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A general circulation model (GCM) aims to describe geophysical flow by integrating a variety of fluid-dynamical, chemical, or even biological equations that are either derived directly from physical laws (e.g. Newton's law) or constructed by more empirical means. There are both atmospheric GCMs (AGCMs) and ocean GCMs (OGCMs). When coupled together (along with other components such as a sea ice model and a land model) an ocean-atmosphere coupled general circulation model (O-A GCM) forms the basis for a full climate model.
Because the number of prognostic variables is limited, many parameters of model output are diagnostic variables. GCMs employ parameterizations that have usually been derived empirically to represent processes that are not directly accounted for in the model but must be represented in the model, such as waves above the Nyquist frequency.
A minimal GCM (also SGCM, for simple general circulation model) consists of a dynamical core, for example the primitive equations, energy input into the model, and energy dissipation in the form of scale-dependent friction, so that atmospheric waves with the highest wavenumbers are the ones most strongly attenuated.
A recent trend in GCMs is to extend them to become Earth system models, that would include such things as submodels for economic growth and its effect on carbon dioxide emissions.
See also: climate model.
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