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Submitted to: Crop, Environment & Bioinformatics
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/1/2004 Publication Date: 10/18/2004 Citation: Kimball, B.A. 2004. Global environmental change: implications for agricultural productivity. Crop, Environment & Bioinformatics 1:251-263. Interpretive Summary: Atmospheric concentrations of CO2 are increasing, and predictions from climate models suggest there will be a consequent global warming and changes in precipitation patterns. Both elevated levels of CO2 and temperature directly affect plant growth, as does water supply, so there likely will be changes in the productively of agricultural crops. This paper reviews the results of experiments of elevated CO2 interacting with soil water and soil nitrogen on the productivity of several major crops. It also reviews studies which used plant growth models with scenarios of global climate change to forecast future productivity world wide. The elevated CO2 generally increased crop yields with the magnitude of the response varying with crop type and nutrient and water status. The modeling studies, which accounted for physiological effects of elevated CO2 and for farm-level adaptations to global change (e.g., change planting date), with various global change scenarios suggested that cereal yields in developed countries may increase 3-8% by the 2080s while those in developing countries, which tend to be in more tropical climates, may decrease 2-7%. This research benefits all producers and consumers of food and fiber. Technical Abstract: Atmospheric concentrations of CO2 are increasing, and predictions from climate models suggest there will be a consequent global warming and changes in precipitation patterns. Altered levels of CO2, temperature, and water all directly affect plant growth, so there likely will be changes in the productivity of agricultural crops. Increased levels of CO2 generally have increased the yields of most crops, as determined from many years of work using chambers or greenhouses and confirmed more re-cently using free-air CO2 enrichment (FACE) tech-nology in open fields. Yield responses to elevated CO2 are generally higher when there are ample nutrients than when nutrients are limiting. Elevated CO2 also tends to partially close leaf stomata, thereby causing plant canopy temperatures to warm while reducing water requirements slightly, with the reduction varying by crop species. However, if air temperatures rise along with CO2 concentration as predicted, water requirements are likely to increase slightly in comparison to present-day conditions. Considering global warming alone, whether plants will grow faster or slower depends on whether they are below or above their optimum growth temperature. Temperatures change with season and time of day, so at any given time, plants may be be-low, at, or above their optimum. Plant growth models integrate such changing temperature effects on physiological processes and growth through time. Simpler models step through growing seasons day by day, whereas the more sophisticated models have an hourly time step and simulate diurnal patterns. Most present-day models ignore many processes and interactions that may be important. Nevertheless, they have had some respectable validations, and they are useful tools for estimating future agricultural productivity. Some recent simulations, which accounted for physiological effects of elevated CO2 and for farm-level adaptations to global change (e.g., change planting date), with various global change scenarios suggested that cereal yields in developed countries may increase 3-8% by the 2080s. On the other hand, yields in developing countries, which tend to be in more tropical climates, may decrease 2-7%. Therefore, the hardship of lower agricultural productivity may fall on those least able to cope. |
