**4. Predicting climate trends based on climate models**

Since the Earth's climate system is so large and does not allow controlled experiments, scientists have used mathematical models known as global circulation models (G.C.M.S) to evaluate known processes taking place and their possible interaction. At least ten global atmospheric circulation models have been developed by meteorological scientists in various research groups and used to predict the effects of rising greenhouse gases. The results of these simulations show an increase in average global warming in the range of 3 to 9 degrees Fahrenheit (1.5 to 4.5 degrees Celsius) by the end of the next century [5].
