Researchers from the National Center for Atmospheric Research (NCAR) entered various scenarios into their computer models to simulate the effects of elevated carbon dioxide (CO2) in the atmosphere on cotton crop yields. If carbon dioxide emissions increase at their present rate, many scientists believe that the atmospheric concentrations of greenhouse gases are likely to double compared to pre-industrial levels by the year 2060.
Along with climate change, atmospheric CO2 enhances plant growth by stimulating photosynthesis. In one scenario, adaptations to farming practices resulting from a lengthened growing season, elevated CO2-induced climate change and enhanced plant growth, were all
factored into model simulations. The results predicted that cotton yields would increase by as much as 26-36 percent.
"Cotton is a very important economic crop for U.S. agriculture, and the impacts of climate change on cotton production have not been examined on a regional scale before," said Linda Mearns, a co-author of the study and a researcher at NCAR's Environmental and Societal Impacts Group.
Ruth Doherty, also a co-author and researcher at NCAR's Environmental and Societal Impacts Group, added that these cotton model projections are the first of their kind, and the climate scenarios used are simplistic. For example, the climate models project climate change based on an instantaneous doubling of CO2, when in reality such increases would occur gradually over this century, possibly changing the outcomes. Still, in most of the scenarios there was a trend towards increased cotton yields in the future.
Two climate models were used in the study - a large-scale global climate model that used 300 by 300 kilometer (approx. 186 by 186 mile) grids, and a fine-scale regional climate model that used 50 by 50 kilometer (approx. 31 by 31 mile) grids. A climate model is a simplified mathematical representation of the Earth's climate system, including data on the physical, geophysical, chemical and biological processes that govern the climate system. Fine-scale models with higher resolution may be more accurate, but in order to gain information about the future regional climate, results from the global model must be used to initialize and control the regional model.
Using these two models, three scenarios were simulated. The first scenario simply looked at the impact that the climate change resulting from an instantaneous doubling of CO2 would have on cotton yields in the Southeastern U.S.-including North Florida, Georgia, North Carolina, South Carolina, Alabama, Mississippi, Louisiana, Arkansas, and part of Tennessee. For this scenario the fine scale model predicted a decrease of 10 percent in cotton yield over the region, while the large-scale model showed a 4 percent increase in yields.
When the climate change resulting from CO2 doubling was combined with the potential for enhanced cotton plant growth as a result of greater carbon availability, the fine scale model showed a 5 percent increase in yields, while the large scale model predicted a 16 percent increase.
Finally, when the first two factors of CO2 doubling and enhanced growth were combined with farming adaptations like planting crops earlier to take advantage of a longer growing season, the fine scale model predicted a 26 percent increase, and the large scale model predicted a 36 percent increase.
The research is part of a larger project that examines the impact of different spatial scales of climate change scenarios on yields of corn, wheat, sorghum, soybean and cotton in the Southeastern U.S. The study was also partly funded by the Environmental Protection Agency.
The findings will be presented on December 10, at a poster session of the American Geophysical Union (AGU) Fall Meeting in San Francisco, Calif. A paper will be published next year in a special issue of the journal Climate Change.
NCAR is primarily sponsored by the National Science Foundation.
For more information, please see: http://www.gsfc.nasa.gov/topstory/20011210cottonclimate.html