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The Net Effect of Predicted CO2-Induced Climate Change and the Known Biological Benefits of High-CO2 Air on English and Welsh Wheat Yields
Reference
Richter, G.M. and Semenov, M.A.  2005.  Modelling impacts of climate change on wheat yields in England and Wales: assessing drought risks.  Agricultural Systems 84: 77-97.

What was done
The authors note that "with global warming, evapotranspiration is likely to increase and, with more variable rainfall, droughts could occur more often."  Hence they decided to evaluate the impact of potential climate change on drought indicators and yields of winter wheat in England and Wales using a crop simulation model (Sirius) that also incorporates the effects of elevated atmospheric CO2 concentration and temperature on crop growth and development.  The CO2 scenario driving the model was one of medium to high anthropogenic emissions that raise the air's CO2 concentration from 334 ppm (the 1961-1990 baseline) to 554 ppm in the 2050s.

What was learned
Richter and Semenov report that probability distributions derived from multiple simulations using representative weather, soil types and sowing dates indicate that maximum soil moisture deficit "is likely to increase in the future, especially on shallow soils, and the probability of potential yield reductions exceeding 25% will increase by 10% until the 2050s."  However, they found that, in reality, "average wheat yields are likely to increase [our italics] by 1.2 to 2 t/ha (15-23%) by the 2050s because of a CO2-related increase in radiation use efficiency."

What it means
Once again, the power of the direct biological impact of atmospheric CO2 enrichment is calculated to be strong enough to not only overturn predictions of yield losses due to CO2-induced climatic deterioration (which we believe to be way overblown in the first place), but to actually turn them into sizeable yield increases.

Reviewed 31 August 2005