| 英文摘要: | Trends in average crop yield i.e., crop output per unit area, are the basis for numerous forecasts of the future global expanse of agriculture. Although a number of studies predict a sizable expansion in global cropland area through the year 2050, some argue, to the contrary, that peak cropland is at hand. This paper analyzes historical trends in the 'correlation' between annual global cropland and annual crop production using a new measure called the elasticity of cropland with respect to production (crop output). Three different statistics of elasticity—the mean, the frequency of different combinations of directional changes in crop area and output, and time trend, each computed over different but fixed time intervals (5, 10, 15 and 20 years, which were chosen arbitrarily) suggest that the global area of cropland is set to increase with consumption. Achieving an absolute reduction in global cropland hinges on increasing crop yields beyond anything seen in the last fifty years. While this is consistent with several existing forecasts, the salience of an elasticity-based analysis is that it captures the effect of changing marginal as well as average crop yield as opposed to just the latter. The elasticity-based approach is applicable to trends in the exploitation of other scarce natural resources as well as releases of different pollutants. |