General Circulation Model

A global climate model or general circulation model (GCM) aims to describe climate behavior 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). An AGCM and an OGCM can be coupled together to form an atmosphere-ocean coupled general circulation model (AOGCM). With the addition of other components (such as a sea ice model or a land model), the AOGCM becomes the basis for a full climate model. Within this structure, different variations can exist, and their varying response to climate change may be studied (e.g. Sun and Hansen, 2003).

A recent trend in GCMs is to extend them to become Earth system models, that include such things as submodels for atmospheric chemistry or a carbon cycle model to better predict changes in carbon dioxide concentrations resulting from changes in emissions. In addition this approach allows feedback between these systems to be taken into account. For example, Chemistry-Climate models allow the possible effects of climate change on the recovery of the ozone hole [1] to be studied.

Climate prediction uncertainties depend on uncertainties in both models and the future course of industrial growth and technology (which is currently the largest unknown) (see IPCC scenarios below). Progress has been made in incorporating more realistic physics in the models, but significant uncertainties and unknowns remain. [2]

Note that many simpler levels of climate model exist; some are of only heuristic interest; others continue to be scientifically relevant.