Science 342, 617–621 (2013)

In recent years, global surface temperatures have had smaller increases than expected, with the ocean warming instead. Yair Rosenthal, of Rutgers University, USA, and co-workers report on Pacific Ocean heat content for the last 10,000 years to provide context for current changes. They use proxy records from sediment cores collected around Indonesia for the reconstruction.

Intermediate (∼450–900m depth) water temperatures are shown to cool by 2 °C from 7,000 years ago until the last century. During that period, the upper ocean did not have such a significant change, with sea surface temperature cooling around 0.5 °C from 9,000 years ago to the twentieth century. Although the Pacific Ocean heat content has been higher over the Holocene than the present day, a comparison with the past decade indicates that the current rate of change is the higher than the long-term trend. The ocean heat content responds slowly to surface changes, and the recent rapid increase shown here indicates that the committed response from anthropogenic forcing may be large.