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Anthropogenic emissions of short-lived climate forcers (SLCFs) affect both air quality and climate. How much regional temperatures are affected by ambitious SLCF emission mitigation policies, is however still uncertain. We investigate the potential temperature implications of stringent air quality policies, by applying matrices of regional temperature responses to new pathways for future anthropogenic emissions of aerosols, methane (CH4) and other short-lived gases. These measures have only minor impact on CO2 emissions. Two main options are explored, one with climate optimal reductions (i.e. constructed to yield a maximum global cooling) and one with maximum technically feasible reductions. The temperature response is calculated for four latitude response bands (90-28° S, 28° S-28° N, 28-60° N, and 60-90° N) by using existing regional temperature change potential (ARTP) values for four emission regions: Europe, East Asia, shipping, and the rest of the world. By 2050, we find that global surface temperature can be reduced by -0.3 ± 0.08 °C with climate-optimal mitigation of SLCFs relative to a baseline scenario, and as much as -0.7 °C in the Arctic. Cutting CH4 and BC emissions contribute the most. This could offset warming equal to approximately 15 years of current global CO2 emissions. If SLCFs are mitigated heavily, we find a net warming of about 0.1 °C, but when uncertainties are included a slight cooling is also possible. In the climate optimal scenario, the largest contributions to cooling comes from the energy, domestic, waste, and transportation sectors. In the maximum technically feasible mitigation scenario, emission changes from the sectors industry, energy, and shipping will give warming. Some measures, such as in the sectors agriculture waste burning, domestic, transport, and industry, have outsized impact on the Arctic, especially by cutting BC emissions in winter in areas near the Arctic. [ABSTRACT FROM AUTHOR]

We present a case study where emission metric values from different studies are applied to estimate global and Arctic temperature impacts of emissions from a Northern European country. This study assesses the climate impact of Finnish air pollutant and greenhouse gas emissions in 2000-2010 as well as future emissions until 2030. The pollutants included are SO2, NOX, NH3, NMVOC, BC, OC and CO as well as CO2, CH4 and N2O, and our study is the first one for Finland to include all of them in one coherent dataset. These pollutants have different atmospheric lifetimes and influence the climate differently; hence, we look at different climate metrics and time horizons. The study uses the Global Warming Potential (GWP), the Global Temperature change Potential (GTP) and the Regional Temperature change Potential (RTP) with different time scales for estimating the climate impacts by species and sectors globally and in the Arctic. We compare the climate impacts of emissions occurring in winter and summer. This assessment is an example of how the climate impact of emissions from small countries and sources can be estimated, as it is challenging to use climate models to study the climate effect of national policies in a multi-pollutant situation. Our methods are applicable to other countries and regions and present a practical tool to analyse the climate impacts in multiple dimensions, such as assessing different sectors and mitigation measures. While our study focuses on short-lived climate forcers, we find that the CO2 emissions have the most significant climate impact, and the significance increases with longer time horizons. In the short term, emissions of especially CH4 and BC played an important role as well. The warming impact of BC emissions is enhanced during winter. There can be relatively large differences between results from studies using different metrics, which can partly be explained by different study setup and inherent uncertainty. [ABSTRACT FROM AUTHOR]

We calculate the absolute regional temperature change potential (ARTP) of various short lived climate forcers (SLCFs) based on detailed radiative forcing (RF) calculations from four different models. The temperature response has been estimated for four latitude bands (90-28° S, 28° S-28° N, 28-60° N, and 60-90° N). The regional pattern in climate response not only depends on the relationship between RF and surface temperature, but also on where and when emissions occurred and atmospheric transport, chemistry, interaction with clouds, and deposition. We present four emissions cases covering Europe, East Asia, the global shipping sector, and the globe. Our study is the first to estimate ARTP values for emissions during Northern Hemisphere summer (May-October) and winter season (November-April). The species studied are aerosols and aerosol precursors (black carbon (BC), organic carbon (OC), SO2, NH3), ozone precursors (NOx, CO, volatile organic compound (VOC)), and methane (CH4). For the response to BC in the Arctic, we take into account the vertical structure of the RF in the atmosphere, and an enhanced climate efficacy for BC deposition on snow. Of all SLCFs, BC is the most sensitive to where and when the emissions occur, as well as giving the largest difference in response between the latitude bands. The temperature response in the Arctic is almost 4 times larger and more than 2 times larger than the global average for Northern Hemisphere winter emissions for Europe and East Asia, respectively. The latitudinal breakdown gives likely a better estimate of the global temperature response as it accounts for varying efficacies with latitude. An annual pulse of non-methane SLCFs emissions globally (representative of 2008) leads to a global cooling. Whereas, winter emissions in Europe and East Asia give a net warming in the Arctic due to significant warming from BC deposition on snow. [ABSTRACT FROM AUTHOR]

Dedicated model simulations by four general circulation and chemistry-transport models are used to establish a matrix of specific radiative forcing, defined as the radiative forcing per unit change in mass emitted, as a function of the near-term climate forcer emitted, its source region, and the season of emission. Emissions of eight near-term climate forcers are reduced: sulphur dioxide, the precursor to sulphate aerosols; black carbon aerosols; organic carbon aerosols; ammonia, a precursor to nitrate aerosols; methane; and nitrogen oxides, carbon monoxide, and volatile organic compounds, the precursors to ozone and to secondary organic aerosols. The focus is on two source regions, Europe and East Asia, but the shipping sector and global averages are also included. Emission reductions are applied over two time periods: May–Oct and Nov–Apr. Models generally agree on the sign and ranking of specific radiative forcing for different emitted species, but disagree quantitatively. Black carbon aerosols, methane, and carbon monoxide exert positive specific radiative forcings. Black carbon exerts the strongest specific radiative forcing, even after accounting for rapid adjustments from the semi-direct effect, and is most efficient in local summer. However, although methane and carbon monoxide are less efficient in a specific sense, the potential for decreasing the mass emitted is larger. Organic carbon aerosols, sulphur dioxide, ammonia, and emissions by the shipping sector exert negative specific radiative forcings, with local summer emission changes being again more efficient. Ammonia is notable for its weak specific radiative forcing. For aerosols, specific radiative forcing exerted by European emissions is stronger than for East Asia, because the European baseline is less polluted. Radiative forcing of European and East Asian emission reductions is mainly exerted in the mid-latitudes of the Northern Hemisphere, but atmospheric transport yields sizeable radiative forcings in neighbouring regions, such as the Arctic. Models disagree on the sign of the net radiative forcing exerted by reductions in the emissions of nitrogen oxides and volatile organic compounds, because those reductions trigger complex changes in the oxidising capacity of the atmosphere, translating into radiative forcings by aerosols, methane, and ozone of different signs. The response of nitrate aerosols to nitrogen oxide reductions is particularly important in determining the sign of the corresponding radiative forcing. Model diversity comes from different modelled lifetimes, different unperturbed baselines, and different numbers of species and radiative forcing mechanisms represented. The strength of the aerosol-chemistry coupling is also diverse, translating into aerosol responses to perturbations of ozone precursors of different magnitudes. [ABSTRACT FROM AUTHOR]

Dedicated model simulations by four general circulation and chemistry-transport models are used to establish a matrix of specific radiative forcing, defined as the radiative forcing per unit change in mass emitted, as a function of the near-term climate forcer emitted, its source region, and the season of emission. Emissions of eight near-term climate forcers are reduced: sulphur dioxide, the precursor to sulphate aerosols; black carbon aerosols; organic carbon aerosols; ammonia, a precursor to nitrate aerosols; methane; and nitrogen oxides, carbon monoxide, and volatile organic compounds, the precursors to ozone and to secondary organic aerosols. The focus is on two source regions, Europe and East Asia, but the shipping sector and global averages are also included. Emission reductions are applied over two time periods: May-Oct and Nov-Apr. Models generally agree on the sign and ranking of specific radiative forcing for different emitted species, but disagree quantitatively. Black carbon aerosols, methane, and carbon monoxide exert positive specific radiative forcings. Black carbon exerts the strongest specific radiative forcing, even after accounting for rapid adjustments from the semi-direct effect, and is most efficient in local summer. However, although methane and carbon monoxide are less efficient in a specific sense, the potential for decreasing the mass emitted is larger. Organic carbon aerosols, sulphur dioxide, ammonia, and emissions by the shipping sector exert negative specific radiative forcings, with local summer emission changes being again more efficient. Ammonia is notable for its weak specific radiative forcing. For aerosols, specific radiative forcing exerted by European emissions is stronger than for East Asia, because the European baseline is less polluted. Radiative forcing of European and East Asian emission reductions is mainly exerted in the mid-latitudes of the Northern Hemisphere, but atmospheric transport yields sizeable radiative forcings in neighbouring regions, such as the Arctic. Models disagree on the sign of the net radiative forcing exerted by reductions in the emissions of nitrogen oxides and volatile organic compounds, because those reductions trigger complex changes in the oxidising capacity of the atmosphere, translating into radiative forcings by aerosols, methane, and ozone of different signs. The response of nitrate aerosols to nitrogen oxide reductions is particularly important in determining the sign of the corresponding radiative forcing. Model diversity comes from different modelled lifetimes, different unperturbed baselines, and different numbers of species and radiative forcing mechanisms represented. The strength of the aerosol-chemistry coupling is also diverse, translating into aerosol responses to perturbations of ozone precursors of different magnitudes. [ABSTRACT FROM AUTHOR]