oceans have cooled substantially during some of the warmest years in recent times, claims a study. During the years 2003 and 2005, which saw the highest global average surface temperatures in more than a century, the top 750 metres of the oceans lost around one-fifth of the heat accumulated over the past 50 years, says the paper that will appear in a forthcoming issue of Geophysical Research Letters.

Oceans cover two-thirds of Earth's surface and have far more heat-storing capacity than air or land. Overall, they have warmed in recent decades. Between 1955 and 1998, for example, all of the world's oceans, down to a depth of 3,000 metres, warmed by 0.037