Global crop yield reductions due to surface ozone exposure: 1. Year 2000 crop production losses and economic damage

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 year 2000 global yield reductions of three key staple crops (soybean, maize, and wheat) due to surface ozone exposure using hourly O₃ concentrations simulated by the Model for Ozone and Related Chemical Tracers version 2.4 (MOZART-2). We calculate crop losses according to two 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. Our results indicate that year 2000 O₃-induced global yield reductions ranged, depending on the metric used, from 8.5-14% for soybean, 3.9-15% for wheat, and 2.2-5.5% for maize. Global crop production losses totaled 79-121 million metric tons, worth $11-18 billion annually (USD₂₀₀₀). Our calculated yield reductions agree well with previous estimates, providing further evidence that yields of major crops across the globe are already being substantially reduced by exposure to surface ozone - a risk that will grow unless O₃-precursor emissions are curbed in the future or crop cultivars are developed and utilized that are resistant to O₃.