Increasing concentration of the greenhouse gasses results in heating of the atmosphere:

Heat and moisture fluxes from the atmosphere into the ocean intensify. Since the formation of the deep waters in the North Atlantic is driven by the cooling of salty surface waters, surface warming/freshening will act to slow down the overturning of water in the NorthAtlantic:

Formation of the North Atlantic Deep Water is a crucial branch of the global thermohaline circulation (THC). Understanding the dynamics of the response of THC to global warming is a challenging problem. We approach it by doing systematic studies of the mechanisms causing THC weakening in a climate model of intermediate complexity. This model (MIT_UWash model) is a result of ongoing collaboration with the Massachusetts Institute of Technology (particularly with A. Sokolov and P.H. Stone). Such a model permits detailed analysis of the complicated feedbacks between the atmosphere and THC. The output of this model is also used in several model intercomparison studies.