Ocean heat uptake and its consequences for the magnitude of sea level rise and climate change

• Published in: Geophysical research letters Vol. 39; no. 18
• Main Authors: Kuhlbrodt, T., Gregory, J. M.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.09.2012; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Climate change; CMIP5 models; Correlation; Earth; Earth sciences; Earth, ocean, space; Exact sciences and technology; Marine; Mathematical models; ocean heat uptake; Oceans; Sea level; sea level rise; Southern Ocean; Thermal expansion; Uptakes; Antarctic Ocean; Atlantic Ocean; North Atlantic; atmosphere; projects; General circulation models; world ocean; thickness; stratification; Carbon dioxide; global; digital simulation; greenhouse gas; temperature; Vortex; uncertainties; climate change; efficiency; concentration; Climate models; climate; Uptake; expansion; Vertical profile; diffusivity; warming; transient phenomena; Comparative study
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2012GL052952

Under increasing greenhouse gas concentrations, ocean heat uptake moderates the rate of climate change, and thermal expansion makes a substantial contribution to sea level rise. In this paper we quantify the differences in projections among atmosphere‐ocean general circulation models of the Coupled Model Intercomparison Project in terms of transient climate response, ocean heat uptake efficiency and expansion efficiency of heat. The CMIP3 and CMIP5 ensembles have statistically indistinguishable distributions in these parameters. The ocean heat uptake efficiency varies by a factor of two across the models, explaining about 50% of the spread in ocean heat uptake in CMIP5 models with CO2increasing at 1%/year. It correlates with the ocean global‐mean vertical profiles both of temperature and of temperature change, and comparison with observations suggests the models may overestimate ocean heat uptake and underestimate surface warming, because their stratification is too weak. The models agree on the location of maxima of shallow ocean heat uptake (above 700 m) in the Southern Ocean and the North Atlantic, and on deep ocean heat uptake (below 2000 m) in areas of the Southern Ocean, in some places amounting to 40% of the top‐to‐bottom integral in the CMIP3 SRES A1B scenario. The Southern Ocean dominates global ocean heat uptake; consequently the eddy‐induced thickness diffusivity parameter, which is particularly influential in the Southern Ocean, correlates with the ocean heat uptake efficiency. The thermal expansion produced by ocean heat uptake is 0.12 m YJ−1, with an uncertainty of about 10% (1 YJ = 1024 J). Key Points The spread of the OHU efficiency explains half of the spread in total OHU Most models are biased towards a too weak stratification and a too strong OHU The Southern Ocean and its stratification dominate global OHU in the models