Determining the net effect of these complex changes on global agricultural capacity is difficult at best. Where negative effects are
expected, it is important to remember that they are negative effects on production potential. In many regions, appropriate
improvements in crop varieties, and in crop, soil and water management techniques, will continue to increase yields and more than compensate for the depressing effects of global warming. Hence major prospective studies do not expect global-level food
shortages, and conclude that climate change is likely to slow the expected increase of world food production only slightly, if at all, at least in the first half of this century (Bruinsma 2003).
However, even though world agricultural production today broadly meets world demand, food insecurity is still widespread because it is individual families and countries that have to buy or produce the crops they need. Even when global food production appears adequate, effects at local and country level can increase food insecurity. Moreover, in negatively affected areas, the losses in production potential will have the effect of “raising the bar” for future yield improvements – whereas previous research and development efforts produced equivalent yield improvements, in future a proportion of the effort will be needed simply to maintain current levels of production. The International Institute for Applied Systems Analysis (IIASA) has made a thorough study of how production potential might change with climate change (Fischer and others 2002a, b and c).
The agroecological zones methodology was used, comparing the growing requirements of major crops with data on soils, slopes and changing rainfall and temperatures. Looking at the effect of a 3ºC temperature rise on the areas, the study found that with rainfall levels unchanged, there would be a very small global gain of one per cent in land suitable for growing rainfed wheat, rice or maize. Increased rainfall levels (expected due to global warming) would raise this to a 4-5 per cent gain. However, the great majority of the potential cropland increases lie in sparsely populated areas of Canada and Russia and would depend on the cultivation of northerly lands that at present lie uncultivated.