A report by the Pew Center on Global Climate Change, "Observed Impacts of Global Climate Change in the U.S.," by Camille Parmesan of The University of Texas at Austin and Hector Galbraith of Galbraith Environmental Sciences and the University of Colorado-Boulder, reviews the broad range of ecological changes that have occurred in response to human-induced changes in the global and U.S. climate.
According to the scientists' report, the average temperature on Earth has increased by approximately 1 degree Farenheit over the past century. And there is now strong evidence that this global warming is largely due to human emissions of greenhouse gases from a growing fossil fuel economy. Unless these emissions are checked, additional warming of 2 to 10 degrees is projected by the end of the 21st century. There are abundant signs, however, that the warming has already been sufficient to induce significant changes in the ecosystems and wildlife of the United States.