Current assessments of effects of global environmental change on wheat production

Assessment of the impacts of GEC on global wheat production is based, of necessity, on modelling that uses limited information about crop responses. A number of forecasts of the impacts have been made. The 1995 Summary of the Intergovernmental Panel on Climate Change (IPCC) (Watson et al., 1996) emphasized the considerable uncertainty in estimating impacts of doubling pre-industrial [CO2] and increasing temperatures by 4°C. These authors wrote that variability in estimated yield impacts among countries, methods of analysis and crops, makes it difficult to generalize results across areas or for different climate scenarios. However, they tentatively concluded that wheat production will decrease substantially. Generally, modelling studies predict that wheat will be grown at higher latitudes (i.e. mainly further north) and that production in regions closer to the Equator will decrease (Leemans and Solomon, 1993; Rosenzweig and Parry, 1994). Adams et al. (1990) suggested a major decrease in wheat production in the USA. In Rosenzweig and Parry's study of the impacts of 555 |mmol CO2 mol-1 and approximately 4°C increase in temperature by 2060, simulated global agricultural production of major cereal crops declined, despite assuming farm-level adaptation and future technological improvements. With 2°C warming, yields might improve by 12% (due to longer crop duration) but a 4°C warming would decrease global production (this contrasts with Leemans and Solomon, 1993, who predict an increase). Thus, 'slight-to-moderate negative effects' were projected to result from GEC. As a consequence of GEC and world population increase, the proportion of the population at risk of hunger may increase, by 6-50%. GEC would increase the disparities between developed and underdeveloped agriculture. We have some doubts about the reliability of current simulation models for assessment of global production of wheat (see below) but, in any case, uncertainties about the nature of GEC probably outweigh the uncertainties in crop response. We share with Evans (1998) the view that feeding the greatly increased human population 'can be done, but to do so sustainably in the face of climatic change, equitably in the face of social and regional inequalities, and in time when few seem concerned, remains one of humanity's greatest challenges'.

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