Warming shouldn't wither U.S. farming.

Warming Shouldn't Wither U.S. Farming

Global warming in the next half-century should not seriously damage U.S. agriculture as a whole, although it may hurt farming in some states, according to the first comprehensive study to address how climate change will affect agriculture in the United States.

"The U.S. agricultural sector appears to be relatively resilient. We don't see major catastrophic effects on the welfare of producers or consumers of agricultural products," reports economist Richard M. Adams from Oregon State University in Corvallis.

Because of significant economic and scientific uncertainties underlying the issue of climate change, the study cannot yield firm predictions. Depending on the magnitude of climate change, U.S. agriculture might gain or lose, the researchers say. But even modest precipitation changes and temperature hikes should drive a general northward shift in the farming of current crops, Adams and his nine coauthors conclude in the May 17 NATURE.

In the projections, "some regions are particularly hard hit," Adams says. "Some areas have a potentially large amount of land shifting out of production, and that would translate into fairly sizable economic consequences in those regions." Other scientists contend farmers may be able to adapt by using different techniques or crops.

The new study started with two climate models that project how regional temperatures, rainfall and evaporation would change with a doubling of atmospheric carbon dioxide, which could effectively occur by 2030 due to increasing concentrations of many greenhouse gases. One model predicts relatively mild U.S. changes, while the other shows greater warming and loss of precipitation.

The team fed these results into agricultural models that simulate how wheat, corn and soybean crops would respond to climate changes. Because carbon dioxide fertilizes such plants, the growth models include a factor that increases photosynthetic rates in the double-carbon-dioxide world. The output of such simulations was then fed into an economic model for U.S. agriculture.

The results show that in the mild climate-change scenario, the fertilization factor offsets the adverse climate effect, and agricultural yield increases in most areas, Adams and his colleagues report. That translates to a net gain of more than $10 billion for agricultural producers and consumers in the United States, they say. With more severe climate change, crop yields tend to drop, causing a net loss of about $10 billion, borne mostly by consumers. Such changes amount to about 8 percent of the 1982 market value of U.S. crop and livestock production.

In either scenario, the demand for irrigation increases in most areas, potentially causing water supply problems, the authors point out.

Though the study represents an important first attempt, it has some clear limitations. Economist John Reilly of the U.S. Department of Agriculture notes that the economic projections could differ significantly if the analysis included global market forces and the impact of climate change on the rest of the world. Moreover, he asserts, the study does not realistically allow for farmers' adaptations, which might prevent agriculture from shifting northward.

On the other hand, plant scientist Cynthia Rosenzweig of the Goddard Institute of Space Sciences in New York City, who coauthored the new report, cautions that if drought frequency increases -- a possibility not fully considered in the study -- global warming will have much more severe economic effects on U.S. agriculture and society in general.

Joel B. Smith of the Environmental Protection Agency, which funded the project, says it demonstrates that increasing carbon dioxide levels will not necessarily improve agricultural yield, as some have suggested. "I think it points out some of the risks of global warming," he says.