Climate change penalty and benefit on surface ozone: a global perspective based on CMIP6 earth system models

Abstract

This work presents an analysis of the effect of climate change on surface ozone discussing the related penalties and benefits around the globe from the global modeling perspective based on simulations with five CMIP6 (Coupled Model Intercomparison Project Phase 6) Earth System Models. As part of AerChemMIP (Aerosol Chemistry Model Intercomparison Project) all models conducted simulation experiments considering future climate (ssp370SST) and present-day climate (ssp370pdSST) under the same future emissions trajectory (SSP3-7.0). A multi-model global average climate change benefit on surface ozone of -0.96±0.07 ppbv oC-1 is calculated which is mainly linked to the dominating role of enhanced ozone destruction with higher water vapour abudances under a warmer climate. Over regions remote from pollution sources, there is a robust decline in mean surface ozone concentration on an annual basis as well as for boreal winter and summer varying spatially from -0.2 to -2 ppbv oC-1, with strongest decline over tropical oceanic regions. The implication is that over regions remote from pollution sources (except over the Arctic) there is a consistent climate change benefit for baseline ozone due to global warming. However, ozone increases over regions close to anthropogenic pollution sources or close to enhanced natural Biogenic Volatile Organic Compounds (BVOC) emission sources with a rate ranging regionally from 0.2 to 2 ppbv oC-1, implying a regional surface ozone penalty due to global warming. Overall, the future climate change enhances the efficiency of precursor emissions to generate surface ozone in polluted regions and thus the magnitude of this effect depends on the regional emission changes considered in this study within the SSP3_7.0 scenario. The comparison of the climate change impact effect on surface ozone versus the combined effect of climate and emission changes indicates the dominant role of precursor emission changes in projecting surface ozone concentrations under future climate change scenarios.

Reviewing the links and feedbacks between climate change and air pollution in Europe

“…Using simulations with five CMIP6 models considering future climate (ssp370SST) and present-day climate (ssp370pdSST) under the same future emissions trajectory (SSP3-7.0), Zanis et al (2022) estimated a non-robust slight ozone benefit over Europe on an annual basis and in winter, which becomes slightly positive but non-robust among the models (an ozone penalty of 0.2 ppb °C−1 ) during summer. These slightly negative or positive (in summer) signals Europe are attributed: 1) to the generally much lower NOx emissions, 2) to contributions from enhanced BVOC emissions and lightning NOx emissions, and 3) the competitive role of the large-scale background ozone chemical destruction linked to more water vapor under global warming.…”

The Future Climate and Air Quality Response From Different Near‐Term Climate Forcer, Climate, and Land‐Use Scenarios Using UKESM1

“…In the climate change only scenario (ssp370SST − pdSST), annual mean surface O 3 concentrations reduce, globally by 13% in 2095 over regions remote from large sources of anthropogenic pollution (Table S3 in Supporting Information S1). This reduction is attributed to the increased amounts of water vapor in a warmer world, ∼5°C by 2100 relative to the present day in UKESM1, leading to more hydroxyl formation and enhanced loss of O 3 in the absence of major sources of pollution, namely NO x (Doherty et al., 2013; Fiore et al., 2012; C. E. Johnson et al., 1999; Zanis et al., 2022). However, UKESM1 also simulates that climate change will enhance local net O 3 production rates and increase annual mean surface O 3 concentrations (up to 5 ppb by 2095) across polluted continental regions of north east United States, central Europe, northern India, and eastern China.…”

“…However, UKESM1 also simulates that climate change will enhance local net O 3 production rates and increase annual mean surface O 3 concentrations (up to 5 ppb by 2095) across polluted continental regions of north east United States, central Europe, northern India, and eastern China. This is a stronger response than occurs in other CMIP6 models and could be due to the larger temperature response simulated by UKESM1 (Zanis et al, 2022). A small increase in annual mean surface O 3 concentrations (up to 2 ppb by 2095) is simulated across the major biogenic (low NOx) regions by UKESM1, although not by all CMIP6 models (Zanis et al, 2022), due to the enhancement of BVOC emissions from increasing temperatures (Figure S3 in Supporting Information S1).…”

“…Future land‐use policies (ssp126Lu) have a negligible impact on climate (in terms of global ERF) but are slightly detrimental to global surface air quality (increasing both O 3 , 2% and PM 2.5 , 7% by 2095). Therefore feedbacks on NTCFs from such Earth system changes can impact climate and air quality and will also be an important component to consider as part of any future mitigation strategy (Martin et al., 2015; Wang et al., 2020; Zanis et al., 2022).…”

“…A small increase in annual mean surface O 3 concentrations (up to 2 ppb by 2095) is simulated across the major biogenic (low NOx) regions by UKESM1, although not by all CMIP6 models (Zanis et al, 2022), due to the enhancement of BVOC emissions from increasing temperatures (Figure S3 in Supporting Information S1). The increase in annual mean surface O 3 concentrations of 2.5 ppb (9%) across the Arctic by 2100 is attributed to a dynamically induced enhancement of the stratosphere-troposphere exchange process of O 3 resulting from climate change (Zanis et al, 2022).…”