Note: This data set has now been superseded by a new data set on the effects of climate change on global food production under SRES emissions and socio-economic scenarios produced by the same authors. Users are recommended to use the new data instead. SEDAC is maintaining this web site for reference purposes.

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.
 

1. 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.
2. 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.
3. 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.
4. 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.