Using a global coupled model of intermediate complexity (2D atmosphere, 3D ocean), the behavior of the thermohaline circulation is explored for various increased CO2 scenarios. A novel feature of the model is our ability to adjust the model’s sensitivity to CO2 increases by changing the strength of the cloud feedback. By varying the rate and duration of increases in atmospheric CO2, the model’s sensitivity, and the river runoff scheme for perturbations in freshwater forcing, we are able to obtain and analyze a spectrum of behaviors, ranging from little change in the thermohaline circulation to a full shutdown of sinking in the North Atlantic. We find that the thermohaline circulation is particularly sensitive to changes in river runoff into the Arctic Ocean. The strength of the meridional overturning circulation in the Atlantic is compared to changes in the steric height difference between the North Atlantic and the South Atlantic.We find a strong correlation between changes in overturning strength and the strength of the steric height gradient; moreover, we find a reversal in the sign of the gradient when the circulation undergoes a collapse.