Climate change impacts on the potential productivity of corn and winter wheat in their primary United States growing regions

We calculate the impacts of climate effects inferred from three atmospheric general circulation models (GCMs) at three levels of climate change severi ty associated with change in global mean temperature (GMT) of 1.0, 2.5 and 5.0 degrees C and three levels of atmospheric CO2 concentration ([CO2]) - 3 65 (no CO2 fertilization effect), 560 and 750 ppm - on the potential produc tion of dryland winter wheat (Triticum aestivum L.) and corn (Zea mays L.) for the primary (current) U.S. growing regions of each crop. This analysis is a subset of the Global Change Assessment Model (GCAM) which has the goal of integrating the linkages and feedbacks among human activities and resul ting greenhouse gas emissions, changes in atmospheric composition and resul ting climate change, and impacts on terrestrial systems. A set of represent ative farms was designed for each of the primary production regions studied and the Erosion Productivity Impact Calculator (EPIC) was used to simulate crop response to climate change. The GCMs applied were the Goddard Institu te of Space Studies (GISS), the United Kingdom Meteorological Transient (UK TR) and the Australian Bureau of Meteorological Research Center (BMRC), eac h regionalized by means of a scenario generator (SCENGEN). The GISS scenari os have the least impact on corn and wheat production, reducing national po tential production for corn by 6% and wheat by 7% at a GMT of 2.5 degrees C and no CO2 fertilization effect, the UKTR scenario had the most severe imp act on wheat, reducing production by 18% under the same conditions; BMRC ha d the greatest negative impact on corn, reducing produc tion by 20%. A GMT increase of 1.0 degrees marginally decreased corn and wheat production. Inc reasing GMT had a detrimental impact on both corn and wheat production, wit h wheat production suffering the greatest losses. Decreases for wheat produ ction at GMT 5.0 and [CO2] = 365 ppm range from 36% for the GISS to 76% for the UKTR scenario. Increases in atmospheric [CO2] had a positive impact on both corn and wheat production. AT GMT 1.0, an increase in [CO2] to 560 pp m resulted in a net increase in corn and wheat production above baseline le vels (from 18 to 29% for wheat and 2 to 5% for corn). Increases in [CO2] he lp to offset yield reductions at higher GMT levels; in most cases, however, these increases are not sufficient to return crop production to baseline l evels.