In this study we have used the monthly data resulted from the calculation of temperature and precipitation for a 52-year period (1951-2003).The doubling effect of carbon dioxide (CO2) on temperature and precipitation was modeled as the most important climatic parameters. The resulting Hythergraph and Ambrothermic models for Tabriz indicate monthly increases of temperature and precipitation during the CO2 doubling periods. A comparison of the present and simulated Ambrothermic models applying Goddard Institute of Space Studies (GISS) shows precipitationand temperaturechanges in Tabriz. A decrease in the duration and intensity of cold period and freezing days, a reduction in spring and winter precipitation, a shift in precipitation from snow to rain, the extension of growth season, the increase in temperature and the resulting dryness are the signs of such changes.