Elevated Atmospheric Carbon Dioxide: Drought

In this introductory chapter, we consider the effect of elevated levels of CO2 on the growth of plants under drought. Drought is our £rst topic, because it causes most (40.8%) of the crop losses in the United States (Boyer 1982), and it is predicted that as CO2 concentration increases in the atmosphere, large areas, especially the crop-producing latitudes of the central United States, will become drier. We know as a fact that the CO2 concentration in the atmosphere is increasing, as documented by the careful measurements of Keeling (1970). (See Appendix for a biography of Charles David Keeling.) The increase is thought to be due to the increased burning of fossil fuels, which has occurred since the middle of the last century (Figure 1.1). The CO2 concentration in the atmosphere has risen from 316 ppm in 1958 to 385 ppm in 2008 (Dlugokencky 2009). Figure 1.2 shows the CO2 concentration between 1959 and 1979 (Idso 1982), and Figure 1.3 shows the concentration between 1980 and 2005 (Schnell 2005).