National and international human rights laws are too limited in scope to fully address L&D. This is because climate change responsibilities and harms are geographically split. Most greenhouse gas emissions take place in industrialised nations, whereas most L&D affects individuals in the least developed or developing states. Human rights protection may reduce the harm caused to particular communities, including through adaptation measures, but its effectivity largely depends on the resources available to national authorities. Without enhanced support from the international community, the most vulnerable states may have little capacity to effectively protect their populations. This suggests that approaches to address L&D are more likely to take place at an international level.
There are two main sources of international law: customs and treaties (Statute of the International Court of Justice, art. 38(1)). Norms of customary international law are constituted by the general practice of states accepted as law (Statute of the International Court of Justice, art. 38(1)(b)). A treaty is instead an agreement through which two or several states voluntarily commit to comply with certain obligations. When a state fails to respect its international obligations, including obligations stemming from customary international law and treaty law, this state has a secondary obligation to cease the wrongful act and perform its international obligation and to make adequate reparation to any state injured (ILC Articles on Responsibility of States for Internationally Wrongful Acts, arts. 29–31).
Section 7.4.1 examines whether excessive greenhouse gas emissions could constitute a breach of a norm of customary international law—the no-harm principle—and consequently entails an obligation to make reparation for the injury caused to the territory of other states. Section 7.4.2 turns to the treaty-based international climate law regime. Thus, we elude, for the sake of brevity, any discussion of other treaty-based regimes, such as the provisions on pollution of the marine environment contained in the UN Convention on the Law of the Seas or the work of the International Law Commission on the protection of the atmosphere.
7.4.1 The Obligation of States Not to Cause Serious Environmental Harm
The contemporary international legal system is based on the principle that states are equal sovereigns. States could not be equal sovereigns if it was permitted for one state to interfere with the internal affairs of another state in any manner that would seriously affect the latter. Likewise, states would not be genuinely equal sovereigns if one state was permitted to render the territory of another state uninhabitable or otherwise to significantly affect the conditions under which that territory can be used, for instance through causing serious environmental harms across international borders (see Order of 13 December 2013 in the joined proceedings Construction of a Road in Costa Rica along the San Juan River (Nicaragua v. Costa Rica); Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v. Nicaragua), Provisional Measures ICJ Rep 2013, 398).
The no-harm principle, as a corollary of the principle of equal sovereignty, was first recognised in the 1941 arbitral award in the Trail Smelter case. This case concerned a dispute between Canada and the United States over air pollution arising from a smelter in Canada, which was brought by dominant winds towards the US State of Washington, causing serious environmental damages. In an oft-cited passage, the tribunal declared that:
under the principles of international law […] no state has the right to use or permit the use of its territory in such a manner as to cause injury by fumes in or to the territory of another or the properties of persons therein, when the case is of serious consequences and the injury is established by clear and convincing evidence (Trail Smelter Arbitration: 1905).
This principle was confirmed in further decisions of international courts and tribunals (e.g. Corfu Channel, 22; Case concerning the Gabcikovo-Nagymaros Project, para. 53; Case Concerning Pulp Mills on the River Uruguay, paras. 101, 193 [hereinafter: Pulp Mills]). It was also recognised in international declarations (e.g. United Nations Rio Declaration on Environment and Development, principle 2; Declaration of the United Nations Conference on the Human Environment, principle 21; UNGA Res. 2996 (XXVII)) and, although less systematically, in treaties, including a mention in the preamble to the UN Framework Convention on Climate Change. In the Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, the International Court of Justice recognised
the general obligation of States to ensure that activities within their jurisdiction and control respect the environment of other States or of areas beyond national control is now part of the corpus of international law relating to the environment (para 29).
The no-harm principle requires states to refrain from engaging in activities which would cause significant transboundary harm and to prevent persons or entities within its jurisdiction to carry out such activities. Beyond this general understanding, the modalities of the no-harm principle are debated. As with any customary norm, it is difficult to establish the exact scope of this duty to prevent significant transboundary harm. In its previous cases, the ICJ has clarified little the content of the duty to prevent significant transboundary harm. Generally, it has been understood as one of due diligence (Pulp Mills, para 101; ILC 2001:154, para. 7). This means that a state is required to act in a way that can be expected from a “good government” (ILC 2001: 155, para. 17) and to exert its best efforts to minimise the risk of significant transboundary harm (ILC 2001: 154, para. 7). As such, the no-harm principle is an obligation of conduct, not of result. Thus, a state is not responsible for harm that occurs despite its reasonable efforts to prevent it or—in case that it is not possible—to minimise the risk. The International Law Commission has acknowledged in its work on the Articles on the Prevention of Transboundary Harm from Hazardous Activities that a different degree of care is expected from states with fewer capacities and economic difficulties (ILC 2001:155, para. 17). When applying this criterion to climate change, it must also be kept in mind that treaties may contribute in different ways to the development of customary international law. Despite the continuing work of the ILC on the role of treaties in identifying customary international law (see e.g. Wood 2015: 14 ff), there remain fundamental uncertainties on how the multilateral environmental agreements shape, crystallise and form the content of customary international law.
State practice and cases where the no-harm rule was invoked generally dealt with activities at or around a shared border. These activities included for instance emitting toxic fumes that caused damages in the woods of the neighbouring state, dredging in a shared river and altering its waters (e.g. Lac Lanoux Arbitration) or else polluting it through mills (e.g. Pulp Mills) or construction activities close to it. This raises the question whether the no-harm principle is applicable to climate change.
Climate change differs from most aforementioned cases in at least three pivotal points. Firstly, damages from climate change result not from a single activity of a state but of its reliance on fossil fuels as an economic motor, i.e. from many activities. Secondly, damages from climate change results not from the conduct of a single state but from the concomitant conduct of multiple states, with the resulting harm not confined to a single state but affecting virtually all states. Thirdly and relatedly, the harm results not from any particular activity, but from an accumulation of activities over decades.
For these reasons, in the 1990s, the International Law Commission excluded phenomena such as creeping pollution and pollution deriving from ordinary economic activities from its work on the Articles on the Prevention of Transboundary Harm from Hazardous Activities (Rao 2000:9). The International Law Commission considered these situations too complex, and possibly too politically sensitive, to make statements about their legal nature. Although the Articles are not binding as such and do not reflect existing customary international law in their entirety, this is indicative of the difficulty of applying the no-harm principle to new situations.
The multiplicity of states contributing to climate change and impacted by its consequences at least complicates the application of the no-harm rule. Scholars have questioned the applicability of the no-harm principle to circumstances where harm is caused not directly by a single source, but by multiple diffuse sources over a long period of time, which accumulate and result in harm (Zahar 2014; Okawa 2010:307; Scovazzi 2001:61). Most cases before the international courts and tribunals are decided over situations where a single activity caused harm to another state. Environmental harm accruing because of the conduct of multiple states was discussed in the pleadings before the ICJ in one case. In their submissions on the Legality of the Threat or Use of Nuclear Weapons, some states raised concerns with the possibility that the repeated use of nuclear weapons over a relatively short span of time would create a “nuclear winter”—a cataclysmic upheaval of the climate system which could wipe out most of life on our planet (Mexico 1995, para 65; Egypt 1995, para 32; Ecuador, para D). When mentioning that the damages caused by nuclear weapons could not “be contained in either space or time” and had “the potential to destroy all civilization and the entire ecosystem of the planet,” (Legality of the Threat or Use of Nuclear Weapons, para. 35) the International Court of Justice made no distinction between mediated damages and damages caused by cumulative causation but implied that the no-harm principle applied equally to both (see also Dissenting Opinion of Judge Weeramantry: 456–458; Mayer 2015:8).
If there is indeed an obligation for states not to cause transboundary environmental harms through greenhouse gas emissions, its modalities remain ill-defined (see also Mayer 2016b, 2018a). In particular, the scope of the no-harm principle is ill-determined. In general, the duty to prevent significant harm exists whenever a state has or should have been able to foresee the risk of harm. Unfortunately, there is no interpretation of these modalities of the no-harm principle by the International Court of Justice or sufficient clarification through the work of the International Law Commission. However, it appears possible to assume that a state must have had at least some scientific hints of the impacts of greenhouse gas emissions. Thus, the historical failure of a state to prevent activities generating excessive greenhouse gas emissions does not constitute a breach of the no-harm rule until at least some scientific evidence suggested that they may have a serious impact on the climate system. It is also unclear to what extent a state must have been able to foresee the specific damage that might occur. Very few cases involving indeterminate damage have been decided by international courts and tribunals. In the Naulilaa case, an Arbitral Panel held that Germany should have anticipated that its attack on some Portuguese colonies would likely expose Portugal to further turmoil in an unstable colonial context, although Germany could not have foreseen the nature and extent of the turmoil that unfolded. On this basis, the Panel condemned Germany to the payment of an “equitable additional compensation” established ex aequo et bono (Responsabilité de l’ Allemagne à raison des dommages causés dans les colonies portugaises du sud de l’Afrique: 1032-3).
Another area of uncertainty exists with regards to the stringency of the due diligence obligation of states under the no-harm principle. The International Court of Justice held that in order to fulfil its obligation to exercise due diligence in preventing significant transboundary environmental harm, a state must carry out an environmental impact assessment when there is a risk of such harm and, if the risk of significant transboundary harm is confirmed, notify and consult with any states potentially affected (see e.g. Certain Activities and Construction of a Road, paras. 104, 168). Where a state has acted in due diligence to prevent significant transboundary harm, it cannot be made responsible for harm that occurs nonetheless, in which case a state has to prevent further damages. This, however, does not result in a right for a state to veto an activity conducted in another state. Notably, in relation to environmental matters, the ICJ has often put emphasis on procedure, including the obligation to conduct an environmental impact assessment, rather than substantive obligations to refrain from a certain conduct. However, it is reasonable to assume that a state must ultimately refrain from certain activities if that is the only way to prevent significant harm. Nevertheless, the question of the actual content of the no-harm rule, especially in the context of climate change where procedural processes such as consulting with all potentially affected states is often unhelpful, will remain difficult to be answered.
States certainly are not under an obligation to stop all greenhouse gas emissions at once (see e.g. Voigt 2015:162). The scope of their due diligence obligation depends on their capacity. The obligation of all states under the no-harm principle is one of employing all their best efforts to limit and reduce greenhouse gas emissions from activities within their jurisdiction in order to prevent and minimise injurious effects on other states. In any event, the question whether a state has fulfilled its obligations of due diligence must be assessed in the light of the specific circumstances and the norms of customary international law emerging from the general practice of states accepted as law (see e.g. Certain Activities carried out by Nicaragua in the Border Area, Separate Opinion of Judge Donoghue, para. 10). Especially, the extent to which efforts of economic growth shape the understanding of due diligence remains unclear and should be further researched within the concept of sustainable development.
Thus, there remain many difficulties in defining the modalities of application of the no-harm principle in relation to climate change. Some authors such as Verheyen (2005: 146) conclude that the vagueness of the customary no-harm rule provides for space for interpretation. Certainly, only an authoritative interpretation by an international court or tribunal, or possibly by the International Law Commission, could help disentangling the debates. In 2013, the International Law Commission has initiated a project on the protection of the atmosphere, which could possibly address the issue of climate change.
7.4.2 State Responsibility Following a Breach of the No-Harm Principle
The breach of an obligation is to be sanctioned for a legal system to be meaningful. Accordingly, it is a well-established principle of customary international law that a state whose conduct breaches its international obligation commits an internationally wrongful act entailing its international responsibility (ILC Articles on the Responsibility of States for Internationally Wrongful Acts, art. 1 and 2). Whereas the above section discusses whether and under which assumptions greenhouse gas emissions could amount to a breach of the no-harm rule, this section will look at the legal consequences resulting from these emissions, based on the hypothetical premise that they constitute an internationally wrongful act. It is important to bear in mind that certain questions, such as foreseeability and multiplicity of actors, are problematic not only concerning the characterisation of a state conduct as an internationally wrongful act, but also to assess whether any particular state is responsible for it.
State responsibility involves two main legal consequences: the continued duty of performance—which involves the obligation to cease a continuing internationally wrongful act—and the obligation to make reparation for any injury (ibid, art. 28–39). The obligations following a breach of the no-harm rule depends on the content of this obligation in the context of climate change, which is difficult to determine. As a consequence of the continued duty of performance, states would have to cease these emissions that are considered an internationally wrongful act. Of greater importance to the present discussion is the other consequence involved by the international responsibility of a state, namely, the obligation to make good for any injury caused by the internationally wrongful act. This obligation is generally analysed by reference to the judgment of the Permanent Court of International Justice in the case of the Factory at Chorzów, according to which “reparation must, as far as possible, wipe out all the consequences of the illegal act and re-establish the situation which would, in all probability, have existed if that act had not been committed” (at 47). Accordingly, the International Law Commission concluded that “[f]ull reparation for the injury caused by the internationally wrongful act shall take the form of restitution, compensation and satisfaction, either singly or in combination” (ILC Articles on the Responsibility of States for Internationally Wrongful Acts, art. 34). “Full reparation” is understood as reparation for the full value of the injury. Restitution consists often in returning something wrongfully taken, whereas compensation—in practice the most common form of reparation—is the payment of the financial value of something that cannot be returned or other damage done. Satisfaction relates to measures such as apologies, usually limited to reparation for symbolic harms.
For a claim for reparation to be successful, it is, presumably, necessary to establish that an activity has caused harm in a way that the harm would not have occurred without the activity. The causal link between greenhouse gas emissions and its adverse impacts is a long and complex one, which will make this argument difficult to establish. Yet, the law of state responsibility appears slightly more flexible in this regard than many national legal systems. Rather than a strict limitation to the “direct” consequence, injury in international law is extended to any consequence unless it is “too indirect, remote, and uncertain to be appraised” (Trail Smelter Arbitration: 1931; ILC 2001: 92, para. 10). Assessing the value of the injury on the basis of which compensation should be paid would however face many difficulties. Particular damages would have to be attributed to climate change in abstraction from the multitude of natural or social processes in which they unfold. Things that have no inherent economic value (e.g. human lives, health, culture, ecosystems) would have to be given one (see chapter by Serdeczny 2018). The value of future harms would need to be discounted at an arbitrary rate. Responsibility would then need to be allocated among states on the basis of their respective share of the wrongdoing, despite the indeterminacy of the threshold beyond which greenhouse gas emissions become excessive and wrongful and the contribution of the injured state to its damages (see e.g. Reis 2011:183). This would lead to never-ending controversies, nullifying the role of international law in settling international disputes through pacific means.
However, such a perilous analysis may not be necessary. When concluding that responsibility for an internationally wrongful act involves an obligation to make “full reparation,” the International Law Commission referred to the usual practice of international courts and tribunals dealing with relatively small quantum of damages (ILC 2000: 2). Like in the Naulilaa case (Responsabilité de l’ Allemagne à raison des dommages causés dans les colonies portugaises du sud de l’Afrique), larger injuries—such as reparations for wars and other mass atrocities, for unlawful trade measures, for nation-wide expropriation programs or for hazardous activities—have never led to full reparation, but rather to an agreement on lump-sum compensation. Relevant judicial decisions or international negotiations considered the capacity of the responsible state to pay, the need of the injured parties for reparation, the possible disproportion of the injury to the “culpability” of the responsible state, and the limits of the fundaments for a collective responsibility (Mayer 2017; Eritrea-Ethiopia Claims Commission:522, para. 22; Mayer 2016a). The International Law Commission has promoted in its work on the allocation of loss in the case of transboundary harm arising out of hazardous activities an approach to balance the interests of the responsible and the injured party (ILC 2006: 58ff).
7.4.3 Relationship Between the Climate Regime and the No-Harm Principle
A possible objection to the reasoning presented in this section relates to the existence of a treaty-based international climate law regime. Some scholars argued that the UN Framework Convention on Climate Change and following treaties as well as decisions adopted by the Conference of the Parties precluded the application of norms of international law such as the no-harm principle and the law of state responsibility for L&D (see Zahar 2015).
Such an argument would have to be based on the doctrine of lex specialis (“special law”). This notion prescribes that a more specific rule prevails over a general one. However, this is only the case when there is an actual norm conflict between the two rules. In this context, the International Law Commission stated that for the lex specialis doctrine to apply, “it is not enough that the same subject matter is dealt with by two provisions; there must be some actual inconsistency between them, or else a discernible intention that one provision is to exclude the other” (ILC 2001:140; see also Mavrommatis Palestine Concessions: 31). Absent such actual inconsistency or discernible intention to exclude the more general rule, both rules should be “be interpreted so as to give rise to a single set of compatible obligations” (ILC 2006:178).
There is certainly no ground to believe that states, as a whole, intended to exclude the application of the no-harm rule when establishing the international climate law regime. Similarly, inconsistencies between the climate regime and the customary no-harm rule do not necessarily arise (Mayer 2014; Verheyen 2005). The ultimate objective of the UNFCCC, to “prevent dangerous anthropogenic interference with the climate system” (UNFCCC, art. 2), is certainly not inconsistent with the no-harm principle, and the specific commitments made by states under successive international climate agreements do not exclude the existence of more demanding obligations under customary international law. The obligation to prevent significant transboundary harm, insofar as it may apply to emissions of greenhouse gases, should thus be interpreted consistently with the climate regime “so as to give rise to a single set of compatible obligations” (ILC 2006a, para. 4). Hence, the commitments entered into through the climate regime do not replace the no-harm rule—and vice versa –but both simultaneously work towards bringing states closer to compliance with their obligations arising under international law (see Mayer 2018b). In this regard a number of vulnerable states have made several statements emphasising that successive international climate change agreements do not in principle derogate the application of principles of general international law (see e.g. Declarations of Kiribati, Fiji, and Nauru upon signature of the UNFCCC and other declarations upon signature of the Paris Agreement. Arguably, the customary rule, should it apply and be triggered in the context of climate change, requires efforts that go beyond that of the climate regime in so far as those are not sufficient to actually prevent harm.