The Response of Natural Ecosystems to the Rising Global CO2 Levels

Abstract

Evidence from many sources shows that the concentration of atmospheric CO2 is steadily rising (61, 17). This rise is strongly correlated with the increase in global consumption of fossil fuels (104). There are also significant contributions from the clearing of forests, especially in the tropics (136, 55). Controversy continues, however, as to whether the biosphere is presently a source or a sink for carbon (see 52, 54, 56). Despite this controversy, most scientists agree that rising CO2 levels will have substantial direct and indirect effects on the biosphere (80). Because CO2 is a greenhouse gas, its increase in the atmosphere may influence the earth's energy budget. Several climatologists have used general circulation models to predict changes in mean annual global temperature (58, 108). While these models differ in detail, they all predict increased global warming and substantial shifts in precipitation patterns. Recently, some scientists (60) have questioned the predictions of these models. But regardless of changes in global temperature and other climate variables, rising CO2 can influence world ecosystems by direct effects on plant growth and development. The large body of literature on the response of crops and intensively managed forests to elevated CO2 is not treated in this review because there are