A peer-reviewed open access journal published by the National Institute of Environmental Health Sciences

Mitigation of greenhouse gas emissions often reduces co-emitted air pollutants, with advantages for human health. Avoided mortality from air pollution, a co-benefit of CO2 abatement, is estimated under global climate change mitigation scenarios to be in the range of US$50–US$380 per tonne of CO2. This exceeds the projected mitigation costs for 2030 and 2050, and is within the lower range of costs expected in 2100. Actions to reduce greenhouse gas (GHG) emissions often reduce co-emitted air pollutants, bringing co-benefits for air quality and human health. Past studies1,2,3,4,5,6 typically evaluated near-term and local co-benefits, neglecting the long-range transport of air pollutants7,8,9, long-term demographic changes, and the influence of climate change on air quality10,11,12. 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: reducing co-emitted air pollutants, and 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 modelling 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 US$50–380 per tonne of CO2, 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.

With much of the world's population residing in urban areas, an understanding of air pollution exposures at the city level can inform mitigation approaches. Previous studies of global urban air pollution have not considered trends in air pollutant concentrations nor corresponding attributable mortality burdens. We aimed to estimate trends in fine particulate matter (PM_2·5) concentrations and associated mortality for cities globally. We use high-resolution annual average PM_2·5 concentrations, epidemiologically derived concentration response functions, and country-level baseline disease rates to estimate population-weighted PM_2·5 concentrations and attributable cause-specific mortality in 13 160 urban centres between the years 2000 and 2019. Although regional averages of urban PM_2·5 concentrations decreased between the years 2000 and 2019, we found considerable heterogeneity in trends of PM_2·5 concentrations between urban areas. Approximately 86% (2·5 billion inhabitants) of urban inhabitants lived in urban areas that exceeded WHO's 2005 guideline annual average PM_2·5 (10 μg/m³), resulting in an excess of 1·8 million (95% CI 1·34 million–2·3 million) deaths in 2019. Regional averages of PM_2·5-attributable deaths increased in all regions except for Europe and the Americas, driven by changes in population numbers, age structures, and disease rates. In some cities, PM_2·5-attributable mortality increased despite decreases in PM_2·5 concentrations, resulting from shifting age distributions and rates of non-communicable disease. Our study showed that, between the years 2000 and 2019, most of the world's urban population lived in areas with unhealthy levels of PM_2·5, leading to substantial contributions to non-communicable disease burdens. Our results highlight that avoiding the large public health burden from urban PM_2·5 will require strategies that reduce exposure through emissions mitigation, as well as strategies that reduce vulnerability to PM_2·5 by improving overall public health. NASA, Wellcome Trust.

A peer-reviewed open access journal published by the National Institute of Environmental Health Sciences