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The Effects of Warming on Winter Wheat Yields in Semi-Arid China
Reference
Xiao, G., Zhang, Q., Li, Y., Wang, R., Yao, Y., Zhao, H. and Bai, H. 2010. Impact of temperature increase on the yield of winter wheat at low and high altitudes in semiarid northwestern China. Agricultural Water Management 97: 1360-1364.

Background
The authors write that "the impact of future climate change on crop production has been widely predicted by modeling the interaction between crops and climate change," and that it is currently believed that "overall crop yields will decrease by 5-10% in China by 2030 as a result of climatic changes, and that the yields of wheat, rice and maize will be greatly reduced." However, they report that "the direct fertilization effect of rising CO2 will offset these losses," citing Ewert et al. (2002) and Long et al. (2006). In addition, they report that few real-world observations of the impacts of climate change on crop production have been reported; and they thus decided to address this deficiency.

What was done
Xiao et al. conducted two sets of field experiments to evaluate the effects of different degrees of warming on the productivity of winter wheat (Triticum aestivum L.) from 2006 to 2008 in the semiarid northwestern part of China: one set at the Tongwei County experiment station located at the foot of Lulu Mountain (35°13'N, 105°14'E) at an altitude of 1798 meters above sea level, and another set at the mountain's summit at an altitude of 2351 meters. At each of these locations, the seven scientists established four different air temperature treatments (ambient and ambient plus 0.6, 1.4 and 2.2°C), which they created by placing electric heating wires on the surface of the soil between the rows of wheat, which induced the 0.6-2.2°C air temperature increases they measured continuously at a height of 20 cm above the tops of the wheat canopies.

What was learned
Citing Gao et al. (2002), the Chinese researchers say it has been predicted that "the average temperature in the semiarid northwest portion of China in 2050 will be 2.2°C higher than it was in 2002," and they report that based on the observed results of their study, this increase in temperature "will lead to a significant change in the growth stages and water use of winter wheat," such that "crop yields at both high and low altitudes will likely increase," by 2.6% at low altitudes and 6.0% at high altitudes.

What it means
Even without the benefits of the aerial fertilization effect and the anti-transpiration effect of the ongoing rise in the air's CO2 content, the increase in temperature that is predicted by climate models for the year 2050, if it ever comes to pass, will likely lead to increases in winter wheat production in the northwestern part of China, not the decreases that climate alarmists routinely predict.

References
Ewert, F., Rodriguez, D., Jamieson, P., Semenov, M.A., Mitchell, R.A.C., Goudriaan, J., Porter, J.R., Kimball, B.A., Pinter Jr., P.J., Manderscheid, R., Weigel, H.J., Fangmeier, A., Fereres, E. and Villalobos, F. 2002. Effects of elevated CO2 and drought on wheat: testing crop simulation models for different experimental and climatic conditions. Agriculture, Ecosystems and Environment 93: 249-266.

Gao, S.H., Guo, J.H., Zhang, Y., Pan, Y.R. and Zhao, S.Q. 2002. The impacts of higher-temperature on wheat growth and development and yield in China. Environmental Science 5: 176-178.

Long, S.P., Ainsworth, E.A., Leakey, A.D.B., Nosberger, J. and Ort, D.R. 2006. Food for thought: lower-than-expected crop yield simulation with rising CO2 concentrations. Science 312: 1918-1921.

Reviewed 10 November 2010