about 150 percent. The increases are mainly a result of the burning of fossil fuels and the clearing of forests. The average global temperature has risen about 1 degree Celsius since the late 1800. Though it has not been proven that there is a relationship between greenhouse gases levels and the surface temperature, it is likely that the relationship exists. Scientists believe that if people wait until the 2100 when people can more accurately model climate changes, it will be too late to change the severe impacts of climate change. Scientists have predicted that by 2050, the atmospheric carbon dioxide level will be twice the pre-industrial level.
             Rising global temperatures are expected to raise sea level, and change precipitation and other local climate conditions. Changing regional climate could alter forests, crop yields, and water supplies. It could also threaten human health, and harm birds, fish, and many types of ecosystems. Deserts may expand into existing range-lands, and the character of some of our National Parks may be permanently alte
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