Some common model biases in the Southern Ocean have been identified, resulting in some uncertainty
in oceanic heat uptake and transient climate response.
The probabilistic analyses of DAI reported in this section draw substantially on (subjective) Bayesian probabilities to describe key uncertainties in the climate system, such as climate sensitivity, the rate
of oceanic heat uptake, current radiative forcing, and indirect aerosol forcing.
Lewis and Curry arrive at their lower equilibrium climate sensitivity estimate by using updated compilations of the earth's observed temperature change,
oceanic heat uptake, and the magnitude of human emissions, some of which should cause warming (e.g., greenhouse gases), while the others should cool (e.g., sulfate aerosols).
He notes that the high end is driven by uncertainties in
the oceanic heat uptake data earlier in the record.
Most of
the oceanic heat uptake that determines the degree of disequilibirum occurs either in the Southern Ocean or in the Atlantic Ocean where it is associated with an overturning circulation consisting of less dense waters moving northward near the surface throughout the Atlantic with sinking in the subpolar North Atlantic and a return flow of denser water at depth.
The relationship between the effective climate sensitivity and
the oceanic heat uptake was first described by Hansen et al. (1984, 1985) using a box diffusion model.
Details of the individual model s sub-grid scale parametrizations also affect both the effective climate sensitivity and
the oceanic heat uptake (Weaver and Wiebe, 1999).
Since
the oceanic heat uptake is directly related to the thermal expansion, the range for thermal expansion is correspondingly increased due to the compensation noted above (see Chapter 11 for a complete discussion of sea level rise).
Models differ considerably in their estimates of the strength of different feedbacks in the climate system, particularly cloud feedbacks,
oceanic heat uptake and carbon cycle feedbacks, although progress has been made in these areas.