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COTTON
DOESN'T SHRINK FROM CLIMATE CHANGE A
new NASA-funded study finds that cotton yields are likely to increase in the Southeastern
United States if carbon dioxide levels continue to rise as projected this century,
and if farmers can adapt their agricultural practices to the resulting climate
change. 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. Editor's
Note: AGU Title, Time and Location
"The Effect of the Spatial Resolution
of Climate Scenarios on Cotton Production in the SE USA," Monday, December
10, 2001, 1:30 P.M., Moscone Center Hall D. Back
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