A two-phase response of the Southern Ocean to an increase in greenhouse gas concentrations

The response of the Southern Ocean to an increase in atmospheric greenhouse gas concentrations simulated by a global atmosphere-ocean-sea-ice model ca n be decomposed in two different phases. Firstly, the ocean damps the surfa ce 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 decre ase in ice area in the Southern Ocean is much larger than in the Northern H emisphere. This large but delayed response has consequences for the interpr etation of both observations and model results.