Between 2003 and 2005, the top layers of the world's oceans cooled slightly, but scientists aren't sure where the heat went.
According to climate data gathered worldwide, 2003, 2004, and 2005 are three of the five warmest years since reliable record keeping of global air temperatures began more than a century ago. However, oceanographic surveys suggest that on average, the upper 750 meters of the world's ice-free oceans cooled about 0.03°C during that 3-year period.
This cooling reverses an oceanic-warming trend observed since the 1950s, oceanographer John M. Lyman and his colleagues report in the Sept. 28 Geophysical Research Letters. Between 1993 and 2003, the average temperature of the upper layers of the icefree ocean rose about 0.09°C, they note.