For several reasons, then, a prudent range for impact on global agricultural capacity by the 2080s could thus easily involve greater damage than the direct preferred estimates in this study and could perhaps lie in the range of reductions of 10 to 25 percent. Even if global productive potential were cut by only 3 percent, the results find an inequitable distribution of the effects, driven by the fact that the poor countries tend to be located in lower latitudes, where temperatures are already at or above optimal levels. On average developing countries would suffer losses of 9 percent and median losses for these countries would amount to 15 percent. Confirming previous studies, the results here indicate that the losses would be most severe in Africa (estimated here at 17 percent average loss and 18 percent median loss in agricultural capacity) and Latin America (13 percent average and 16 percent median loss). The losses would be much larger if the benefits from carbon fertilization failed to materialize (averaging about 21 percent for all developing countries, 28 percent for Africa, and 24 percent for Latin America).
In terms of geopolitics, the results here are particularly important for the cases of China and India. China is already the second-largest emitter of carbon dioxide (after the United States but ahead of the European Union), and its cooperation will surely be crucial to effective action against global warming. Although the central estimate in this study finds China a modest gainer in agriculture under business as usual (increase in agricultural capacity by about 7 percent with carbon fertilization), the estimate turns to a loss (7 percent reduction in agricultural capacity) if carbon fertilization effects do not materialize or are offset by excluded damages. For India, there is no ambiguity: Prospective losses are massive (on the order of 30 to 40 percent).
For Australia, one of the two steadfast opponents of the principal international initiative to date against global warming (the Kyoto Protocol), the results also suggest that a more positive position on global warming abatement would be in its long-term interests. The estimates for Australia indicate losses of around 16 percent even with carbon fertilization (with potentially much larger losses suggested by the Ricardian estimates). As for the United States, the other principal opponent, although the estimates show an aggregate gain of 8 percent in the case with carbon fertilization, they indicate a comparable loss (6 percent) if carbon fertilization is excluded. Moreover, regional losses are pronounced: by about 30 to 35 percent in the Southeast and in the Southwest Plains, if carbon fertilization is excluded (and about 20 to 25 percent if it is included).
For an initial phase of modest global warming, average impacts on agriculture are ambiguous and may be benign globally on average, but it would be a serious mistake to infer from such a diagnosis that little should be done to curb climate change. This study has sought to sharpen analysis of agricultural impacts by bringing to bear rigorous and detailed estimates available for regional climate change and quantitative models of agricultural impact. The new estimates in this study strongly suggest that by late in the present century the global effects under business as usual global warming would turn malignant for agriculture globally and that the damages would be the most severe and begin the soonest where they can least be afforded: in the developing countries. Moreover, it would be a serious mistake to downplay the risks of future agricultural losses from global warming on grounds that technological change, for example in new seed varieties, will offset any negative climatic effects. A close look at the pace of yield increases in the past two decades, combined with attention to the prospective rise in global food demand and the conversion of a substantial portion of agricultural land from food to energy crops, suggests that there is little margin for complacency about erosion in agricultural potential from global warming.
Rights: Copyright 2007 William R. Cline.
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