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Agriculture (Species -- Wheat: Biomass) -- Summary
Many laboratory and field experiments have demonstrated a pervasive positive influence of elevated levels of atmospheric CO2 on the magnitude of biomass and grain production in wheat (Triticum aestivum L.).  We here briefly summarize the findings of the subset of those studies for which we have written Journal Reviews.

In one study, Dijkstra et al. (1999) grew winter wheat in open-top chambers and field-tracking sun-lit climatized enclosures maintained at atmospheric CO2 concentrations of ambient and ambient plus 350 ppm CO2 for two years, determining that the elevated CO2 increased both final grain yield and total aboveground biomass by 19%.  In another study, Masle (2000) grew two varieties of wheat for close to a month in greenhouses maintained at atmospheric CO2 concentrations of 350 and 900 ppm, finding that the CO2-enriched plants exhibited biomass increases of 52 to 93%, depending upon variety and vernalization treatment.

Based on a plethora of experimental observations of this nature (see wheat biomass in the Plant Growth Data section of our website for other examples), many scientists developed yield prediction models for wheat.  Using the output of several such models, Alexandrov and Hoogenboom (2000) estimated the impact of typically predicted climate changes on wheat production in Bulgaria in the 21st century, finding that a doubling of the air's CO2 concentration would likely enhance wheat yields there between 12 and 49% in spite of a predicted 2.9 to 4.1C increase in air temperature.  Likewise, Eitzinger et al. (2001) employed the WOFOST crop model to estimate wheat production in northeastern Austria in the year 2080.  For a doubled atmospheric CO2 concentration with concomitant climate changes derived from five different general circulation models of the atmosphere, they obtained simulated yield increases of 30 to 55%, even in the face of predicted changes in both temperature and precipitation.

Southworth et al. (2002) used the CERES-Wheat growth model to calculate winter wheat production during the period 2050-2059 for ten representative farm locations in Indiana, Illinois, Ohio, Michigan and Wisconsin, USA, for six future climate scenarios.  They report that some of the southern portions of this group of states would have exhibited climate-induced yield decreases had the aerial fertilization effect of the CO2 increase that drove the predicted changes in climate not been included in the model.  When they did include the increase in the air's CO2 concentration (to a value of 555 ppm), however, they note that "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."  The few minor decreases, however, 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; hence, they would have to be considered highly unlikely to ever occur.

In discussing their findings, Southworth et al. 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 5C temperature increases)," and that Cuculeanu et al. (1999) found modeled yields of winter wheat in southern Romania to increase by 15 to 21% across five sites.  Also, they note that Harrison and Butterfield (1996) "found increased yields of winter wheat across Europe under all the climate change scenarios they modeled."

The final paper to deal with this subject that we have reviewed to this point in time is that of Van Ittersum et al. (2003), who performed a number of simulation experiments with the Agricultural Production Systems Simulator (APSIM)-Nwheat model in which they explored the implications of possible increases in atmospheric CO2 concentration and near-surface air temperature for wheat production and deep drainage at three sites in Western Australia differing in precipitation, soil characteristics, nitrogenous fertilizer application rates and wheat cultivars.  They first assessed the impact of the ongoing rise in the air's CO2 content, finding that wheat grain yield increased linearly at a rate of 10-16% for each 100-ppm increase in atmospheric CO2 concentration, with only a slight concomitant increase in deep drainage (a big win-tiny loss outcome).  For a likely future CO2 increase of 200 ppm, for example, increases in grain yield varied between 3 and 17% for low nitrogen fertilizer application rates and between 21 and 34% for high rates of nitrogen application, with the greatest relative yield response being found for the driest site studied.

When potential warming was factored into the picture, the results proved even better.  The positive effects of the CO2 increase on wheat grain yield were enhanced an extra 3-8% when temperatures were increased by 3C in the model simulations.  These yield increases were determined to result in an increased financial return to the typical Western Australian wheat farmer of 15-35%.  In addition, the imposition of the simultaneous temperature increase lead to a significant decline in deep drainage, producing a truly win-win situation that enhanced the average farmer's net income by an additional 10-20%.  Consequently, it was determined that the CO2-induced increase in temperature predicted by the world's climate alarmists could well increase the net profitability of Western Australian wheat farmers by anywhere from 25-55%, while at the same time mitigating what van Ittersum et al. refer to as "one of Australia's most severe land degradation problems."

In light of these several observations, it should be clear to most everyone that in a wide variety of circumstances, atmospheric CO2 enrichment significantly increases the biomass production and yield of wheat plants, thereby benefiting both wheat producers and consumers alike.

References
Alexandrov, V.A. and Hoogenboom, G.  2000.  The impact of climate variability and change on crop yield in Bulgaria.  Agricultural and Forest Meteorology 104: 315-327.

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.

Dijkstra, P., Schapendonk, A.H.M.C., Groenwold, K., Jansen, M. and Van de Geijn, S.C.  1999.  Seasonal changes in the response of winter wheat to elevated atmospheric CO2 concentration grown in open-top chambers and field tracking enclosures.  Global Change Biology 5: 563-576.

Eitzinger, J., Zalud, Z., Alexandrov, V., van Diepen, C.A., Trnka, M., Dubrovsky, M., Semeradova, D. and Oberforster, M.  2001.  A local simulation study on the impact of climate change on winter wheat production in north-east Austria.  Ecology and Economics 52: 199-212.

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.

Masle, J.  2000.  The effects of elevated CO2 concentrations on cell division rates, growth patterns, and blade anatomy in young wheat plants are modulated by factors related to leaf position, vernalization, and genotype.  Plant Physiology 122: 1399-1415.

Southworth, J., Pfeifer, R.A., Habeck, M., Randolph, J.C., Doering, O.C. and Rao, D.G.  2002.  Sensitivity of winter wheat yields in the Midwestern United States to future changes in climate, climate variability, and CO2 fertilization.  Climate Research 22: 73-86.

van Ittersum, M.K., Howden, S.M. and Asseng, S.  2003.  Sensitivity of productivity and deep drainage of wheat cropping systems in a Mediterranean environment to changes in CO2, temperature and precipitation.  Agriculture, Ecosystems and Environment 97: 255-273.