INFLUENCE OF THE GREENHOUSE-EFFECT ON YIELDS OF WHEAT, SOYBEAN AND CORN IN THE UNITED-STATES FOR DIFFERENT ENERGY SCENARIOS

The increase of atmospheric carbon dioxide has positive effects on agricultural productivity (photosynthesis stimulation), but in some regions it has negative effects (drought due to the temperature rise) as well. The central part of the United States in summer is predicted to be one of such regions, where the influence of the CO2 increase should be assessed considering both the effects. Such calculations have been made for spring wheat, soybean and corn in a series of papers, a summary of which is presented here. Since the CO2 emission rate depends on fossil fuel consumption, energy scenarios with different fossil fuel consumption are assumed. Positive effects of CO2 are expressed by a model which simulates actual data. In the absence of an appropriate model negative effects are assumed to be proportional to the temperature rise, which is shown to be unexpectedly good. The difference between C3 (soybean and wheat) and C4 (corn) plants is also considered. Changes of their yields in the next century are calculated. Results show that in this region (probably up to 42-45-degrees-N) in summer an unlimited increase of atmospheric CO2 is not desirable for the above three crops even if positive effects of CO2 are taken into account. This work is not intended to give prediction of future crop production, but to show illustrative examples for the above argument. Thus assumptions are made so as to overestimate positive effects and underestimate negative effects, but results show that even in such cases an unlimited increase of CO2 is not necessarily desirable for the specified regions.