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Can US farmers beat the heat?

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Joey McLeister / AP / File

(Read caption) Norm Johnson walks through one of his non-irrigated cornfields on his farm in Becker, Minn., July 11, 2006. Will extreme heat from climate change ruin US agriculture?

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Michael Roberts and Wolfram Schlenker have been conducting some important research on how U.S extreme heat affects agricultural yields. Their work has at least two implications. Agricultural yields are rising over time but their statistical work rejects the optimistic hypothesis that farmers are better able to "withstand" heat waves now than in the past. Intuitively, they are estimating the marginal effect of heat waves on crop yields at different points in time. If we are getting better at coping with the heat, then this negative "heat wave effect" should be converging to zero over time. They reject this claim. To quote the authors;

"Meerburg et al. argue that yields in the United States have been trending upward and are expected to do so in the future. We agree with this point but emphasize that we controlled or it in our earlier analysis. Increasing state-specific yield trends are highly significant in all of our regression specifications. At the same time, the relative influence of extreme heat was found to be the same in the earlier and later years of our sample. This indicates that breeders have been successful at raising average yields but not, so far, at significantly improving heat tolerance. To clarify: yields are predicted to decline 30–82% compared to what they would have been without climate change. These predictions hold growing locations fixed and exclude CO2 fertilization and possible future adaptations."

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