Background
The authors note that "wheat is currently the most widely grown crop in the world," and that winter wheat - a highly adaptable, fall-sown, long-duration crop - is "extensively grown throughout the United States and Europe."  In fact, the five states of Indiana, Illinois, Ohio, Michigan and Wisconsin, which are the subject of this study, produce about 1% of the world's winter wheat, even though they are on the margins of the major US wheat production areas.

What was done
For the five-state area mentioned above, the authors used the CERES-Wheat growth model to calculate winter wheat production during the period 2050-2059 "for ten representative farm locations in the 5 states for 6 future climate scenarios," as well as for a future atmospheric CO2 concentration of 555 ppm.

What was learned
The authors report that many southern areas would have exhibited climate-induced yield decreases had the CO2 fertilization effect not been included in the model.  When they increased the air's CO2 concentration to a value of 555 ppm, however, "wheat yields increased 60 to 100% above current yields across the central and northern areas of the study region," while in the southern areas "small increases and small decreases were found," although the decreases were associated with the more extreme Hadley Center greenhouse run that presumed a 1% increase in greenhouse gases per year and a doubled climate variability.

What it means
The results of this study bode well for the future of winter wheat production in Indiana, Illinois, Ohio, Michigan and Wisconsin, USA.  In addition, the authors note that other modeling studies have obtained similar results for other areas.  They report, for example, that Brown and Rosenberg (1999) found winter wheat yields across other parts of the United States to increase "under all climate change scenarios modeled (1, 2.5, and 5°C temperature increases)."  In southern Romania, they cite the study of Cuculeanu et al. (1999) as indicating that modeled yields of winter wheat "increased 15 to 21% across 5 sites."  Last of all, they note that Harrison and Butterfield (1996) "found increased yields of winter wheat across Europe under all the climate change scenarios they modeled."

In conclusion, since the authors note that "winter wheat is planted in the fall, germinates, and can survive snow cover and temperatures to at least -30°C," it would appear that its production over vast reaches of the planet would be dramatically increased over what it is now in a warmer and CO2-enriched world of the future.

References
Brown, R.A. and Rosenberg, N.J.  1999.  Climate change impacts on the potential productivity of corn and winter wheat in their primary United States growing regions.  Climatic Change 41: 73-107.

Cuculeanu, V., Marcia, A. and Simota, C.  1999.  Climate change impact on agricultural crops and adaptation options in Romania.  Climate Research 12: 153-160.

Harrison, P.A. and Butterfield, R.E.  1996.  Effects of climate change on Europe-wide winter wheat and sunflower productivity.  Climate Research 7: 225-241.