Recent estimates of global temperature rises in the upper ocean may have been too low.

Oceans absorb the majority of the heat resulting from global warming. Paul Durack of the Lawrence Livermore National Laboratory in California and his colleagues used a range of climate models and satellite observations to reassess observed changes in ocean warming between 1970 and 2004. They concluded that upper-ocean warming has been underestimated by as much as 58%, mainly because of sparse data from oceans in the Southern Hemisphere.

A separate study by William Llovel and his colleagues at NASA's Jet Propulsion Laboratory in Pasadena, California, showed that the ocean's upper 2,000 metres have strongly warmed since 2005. However, at depths below 2,000 metres, the ocean has absorbed negligible amounts of heat during this period.

These two studies have implications for accurately assessing the effects of climate change on sea-level rise.

Nature Clim. Change; (2014)