Abstract
Here we quantify the regional co-benefits to future air quality on annual to daily mean timescales from implementing mitigation measures to stabilise future climate. Two consistent future emissions pathways are used within the composition-climate model HadGEM3-UKCA: one is a reference pathway of future economic growth and development (REF), whilst the Representative Concentration Pathway 4.5 (RCP4.5) assumes the same development pathway but stabilises anthropogenic radiative forcing at 4.5 W m−2 in 2100. Implementing greenhouse gas (GHG) mitigation measures in RCP4.5 reduces global mean air pollutant emissions by up to 30% in the 2050s, in addition to mitigating climate. Annual mean surface concentrations of ozone and PM2.5 decrease by 10%–20% from the combined reductions in emissions and climate change. The number of days exceeding the World Health Organization’s (WHO) daily mean air quality standards are reduced by up 47 days for ozone and 15 days for PM2.5 over different world regions. The air quality co-benefits from mitigation measures are mainly achieved from reductions in anthropogenic emissions, although benefits can be offset due to changes in climate. In terms of anthropogenic climate forcing, while the reduction in global mean effective radiative forcing (ERF) in 2050, relative to the 2000s, due to enacting carbon dioxide mitigation measures (−0.43 W m−2) is enhanced by decreases in tropospheric ozone (−0.26 W m−2) and methane (−0.2 W m−2), it is partially offset by a positive aerosol ERF from reductions in aerosols (+0.35 W m−2). This study demonstrates that policies to mitigate climate change have added co-benefits for global and regional air quality on annual to daily timescales. Furthermore, the effectiveness of the GHG policies in reducing anthropogenic climate forcing is enhanced in the near-term by reductions in ozone and methane despite the increased forcing due to reductions in aerosols.
Highlights
The air pollutants ozone (O3) and particulate matter (PM) can have a detrimental impact on human health (Lelieveld et al 2015) and variable impacts on ecosystems (Fowler et al 2009)
This study demonstrates that policies to mitigate climate change have added co-benefits for global and regional air quality on annual to daily timescales
We use a coupled compositionclimate model to assess the impact of future climate mitigation measures on air pollutants by using simulations with the same air pollutant controls but different climate policies
Summary
The air pollutants ozone (O3) and particulate matter (PM) can have a detrimental impact on human health (Lelieveld et al 2015) and variable impacts on ecosystems (Fowler et al 2009) Both pollutants are ‘Near Term Climate Forcers’ (NTCFs) because they influence climate in the short-term (due to their short atmospheric lifetime) by perturbing the Earth’s radiative balance (Myhre et al 2013). Policies focussed on the mitigation of climate, through the reduction of GHGs, can inadvertently impact the concentration and spatial distribution of air pollutants in the atmosphere (von Schneidemesser et al 2015). This can occur through changes in the rate of air pollutants co-emitted from carbon sources and by changes in the physical climate. It is important to consider the impact from air quality and climate mitigation measures together as future air quality will be determined by the combined effect of both
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