A storyline of ozone pollution extremes in warmer climates

Tamara Emmerichs, Fuzhen Shen, Sergey Gromov, Michaela Hegglin, Andreas Wahner, and Domenico Taraborrelli

Abstract

High ozone levels pose a significant threat to human health and ecosystems, especially during extreme weather events. These are expected to become more frequent and intense with climate change, exacerbating the interactions between weather, vegetation, and air pollution. Traditionally a climate change penalty is expected for ground-level ozone is expected. However, models do not even agree on the sign of the change over most of the continents suggesting an important role for vegetation. We address this uncertainty by incorporating realistic vegetation responses to abiotic stress into a global atmospheric chemistry model. We develop novel storyline scenarios of air pollution, contrasting the actual climate of 2018-2020 with two different levels of warming. Our results show that under warming, vegetation and local photochemistry generally conspire to exacerbate ozone pollution extremes, while a concurrent moistening of the free troposphere leads to a lower ozone background. The competition between these two effects depends on the degree of warming and will determine whether climate change results in a penalty or a benefit. However, the role of changing pollutant emissions remains uncertain and should be addressed in future studies.