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United States Department of Agriculture

Agricultural Research Service

Title: Global Food Insecurity. Treatment of Major Food Crops with Either Elevated Carbon Dioxide Or Ozone under Large-Scale Fully Open-Air Conditions Suggest Recent Models May Have over-Estimate Future Yields.

item Ainsworth, Elizabeth
item Morgan, Patrick

Submitted to: Review Article
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 29, 2005
Publication Date: November 1, 2005
Citation: Long, S.P., Ainsworth, E.A., Leakey, A.B., Morgan, P.B. 2005. Global food insecurity. Treatment of major food crops with either elevated carbon dioxide or ozone under large-scale fully open-air conditions suggest recent models may have over-estimate future yields. Philosophical Transactions of the Royal Society. 360:2011-2020.

Interpretive Summary: Global atmospheric changes predicted for the next century include rising atmospheric carbon dioxide concentration, ozone concentration and temperature. Predictions of future crop yields suggest that production will increase in the temperate zone, but decrease in the tropics, with a moderate temperature increase. If elevated atmospheric CO2 is included in current models, then yields are predicted to be significantly higher. However, these models are based on studies performed in greenhouses and controlled environmental chambers, and ignore the detrimental effects of rising ozone concentration. Open-air field studies of crops grown under elevated CO2 and O3 show smaller than predicted increases in yield. These findings suggest that current projections of future global food production are over-optimistic.

Technical Abstract: Predictions of yield for the globes major grain and legume arable crops suggest that, with a moderate temperature increase, production may increase in the temperate zone, but decline in the tropics. In total, global food supply may show little change. Security comes from inclusion of the direct effect of rising [CO2], which significantly stimulates yield by decreasing photorespiration in C3 crops and transpiration in all crops. Evidence for a large response to [CO2] is largely based on studies made with chambers at small scales, which would be unacceptable for standard agronomic trials of varieties or agrochemicals. Yet, predictions of the globes future food security are based on such inadequate information. Free Air Concentration Enrichment (FACE) technology now allows investigation of the effects of rising [CO2] and ozone on field crops under fully open-air conditions at an agronomic scale. Experiments with rice, wheat, maize and soybean show smaller increases in yield than anticipated from studies in chambers. Experiments with increased ozone show large yield losses (20%) which are not accounted for in projections of global food security. These findings suggest that current projections of global food security are over-optimistic. The fertilization effect of CO2 is less than that used in many models, while rising ozone will cause large yield losses in the N. Hemisphere. Unfortunately, FACE studies have been limited in geographical extent and interactive effects of CO2, ozone and temperature have yet to be studied. Without more extensive study of the effects of these changes at an agronomic scale in the open-air, our ever-more sophisticated models will continue to have feet of clay.

Last Modified: 4/22/2015
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