Nature Climate Change | 2021
Projected ocean warming constrained by the ocean observational record
Abstract
The ocean absorbs most of the excess heat from anthropogenic climate change, causing global ocean warming and sea-level rise with a series of consequences for human society and marine ecosystems. While there have been ongoing efforts to address large uncertainties in future projections, to date the projected ocean warming has not been constrained by the historical observations. Here, we show that the observed ocean warming over the well-sampled Argo period (2005–2019) can constrain projections of future ocean warming and that the upper-tail projections from latest climate models with high climate sensitivities are unrealistically large. By 2081–2100, under the high-emission scenario, the upper 2,000\u2009m of the ocean is likely (>66% probability) to warm by 1,546–2,170\u2009ZJ relative to 2005–2019, corresponding to 17–26\u2009cm sea-level rise from thermal expansion. Further narrowing uncertainties requires maintenance of the ocean observing system to extend the observational record. Ocean heat content is increasing, yet projections have not been constrained by observations. Using Argo data and CMIP6 models shows high climate sensitivity models overestimate increases; constrained projections estimate sea-level rise, from 0 to 2,000\u2009m thermal expansion, of 17–26\u2009cm by 2081–2100.