Summary: When discussing the implications of global warming and the steps needed to control greenhouse gas emissions, one needs to consider the range of projected temperature increases and the degree of uncertainty in these estimates. In July 1995, GAO reported (see GAO/RCED-95-164) on the limitations of general circulation computer models used to make such predictions. This testimony is based on the findings of that report. Although the accuracy of general circulation models has improved during the past decade, these models are still limited by incomplete and inaccurate representations of the processes affecting climate and by insufficient computing power. These limitations do not change the likelihood that the climate will change as a result of increased greenhouse gas emissions. They do, however, limit the ability to predict with certainty how the climate will respond--how much warming will occur, how soon it will happen, and what the regional effects will be. Efforts are under way to collect and analyze data, improve representations of various climatic processes, and develop and use more powerful computers. These efforts, which could take a decade or more, should improve the accuracy of the models.
