The influence of transient surface fluxes on North Atlantic overturning ina coupled GCM climate change experiment

The mechanism by which the model-simulated North Atlantic thermohaline circ ulation (THC) weakens in response to increasing greenhouse gas (GHG) forcin g is investigated through the use of a set of five multi-century experiment s. Using a coarse resolution version of the GFDL coupled climate model, the role of various surface fluxes in weakening the THC is assessed. Changes i n net surface freshwater fluxes (precipitation, evaporation, and runoff fro m land) are found to be the dominant cause for the model's THC weakening. S urface heat flux changes brought about by rising GHG levels also contribute to THC weakening, but are of secondary importance. Wind stress variations have negligible impact on the THC's strength in the transient GHG experimen t.