Global Crop Yield Reductions due to Surface Ozone Exposure: 1. Year 2000 Crop Production Losses, Economic Damage, and Implications for World Hunger

Exposure to elevated concentrations of surface ozone (O3) causes substantial reductions in the agricultural yields of many crops. As emissions of O3 precursors rise in many parts of the world over the next few decades, yield reductions from O3 exposure appear likely to increase the challenges of feeding a global population projected to grow from 6 to 9 billion between 2000 and 2050. This study estimates present day (year 2000) global yield reductions of three key staple crops (soybean, maize, and wheat) due to surface ozone exposure using simulated hourly O3 concentrations by the Model for Ozone and Related Chemical Tracers version 2.4 (MOZART-2). We calculate crop losses according to two different metrics of ozone exposure—seasonal daytime (08:00-19:59) mean O3 (M12) and accumulated O3 above a threshold of 40 ppbv (AOT40)—and predict crop yield losses using crop-specific O3 concentration-response functions established by field studies. We additionally calculate the economic value of crop production losses as well as the number of people who could avoid undernourishment if crop reductions due to ozone exposure were eliminated. Our results indicate that year 2000 O3-induced global yield reductions ranged from 8.5-14% for soybean, 3.9-15% for wheat, and 2.2-5.5% for maize, depending on the metric used. Global crop production losses totaled 79-121 million metric tons, worth $11-18 billion annually (USD2000). We further calculate that the dietary energy equivalent of O3-induced crop losses could have lifted 180-312 million people, or 21-36% of the year 2000 global undernourished population, above the undernourishment threshold as defined by the United Nations Food and Agriculture Organization. Our calculated yield reductions agree well with previous estimates, providing further evidence that yields of major crops across the globe are already being reduced by exposure to surface ozone—a risk that will grow unless O3 precursor emissions are curbed in the future.