Global Warming

Increasingly, emissions of heat-trapping greenhouse gases from energy production, industry, transportation, agriculture, and other human endeavors are concentrating in the earth's atmosphere. Many scientists believe that the buildup of these gases is creating a greenhouse effect that will lead to global warming. The most highly developed tools now available to predict climatic changes are complex computer models called general circulation models. These models, whose development is supported by the U.S. Global Change Research Program and five federal agencies, have become more accurate in recent decades, but major uncertainties still limit their predictive abilities. This report identifies (1) factors limiting the accuracy of general circulation models' estimates of future climatic changes and (2) federal outlays for general circulation models for fiscal years 1992-94.

GAO found that: (1) although GCM have improved their ability to predict future climatic changes over the last decade, their estimates are still limited by their incomplete or inaccurate representations of climate-affecting processes and by insufficient computer power; (2) scientists do not fully understand how the climate system responds to potentially important physical, chemical, and biological processes; (3) the lack of computer power requires scientists to use simplified assumptions and structures that increase the uncertainty of the models' predictions; (4) scientists are conducting research to overcome the limitations of the computer models; and (5) five federal agencies spent about $122.6 million for various global modeling projects, which represented about 3 percent of the global change research program's budget for FY 1992 through 1994.