Climate and health implications of future aerosol emission scenarios

Anthropogenic aerosols have a net cooling effect on climate and also cause adverse health effects by degrading air quality. In this global-scale sensitivity study, we used a combination of the aerosol-climate model ECHAM-HAMMOZ and the University of Victoria Earth System Climate Model to assess the climate and health effects of aerosols emissions from three Representative Concentration Pathways (RCP2.6, RCP4.5, and RCP8.5) and two new (LOW and HIGH) aerosol emission scenarios derived from RCP4.5, but that span a wider spectrum of possible future aerosol emissions. All simulations had CO2 emissions and greenhouse gas forcings from RCP4.5. Aerosol forcing declined similarly in the standard RCP aerosol emission scenarios: the aerosol effective radiative forcing (ERF) decreased from -1.3 Wm(-2) in 2005 to between -0.1 Wm(-2) and -0.4 Wm(-2) in 2100. The differences in ERF were substantially larger between LOW (-0.02 Wm(-2) in 2100) and HIGH (-0.8 Wm(-2)) scenarios. The global mean temperature difference between the simulations with standard RCP aerosol emissions was less than 0.18 degrees C, whereas the difference between LOW and HIGH reached 0.86 degrees C in 2061. In LOW, the rate of warming peaked at 0.48 degrees C per decade in the 2030s, whereas in HIGH it was the lowest of all simulations and never exceeded 0.23 degrees C per decade. Using present-day population density and baseline mortality rates for all scenarios, PM2.5-induced premature mortality was 2 371 800 deaths per year in 2010 and 525 700 in 2100 with RCP4.5 aerosol emissions; in HIGH, the premature mortality reached its maximum value of 2 780 800 deaths per year in 2030, whereas in LOW the premature mortality at 2030 was below 299 900 deaths per year. Our results show potential trade-offs in aerosol mitigation with respect to climate change and public health as ambitious reduction of aerosol emissions considerably increased warming while decreasing mortality.