Geographic distribution of the diapycnal component of thermohaline circulations in coupled climate models

Data archives from four global coupled ocean-atmosphere models are used to construct maps of diapycnal mass flux through selected isopycnal surfaces in the model oceans. The maps illustrate location and strength of the up and downwelling limbs of thermohaline-forced overturning loops whose stability in the face of rising atmospheric carbon dioxide (CO2) concentrations is of major concern in century-scale climate prediction. The up and downwelling limbs simulated by the four models for present-day greenhouse gas concentrations are compared with observational estimates. Predicted changes in the overturning brought about by gradually rising atmospheric CO2 content are compared model-to-model. While all four models predict some decline in the rate of Atlantic overturning during CO2-induced global warming, the geographic layout of the overturning circulations in each model is found to be insensitive to the changing climate.