Observational and theoretical studies of greenhouse climate effects

The carbon dioxide concentration in the atmosphere has increased by about 25% over the last 150 years and will surely continue to increase as a result of fossil fuel combustion. Enhancement of the atmospheric effect by elevated levels of CO/sub 2/ and other trace gases may over the next century increase global average surface air temperature by a few degrees Celsius to levels unprecedented in human history. Even eliminating emissions of CO/sub 2/ will not prevent global climate change because the combined greenhouse effect of less abundant but radiatively important gases such as methane and chlorocarbons is likely to be just as large as the impact of projected increases in carbon dioxide concentration. Quantitative estimates of future warming that could result from continued increases in greenhouse gas concentrations come from sophisticated mathematical models, which are the modern climatologists' primary prognostic tool. The current limitations and uncertains in these model results, however, prevent definitive predictions of the regional climatic responses that make up the projected global change. Deficiencies in the historical climate record prevent confirmation of the climate model predictions, but future research offers the potential for improved understanding. 25 refs., 10 figs.