Co-benefits of Global Greenhouse Gas Mitigation for Future Air Quality and Human Health

Abstract

Actions to reduce greenhouse gas (GHG) emissions often reduce co-emitted air pollutants, bringing co-benefits for air quality and human health. Past studies^1-6 typically evaluated near-term and local co-benefits, neglecting the long-range transport of air pollutants^7-9, long-term demographic changes, and the influence of climate change on air quality^10-12. Here we simulate the co-benefits of global GHG reductions on air quality and human health using a global atmospheric model and consistent future scenarios, via two mechanisms: a) reducing co-emitted air pollutants, and b) slowing climate change and its effect on air quality. We use new relationships between chronic mortality and exposure to fine particulate matter¹³ and ozone¹⁴, global modeling methods¹⁵, and new future scenarios¹⁶. Relative to a reference scenario, global GHG mitigation avoids 0.5±0.2, 1.3±0.5, and 2.2±0.8 million premature deaths in 2030, 2050, and 2100. Global average marginal co-benefits of avoided mortality are $50-380 (ton CO₂)^-1, which exceed previous estimates, exceed marginal abatement costs in 2030 and 2050, and are within the low range of costs in 2100. East Asian co-benefits are 10-70 times the marginal cost in 2030. Air quality and health co-benefits, especially as they are mainly local and near-term, provide strong additional motivation for transitioning to a low-carbon future.

Fig. 1

Global population-weighted surface (a) annual average PM_2.5, and (b) 6-month ozone-season average of 1-hr. daily maximum ozone, averaged over four model years, for the reference scenario (REF), the GHG abatement scenario (RCP4.5), and a simulation with REF emissions and RCP4.5 meteorology (eREFm45).

Fig. 2

Effects of GHG mitigation on annual average PM_2.5 (μg m⁻³) and the 6-month ozone season average of daily 1-hr. maximum ozone (ppb) in 2100, averaged over four model years, for the total change (RCP4.5-REF), and components due to changes in meteorology from climate change (eREFm45-REF), and emissions (RCP4.5-eREFm45).

Fig. 3

Premature mortality from PM_2.5 (CPD plus lung cancer) and ozone (respiratory), evaluated for future concentrations relative to 2000 levels, in the REF and RCP4.5 scenarios, globally and in selected world regions. Co-benefits can be estimated as the difference between REF and RCP4.5. In the global panel, points in 2100 are offset horizontally to show uncertainty bars, which reflect the 95% confidence intervals on the CRFs and neglect other uncertainties.

Fig. 4

Co-benefits of avoided premature mortality from PM_2.5 (CPD plus lung cancer) and ozone (respiratory) in 2030, 2050, and 2100 (deaths per year per 1000 km²).

Fig. 5

Regional marginal co-benefits of avoided mortality under high (red) and low (blue) VSLs, and global marginal abatement costs (the carbon price), as the median (solid green line) and range (dashed green lines) of 13 models. Marginal benefits are the total benefits (sum of ozone respiratory, PM_2.5 CPD, and PM_2.5 lung cancer mortality) divided by the total CO₂ reduction, in each year under RCP4.5 relative to REF. Uncertainty in benefits reflects 95% confidence intervals on the CRFs.