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General circulation models (GCMs) are mathematical models (i.e. computer simulations) of atmospheric and oceanic properties and processes that attempt to describe earth's climate system(The global climate system is a consequence of, and a link between, the atmosphere, oceans, the ice sheets (cryosphere), living organisms (biosphere) and the soils, sediments and rocks). Developed in 1960s, they have become the chief tools in analyzing effects of Global climatic change.CO2 doubling as one of the most important parameter affecting atmosphere was simulated using the resultant monthly indexes of temperature and precipitation on grid points in Tabriz for a 53-year time period
(1952-2003). The resulting Hythergraph and Ambrothermic model of Geophysical Fluid Dynamics Laboratory (GDFL) for Tabriz indicate monthly increases of temperature and precipitation during the CO2 doubling periods.