Editing General circulation model (section)

{{Short description|Type of climate model}}
{{Redirect|AGCM|the Italian competition regulator|Autorità Garante della Concorrenza e del Mercato}}
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[[File:AtmosphericModelSchematic.png|thumb|right|350px|Climate models are systems of [[differential equation]]s based on the basic laws of [[physics]], [[Fluid dynamics|fluid motion]], and [[chemistry]]. To "run" a model, scientists divide the planet into a 3-dimensional grid, apply the basic equations, and evaluate the results. Atmospheric models calculate [[winds]], [[heat transfer]], [[radiation]], [[relative humidity]], and surface [[hydrology]] within each grid and evaluate interactions with neighboring points.<ref name=noaa200/>]]

A '''general circulation model''' ('''GCM''') is a type of [[climate model]]. It employs a [[mathematical model]] of the general circulation of a planetary [[atmosphere]] or ocean. It uses the [[Navier–Stokes equations]] on a rotating sphere with [[thermodynamics|thermodynamic]] terms for various energy sources ([[radiation]], [[latent heat]]). These equations are the basis for computer programs used to [[simulation|simulate]] the Earth's atmosphere or oceans. Atmospheric and oceanic GCMs (AGCM and [[Ocean general circulation model|OGCM]]) are key components along with [[sea ice]] and [[Land|land-surface]] components.

GCMs and global climate models are used for [[weather forecasting]], understanding the [[climate]], and forecasting [[climate change]].

Atmospheric GCMs (AGCMs) model the atmosphere and impose [[sea surface temperature]]s as boundary conditions. Coupled atmosphere-ocean GCMs (AOGCMs, e.g. [[HadCM3]], [[EdGCM]], [[GFDL CM2.X]], ARPEGE-Climat)<ref>[http://www.cnrm.meteo.fr/gmgec/site_engl/arpege/arpege_en.html]  {{webarchive|url=https://web.archive.org/web/20070927215849/http://www.cnrm.meteo.fr/gmgec/site_engl/arpege/arpege_en.html|date=27 September 2007}}</ref> combine the two models. The first general circulation climate model that combined both oceanic and atmospheric processes was developed in the late 1960s at the [[NOAA]] [[Geophysical Fluid Dynamics Laboratory]]<ref>{{cite web |title=NOAA 200th Top Tens: Breakthroughs: The First Climate Model |url=http://celebrating200years.noaa.gov/breakthroughs/climate_model/welcome.html |work=noaa.gov}}</ref> AOGCMs represent the pinnacle of complexity in climate models and internalise as many processes as possible. However, they are still under development and uncertainties remain.  They may be coupled to models of other processes, such as the [[carbon cycle]], so as to better model feedback effects. Such integrated multi-system models are sometimes referred to as either "earth system models" or "global climate models."

Versions designed for decade to century time scale climate applications were created by [[Syukuro Manabe]] and [[Kirk Bryan (oceanographer)|Kirk Bryan]] at the [[Geophysical Fluid Dynamics Laboratory]] (GFDL) in [[Princeton, New Jersey]].<ref name="noaa200">{{cite web |url=http://celebrating200years.noaa.gov/breakthroughs/climate_model/welcome.html |title=The First Climate Model |publisher=NOAA 200th Celebration |year=2007}}</ref> These models are based on the integration of a variety of fluid dynamical, chemical and sometimes biological equations.