Climate and Air Quality Impacts of Combined Climate Change and Air Pollution Policy Scenarios

Abstract

This report describes an assessment of the co-benefits for air pollution of recently developed climate mitigation scenarios that inform the European Union policy making. The climate mitigation scenarios were obtained with the POLES equilibrium model for a business-as-usual and greenhouse gas reduction case. In the present work, these scenarios were expanded to air pollution emissions. The resulting set of global -spatially and sector disaggregated- air pollution emissions were evaluated with the global chemistry transport model TM5, to calculate levels of particulate matter and ozone. Subsequently, air pollution impacts on human health, ecosystems and climate were evaluated. The resulting set of four scenarios thus reflect various combinations of worldwide air pollution and climate policies: BAU (no further climate and air pollution policies since the 2000 base-year); CARB (climate policy only), BAP (no further climate policy, but progressive air pollution policies, to address worldwide increasing levels of air pollution) and CAP (combination of ambitious climate and air pollution policies). The implementation of a global climate policy (CARB) has substantial co-benefits for reducing air pollutant emissions. Compared to BAU, in 2050 global emissions of SO2 are reduced by ca. 75 %, NOx by 55 %, CO (40 %) and other pollutants VOC, OC and BC) about 25% %. These emission reductions result from cleaner technologies and decreased fuel demand, and correspond to a CO2 emission reduction of more than 60 %. Advanced air pollution abatement technologies can obtain similar air pollutant reductions ranging between 35 % (NOx), 45 % (OC, BC), 60 % (SO2) and 70% (CO), however in this case the CO2 emissions reach unabated levels of 55 Pg CO2/yr. The combined air pollution and climate policy case (CAP) further reduces BAP air pollution emissions by 10-30 %. Noticeable are the decreases of methane emissions by ca. 60 %, which have important impacts on ozone air quality and climate. The environmental benefits of the emission reductions are substantial. In 2050, average global life expectancy increases by 3.2 months/person for BAP (compared to BAU) and further increases by 3.7 to 6.9 months/person if additionally climate policies are introduced (CAP). Compared to 2000, only the CAP scenario leads to global improvement of life-expectancy (by about 3 months/person), while all other scenarios lead to higher particulate concentration and lower life expectancies, mainly driven by pollution developments in South and East Asia. These improvements in CAP are due to decreasing concentrations of primary (OC, BC) and secondary (SO4, NO3) aerosol. This work shows that combining air pollution and climate policies is in some regions the only way to stabilize or decrease the levels of air pollution and reducing impacts on human health. The global average life expectancy, however, masks large regional differences: e.g. current and future levels of air pollution in Asia are much larger than in Europe or the United States. Crop losses due to ozone are reduced by 4.7 % by implementing progressive air pollution policies, and could be reduced by another 2 %, by introducing additional climate policies. Climate policies target at limiting long-term (2100) climate change. On the intermediate time-scales (2030-2050), however, there might be important trade-offs to be considered in climate and air pollution policies, since reducing particulate matter and precursor (especially sulfur) emissions, are likely to lead to a net positive radiative forcing and a warming of climate. Since reductions of particulate matter and ozone are necessary to protect human health and vegetation, combined air pollution and climate policies are more beneficial for both climate and air pollution than stand-alone policies. There is scope to preferentially mitigate emissions of Black Carbon and methane, which is beneficial for climate and human health.