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

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 (O3), 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.

The Air Pollution Human Health Burden in Different Future Scenarios That Involve the Mitigation of Near‐Term Climate Forcers, Climate and Land‐Use

“…The air pollutant data used in this study has been obtained from the CMIP6 data archive which is hosted at the Earth System Grid Federation and is freely available to download from https://esgf-node.llnl.gov/search/cmip6/. A list of the CMIP6 model diagnostics used in this study from each scenario are provided in Table S1 in Supporting Information S1, along with the relevant data citation for each experiment provided in Table S2 in Supporting Information S1 of the companion paper Turnock et al (2022). Additional simulation data relevant to this publication from the non-AerChemMIP experiment ssp370SST-pdEmis is archived on Zenodo at the following location https://doi.org/10.5281/zenodo.5884604.…”

“…A detailed explanation of the model setup, emission scenarios and simulations performed for this study can be found in the companion paper (Turnock et al, 2022), with a brief summary also presented here. We use the fully coupled Earth system model, UKESM1, which contains an interactive stratosphere-troposphere chemistry and aerosol scheme coupled to the physical atmosphere ocean climate model, along with other relevant Earth system components such as a terrestrial carbon and nitrogen cycle coupled to a dynamical vegetation model (Sellar et al, 2019(Sellar et al, , 2020.…”

“…Additional scenarios have also been undertaken to isolate any impact from solely future changes in climate (pdSST), anthropogenic emissions (pdEmis), and land-use (ssp126LU), which can increase natural sources of NTCFs. Future details of the emission changes in these scenarios can be found in Turnock et al (2022). All the scenarios listed in Table 1 have been conducted in UKESM1 over the period 2015-2100.…”

“…Scenarios considering only the impact from changes in climate and land-use highlighted important differences at a regional level. Here we use the same scenarios as in Turnock et al (2022) to calculate the air pollution health burden resulting from changes in surface O 3 and PM 2.5 concentrations in a wide range of future scenarios simulated by the United Kingdom Earth System Model (UKESM1, Sellar et al, 2019), as part of AerChemMIP. We quantify the change in the air pollution health burden for scenarios that include the mitigation of different NTCFs, both individually and in combination, as well as isolating the impacts from transient changes in climate, emissions, and land-use.…”

“…Significantly lower air pollution (PM 2.5 ) mortality estimates of ∼800,000 per year by 2100 are estimated to occur across Africa in a future scenario that involves reduced warming levels and air pollutant emission reductions, compared to a higher warming scenario with weaker emission mitigation resulting in ∼1.3 million per year by 2100 (Shindell et al, 2022). Turnock et al (2022) analyzed both the air quality and climate impacts from changes in NTCFs in a wide range of future mitigation pathways, conducted as part of the Aerosol and Chemistry MIP (AerChemMIP), an endorsed MIP of CMIP6. Within AerChemMIP, the future mitigation scenarios consider different pathways of both strong (working toward implementing best available technology for maximum feasible reductions) and weak (delays to implementing current control legislation and any future reductions) pollution control measures, which impact the emissions of NTCFs.…”