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.

► Surface O3 is having a substantial impact on the yields of key crops. ► Yields of wheat, soybean, and maize were reduced by up to 15% globally in 2000. ► Global year 2000 crop production losses totaled 79–121 million metric tons. ► Agricultural losses are estimated to be worth $11–18 billion USD2000 annually.