| A final concern related to the ongoing rise in the air's CO2 concentration is the worry that it may lead to catastrophic global warming. There is little reason to believe that such will ever occur, however, for several observations of historical changes in atmospheric CO2 concentration and air temperature suggest that it is climate change that drives changes in the air's CO2 content and not vice versa. In a study of the global warmings that signaled the demise of the last three ice ages, for example, Fischer et al. (1999) found that air temperature always rose first, followed by an increase in atmospheric CO2 some 400 to 1000 years later. Likewise, Petit et al. (1999) found that for all of the glacial inceptions of the past half-million years, air temperature consistently dropped before the air's CO2 content did, and that the CO2 decreases lagged the temperature decreases by several thousand years. In addition, the multiple-degree-Centigrade rapid warmings and subsequent slower coolings that occurred over the course of the start-and-stop demise of the last great ice age are typically credited with causing the minor CO2 concentration changes that followed them (Staufer et al., 1998); and there are a number of other studies that demonstrate a complete uncoupling of atmospheric CO2 and air temperature during periods of significant climate change (Cheddadi et al., 1998; Gagan et al., 1998; Raymo et al., 1998; Indermuhle et al., 1999). Hence, there are no historical analogues for CO2-induced climate change; but there are many examples of climate change-induced CO2 variations. |
