The field data was collected at the ARS Central Great Plains Research Station in Akron, Colo. The projections included an increase in equivalent atmospheric carbon dioxide (CO2) levels from 380 parts per million by volume (ppmv) in 2005 to 550 ppmv in 2050. The projections also included a 5-degree Fahrenheit increase in summer temperatures in Colorado from 2005 to 2050. The ARS scientists used these projections to calculate a linear increase of CO2 and temperature from 2050 to 2100.
Ahuja's team used the Root Zone Water Quality Model (version 2) for crop rotations of wheat-fallow, wheat-corn-fallow, and wheat-corn-millet to see how yields might be affected in the future. They simulated different combinations of three climate change projections: rising CO2 levels, rising temperatures, and a shift in precipitation from late spring and sum¬mer to fall and winter. They ran the model with the projected climate for each of the 15 to 17 years of field crop data for each cropping system.
When the researchers used all three climate factors to generate yield projections from 2005 to 2100, the yield estimates for the three cropping systems dropped over time. Declines in corn and millet yields were more significant than declines in wheat yields. More
