The response of the Southern Ocean to an increase in atmospheric greenhouse gas concentrations simulated by a global atmosphere-ocean-sea-ice model can be decomposed in two different phases. Firstly, the ocean damps the surface warming because of its large heat capacity. Secondly, one century after the major increase in greenhouse gases, the warming is amplified because of a positive feedback that is associated with a stronger oceanic meridional heat transport toward the Southern Ocean. Consequently, the long-term decrease in ice area in the Southern Ocean is much larger than in the Northern Hemisphere. This large but delayed response has consequences for the interpretation of both observations and model results. ¿ 2001 American Geophysical Union