Changes in the climate system’s energy budget are predominantly revealed in ocean temperatures1,2 and the associated thermal expansion contribution to sea-level rise2. Climate models, however, do not reproduce the large decadal variability in globally averaged ocean heat content inferred from the sparse observational database3,4, even when volcanic and other variable climate forcings are included. The sum of the observed contributions has also not adequately explained the overall multi-decadal rise2. Here we report improved estimates of near-global ocean heat content and thermal expansion for the upper 300 m and 700 m of the ocean for 1950–2003, using statistical techniques that allow for sparse data coverage5,6,7 and applying recent corrections8 to reduce systematic biases in the most common ocean temperature observations9. Our ocean warming and thermal expansion trends for 1961–2003 are about 50 per cent larger than earlier estimates but about 40 per cent smaller for 1993–2003, which is consistent with the recognition that previously estimated rates for the 1990s had a positive bias as a result of instrumental errors8,9,10. On average, the decadal variability of the climate models with volcanic forcing now agrees approximately with the observations, but the modelled multi-decadal trends are smaller than observed. We add our observational estimate of upper-ocean thermal expansion to other contributions to sea-level rise and find that the sum of contributions from 1961 to 2003 is about 1.5 ± 0.4 mm yr-1, in good agreement with our updated estimate of near-global mean sea-level rise (using techniques established in earlier studies6,7) of 1.6 ± 0.2 mm yr-1.
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This paper is a contribution to the Commonwealth Scientific Industrial Research Organization (CSIRO) Climate Change Research Program and Wealth from Oceans Flagship and was supported by the Australian Government’s Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems Cooperative Research Centre. C.M.D., J.A.C., N.J.W. and S.E.W. were partly funded by the Australian Climate Change Science Program. We acknowledge the modelling groups, the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and the WCRP’s Working Group on Coupled Modelling (WGCM) for their roles in making available the WCRP CMIP-3 multi-model data set. Support for P.J.G. and this data set at the Lawrence Livermore National Laboratory was provided by the Office of Science, US Department of Energy. The Centre for Australian Weather and Climate Research is a partnership between CSIRO and the Australian Bureau of Meteorology.
Author Contributions C.M.D. completed the analysis to determine the changes in ocean heat content and thermosteric sea-level rise and shared responsibility for writing the manuscript. J.A.C. conceived the study, directed the analysis and shared responsibility for writing the manuscript. N.J.W. completed the analysis of the sea-level data and provided the software for the sea-level and thermosteric sea-level reconstructions. P.J.G. analysed the model results. S.E.W. provided the corrections for the XBT data and the climatology, and made valuable comments. P.M.B. provided the pressure corrections to the Argo data. J.R.D. quality-controlled the Argo data. All authors contributed to the final version of the manuscript.
The file contains Supplementary Notes and Supplementary Table S1 with detail of and a table summarizing the climate models results used in the manuscript.