∗ Corresponding Author. Address:

Submitted to J. Climate Observations show the oceans have warmed over the past 40 years, with appreciable regional variation and more warming at the surface than at depth. Comparing the observations with results from two coupled ocean-atmosphere climate models (PCM and HadCM3) that include anthropogenic forcing shows remarkable agreement between the observed and model-estimated warming. In this comparison the models were sampled at the same locations as gridded yearly observed data. In the top 100 m of the water column the warming is well separated from natural variability, including both variability arising from internal instabilities of the coupled ocean-atmosphere climate system and that arising from volcanism and solar fluctuations. Between 125 and 200 m the agreement is not significant, but then increases again below, and remains significant down to 600 m. Analysis of PCM’s heat budget indicates the warming is driven by an increase in net surface heat flux that reaches 0.7 watts m −2 by the 1990s; the downward longwave flux increases by 3.7 watts m −2, which is not fully compensated by an increase in the upwar