What was done
The crop growth model CERES-Barley version 2.1 (Otter-Nacke et al., 1991) was used to assess the direct biological effect of a doubling of the air's CO2 concentration (from 350 to 700 ppm) on the growth and yield of spring barley in the Czech Republic, along with the indirect effect on growth and yield produced by the climate changes that are predicted to accompany such a CO2 increase, as simulated by several GCMs, including ECHAM4, HadCM2, NCAR-DOE and seven other GCMs available from the IPCC-DDC.

What was learned
The indirect effect on spring barley yield caused by changed weather conditions was mostly negative, ranging from -19% to +5% for the several climate scenarios applied to three different production regions of the Czech Republic. However, the authors report that "the magnitude of the direct [biological] effect of doubled CO2 on the stressed yields for the three test sites is 35-55% in the present climate and 25-65% in the 2 x CO2 climates," and they note that "the stressed yields would increase in 2 x CO2 conditions by 13-52% when both direct [biological] and indirect [climatic] effects were considered." In addition, they report that "the decrease of the mean yields due to the indirect [climatic] effect of doubled CO2 may be reduced, and it might be even turned to increase, if the spring barley is planted 45-60 days sooner," concluding that "application of the earlier planting date would result thus in an additional 15-22% increase of the yields in 2 x CO2 conditions."

What it means
Clearly, in the words of Trnka et al., "the positive direct effect of doubled CO2 dominates [our italics] over the negative effect of changed weather conditions." What is more, they note that the results they obtained "might be applied to vast regions of Central Europe with similar environmental characteristics," in what should be welcome news for people who are being told by many of their national leaders that negative impacts of projected CO2-induced global warming are of greater import than either global terrorism or nuclear war.

Reference
Otter-Nacke, S., Ritchie, J.T., Godwin, D.C. and Singh, U. 1991. A User's Guide to CERES Barley - V2.10, Manual IFDC-SM-3, International Fertilizer Development Center Simulation.