Multiple equilibria and asymmetric climates in the CCM3 coupled to an oceanic mixed layer with thermodynamic sea ice

Multiple equilibria and asymmetric climates are found in an atmospheric GCM coupled to an upper mixed layer ocean with thermodynamic sea ice on an aquaplanet. The model is run in a configuration close to that employed in the Budyko-Sellers type energy balance models. All externally specified fields are constant over the year, zonally symmetric and symmetric about the equator. The amplitude of a specified ocean heat transport is varied and within a certain range a number of distinctly different stationary states are found: An ice-covered planet, a cold'' climate, a present-day''-like climate and an ice-free warm'' climate. Asymmetric states with large sea ice extents in one hemisphere and none in the other are also found. This work can be considered a step towards understanding why many simpler climate models exhibit multiple equilibria while more comprehensive AGCMs tend not to.