Has a well-meaning international effort to cut pollution from ships contributed to a sudden warming of the waters in the north Atlantic this year? That is the extraordinary claim made this week in an article in Science magazine, the journal of the American Association for the Advancement of Science. It asserts that limits on the sulphur content of fuels used by ships have helped reduce sulphur pollution from those vessels by 80 per cent – but at the inadvertent cost of reducing cloud formation over the oceans and so speeding global warming.