Abstract
This paper describes the use of a county-level approximation of the grid cells of a general circulation model as an approach to using environmental and resource data in analyzing the effects of climate change. As a demonstration, the effects are estimated of a possible climate change due to a doubling of atmospheric CO2 on the production of soybeans using two simple approaches based on grid cell averages of county-level yield data. With the first approach, we assume that the future yields will be determined by current climate-yield relationships. The actual 1978 climate (approximate growing-degree days and precipitation in the growing season) corresponding to 1978 yield levels is calculated. The climate characteristics of grid cells with major (grid cell-averaged yield of 56.9–299.3 kg/ha) and minor (1.6–11.6 kg/ha) soybean yield are estimated. Potential future major and minor yields are then estimated from a simulated changed climate. With the second approach, future yields are estimated using a multiple regression equation that relates yield to simulated June and August temperature and July, August, and September-June precipitation. These two simple analyses, which ignore many important factors such as soil fertility, technological advances, development of new soybean varieties, and the validity of the climate simulations, show that soybean yields might decline in the areas where the crop is now grown, but that soybean agriculture could expand northwards and eastwards if other factors permit. These analyses confirm that it is possible to perform analyses of the effects of climate change using county-level data, although such analyses would have to consider additional factors before the results themselves would be credible.
