Quantifying underestimates of long-term upper-ocean warming

• Published in: Nature climate change Vol. 4; no. 11; pp. 999 - 1005
• Main Authors: Durack, Paul J., Gleckler, Peter J., Landerer, Felix W., Taylor, Karl E.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.11.2014; Nature Publishing Group
• Subjects: 704/106/829/2737; Climate Change; Climate Change/Climate Change Impacts; Climate models; Enthalpy; Environment; Environmental Law/Policy/Ecojustice; Global warming; letter; Marine; Ocean warming; Satellite altimetry
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/nclimate2389

The ocean stores over 90% of the heat due to anthropogenic warming. This study uses satellite observations and climate models to investigate the warming of the upper ocean (0–700 m) and finds that warming is biased low, most likely because of poor Southern Hemisphere sampling. Applying adjustments results in a large increase in upper-ocean heat content estimates. The global ocean stores more than 90% of the heat associated with observed greenhouse-gas-attributed global warming 1 , 2 , 3 , 4 . Using satellite altimetry observations and a large suite of climate models, we conclude that observed estimates of 0–700 dbar global ocean warming since 1970 are likely biased low. This underestimation is attributed to poor sampling of the Southern Hemisphere, and limitations of the analysis methods that conservatively estimate temperature changes in data-sparse regions 5 , 6 , 7 . We find that the partitioning of northern and southern hemispheric simulated sea surface height changes are consistent with precise altimeter observations, whereas the hemispheric partitioning of simulated upper-ocean warming is inconsistent with observed in-situ -based ocean heat content estimates. Relying on the close correspondence between hemispheric-scale ocean heat content and steric changes, we adjust the poorly constrained Southern Hemisphere observed warming estimates so that hemispheric ratios are consistent with the broad range of modelled results. These adjustments yield large increases (2.2–7.1 × 10 22 J 35 yr −1 ) to current global upper-ocean heat content change estimates, and have important implications for sea level, the planetary energy budget and climate sensitivity assessments.