(a) An Internationally Wrongful Act
16 The 1996 proposals of the International Law Commission (‘ILC’) for making States strictly liable for significant transboundary harm proved to be too progressive and have been abandoned (see also Title and texts of the preamble and the draft principles on the allocation of loss arising out of hazardous activities adopted by the Drafting Committee on second reading, 2006, 1). Hence, the international liability of a State may only be incurred on the basis of an internationally wrongful act. It is a well-established principle that ‘every internationally wrongful act of a State entails the international responsibility of that State’ (Draft Articles on Responsibility of States for Internationally Wrongful Acts [‘2001 ILC Draft Articles’], 2001, 2). Thus, the responsibility of the State results from the violation of international law, regardless of its consequences. It can be a breach of conventional or customary international law that may be committed through an act or omission. Indeed, the remarkable development of States’ primary obligations is related to both the multiplication and increasing precision of conventional obligations, but also to the strengthening of a foundation made of customary rules. In both respects, the densification of State obligations mechanically increases the potential for litigation. Consequently, the breached primary obligation can be found within the specific climate change legal regime but also in other special regimes and general international law.
17 Treaty law is the main source of obligations in international environmental law, containing more specific obligations than customary law. Depending on the States involved in an international litigation on climate change, the UNFCCC, the Kyoto Protocol, and the Paris Agreement are directly relevant. Whether the UNFCCC imposes legally enforceable obligations is disputed in the literature. The predominant view appears to be that as a framework convention it does not stipulate enforceable primary legal norms of international law, but provides a general framework whose rules lack specificity and are subject to the treaty’s compliance procedures only (Schwarte and Byrne, 2010, 1). Regarding the reduction of GHG emissions, the most specific provision, Article 4 (2) UNFCCC, provides that Parties ‘shall adopt national policies and take corresponding measures on the mitigation of climate change, by limiting its anthropogenic emissions of greenhouse gases’. Although vague, this provision ‘stipulate[s] a commitment’ and ‘arguably could be the basis of a liability claim’ (Faure and Nollkaemper, 2007, 123; Voigt, 2008, 6). Similarly, one could also think of Article 4 (4) UNFCCC which established a ‘commitment’ to ‘assist the developing country parties that are particularly vulnerable to the adverse effects of climate change in meeting costs of adaptation to those adverse effects’, or even of Article 5 UNFCCC (technology transfer). For its part, the Kyoto Protocol set out more specific and quantified obligations, in particular with regard to the reduction of GHG emissions. Because they are specific, these obligations could be a basis for litigation. Lastly, the Paris Agreement sets out a general objective that is more detailed than the one found in the UNFCCC and in the light of which it must be interpreted: ‘[h]olding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels’ (Art 2.1 (a) Paris Agreement). The obligations laid down in this agreement are essentially procedural. Regarding mitigation, the obligation is not really substantial as ‘each Party shall prepare, communicate and maintain successive nationally determined contributions that it intends to achieve. Parties shall pursue domestic mitigation measures, with the aim of achieving the objectives of such contributions’ (Art 4 (2) Paris Agreement). But the Party contribution shall ‘reflect its highest possible ambition, reflecting its common but differentiated responsibilities and respective capabilities, in the light of different national circumstances’ (Art 4 (3) Paris Agreement). This implies ‘a due diligence standard which requires governments to act in proportion to the risk at stake’ (Voigt, 2016, 158).
18 Other conventions could also be relevant, such as the United Nations Convention on the Law of the Sea (‘UNCLOS’) and others treaties combating pollution of the marine environment, the Montreal Protocol on substances that deplete the ozone layer, or treaties seeking to reduce long-range transboundary air pollution. One could also think of the Convention on Biological Diversity, the UNESCO World Heritage Convention, or even human rights treaties. Very limited case law exists in this regard. For instance, an application has been made by environmental organizations and private citizens to include several sites on the List of World Heritage in Danger, on the basis of Article 11 (4) World Heritage Convention, because climate change threatens the future of these sites, including the Himalayan mountain range (Thorson, 2009, 255). Several petitions were also made to the World Heritage Committee raising the prospect of GHG emissions causing damage, through climate change, to World Heritage sites such as the Great Barrier Reef in Australia (Peel, 2016, 1009).
19 Without getting into too much detail, climate treaties and other conventions provide a fragile basis to support a finding of State liability given that the obligations are vague, attenuated, sometimes conditional, and often indirect. That is why it is interesting to also examine the possibility of invoking, in and of itself or in addition to the violation of a conventional obligation, customary obligations. From this point of view, the obligation not to harm the environment in other States or the environment in areas beyond national jurisdictions (the so called ‘no-harm rule’) provides an interesting lead. It is an old rule that recent case law has clarified while highlighting potential implications. Thus, it is not an obligation not to cause damage, but a positive obligation, a duty of due diligence. States must act with due diligence in order to ensure to the highest possible extent that dangerous activities which are being carried out on their territory or within their jurisdiction do not cause harmful consequences. This obligation is extremely wide. It is an obligation of ‘means’ and not of results: ‘an obligation to deploy adequate means, to exercise best possible efforts, to do the utmost, to obtain this result’ (Responsibilities and Obligations of States Sponsoring Persons and Entities with Respect to Activities in the Area, 2011, 39 [‘Responsibilities and Obligations’]). It is very strict: ‘it is an obligation which entails not only the adoption of appropriate rules and measures, but also a certain level of vigilance in their enforcement and the exercise of administrative control applicable to public and private operators, such as the monitoring of activities undertaken by such operators’ (Pulp Mills on the River Uruguay, Argentina v Uruguay, 2010, para 197; see also Pulp Mills on the River Uruguay (Argentina v Uruguay)). The International Tribunal for the Law of the Sea (ITLOS) Chamber has even considered that the ‘precautionary approach is also an integral part of the general obligation of due diligence’ (Responsibilities and Obligations, para 131). Moreover, the general duty of due diligence includes a number of procedural obligations (information, notification, cooperation, impact assessment, and continuous monitoring) that could also be relied upon successfully in the context of litigation regarding large infrastructure projects (the construction of a pipeline), industrial projects (construction, on a large scale, of coal-fired power plants) that emit a lot of GHG, or on the contrary geo-engineering projects designed to mitigate climate change.
20 This broad interpretation of due diligence, the customary nature of which is established, has significant consequences for States. Due to its ‘umbrella’ character, due diligence could make up for the potential shortcomings of treaties. Beyond its preventive role, it paves the way for increasing litigation based on an increasing knowledge of the thresholds not to be crossed in order to ‘prevent dangerous anthropogenic interference with the climate system’. It is all the more interesting in a matter like climate change that this direct obligation of the State has an indirect impact on private stakeholders within the State’s territory or jurisdiction, who are responsible for a very large part of GHG emissions. Due diligence is also seen as an attractive basis for State responsibility claims for climate change damage as it is binding on all States, including major emitters who lack specific emissions reduction obligations under the Kyoto Protocol or Paris Agreement (Peel, 2016, 1009). It is in any case an interesting basis that could be relied upon in addition to conventional ones. Indeed, the customary obligation of due diligence complements conventional obligations, keeping in mind that to this day the commitments to reduce emissions pursuant to conventions are inadequate and insufficient to ‘prevent dangerous anthropogenic interference with the climate system’. A State may comply with its conventional commitments while failing to comply with its customary obligations. As for conventional obligations, they must be interpreted in the light of the customary obligation, which can result in broader obligations. In practice, conventional and customary due diligence obligations mutually feed and shed light on each other. The recent award on the South China Sea perfectly reflects the catalysis, possibly even the symbiosis, that can take place between these different kinds of obligations (The South China Sea Arbitration, The Republic of Philippines v The People's Republic of China, 2016, paras 941–48). Thus, despite being vague, the customary basis can remain relevant, including in the case of a dispute between two States that are Parties to the Paris Agreement.
21 It is now established that state of necessity is one of the circumstances that can preclude a finding of wrongfulness. Could a State invoke necessity to be exonerated from its obligations to prevent and limit climate change, and more generally of all its obligations on this matter? Economic necessity in particular could be argued, given the States’ development imperatives. The International Center for Settlement of Investment Disputes (‘ICSID’) arbitral tribunals have accepted that a catastrophic economic situation threatening the living conditions of a population could justify a state of necessity (Metalpar SA and Buen Aire SA v Argentine Republic, 2008, para 208). On the other hand, the ICJ has accepted the possibility of an ecological state of necessity (Gabčikovo-Nagymaros Project, para 51). Yet, even though it is easy to compare emissions per capita, which can differ significantly from one State to the next, to this day there is no consensus as to what would constitute necessary emissions—required for subsistence—and what would be deemed superfluous emissions. Thus, this route seems rather complicated, except perhaps in the most extreme case of the lowest or largest emitters. Perhaps the actual carbon footprint of a State should be taken into account, excluding emissions related to exports. This seems all the more difficult given that necessity is construed in a restrictive manner to avoid any abuse. Besides, necessity can justify the violation of international law only to the extent that it ‘does not seriously impair an essential interest of the State or States towards which the obligation exists, or of the international community as a whole’ (Art 25 (1) 2001 ILC Draft Articles). This is another hurdle that subjects of international law must overcome to be able to rely on necessity to escape liability.
22 Considerations as to whether the responsible States had the opportunity to take preventive action, the foreseeability of harm, and the proportionality of the measures chosen to reduce the harm, will also be relevant to the determination of the standard of care the State has to follow (Peel, 2016, 1009). Moreover, this standard of care is not set in stone. It evolves over time alongside scientific and technological knowledge and in space, depending on the different capacities of States, which themselves also evolve over time. As years go by, States’ obligations become increasingly onerous, lightening in equal measure the burden of proof. Foreseeability of harm continuously improves, thanks in particular to the work of the IPCC, some of it at least being co-decided with representatives of States. Proportionality also evolves with scientific knowledge. It requires an assessment of the balance between the defendant’s and the claimant’s interests. Yet the risk involved for some States, in particular small island States, is so great, including substantial or even total loss of territory, that only significant reduction measures of GHGs could be considered proportionate (Voigt, 2008, 13). Further to the Stern Review in 2006, a significant number of economic papers have established that the costs of inaction would ultimately become far greater than the costs of action (Stern, 2006, ii).
(b) Attributing Harm to a State
23 For a State to be found liable, a causal link must be established between the harm done and the violation of international law. In theory, a State is only responsible for the actions of public authorities and of its own entities, not for those of private individuals—who are responsible for the most part of GHG emissions—except indirectly if it does not comply with its due diligence obligations in this respect. Thus, in principle, a State cannot be held responsible on the basis that its GHG emissions have caused harm, but because it has failed to take necessary and adequate measures in order to regulate emitting activities carried out within its territory or jurisdiction. From this point of view, a State is accountable for activities on its territory and under its effective control. In other situations, the lack of action by public authorities has been condemned (Armed Activities on the Territory of the Congo, Democratic Republic of the Congo v Rwanda, 2005, para 180; Armed Activities on the Territory of the Congo Cases), as well as normative initiatives by legislators that contradicted a conventional covenant (Metalclad Corporation v The United Mexican States, 2000, paras 109–11). As found by the seabed disputes chamber of the ITLOS, ‘it is not considered reasonable to make a State liable for each and every violation committed by persons under its jurisdiction, it is equally not considered satisfactory to rely on mere application of the principle that the conduct of private persons or entities is not attributable to the State under international law’ (Responsibilities and Obligations, para 112). Similarly, an international organization could be held liable both for the initiatives of its normative bodies and for the actions of its services (Art 4 Draft Articles on the Responsibility of International Organizations [‘2011 ILC Draft Articles’], 2011).
24 As mentioned above (see para 2), the human origin of climate change is no longer in question. It has been established by IPCC reports. Nevertheless, the climate system is complex and not linear. Even though there are clear estimates of different countries’ relative contributions to the absolute tons of GHGs emitted globally, at least since the 1990s, sources of emissions are varied, vague, and untraceable. Thus, while the overall causation leaves no doubt, the same cannot be said of specific causation.
25 With regard to due diligence obligations, however, the burden of proof is less challenging. Indeed, it will be easier to show that a State has failed to take all the measures it should have taken. Proof must be provided not as to the existence of a risk but as to the lack of implementation by the State of legislation and regulation that would have enabled such State to be made aware of such risk, to assess its probability and gravity, and to take measures in order to avoid its occurrence. Proof of such failure is not particularly difficult to establish (Kerbrat and Maljean-Dubois, 2014, 929). Indeed, as due diligence obligations are obligations of conduct, it is not necessary to prove that the environment was substantially harmed (except at a later stage when determining the right method of compensation) but simply that the State has failed to meet its obligations of conduct by not having taken all the measures that should have been taken.
26 Climate change constitutes a challenge for international law, but the latter has shown on many occasions its ability to adapt. A number of leads would be worth looking into, even though the standard of proof that would be accepted by an international jurisdiction remains unclear. As a matter of fact, each GHG emission increases the risk of specific harm by adding, in cumulative terms, to the GHG already present in the atmosphere. Thus, one could suggest that causation could be established on the sole basis of contribution to the problem of climate change by a specific actor. The issue of how much damage might have been caused by this contribution is irrelevant in this respect, although it will play a role at the stage of apportioning costs (Voigt, 2008, 16). It must be pointed out that the fact that the injury was at least partially caused by the polluting activity of the Trail Smelter in Canada appeared to be sufficient (Voigt, 2008, 15; Trail Smelter Case, 1938, 1941; Trail Smelter Arbitration). Or that, in another case, a proximate cause was found, largely based on empirical interpretation (Preliminary Decision No 7, 2007, para 13). In spite of the developments of scientific knowledge, it is still relevant to consider whether the precautionary principle could not lighten the standard of proof (Faure and Nollkaemper, 2007, 1588). Indeed, we may not be in a context of uncertainty as to the overall causation any more, but the determination of specific causation does remain subject to uncertainty.