Climate change: Does it matter?

Ever since Svante Arrhenius, early in this century, calculated how much our use of fossil fuel might raise the surface temperature of the earth, there have been speculations concerning the impact of this and other human‐induced climate changes on society (Arrhenius, 1908). The conversion of this speculation about impacts into well established estimates has been hampered by uncertainties concerning the rate at which the climate forcing activities are changing, uncertainties in our knowledge of the nature of the climate changes that will follow the changes in forcing, uncertainties in the reaction of important ecosystems to the changing climate, and the lack of any widely adopted and tested methodology for estimating societal impacts of a climate change. Despite these difficulties, a number of studies in the United States in the period 1991–1994 have considered the impact of a human‐induced climate change, and other studies have discussed the methodological issues inherent in such work. In this review, changes in all the systems mainly involving physical processes, e.g., atmosphere, ocean, ice caps, glaciers, and the hydrological cycle, will be regarded as part of the climate and not discussed here. The effect of changes in any of these physical systems on the biosphere, including humans and human societies, will be called impacts, and studies of these impacts will be at least sampled in this review. Changes in stratospheric ozone are sometimes considered to be climate changes, but this review will be restricted to the climate changes caused by increases in the concentrations of infrared‐trapping gases in the atmosphere.