Experts have long been interested in the relationship of crop production to climate and to seasonal and interannual climate fluctuations. It is a natural extension for these studies now to consider a unidirectional change, or a change in variability, superimposed on the kinds of fluctuations that farmers have had to contend with since the dawn of settled agriculture.
There are at least two observational approaches to determining the sensitivity of crop productivity to a climate change. A crop planted yearly in a specific location can be repeatedly observed over a period of years--a period during which different growing conditions are likely to occur. Alternatively, the productivity of a widely planted crop can be related to the climate in each area in which it is planted [e.g., Leemans and Solomon, 1993]. The data from such observations is usually converted into an empirical crop-climate model.
The estimation of crop impacts using climate model outputs applied to crop-climate models has been underway for a decade or more; recent progress involves the use of such models to test the sensitivity of the crop to the direct carbon dioxide fertilization effect [e.g., Rosenberg, 1993; Rosenzweig and Parry, 1994], and the effect of changes in climate variability [ Mearns et al., 1992].
In an actual climate change situation the direct effects of changing weather parameters on crops will be combined with any indirect impacts working through the changes in pest prevalence [ Patterson, 1993].
In addition to row crops, beef production impacts have been considered using both a rangeland model and a beef production model to estimate the shift in beef production in the western United States [ Baker et al., 1993], and impacts on animal production more broadly have been considered by Ames [1993].
In general, the results of these studies indicate that in a prosperous modern society, such as the United States or western Europe, the agricultural enterprise is sufficiently flexible that for anything short of a very rapid climate change effective adaptation can take place. However, lesser developed countries could experience food production problems not alleviated by the adaptive measures available to them. Thus studies of climate impacts on major Third World crops, such as rice, are particularly important [ Bachelet and Gay, 1993]. Rosenzweig and Parry [1994] suggest that even though the total impact on world food supply could be small, the disparity in food production between developed and developing countries will increase, possibly adding to international tensions.