increasing level of CO2 emission is well documented and is depicted in Figure 1. The increase of CO2 emissions has been most drastic during the past 50 years and now stands at approximately 6000 million metric tons of carbon per year.2 It is likely that unless non-fossil fuel energy sources are developed soon, the rate of emissions will continue to rise. The consequence of this anthropogenic CO2 emission is an increase in the CO2 concentration in the atmosphere. All fossil fuel emissions do not directly contribute to an increase in concentration, because there is complex carbon cycling through several so called "reservoirs" in the Earth system, namely the atmosphere, the biosphere, the ocean, and the fossil fuel inventory. This "carbon cycle" controls the CO2 concentration in the atmosphere by processes involving chemical equilibrium between the ocean and the atmosphere. Global climate models (GCM's) predict that a doubling of atmospheric CO2 concentration will lead to an increase in global mean temperature between 1.5 and 4.5°C due to the greenhouse effect. The greenhouse effect can be understood better by examining the radiation budget of the Earth. A small fraction of the short wavelength electromagnetic radiation emitted by the Sun is either absorbed or reflected to space by the Earth's atmosphere. The rest of the short wavelength radiation makes it to the Earth and is absorbed and converted to heat. The Earth loses heat both by evaporation (the hydrologic cycle) and by radiating the heat as long wavelength infrared radiation. The atmosphere warms due to solar and Earth radiation, which it radiates both to space and to the Earth. This radiation warms the Earth. CO2 is one of the main gases which traps the heat in the atmosphere. The atmosphere behaves like a greenhouse that traps sufficient heat to enable the growth of plants. Figure 2 shows global-mean temperature change for the period 1861 to 1989 relative to the average for 1951 to 1980, and is obtained from the assessment of the Intergovermental Panel on Climate Change (IPCC).3 This global-mean temperature is a combination of the temperature measured over land and sea and is smoothed. The graph shows that the Earth has warmed by about 0.5°C in the last 130 years. Most of the warming occured between 1910 and 1940 and then after 1975. 1990 was the warmest year ever4 and the warmest five years before that were in the 1980's. It is uncertain whether the warming of the last century can be attributed to the natural variability or the greenhouse gases. An unambiguous greenhouse warming may not become apparent for several more years. However, our investigations of the effect of continued reliance on fossil fuels show that it is likely to become quite significant during the next century. What would be the consequences of such a warming? Many climatologists have written extensively about the consequences of a global warming and we provide a summary here. One of the primary effects of global warming is expected to be the drying of continental interiors, with significant negative consequences for agriculture. For example, Hansen, et. al.,5 using the Goddard Institute of Space Studies Global Climate Model (GISS GCM), suggest that a doubling of atmospheric CO2 concentration would cause hot dry conditions in much of the western United States, Canada, and major parts of central Asia. The increased warming could also cause a melting of glacial ice, which may lead to an increase in sea level and lowland flooding in many parts of the world. Many authors
RkJQdWJsaXNoZXIy MTU5NjU0Mg==