1. Introduction

Mitigating emissions of gases and particles inducing climate change is an imperative to limit the effects of global warming. Most important is the greenhouse gas CO₂. According to IPCCs Sixth Assessment Report urgent near-term actions will slow global warming and “secure a livable and sustainable future for all” (IPCC, 2023). In addition to the climate change urgency, the same sources cause emissions of gases and particles often referred to as air pollutants. These emissions are globally the main drivers of illness and mortality due to non-communicative diseases (Health Effects Institute, 2024). Studies show that the annual effect of air pollution on current global welfare loss has been estimated from $4.6 trillion to $5.11 trillion (Peszko et al. 2023) and ~7–8 million people die prematurely each year due to air pollution (Mathew et al. 2024; Health Effects Institute, 2024). Even though air pollution problems are more severe in other regions they still cause problems in the pan-European region, despite much progress since the peak pollution years of the 1970s and 1980s. In 2018, for example, some 417,000 premature fatalities per year occurred in Europe due to fine particu­late matter in ambient air (European Environment Agency, 2020). In Sweden the number of fatalities directly linked to exposure to fine particulate matter is estimated to some 4,700 in 2015 and in addition the number of fatalities linked to vehicle exhaust is estimated to 2,850 (Gustafsson et al. 2018). For the other Nordic countries, the corresponding number is 2,600–3,500 for Denmark, 1,500-1,900 for Finland, 60-70 for Iceland, and 1,400–2,100 for Norway (Lehtomäki et al. 2020). In addition, a recent study shows that Oslo is the Nordic capital with the worst air quality (Soares et al. 2023).

Emissions of several air pollutants are identified to have short term and regionally varied impact on climate change. In general, fine particulate matter in ambient air (PM2.5), including secondary particles like Sulphur aerosols as well as coarser fractions of particulate matter contribute negatively to the radiative forcing of the climate system, while some sub-fractions of PM2.5 like black carbon (BC) as well as tropospheric ozone increase the radiative forcing. Ozone (O₃) is a secondary pollutant formed in the troposphere from emissions of nitrogen oxides (NO_x), methane (CH₄), as well as non-methane volatile organic compounds (NMVOC). On a global scale, today’s atmospheric concentration of particulate matter (including Sulphur aerosols) currently counteracts (masks) global warming to an extent corresponding to a radiative forcing (RF) of -0.9 Watt/m². Current CO₂ concentrations have an RF of ~1.82 W/m². The global average for particulate matter does however hide large regional variation, and the impact of the aerosol components varies (Myhre et al. 2013). As an example, Bond et al. (2013) find that the global average direct RF of BC is 0.9 W/m², with indirect effects adding more unquantified warming. This number has later been revised down to 0.4 W/m² (Myhre et al. 2013) and 0.11 W/m² (Szopa et al. 2021). Emissions that act as ozone precursors currently cause an RF of 0.5 W/m² (Myhre et al. 2013).

The air pollutant gaining most attention recently for its impact on climate change is BC, a soot sub-fraction of PM2.5. One ton BC of emissions is considered to have an impact on radiative forcing equivalent to 120–3,200 ton of CO₂ emissions, dependent on climate metric (Myhre et al. 2013). Recent estimates downplay the climate importance of particles (Szopa et al. 2021) but is yet not specified what this implies for climate metric values. Climate change impact has been identified for all the above presented air pollutants, as well as for the effect of CH₄ emissions on ozone formation (Etminan et al. 2016).

Air pollutants emitted from natural systems and anthropogenic sources with effects on climate change are usually referred to as short-term climate forcers (SLCFs) (Szopa et al. 2021), although other terms such as short-lived climate pollutants and near-term climate forcers can also be found in the literature. SLCF include pollutants such as black carbon, methane (CH₄), tropospheric ozone, and fluorinated gases such as hydrofluorocarbons (HFCs) (Szopa et al. 2021).

Control of SLCF emissions has been calculated to enable a reduction in the speed of global warming, contingent that CO₂ emissions are reduced (D. Shindell et al. 2012; Bowerman et al. 2013; Shoemaker et al. 2013). Even without CO₂ emission reduction, fast reduction of SLCF emissions, particularly hydrofluorocarbons (HFCs), methane, and black carbon can reduce global warming with up to 0.6 °C by 2050 (Sun et al. 2022).

However, the generalization of SLCF impacts is not straightforward. The impacts have a regional nature (Borgar Aamaas et al. 2016) and can be located in other regions than the emission source region (Acosta Navarro et al. 2016).

There is an increased global recognition of the importance of addressing SLCF in global mitigation programs and policies. However, most current air pollution policies and regulations fall short in integrating the climate and pollution challenges of SLCF emissions into a common policy framework, although there is emerging work emphasising this need in different sectors (e.g. the agricultural sector, cf. Valinia et al. (2024)). Poorly designed policies have been linked to a temporary increase in air pollution emissions. An example is policies that drive up fuel prices, which in some cases have been observed to discourage operation of technologies used to control air pollution (Peszko et al. 2023). Even if integrated policies are yet to be implemented, there are several known technologies and other solutions that can reduce both air pollution and radiative forcing from SLCFs. IPCC highlights several measures with inter alia: “implementation of energy efficiency measures, methane capture and recovery from solid-waste management and the oil and gas industry, zero-emissions vehicles, efficient and clean stoves for heating and cooking, filtering of soot (particulate matter) for diesel vehicles, cleaner brick-kiln technology, practices that reduce burning of agricultural waste (super), as well as the eradication of burning of kerosene for lighting"  (Szopa et al. 2021). Other studies highlight air pollution solutions that accentuate PM2.5 emission reductions from sources that are especially BC-intensive, thus enabling co-benefits between human health and climate change (UNECE, 2021). Overall, the general message from applied research is that: “climate and air pollution policies should be developed in an integrated manner. This will ideally enable win-win policies between human health and climate change, and at worst mitigate the risk of mitigating one problem whilst aggravating another” (Peszko et al. 2023).

Air pollution governance has since long been aided by valuing external costs of pollution in monetary terms (monetization), since this allows both the market mechanism to self-adjust via environmental taxes and fees, as well as provides identification of weighing costs against benefits with air pollution control. Further, monetization of external costs of pollution provides an easy way of communicating environmental challenges with finance departments in governments and companies. But as stated above, effects on climate change are hitherto rarely included in the monetization of the externalities of air pollution. To help the development of integrated air pollution policies it is therefore useful to monetize not only the effect on air quality, but also effects on climate change. The effects are however uncertain, and variable dependent on region and time-of-year, so uncertainty estimates are needed to ensure robustness in policy advice from monetization.

Few studies have presented monetized estimates of the climate change effects of SLCF emissions in a manner consistent with the monetized estimates of the health effects of air pollution. D. T. Shindell (2015) concludes that mitigation of emissions affecting climate change should target a broad range of emissions affecting climate change, not only CO₂. The illustrative calculations of the environmental damages of "atmospheric release" is in Shindell estimated to $330-970 billion per year for electricity generation in the United States. Åström and Källmark (2023) proposed unit costs of certain of the air pollutants and compared with external costs on human health for selected countries. However, no study has made an assessment of the combined social externalities of CO₂ emissions and air pollution emissions or made national-scale analysis. Correspondingly, little is known about the current and future total external costs of air pollution acting as SLCFs and other greenhouse gas emissions.

In this report, we present the results from a project aimed to fill at least some of the gaps in the literature. In the project we have studied current and future damage costs of Nordic emissions of greenhouse gases and SLCFs. To maximise the policy relevance of our results we have based our scenario analysis on the emission forecasts and scenarios reported from the Nordic countries to the EU and UNFCCC, as well as on the latest policy scenarios under discussion at the UNECE Air Convention, in which all the Nordic countries are parties. In addition, the project has strived to analyse and present the key remaining uncertainties of importance for Nordic policy makers engaged in air pollution and climate change policies informed by monetization of emissions.

The emissions considered SO2, NOx, PM2.5, BC, OC, and other non-carbon PM2.5 emissions (PM_other). Since HFC6-emissions are of little or no concern for impacts related to air pollution, the work excludes HFC from the analysis.