Attribution of temperature and precipitation changes to greenhouse gases in northwest Iran

Increase of the greenhouse gases has a considerable effect on climatic variables changes such as temperature and precipitation. Three-dimensional models of coupled ocean-atmosphere general circulation, AOGCMs, under all emissions scenarios, are able to simulate past and future climate periods. The present study investigates the possible attribution of climate change to the increase of the greenhouse gases in northwest Iran. Interannual variability range for the long-term (1000 years) of temperature and precipitation, resulting from control run (greenhouse gas constant) CGCM3 model used for the study area in northwest Iran. Then, the range of natural climate variables was determined from two-dimensional graphs of temperature and precipitation based on two-variant normal distribution. Ultimately, the detected trends of climate variables can be compared with the natural climate variability range of the region. The results showed that in different parts of the study area, the range of natural climate variables for temperature and precipitation changes (95% probability) in the west of the study area are less than 1.8 C° and 40%, respectively. These values are less than 4 C° and 40% respectively, in the east of the study area. However, the climate variables in the most regions of the west are almost outside the range of natural climate variables in the recent years (1998-2008). The result indicates the effect of climate changes on the climatic variables for the case study in recent years.