Global Warming:

Limitations of General Circulation Models and Costs of Modeling Efforts

RCED-95-164, Jul 13, 1995

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Pursuant to congressional request, GAO reviewed the accuracy of general circulation models (GCM) in forecasting global warming trends, focusing on the: (1) factors limiting the accuracy of GCM estimates of future climatic changes; and (2) federal expenditures for GCM for fiscal years (FY) 1992 through 1994.

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.