24.1 Introduction

Almost the entire world’s population breathes unsafe air that threatens their health and degrades the environment. Many urban areas are regularly found to have illegally high levels of air pollutants (WHO 2021). Since pre-industrial times, the global concentration of aerosol particles in the atmosphere has more than doubled and air pollution has been identified as the single largest environmental health risk by the World Health Organisation (Tsigaridis et al. Reference Tsigaridis, Krol and Dentener2006: 5143; WHO 2021). Their harmful impacts on human health and the environment have justified the inclusion of ‘atmospheric aerosol loading’ as one of the nine planetary boundaries, the scientific framework designed by Rockström and his co-authors to identify the processes that regulate the stability of the Earth system and set safe operating conditions for a healthy planet (Reference Rockström, Steffen and Noone2009: 17).

The essay identifies selected ethical issues posed by the global governance of air pollution, using the planetary boundaries framework as a conceptual tool. An analysis of legal systems and institutions in the context of the planetary boundaries framework is essential because law, as a regulatory institution, could set limits on human behaviour and thus keep us within planetary boundaries (Chapron Reference Chapron, Epstein and Trouwborst2017; Kotzé & French Reference Kotzé, French, French and Kotzé2021). In addition, law has an intimate and complex relationship with justice and can offer insights into how to design safe but also just boundaries (see Gupta et al. Reference Gupta, Liverman and Prodani2023). Notably, the refined framework, drawn by Rockström et al. and renamed ‘Earth system boundaries’, features an aerosol loading boundary that considers the safety of the Earth system and also accounts for human well-being, considering variations in the harmful effects of aerosols on human health across countries, communities, and generations (Reference Rockström, Gupta and Qin2023).

A detailed mapping of the legal instruments available to protect the atmospheric aerosol loading boundary has shown that they are inadequate to respond to the scale of the challenge (Duvic-Paoli & Webster Reference Duvic-Paoli, Webster, French and Kotzé2021), thus unable to mitigate increasing risks of planetary destabilization. On this basis, the essay aims to shed light on the ethical implications of the legal governance of air pollution facing decision-makers in search of fair, equitable, and effective solutions to keep atmospheric aerosol loading within safe limits.

As a result of the failure of environmental law to respond to the challenges of the Anthropocene era, legal scholarship is becoming more vocal about the need for a fundamental paradigm shift in how law operates (see Adelman Reference Adelman, French and Kotzé2021: 75). A line of criticism has been that environmental law operates in an ethical vacuum that has prevented it from addressing fundamental questions of vulnerability, equity, and fairness. The emphasis of legal positivism on the law as it stands, rather than as it should be, has been criticized for separating law from ethics and discouraging an ethical examination of existing norms (Voigt Reference Voigt2005: 123–124). An evaluation of the law regulating air pollution can therefore offer insightful lessons for the field: it raises multiple ethical questions, ranging from how legal systems can be designed to protect particularly vulnerable communities from the health impacts of air pollution, to whether it is legitimate to rely on global norms, often representative of the interests of powerful countries, to govern localized impacts.

In order to explore the ethical implications of global air governance, the essay uses the planetary boundaries framework as a conceptual tool. The framework proposes quantitative boundaries within which humankind can operate in a stable Earth system, and beyond which the risk of large-scale and irreversible environmental damage is likely. It offers scientifically based thresholds for decision-makers to design sustainable systems and has become a useful concept for legal scholars to imagine new solutions to overcome the ongoing inability of legal systems to mitigate environmental degradation (Kotzé & French Reference Kotzé, French, French and Kotzé2021: 7–8).

The essay proceeds as follows: it sets the scene with a brief overview of how law regulates the problem of atmospheric aerosol loading (Section 24.2). It then moves to identify three central ethical questions that decision-makers must confront when regulating air pollution – related to why govern, how to govern, and where to govern. It uses the planetary boundaries framework as a conceptual lens to explore the ethical implications behind the motivations driving air quality governance (Section 24.3), the framing of a multifaceted environmental problem (Section 24.4), and the global governance of multi-scale impacts (Section 24.5). In doing so, the essay reflects on how the design of more ethically oriented legal systems can enhance environmental law’s response to planetary problems.

24.2 Legal Protection of the Atmospheric Aerosol Loading Planetary Boundary

Before evaluating the ethical questions carried by the planetary boundaries framework, the essay starts with a brief description of legal responses to the problem of atmospheric aerosol loading.

Global cooperation on air pollution has increased in recent years, as evidenced by explicit references to air quality in UN Environment Assembly resolutions (2016, 2018), and in the 2015 Sustainable Development Goals (UNGA 2015: 11.6 and 3.9). However, responses to the problem have not been unified: no global legally binding instrument exists on air pollution, contrary to the international treaties governing climate change (UNFCCC 1992) or biodiversity (CBD 1992).

Instead, global governance on air pollution is fragmented; it is regulated by a multiplicity of legal instruments, each limited materially and/or geographically. This reality is ill-suited to the logic of the planetary boundary that portrays each environmental problem as a coherent and self-contained ensemble. However, a comprehensive mapping of the instruments available to ensure that safe thresholds are not exceeded reveals substantial gaps in the governance of the planetary boundary (Duvic-Paoli & Webster Reference Duvic-Paoli, Webster, French and Kotzé2021). Indeed, instruments relevant to the planetary boundary have restrictive mandates to regulate specific air pollutants or polluting industries (such as aviation or shipping). They are also spatially fragmented, as air pollution is governed through a patchwork of regional frameworks, each differing widely in terms of their maturity and effectiveness. Most regional air pollution frameworks lack legally binding mandates; instead, they operate either as scientific projects (such as the Acid Deposition Monitoring Network in East Asia) or as political networks (such as the Southern African Development Community Regional Policy Framework on Air Pollution). This is explained by the fact that, in relation to air pollution, states generally prefer instruments that facilitate multilateral cooperation while preserving national discretion and accommodating regional differences. However, the general lack of regulatory ambition means that existing multilateral instruments and institutions for the governance of air quality are insufficient to be transformational.

An important exception is the Convention on Long-Range Transboundary Air Pollution (CLRTAP), a sophisticated regional treaty adopted in 1979 under the auspices of the UN Economic Commission for Europe (UNECE 1979). Through an advanced web of eight protocols, the CLRTAP regime regulates different sources of pollution (fixed, mobile, new, existing), different types of pollutants (sulphur dioxide, nitrogen oxides, volatile organic compounds, heavy metals, persistent organic pollutants), and mitigates various environmental problems (acidification, eutrophication, tropospheric ozone). The Convention has been remarkably successful at reducing emissions of air pollutants by 40–80 per cent since 1990 in Europe (UNECE 2019: 3). The decrease in sulphur emissions by at least 80 per cent is noteworthy, although nitrogen emissions remain high (UNECE 2019: 3). The Convention illustrates the positive role that international law can play in improving air quality; however, the scope of the treaty is geographically restricted to Eurasia and North America, which means it cannot adequately accommodate the global scale of the problem as outlined by the planetary boundaries framework.

Now turning to the potential aggregate effect of domestic legislation on the protection of the planetary boundary, it appears to be very limited. Indeed, domestic legislation on air pollution across the world is largely immature. A UN Environment Programme report explains:

Not only is air pollution poorly regulated but even when regulation is in place, it does not guarantee good air quality – in the European Union, for example, member states regularly exceed their legally binding air quality targets (European Environment Agency 2022).

This brief overview of global responses to atmospheric aerosol loading shows that existing legal instruments are inadequate to respond to the scale of the planetary challenge. The question of how to design more effective legal systems is becoming increasingly pressing. In this endeavour, paying attention to the ethical implications of different regulatory interventions is essential to ensure that the measures do not only prevent environmental degradation but do so in a manner that is fair for the communities involved.

24.3 Why Regulate Air Pollution?

The essay now turns to the reasons underpinning the governance of the planetary boundary. Understanding the motivations driving the regulation of an environmental problem is important because they dictate different policy approaches with distinct ethical implications. The planetary boundaries framework justifies the adoption of a boundary on atmospheric aerosol loading on two grounds: the effects of aerosols on (1) health, as a major cause of disease and death globally; and (2) the environment, including on ecosystems, cloud formation, weather patterns, and the climate (Rockström et al. Reference Rockström, Steffen and Noone2009: 17).

The justification aligns with the largely anthropocentric reasons used to substantiate political action on air pollution internationally. The harm done by air pollution to human health, leading the World Health Organisation to declare air pollution a ‘silent public health emergency’ (Ghebreyesus Reference Ghebreyesus2018), is the primary reason for regulatory interventions on air quality. Combined ambient and household air pollution contributes to around eight million premature deaths each year globally from increased mortality from stroke, heart disease, chronic obstructive pulmonary disease, lung cancer, and acute respiratory infections. This burden of disease is deemed to exceed the burdens of malaria, tuberculosis, and AIDS combined (WHO n.d.).

The motivations driving decision-makers for acting upon a policy problem have fundamental consequences on legal design. Notably, when the main objective is to tackle air pollution to protect human health, then ambient air quality standards are used to set limit values below which aerosol concentrations are considered safe and acceptable in terms of their effects on human health. The level of concern regarding the human health impacts of aerosols determines the extent to which regulatory interventions protect communities most sensitive to air pollution, such as children or the elderly. Alternatively, it can be considered acceptable to compromise the health of vulnerable communities to pursue other public policy objectives related to the development of air polluting activities, such as transportation or agriculture (see Lovett Reference Lovett2012). Similarly, taking action in the context of scientific complexity and uncertainty – the atmospheric aerosol loading was one of only two boundaries that could not initially be quantified (Rockström et al. Reference Rockström, Steffen and Noone2009: 18) – raises difficult ethical choices about whether, and if so how, to protect human health from uncertain risks without compromising human development and well-being associated with aerosol-producing activities. In other words, how should agricultural activities be regulated when the health consequences of resulting atmospheric aerosols are difficult to quantify, and restrictions might impact access to healthy and affordable food?

Another difficulty relates to the fact that the raison d’être of the planetary boundary is dual, to protect human well-being while maintaining planetary stability. And yet, the two are not necessarily aligned: indeed, air quality standards aimed at protecting human health, especially when set low, do not necessarily avoid environmental harm and stricter air quality targets can, at times, be needed to prevent the environmental consequences of atmospheric aerosol loading. To do so, one commonly used tool is that of ‘critical load’ found, for instance, in the CLRTAP Protocol to Abate Acidification, Eutrophication and Ground-level Ozone (UNECE 1999). It assesses the effects of air pollutants on ecosystems, working out their tolerance to air pollution before damage becomes irreversible. However, as mentioned earlier, higher levels of protection can negatively impact human well-being in other ways and environmentally based motivations tend to have lower traction as the benefits of regulation are less directly visible and are more difficult to be quantified. In addition, Rockström et al.’s framework for safe and just boundaries suggests that considerations over societal fairness might require higher levels of regulatory interventions, even in cases when we remain in a safe operating space from an ecological, as well as potentially a human health, perspective (Reference Rockström, Gupta and Qin2023: 7).

24.4 How to Frame the Air Pollution Problem?

The essay moves to explore the framing of the air pollution problem, showing how varying understandings of the origins and nature of the problem carry different ethical implications in the context of law-making.

The planetary boundaries framework is generally praised for offering a simple, yet powerful conceptualization of environmental thresholds able to reach beyond the scientific community and capture the imagination of decision-makers (Biermann & Kim Reference Biermann and Kim2020: 513). The inclusion of a stand-alone boundary on aerosols has the advantage of putting air pollution on the same level as other environmental problems, such as climate change or biodiversity loss, for which political awareness is higher. The clarity of the message is, however, weakened by the reference to the technical term of ‘aerosol loading’ to describe what is more commonly known as air pollution (that includes, but is not limited to, aerosol loading).

The planetary boundaries framework presents its environmental thresholds as scientifically determined and, hence, objective. The role of decision-makers is framed as being responsible for a transgression of the boundaries, but no guidance is offered on how this can be achieved (Biermann & Kim Reference Biermann and Kim2020: 503–504). Lawmakers are faced with the complex task of designing measures regulating the multiple activities and actors responsible for air pollution. Many of the air polluting activities, such as transportation and industrial activities, are routine activities that are seen to be indispensable to modern life, and, thus, would be difficult to prohibit out right. Standard setting tools that set legal limits on the emission of certain substances are not enough to encourage the transformational changes needed to reduce air pollution at source, that is, to regulate fossil fuel combustion and land-use changes. As such, despite what the planetary boundaries framework might imply, the protection of the atmospheric aerosol loading boundary does not merely rest on technical choices but rather requires complex economic and societal transformations.

Moreover, identifying the origins of air pollution is not a neutral exercise and rather carries major ethical implications due to the multiple sources of atmospheric aerosol loading. Jasanoff revealed that ‘the finger of blame often points downward – toward the deficient practices of poor, local communities’ (Reference Jasanoff2018: 11). She explained that the pollution in Delhi is due to the annual burning of crop stubble by farmers who are too poor to clear their fields for replanting by less polluting means; but instead of helping farmers buy the equipment they need, states prohibit polluting activities that continue nevertheless due to a lack of affordable alternatives. As a result, legal interventions, often adopting a command-and-control approach that sets specific emission reduction targets, generally fail to incentivize and support transitions to less polluting methods. They also tend to be ineffective because compliance with rules perceived to be unjust and unpractical is generally low.

A final comment related to the framing of the air pollution problem relates to its interactions with other environmental problems. The planetary boundaries framework presents aerosol loading as a self-standing problem operating in isolation from other environmental problems, and interactions between the different boundaries are scientifically difficult to quantify (Richardson et al. Reference Richardson, Steffen and Lucht2023: 2–3). And yet, air pollution is not a self-contained problem; it is closely related to pesticide use, oceanic pollution, waste management, and climate change. As a result, regulatory interventions on air quality can have a positive impact on other environmental problems. But the opposite is also true, and, in this case, complex trade-offs need to be considered. Notably, a reduction in emissions of sulphur dioxide carries destabilizing risks for the climate because they tend to cool the climate (IPCC 2022: C.2.3). Under these circumstances, a major intergenerational equity dilemma emerges as lawmakers must decide whether to prioritize the health of the current generation from the impacts of air pollution over that of future generations that will suffer the climate consequences.

To summarize, the aerosol loading problem has multiple sources, involves various contributing stakeholders, and interacts in complex ways with other environmental problems. But the apparent neutral and narrow framing offered by the planetary boundary logic gives little guidance on how decision-makers should respond to this multifaceted problem and sidelines the ethical implications of regulatory interventions.

24.5 Where to Govern a Multi-Scalar Problem?

A final set of ethical difficulties in the governance of the planetary boundary concerns scale (Lewis Reference Lewis2012). The planetary boundaries framework views the air pollution problem as global, reflecting the intercontinental and regional impacts of atmospheric aerosol loading, but impacts are primarily local. The justifications proposed for the adoption of the atmospheric aerosol loading boundary are paradoxical. On the one hand, the framework approaches aerosol loading as a global challenge; on the other hand, the choice of the boundary is justified in spatially restricted terms, based on regional tipping points (Steffen et al. Reference Steffen, Richardson and Rockström2015: 7; Rockström et al. Reference Rockström, Gupta and Qin2023: 7). The inclusion of atmospheric aerosol loading in the planetary boundaries framework was initially justified by the effects of aerosols on monsoon patterns in Southeast Asia (Rockström et al. Reference Rockström, Steffen and Noone2009: 17), then used as a case study to quantify a regional safe boundary (Steffen et al. Reference Steffen, Richardson and Rockström2015: 5). While scientific advancements have resulted in a preliminary proposal to identify a global threshold beyond which humanity would not be operating within a safe zone (Richardson et al. Reference Richardson, Steffen and Lucht2023: 7–8), it remains to be refined. Indeed, such quantification is complex due to the ‘multiple natural and human-caused sources [of aerosols], differences in chemical composition, seasonality and atmospheric lifetimes, and the consequently very large spatial and temporal heterogeneity in distribution and climatic and ecological impacts of aerosols’ (Richardson et al. Reference Richardson, Steffen and Lucht2023: 7).

The global framing of the planetary boundary, together with its shortcomings, sheds light on the important question of whether air quality can be adequately, and ethically, protected by international law. A first reason for caution relates to the fact that the planetary boundaries framework implicitly reinforces the commonly held idea that air pollution is an outdoor problem and fails to highlight the importance of indoor air quality. Indeed, the planetary boundary logic operates far away from the legal interventions into the intimacy of the home that would be required to, for instance, reduce pollution from the use of open fires and simple stoves. And yet, indoor air quality impacts the health of individuals, and disproportionately vulnerable communities in low- and middle-income countries but is rarely included in air quality legislation globally – only 7 per cent of countries have indoor air quality standards (UNEP 2021a: 9). By framing air pollution as a global and environmental problem, the planetary boundary rationale renders invisible the local and developmental nature of aerosol loading. In turn, this raises the question of whether international law has a role in regulating domestic activities beyond classic collective action problems. If so, does it have sufficient legitimacy to address issues such as indoor pollution, which lie close to individuals’ everyday lives?

Another challenge for global governance is to remain legitimate in the context of a multi-scalar problem. It has been noted that the planetary boundaries framework offers little guidance on ‘how to determine a fair share of the safe operating space and concomitant responsibilities among various actors at multiple levels of governance to stay within this space and to avoid breaching the boundaries’ (Kim & Kotzé Reference Kim and Kotzé2021: 7). Beyond the need to ensure that different scales of governance all work together towards an efficient and just protection of the planetary boundary, the sharing of responsibilities between states at the global level is also an ethical issue. Indeed, imposing identical legal obligations on states when major variations occur depending on the geographic level of industrialization and economic and technological capabilities can appear unfair (Okowa Reference Okowa2000: 6). This is particularly important given that, while the global aerosol loading boundary has not yet been crossed, regional transgressions have been identified (Richardson et al. Reference Richardson, Steffen and Lucht2023: 9).

Past experience in the development of air pollution law suggests that flexible international obligations, tailored to national circumstances, are perceived as fairer. By way of example, the 1985 Helsinki Protocol on the reduction of sulphur emissions adopted a single target, with a common timetable, for all Parties (UNECE 1985); as a result, countries like the United Kingdom and the United States did not join the protocol because it did not account for the particularities of each country. Rather, participation increased, and environmental outcomes were better when states were given the choice of several options about how to reduce their emissions (such as in the 1991 Geneva Protocol on volatile organic compounds (UNECE 1991)), or by setting national emission standards tailored to the circumstances of each state (as in the 1988 Sofia Protocol on nitrogen oxides (UNECE 1988)). Hence, the global lens of the planetary boundaries framework can help increase collective awareness but should not be understood to encourage a uniform approach to the aerosol loading problem; rather, global instruments that accommodate local specificities tend to offer more flexibility and share the burdens of environmental action more fairly.

24.6 Conclusion

The planetary boundaries framework alerted to the scientific limits of the Earth but remained silent on how this should translate in terms of human behaviour. The revised framework, which proposes both safe and just boundaries, emphasizes that safe limits cannot be considered sustainable where resources are unevenly distributed and inequalities high (Rockström et al. Reference Rockström, Gupta and Qin2023). Law, as a regulatory tool designed for social organization, has a critically important role to play to build just societal systems operating within their environmental limits. While a complex web of international treaties, texts, and institutions seeks to mitigate air pollution, it has, so far, been unable to provide an adequate response to protect the planetary boundary. In our search for more efficient legal systems, significant ethical issues ought to be considered.

This essay explored three sets of ethical questions that decision-makers must confront when regulating air pollution. It questioned the motivations underpinning legal responses to air pollution, showing how legal design varies depending on what is deemed worth protecting. It also emphasized the complexity of governing air pollution problem when its sources are multiple, and it reflected on how to reconcile a global focus with the localized impacts of air pollution.

The planetary boundaries framework used as a conceptual tool for legal analysis makes visible essential dilemmas about how to design more efficient and more just legal systems; even its own shortcomings alert us to the complex choices facing decision-makers. Although the planetary boundaries framework initially offered little in terms of guidance on how to prompt radical change, it opens important avenues to craft a viable role for law and governance and build more ethically oriented legal systems to better protect the environment.