Climate Effects on Food Supply
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Documentation
Note: This data set has now been superseded by a new data set on the effects of climate change on global food production under SRES emissions and socio-economic scenarios produced by the same authors.
In the coming decades the agricultural sector faces many challenges stemming from growing global populations, land degradation, and loss of cropland to urbanization. Although food production has been able to keep pace with population growth on the global scale, there are serious regional deficits, and poverty related nutritional deficiencies affect close to a billion people globally. In this century climate change is one factor that could affect food production and availability in many parts of the world, particularly those most prone to drought and famine.
In an effort to better understand the potential global impacts of climate change on agriculture, in 1990 the U.S. Environmental Protection Agency contracted the Goddard Institute for Space Studies to coordinate a major study of the effects of changing temperature and precipitation regimes and increased CO2 concentrations on crop production and its economic implications. The central aim of the study was to provide an assessment of potential climate change impacts on world crop production, including quantitative estimates of yield changes of major food, cash and industrial crops, prices, trade and risk of hunger. Agricultural scientists from 18 countries estimated potential changes in crop growth and production at 125 key agricultural sites using compatible crop models and consistent climate change scenarios. The study assessed the implications of climate change for world crop yields taking into account uncertainty in the level of climate change expected, physiological effects of CO2 on plant growth, and different adaptive responses. Projected yields at the agricultural sites were then aggregated to major trading regions, and fed into a global trade model (the Basic Linked System or BLS) in order to produce regional estimates of potential price increases, food shortages, and risk of hunger.
Over the past eight years, the study has been further developed and refined based on advances in coupled atmosphere-ocean general circulation models (GCMs), crop models applied spatially, and the projected range of adaptation scenarios. The purpose of this web site is to make the data sets on projected crop yields publicly available for query and analysis. The following pages provide important background on the methodology used to create the data set, data limitations, and the scenarios utilized. For those unfamiliar with the study and its assumptions and methodologies, it is recommended to read through the supporting documentation before querying the data set in order to understand how the crop yield scenarios were generated.
Data Limitations
To better interpret the data sets developed by crop modeling studies, users need to be aware of the many uncertainties that could not be addressed.
- Pests and diseases. The potential effects of climate change on crop damage due to pests and diseases was not considered in the study and assumed to remain at the current level. At present damage is estimated to reduce potential global crop yields by 30% each year. Future changes in temperature and precipitation will undoubtedly effect the prevalence and geographic extent of specific pests such as bacteria, nematodes, and insects, which in turn will impact upon crop losses. Unfortunately, these impacts could not be measured in this study.
- Climatic variability. Increased seasonal or annual climatic variability as well as variability across small geographic areas is expected to go hand-in-hand with broader secular trends in temperature increase. These seasonal, annual and geographic variations are not captured very well by existing GCMs, and therefore were not accounted for in this study. For more on this topic, see studies on climate variability in the Southeast United States.
- Extreme weather events. Climate change is predicted to affect the frequency and severity of extreme weather events such as cyclones, hurricanes, and prolonged droughts. Extreme weather events can result in significant crop losses from wind damage, flooding, or inadequate soil moisture. Although it is recognized that extreme weather will affect future yields, it is very difficult to model such stochastic events in a way that provides realistic assessment of their yield impacts.
- Impacts of CO2 enrichment. Thus far, the applications of enhanced concentrations of CO2 to crops have been conducted in highly controlled laboratory experiments. The only exception to this is a major field-based set of experiments in Arizona called the FACE experiments. In all cases the crop growing conditions differ from those in the real world, most notably in the control of weed competitors. Under normal conditions, crops compete with weeds, which also respond to climate change and enriched CO2 . Depending on the circumstances, the effect of climate change may be for weeds to grow faster than field crops. This would have a negative impact on crop yields, and would in all likelihood require greater application of herbicides, a high-cost input.
Other Resources
Parry, M.L., Fischer, C., Livermore, M., Rosenzweig, C., Iglesias, A., 1999. Climate change and world food security: a new assessment. Global Environmental Change 9, 51–67, http://dx.doi.org/10.1016/S0959-3780(99)00018-7
Parry, M.L., Rosenzweig, C., Iglesias, A., Livermore, M., Fischer, C., 2004. Effects of climate change on global food production under SRES emissions and socio-economic scenarios. Global Environmental Change 14, 53–67, http://dx.doi.org/10.1016/j.gloenvcha.2003.10.008
Rosenzweig, C., M. L. Parry, G. Fischer, and K. Frohberg. 1993. Climate change and world food supply.Research Report No. 3. Oxford: University of Oxford, Environmental Change Unit. http://www.ciesin.org/docs/004-046/004-046.html