Ocean heat and carbon uptake in transient climate change: Identifying model uncertainty.

(A. Romanou and J.Marshall), US CLIVAR VARIATIONS, vol. 13, no. 2, pp. pages, 2015.

Abstract

Global warming on decadal and centennial timescales is mediated and ameliorated by the ocean sequestering heat and carbon into its interior. Transient climate change is a function of the efficiency by which anthropogenic heat and carbon are transported away from the surface into the ocean interior (Hansen et al. 1985). Gregory and Mitchell (1997) and Raper et al. (2002) were the first to identify the importance of the ‘ocean heat uptake efficiency’ in transient climate change. Observational estimates (Schwartz 2012) and inferences from coupled atmosphere-ocean general circulation models (AOGCMs; Gregory and Forster 2008; Marotzke et al. 2015), suggest that ocean heat uptake efficiency on decadal timescales lies in the range 0.5-1.5 W m-2K-1 and is thus comparable to the climate feedback parameter (Murphy et al. 2009). Moreover, the ocean not only plays a key role in setting the timing of warming but also its regional patterns (Marshall et al. 2014), which is crucial to our understanding of regional climate, carbon and heat uptake, and sea-level change.

This short communication is based on a presentation given by A. Romanou at a recent workshop, Ocean’s Carbon and Heat Uptake: Uncertainties and Metrics, co-hosted by US CLIVAR and OCB. As briefly reviewed below, we have incomplete but growing knowledge of how ocean models used in climate change projections sequester heat and carbon into the interior. To understand and thence reduce errors and biases in the ocean component of coupled models, as well as elucidate the key mechanisms at work, in the final section we outline a proposed model intercomparison project named FAFMIP. In FAFMIP, coupled integrations would be carried out with prescribed “overrides” of wind stress and freshwater and heat fluxes acting at the sea surface.