Impacts of a nuclear war in South Asia on soybean and maize production in the Midwest United States
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Crop production would decline in the Midwestern United States from climate change following a regional nuclear conflict between India and Pakistan. Using Agro-IBIS, a dynamic agroecosystem model, we simulated the response of maize and soybeans to cooler, drier, and darker conditions from war-related smoke. We combined observed climate conditions for the states of Iowa, Illinois, Indiana, and Missouri with output from a general circulation climate model simulation that injected 5 Tg of elemental carbon into the upper troposphere. Both maize and soybeans showed notable yield reductions for a decade after the event. Maize yields declined 10–40 % while soybean yields dropped 2–20 %. Temporal variation in magnitude of yield for both crops generally followed the variation in climatic anomalies, with the greatest decline in the 5 years following the 5 Tg event and then less, but still substantial yield decline, for the rest of the decade. Yield reduction for both crops was linked to changes in growing period duration and, less markedly, to reduced precipitation and altered maximum daily temperature during the growing season. The seasonal average of daily maximum temperature anomalies, combined with precipitation and radiation changes, had a quadratic relationship to yield differences; small (0 °C) and large (−3 °C) maximum temperature anomalies combined with other changes led to increased yield loss, but medium changes (−1 °C) had small to neutral effects on yield. The exact timing of the temperature changes during the various crop growth phases also had an important effect.
We thank Luke Oman for providing us with the climate model output for Midwestern U.S. This work is partially supported by the Switzerland Federal Department of Foreign Affairs, NSF grant ATM-0730452, and NOAA grant NA08OAR4310873. Authors are also indebted to Mr. George Allez for his meticulous editing to make the article more concise. Finally, the suggestions of three anonymous reviewers significantly improved this manuscript.
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