In Climate Change and World Agriculture, Parry (1990) sketches a broad picture of the effects of climate change in the chapter "Effects on Plants, Soil, Pests and Diseases." He argues that the effects of carbon dioxide (CO2) enrichment, without associated changes in climate, would probably be beneficial for agriculture. Higher temperatures, however, could increase the rate of microbial decomposition of organic matter, adversely affecting soil fertility in the long run. Also, studies analyzing the effects on pests and diseases suggest that temperature increases may extend the geographic range of some insect pests currently limited by temperature.
Rosenzweig and Liverman (1992) compare temperate and tropical regions in "Predicted Effects of Climate Change on Agriculture." The regions differ significantly, both in the biophysical characteristics of their climate and soil and in the vulnerability of their agricultural systems and people to climate change. An analysis of the biophysical impact of climate changes associated with global warming shows that higher temperatures generally hasten plant maturity in annual species, thus shortening the growth stages of crop plants. Global estimates of agricultural impacts have been fairly rough to date, because of lack of consistent methodology and uncertainty about the physiological effects of CO2. Table 4 illustrates production changes in wheat using a General Circulation Model scenario and doubling carbon dioxide concentration. Climate change scenarios that do not include the physiological effects of CO2 predict a decrease in estimated national production, but including the physiological effects of CO2 mitigates the negative effects. Tropical regions appear to be more vulnerable to climate change than temperate regions.
Easterling et al. (1993) use another crop modeling technique, the Erosion Productivity Impact Calculator (EPIC), to determine the relationship between climate and crop growth. The authors analyze the results in "Agricultural Impacts of and Responses to Climate Change in the Missouri-Iowa-Nebraska-Kansas (MINK) Region."
The U.S. Environmental Protection Agency is expected to publish crop modeling studies conducted in 18 countries. These studies, which Rosenzweig et al. (1993) list in Appendix 2 of Climate Change and World Food Supply, simulate the effects of climate change on crop yields, food production, and trade.
The effects of increased ultraviolet-B (UV-B) radiation are also of great concern. In Climate Change: The IPCC Response Strategies, the Intergovernmental Panel on Climate Change (1991) reports increases in UV-B radiation reduce yield in certain agricultural crops. The "Summary of Likely Impacts of Increased UV-B Radiation" provides a brief discussion of crop yields. Olszyk and Ingram (1993) discuss the potential for crop quality reduction due to the "Effects of UV-B and Global Climate Change on Rice Production" in the Environmental Protection Agency International Rice Research Institute (EPA/IRRI) cooperative research plan.