We discuss aspects of the Atlantic thermohaline circulation (THC) and its response to increased greenhouse gas concentration, using a coupled atmosphere-ocean general circulation model (AOGCM) whose oceanic component is a new hybrid-isopycnal model. Two 200-year model integrations are carried out - a control run assuming fixed atmospheric composition and a perturbation run assuming gradual doubling of CO2. We employ no flux corrections at the air-sea interface, nor do we spin up the ocean prior to coupling. The surface conditions in the control run stabilize after several decades. When doubling CO2 at the rate of 1% per year, the model responds with a 2¿C increase in global mean surface air temperature (SAT) after 200 years and a virtually unchanged Atlantic meridional overturning circulation. The latter is maintained by a salinity increase that counteracts the effect of global warming on the surface buoyancy. ¿ 2001 American Geophysical Union