The effect of future ambient air pollution on human premature mortality to 2100 using output from the ACCMIP model ensemble
Authors: Silva Raquel A. , West J. Jason , Lamarque Jean-François , Shindell Drew T. , Collins William J. , Dalsoren Stig , Faluvegi Greg , Folberth Gerd , Horowitz Larry W. , Nagashima Tatsuya , Naik Vaishali , Rumbold Steven T. , Sudo Kengo , Takemura Toshihiko , Bergmann Daniel , Cameron-Smith Philip , Cionni Irene , Doherty Ruth M. , Eyring Veronika , Josse Beatrice , MacKenzie I. A. , Plummer David S. , Righi Mattia , Stevenson David S. , Strode Sarah , Szopa Sophie , Zeng Guang 
Published: February 2016

Abstract. Ambient air pollution from ground-level ozone and fine particulate matter (PM2.5) is associated with premature mortality. Future concentrations of these air pollutants will be driven by natural and anthropogenic emissions and by climate change. Using anthropogenic and biomass burning emissions projected in the four Representative Concentration Pathway scenarios (RCPs), the ACCMIP ensemble of chemistry-climate models simulated future concentrations of ozone and PM2.5 at selected decades between 2000 and 2100. We use output from the ACCMIP ensemble, together with projections of future population and baseline mortality rates, to quantify the human premature mortality impacts of future ambient air pollution. Future air pollution-related premature mortality in 2030, 2050 and 2100 is estimated for each scenario and for each model using a health impact function based on changes in concentrations of ozone and PM2.5 relative to 2000 and projected future population and baseline mortality rates. Additionally, the global mortality burden of ozone and PM2.5 in 2000 and each future period is estimated relative to 1850 concentrations, using present-day and future population and baseline mortality rates. The change in future ozone concentrations relative to 2000 is associated with excess global premature mortality in some scenarios/periods, particularly in RCP8.5 in 2100 (316 thousand deaths/year), likely driven by the large increase in methane emissions and by the net effect of climate change projected in this scenario, but it leads to considerable avoided premature mortality for the three other RCPs. However, the global mortality burden of ozone markedly increases from less than 0.4 million deaths/year in 2000 to between 1.09 and 2.36 million deaths/year in 2100, across RCPs, mostly due to the effect of increases in population and baseline mortality rates. Decreases in PM2.5 concentrations relative to 2000 are associated with avoided premature mortality in all scenarios, particularly in 2100: between −2.39 and −1.31 million deaths/year for the four RCPs due to the reductions in emissions projected in these scenarios. The global mortality burden of PM2.5 is estimated to decrease from 1.7 million deaths/year in 2000 to between 0.95 and 1.55 million deaths/year in 2100 for the four RCPs, due to the combined effect of decreases in PM2.5 concentrations and changes in population and baseline mortality rates. Trends in future air pollution-related mortality vary regionally across scenarios, reflecting assumptions for economic growth and air pollution control specific to each RCP and region. Mortality estimates differ among chemistry-climate models due to differences in simulated pollutant concentrations, and is the greatest contributor to overall mortality uncertainty for most cases assessed here, supporting the use of model ensembles to characterize uncertainty. Increases in exposed population and baseline mortality rates of respiratory diseases magnify the impact on premature mortality of changes in future air pollutant concentrations and explain why the future global mortality burden of air pollution can exceed the current burden, even where air pollutant concentrations decrease.