Sensitivity of winter wheat yields in the Midwestern United States to future changes in climate, climate variability, and CO2 fertilization

This research investigates the potential impacts of climate change on winter wheat Triticum aestiuum L. production, looking at changes both in the mean climate and in climate variabil- ity, under conditions of elevated atmospheric CO2 concentrations. The study region is comprised of the 5 states of Indiana, Illinois, Ohio, Michigan, and Wisconsin in the US. This analysis was conducted for the period 2050-59 for 10 representative farm locations in the 5 states for 6 future climate scenarios using the crop growth model CERES-Wheat. Wheat is currently the most widely grown crop in the world, with approximately 250 million ha planted each year. This region, while not a critical area for winter wheat production under current climate, is in a marginal area that could become a more important production region under a warmer climate. As such, the impacts of climate change on wheat growth are of great significance both regionally and globally. With future atmospheric CO2 concentrations of 555 ppmv, wheat yields increased 60 to 100% above current yields across the central and northern areas of the study region when modeled for 2050-59 climate change scenarios. In the southern areas of the study region, small increases (0.1 to 20%) and small decreases (-0.1 to -15%) were found. These decreases in yield were more frequent under climate conditions associated with the more extreme Hadley Center greenhouse gas run (HadCM2-GHG, representing a 1% increase in greenhouse gases per year) and for the doubled climate variability analyses. Across all sites, earlier planting dates (Sep- tember 2 is optimal) performed best; yields decreased as planting was delayed. These results have im- plications for spring-planted crops. CO2 fertilization effects also are found to be significant for wheat, representing an average yield increase greater than 20% under future climate scenarios, with greater benefits occurring under more moderate future climate scenarios. Without the effects of CO2 fertiliza- tion in the model, many of the southern locations had greater decreases in yields. The overall climate change impact across the study area resulted in large increases in yields with only a few locations exhibiting decreases, and those decreases occurring only under the more extreme climate scenarios.