The Future Climate and Air Quality Response From Different Near‐Term Climate Forcer, Climate, and Land‐Use Scenarios Using UKESM1

Abstract

Abstract Near‐term climate forcers (NTCFs) can influence climate via interaction with the Earth's radiative balance and include both aerosols and trace gas constituents of the atmosphere (such as methane and ozone). Two of the principal NTCFs, aerosols (particulate matter) and tropospheric ozone (O 3 ), can also affect local air quality when present in the lower levels of the atmosphere. Previous studies have shown that mitigation of NTCFs has the potential to improve air quality and reduce the rate of surface warming induced by long‐lived greenhouse gases. Here, we assess the combined air quality and climate impacts from changes in NTCFs under numerous different future mitigation scenarios, relative to a future reference scenario, that were conducted by a single Earth system model (UKESM1) as part of the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). Co‐benefits to both global air quality and climate are only achieved in the future scenario with strong mitigation measures applied to all NTCFs, particularly aerosols and methane, with penalties identified for inaction. When compared to the combined NTCF mitigation scenario, analysis of individual mitigation scenarios shows that there are important non‐linearities and interactions between NTCFs (e.g., aerosols and clouds). If only aerosol components are mitigated, there are still benefits to air quality but detrimental impacts on climate, particularly at the regional scale. In addition, other changes in future land‐use and climate could have important impacts on regional NTCFs, which should be considered when designing future mitigation measures to anthropogenic emissions. Plain Language Summary Components of the Earth's lower atmosphere, such as methane, aerosols, and ozone, have an important influence on the rate by which the climate warms in the short‐term (2050s) and are identified as near‐term climate forcers (NTCFs). Elevated concentrations of these components at the surface can also lead to poor air quality and impacts on human health. Therefore, future strategies to reduce these components provide opportunities to benefit both the rate of climate warming and levels of air pollution. Using a global Earth system model, we simulate the combined impact on future climate and air quality from numerous different ways to reduce NTCFs. We show that the largest benefit to both future climate and air quality is achieved by reducing concentrations of methane and aerosols at the same time. If only aerosols are reduced, then this leads to a benefit to air quality but could accelerate the rate of near‐term warming. However, when reducing NTCFs there are important interactions with the Earth system that need further consideration. Our findings highlight that reducing different NTCFs can have different impacts, particularly regionally, and that measures to benefit both future climate and air quality need to be carefully designed. Key Points Future changes in Near Term Climate Forcers have important implications for both air quality and climate Combined mitigation of aerosols and methane is required to achieve maximum co‐benefits to both future air quality and climate Future changes in land‐use and climate also impact the level of mitigation required to anthropogenic sources of near‐term climate forcers