Coupled atmosphere-ocean general circulation models (AOGCMs) are the most complex models in use, consisting of an Atmosphere general circulation model (AGCM) coupled to an Ocean general circulation models (OGCM). With the addition of other components (such as a sea ice model or a model for evapotranspiration over land), the AOGCM becomes the basis for a full climate model. Some recent models include the biosphere, carbon cycle and atmospheric chemistry as well. AOGCMs can be used for the prediction and rate of change of future climate. They are also used to study the variability and physical processes of the coupled climate system. Global climate models typically have a resolution of a few hundred kilometres. Climate projections from the Hadley Centre make use of the HadCM2 AOGCM, developed in 1994, and its successor HadCM3 AOGCM, developed in 1998. Greenhouse-gas experiments with AOGCMs have usually been driven by specifying atmospheric concentrations of the gases, but if a carbon cycle model is included, the AOGCM can predict changes in carbon dioxide concentration, given the emissions of carbon dioxide into the atmosphere. Similarly, an AOGCM coupled to an atmospheric chemistry model is able to predict the changes in concentration of other atmospheric constituents in response to climate change and to the changing emissions of various gases. Further information is available on: some aspects of ocean simulation in HadCM3 (thermohaline circulation, ventilation, vertical mixing), decadal variability in the ocean of HadCM3. Recently a global coupled climate model with an eddy-permitting ocean resolution has been developed at the Hadley Centre, in order to better represent important oceanic processes.
COUPLED CLIMATE MODELS
MODELS