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Could Global Change Increase Agricultural Production?

The Issue

The Intergovernmental Panel on Climate Change (IPCC) estimated in 1995 that a doubling in atmospheric CO2 would stimulate agricultural yield of several major crops by an average of 30 percent. Such an increase would help solve part of the food shortage problems that the world will face. Scientists attending a meeting sponsored by GCTE/LUCC in Barcelona, Spain, on March 14-18, 1998, will re-examine this figure and discuss the consequences of the other aspects of global change on agricultural production.

The Science

• Scientists will present experimental data suggesting that these predictions were too optimistic. For example, in the most realistic field-scale experiment ever undertaken, crops of wheat exposed to elevated CO2 while under optimal irrigation displayed a yield stimulation of five to 12% in two successive seasons (B. Kimball, US Water Conservation Laboratory, Phoenix, Arizona USA). The FACE technology (Free Air CO2 Enrichment) used for this experiment allows scientists to expose large areas of land to elevated CO2 concentrations (G. Hendrey, Brookhaven National Lab, USA). According to Dr. P.J. Gregory, from the University of Reading, UK, and his colleagues, an 8 to 12 percent increase under optimal conditions would correspond to a 5 to 7 percent increase for wheat under conditions of normal management.

• Moreover, the components of global change associated with elevated CO2, that is the increase in temperature and the variation in precipitation may attenuate the yield benefits expected from elevated CO2. Dr. H. Nakagawa from the Kyoto University, Japan and others will present measurements showing that rice yield will decrease with increasing temperature, even at elevated CO2.

• To further dampen this optimism, losses to pests, diseases and weeds, which are currently estimated to be about 40 percent of actual yield by a recent GCTE synthesis, may be exacerbated because temperature increase might cause a spread of tropical and sub-tropical species into temperate areas and of temperate species into colder climates. Dr. R.W. Sutherst, from the University of Queensland, Australia, will advocate that to respond efficiently to this threat, pest-risk assessment under global change needs to be tackled in a collaborative way between all the sectors involved (agronomists, economists, resource managers, etc.).

• Scientists are including such experimental data into computer models that simulate growth of major crops. In doing so, they increase their ability to predict the effects of climate change and elevated CO2 on agricultural yield in various regions of the world. For example, Semenov and Brooks, from the University of Bristol, UK, predict that wheat may become an economically unsuitable crop for Spain because of the predicted increased occurrence of dry spells.

Practical Information

Global change impact on agriculture will be discussed on the third day of the conference (March 16) in session 3, and during the poster sessions of March 16 and 17. Eleven oral posters are scheduled during the Poster session of March 17. In addition, two ad hoc meetings dealing with agriculture and global change will be held in March 16 and 17 during lunch time.

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