GLOBAL CLIMATE-CHANGE - PROCESSES AND PRODUCTS - AN OVERVIEW

Our knowledge of global climate change has many uncertainties. Whether global air temperature will increase, by how much, and when, are subj ect to debate, but there is little doubt that tropospheric concentrati ons of several trace gases are increasing. While possible increases in the average air temperature is a product of these changes, the increa ses in the trace gases alone will have an effect on agriculture. Incre ases in the ambient concentrations of carbon dioxide are expected to h ave a positive net effect on crop production. In contrast, any increas es in the penetration of surface-level ultraviolet-B (280-320 nm) radi ation, and known increases in surface ozone concentrations, are consid ered to have adverse effects on certain crops. Our present knowledge o f the joint effects on crops of elevated levels of carbon dioxide, ult raviolet-B radiation and ozone, and possible alterations in air temper ature and precipitation patterns, is virtually zero. Therefore, any pr edictions of the effects of global climate change on agriculture are s ubject to significant uncertainties. In contrast, coupling of climate change (only temperature and precipitation) models to crop production has led to a number of future scenarios. In spite of their present lim itations, results from these efforts can be useful in planning for fut ure agriculture.