The team's findings, which appear in the September issue of Climatic Change, are being reprinted this month by Kluwer Academic Publishers as a monograph entitled "Issues in the Impacts of Climate Variability and Change on Agriculture." NCAR scientist Linda Mearns is the editor and lead investigator.
The diverse study team included climatologists, geographers, economists, remote sensing specialists, and statisticians. Its work was supported by multiyear grants from NASA and the U.S. Environmental Protection Agency. Additional support came from the U.S. Department of Agriculture and NCAR's primary sponsor, the National Science Foundation.
Using a set of computer models that account for climatic, economic, and agricultural factors, the team compared present-day conditions to scenarios for a doubled level of atmospheric carbon dioxide, which will occur around 2060 if present trends continue. They then compared the climate portrait of 2060 derived from an Australian global-scale climate model, in which the atmosphere is tracked at points separated by 300 kilometers (186 miles), to the results from a regional climate model nested inside the global model, with a resolution of 50 km (31 mi).
Although the authors note that the Australian model has uncertainties like those from other global models, they are intrigued by how the climate picture evolves as the resolution sharpens. "The general pattern is for [crop] yields to be lower under the finer scale of resolution," says Richard Adams (Oregon State University), who headed one of the project's analyses. However, he adds, "There are substantial regional differences."
Compared to the coarse-scale data, the sharper resolution raises crop productivity in general across the Great Plains and Mississippi Delta but lowers it for many crops elsewhere. For instance, previous work found that corn harvests should decrease by 2060 in the Midwest's Corn Belt and Southeast but increase in the Northern Plains. The finer-scale study accentuates both trends.
When fed into a economic model, the coarse-scale analysis shows that climate change could benefit U.S. agriculture in the year 2060 by roughly $3 billion (in 2000 dollars), even assuming that farmers did not adapt their planting to accommodate the climate shifts. The finer-scale analysis reduces that benefit nearly tenfold, to around $300 million.
By dividing the country into ten agricultural regions, the authors found that seven regions benefit by 2060 in the coarse-scale analysis, but only five come out ahead in the fine-scale analysis. Adaptation could bring one more region (the Northeast) into the plus column.
For the Southeast, the fine-scale model for 2060 shows a loss of 33% of the region's agricultural economic base without adaptation and 20% percent even with adaptation. This occurs in spite of cotton production that could soar well above current levels as the climate warms. "Aside from cotton production, one might expect to see agriculture diminish as an economic force in the Southeast," says Mearns.
One factor making the fine-scale analysis more pessimistic is that it includes many topographic features omitted from the coarser model, such as parts of the Appalachians and details of the Gulf and Atlantic coastlines. When these features are included, the model focuses its more stressful climatic changes on agriculturally productive areas. The result is a less rosy picture for U.S. croplands overall.
According to Mearns, the study confirms that "the scale of scenario matters, both in terms of changes in crop yields and in final national and regional economic results."