ABSTRACT
I. INTRODUCTION The earth’s atmospheric carbon dioxide concentration ([CO2]) has fluctuated between 170 and 300 ppm over the past 160,000 years. However, since the start of the industrial revolution in Western Europe (1750-1800), atmospheric [CO2] has increased from 280 to approximately 365 ppm at present [1,2]. The future [CO2] depends on the degree to which CO2 emissions are controlled. However, with the rapid increase in world population and economic activity, a doubling of the present atmospheric [CO2], assuming a mean annual increase rate of 1.5 ppm, which was observed over the decade 1984-1993 [2], could be expected before the end of the 21st century [1,3,4]. A rise in atmospheric [CO2] may have important effects on global climate. As CO2 is responsible for 61% of global warming [5], a doubling of the atmospheric [CO2] and a rise in other so-called greenhouse gases (methane, nitrous oxide, chlorofluorocarbons) would increase the mean global temperature, possibly as much as 4.5 to 6°C [6,7]. In addition, shifts in regional precipitation patterns as a result of rising atmospheric [CO2] will probably result in decreased soil water availability in many areas of the world [3,8-11].
