted as a possible consequence of global warming, will give renewed urgency to intergovernmental talks in Montreal, Canada, this week on a successor to the Kyoto Protocol.
Harry Bryden at the Southampton Oceanography Centre in the UK, whose group carried out the analysis, says he is not yet sure if the change is temporary or signals a long-term trend. "We don't want to say the circulation will shut down," he told New Scientist. "But we are nervous about our findings. They have come as quite a surprise.