Climate Change and Agriculture

concentration of carbon dioxide (CO 2 ) by some 30 percent since the industrial revolution, and that rise continues at a rate of approximately 0.4 percent per year. Despite its seemingly minute concentration (only 0.035 percent), CO 2 inhibits the escape of longwave (thermal) radiation emitted by the earth throughout the entire atmosphere, a process known as the “greenhouse effect.” The presence of CO 2 and the more abundant water vapor naturally helps to warm our planet from a frigid -18C to a much more hospitable 15C. Humandriven increases in CO 2 concentration now appear to be enhancing the natural greenhouse effect, and many scientists believe that these are leading, or will lead, to surface warming and associated feedback effects on the climate system (Houghton et al. 1996). Other so-called greenhouse gases that are present in even smaller concentrations, but which similarly tend to trap heat, include methane (CH 4 ), nitrous oxide (N 2 O), the chlorofluorocarbons (CFCs), and tropospheric ozone (O 3 ). The effects of all these gases may be expressed as changes in the planet’s radiation balance in W/m/yr. Other changing atmospheric factors that affect climate include ozone, solar irradiance, tropospheric aerosols, and stratospheric aerosols. The increases in greenhouse gases may already be altering the earth’s climate. Global surface temperatures have risen about 0.7C over the last century, leading the Intergovernmental Panel on Climate Change (IPCC) to conclude (Houghton et al. 1996): “The balance of evidence suggests a discernible human influence on global climate.” If allowed to continue, anthropogenic greenhouse-gas emissions seem bound to result in significant climate change in the coming decades. The climatic consequences of increasing greenhouse gases are linked to far-reaching changes in agriculture, as well as in natural ecosystems. It is clear that climate change is likely to affect the regional patterns of temperature, Climate Change and Agriculture