Litigating climate change through international law: Obligations strategy and rights strategy

Abstract Litigation has presented itself as a serious means to vindicate normative commitments about climate change by forcing governments to review their policy priorities. Today, the use of such litigation is not limited to the domestic arena. International law now provides the new principal avenue for such litigation. Two litigation strategies stand out: obligations strategy and rights strategy. Obligations strategy consists of bestowing an erga omnes character to existing obligations regarding the protection of the global environment, thereby providing standing for a non-injured party before international courts. Rights strategy, on the other hand, significantly increases in practice. It consists in the invocation, before national and international courts, of remedies for environmental damages through the legal categories of human rights law. This article sheds light on the potential and limits of these litigation strategies in international law. The argument builds on the specific evolution in the legal architecture of international obligations under the United Nations Framework Convention on Climate Change (UNFCCC). The current structure of the UNFCCC now makes it substantially impossible to bring a claim against individual states regarding their specific measures against climate change. The article, by referring to the history of drafting which produced the specific structure, questions the ability of these litigation strategies to remedy the lack of international consensus and to accommodate the technical intricacy of how to turn normative commitments into actual action for climate change.

This strategy has gained momentum in the wake of a few recent judgments by the International Court of Justice (hereafter ICJ) which allegedly opened the way to hold states responsible for environmental damages without the claimant being an injured state under the law of state responsibility. Mention can be made of the case concerning Whaling in the Antarctic, 12 which was the first to be successfully brought before the ICJ on the basis of a legal claim to protect ocean resources and explicitly meant to address a global environmental problem.
The other strategy witnessed in the current rise of litigation is what is designated here as the rights strategy, a strategy significantly increasing in practice. It consists in the invocation, before national and international courts, of violations of environmental law through the legal categories of international human rights law. 13 The rights strategy does not need the special jus standi argument as long as the environmental harm can be individualized and amounts to a violation of the litigant's human rights. This strategy is becoming increasingly popular among environmental advocators, as is illustrated by the recent ground-breaking judgment of the Dutch Supreme Court in State of the Netherlands v. Urgenda. 14 Petitions whose claims are grounded in human rights treaties have been filed in more than ten jurisdictions across Europe, America, and before international human rights bodies. 15 This article sheds light on the potential and the limits of the abovementioned litigation strategies in international law. The argument builds on the specific evolution in the legal architecture of international obligations under the UNFCCC. The current structure of the UNFCCC makes it substantially impossible to bring a claim against individual states regarding their specific measures regarding climate change. The article, by referring to the history of drafting that produced the specific structure, questions the ability of these litigation strategies to remedy the lack of international consensus and to accommodate the technical intricacy of how to turn normative commitments into actual action against climate change.
The discussion proceeds as follows. After some basic consideration is given to the two abovementioned litigation strategies (Section 2), the article elucidates the legal architecture of the obligations under the UNFCCC to break apart the obligation of a separable nature and the obligation of an inseparable nature amongst the duty bearers (Section 3). The article then elaborates on how the UNFCCC regime is designed to marginalize judicial intervention, which made obligations under the UNFCCC simply not justiciable under the current law of state responsibility (Section 4). It then moves on to the limitations and risks of a resort to international human rights treaties by transposing environmental claims into human rights claims (Section 5). The article ends with a few concluding remarks (Section 6).
2. Litigating climate change through international law: The obligations strategy and the rights strategy 2.1 The obligations strategy: Erga omnes status as jus standi before courts Traditionally, bringing a case pertaining to the global environment to an international court was considered to be very difficult, if not impossible. For example, Gaja admitted that: (n)o state would in fact be able to invoke the responsibility of the wrongdoing state. In the case of heavy pollution of the high seas or unlawful harm to the ozone layer, the responsible state would have an obligation of reparation that would not be owed to any other state and would therefore remain theoretical : : : for they could easily be breached without consequences. 16 This specific obstacle to environmental litigation largely originates in the collective nature of the legal interests at stake, and in the limited possibility for the law of state responsibility to accommodate such collective interests, given its primary focus on bilateral and reciprocal rights and duties. It is in this context that the concept of erga omnes obligations has drawn the attention of international lawyers who have found therein a means to expand the standing necessary to bring such cases before international courts. For example, James Crawford, as the International Law Commission (ILC) Special Rapporteur on state responsibility, argued that the conservation of resources amounting to a common heritage of mankind could give rise to obligations erga omnes partes. 17 Shelton argues that the ICJ recognized the existence of erga omnes environmental obligations in its advisory opinion on the Legality of the Threat or Use of Nuclear Weapons, submitting that the 'common concern' of mankind is necessarily backed up with both institutional arrangements and assurances of enforcement. 18 In the same vein, Bierman defended the idea that certain fundamental norms for the protection of the environment would confer erga omnes status. 19 On the contrary, Brunnée, despite recognizing the collective nature of the legal interest in protecting the global environment, acknowledged that it still remains to be seen whether the obligations are bestowed with erga omnes effect due to the lack of practice. 20 Despite extensive scholarly debates, the nature and possible consequences 21 remained rather vague and arcane. It was not until the judgment in East Timor 22 that the implications  Law', (1996)  of an 'obligation owed to the international community' 23 in the light of jus standi were clarified and substantiated by the ICJ. This enhanced jus standi was also codified by the ILC in its Articles on Responsibility of States for Internationally Wrongful Acts (ARSIWA) of 2001. 24 During the 2010s, the ICJ, making use of the enhanced jus standi codified in ARSIWA, approved the standing of an applicant based on the convention's erga omnes partes nature in its rulingssuch as the case concerning the Obligation to Prosecute or Extradite (Belgium v. Senegal) 25 and Whaling in the Antarctic (Australia v. Japan). 26 Whaling in the Antarctic is particularly relevant for this article, as the case concerns the protection of a collective interest in resource conservation. In this case, Australia asked the ICJ to declare that the Japanese scientific whaling programme (JARPA II) was not in conformity with Article 8 of the International Convention for the Regulation of Whaling (ICRW), and to order its cessation. 27 In doing so, Australia relied on the Obligation to Prosecute or Extradite in establishing its standing before the ICJ for the alleged violation of the ICRW, during oral proceedings. 28 Australia, in establishing the admissibility, 29 claimed that its legal interest derives from the ICRW, which protects the common interest of the whale population for 'nations du monde' 30 and it implies that the obligation under the ICRW is addressed to all other state parties as '(l)'ensemble des États parties ont un "intérêt juridique"'. 31 In the ruling, the ICJ made no reference to the issue of legal interest after it settled the jurisdiction, pursuant to Article 36, paragraph 2 of the ICJ Statute although Australia's claim did not particularly concern its individual legal interest. 32 In light of the above, the Whaling in the Antarctic litigation comes as a decisive milestone for what is designated here as the obligations strategy. As was explained above, the ICJ long avoided an explicit reliance on erga omnes obligations in the operative parts of its decisions. It is said that this dearth of litigation practice concerning erga omnes obligations has contributed the lack of consensus in the legal discourse around the protection of global environment including climate change. 33 It is submitted here that the judgment in Whaling in the Antarctic seems to have brought about a change in legal discourses, including in the practice of the ICJ. The notable example is the position defended by ad hoc Judge Dugard in his opinion on the 2018 judgment. In his dissenting opinion, he established an obligation not to engage in wrongful deforestation, and characterized it as 'an obligation erga omnes' 34 by saying '[t]he obligation not to engage in wrongful deforestation that results in the release of carbon into the atmosphere and the loss of gas sequestration 23 Case Concerning the Barcelona Traction, Light and Power Co Ltd (Belgium v. Spain), Second Phase, Judgment of 5 February 1970, [1970 The result is reflected in Arts. 42 and 48 ARSIWA. 25 See Questions relating to the obligation to prosecute or extradite (Belgium v. Senegal), supra note 12. 26 See Whaling in the Antarctic (Australia v. Japan), supra note 12. 27 Whaling in the Antarctic (Australia v. Japan), Memorial of Australia, 9 May 2011, at 275-7. 28 Whaling in the Antarctic (Australia v. Japan), Statement by Boisson de Chazournes on behalf of Australia, in Verbatim Record (CR 2013/18), 29, at 33-4, para. 19. 29 In response to the question by Judge Bhandari -'What injury, if any, has Australia suffered as a result of Japan's alleged breaches of the ICRW through JARPA II?' See Whaling in the Antarctic, Verbatim Record (CR 2013/13) services is certainly an obligation erga omnes'. 35 With respect to the majority opinion, Judge Dugard provided that it 'failed to make any finding on the valuation of the impairment of carbon sequestration and gas regulation'. 36 In his reasoning, by virtue of an erga omnes obligation, Nicaragua is obliged to pay compensation not because the forest is a resource belonging to Costa Rica, 37 but because Costa Rica is 'the State most immediately affected' by the loss of gas sequestration services as the community interest. 38 While Judge Dugard's opinion does not directly address the issue of admissibility, he argues that the erga omnes status is extended to the obligation regarding loss of gas sequestration. Though such obligation is only presented in general terms, his opinion indicates new opportunities for climate change litigation in line with developing trends in the ICJ cases on erga omnes obligations. 39 2.2 The rights strategy: The turn to human rights While some lawyers struggle to expand access to the ICJ by establishing the standing based on erga omnes obligations, practice has also shown another tendency to file certain cases concerning climate change on the ground of human rights. 40 Scholarship also shows that international environmental law claims are more likely to succeed if they can be transposed into human rights claims, notwithstanding controversies like those on the specific right on environmental protection. 41 Such views build on a number of assumptions such as better developed judicial procedures and the possibility of rights-based-remedy in many jurisdictions. 42 It must be stressed here that this view did not emerge in a complete vacuum. A number of cases before international human rights courts have held states responsible for action or inaction on environmental degradation as a human rights violation, 43 even when the creation of the environmental hazards could not directly be attributed to the state. 44 So far, in these cases, the human rights courts have shown a clear inclination to focus on procedural deficits. If procedural requirements are met, for example, the European Court of Human Rights (ECtHR) will not revise 'the material conclusions of the domestic authorities' unless it is 'in exceptional circumstances'. 45 The case law is built in such a way as to preserve the discretion of a state to strike the best and fairest 35 Ibid., para. 33. 36 Ibid. 37 The majority opinion of the ICJ accepted that the loss of trees and gas sequestration services by deforestation is a direct consequence of Nicaragua's activities towards Costa Rica. balance of competing social interests while it developed some modest substantial minimum standards (e.g., an obligation to adopt a legal framework) for a positive obligation to counter the environmental harms that affect enjoyment of human rights. 46 Following the increasing number of cases that inquire into the nexus between environmental harms and human rights violations, recent developments on the right to a healthy environment under regional human rights bodies are also worthy of mention. 47 In terms of climate change, linking a threat of climate change to human rights violations is well illustrated by the case filed in 2005 by the representatives of the Inuit with the Inter-American Commission on Human Rights, alleging that the failure of the United States to reduce its greenhouse gases (GHG) emissions amounted to a breach of their obligation to protect human rights. 48 While the petition was denied, the case was perceived as a sound judicial attempt to indicate the adverse effect of climate change as a potential violation of human rights. 49 For example, John Knox stated 'the [Inuit] petition raised awareness of the effects that climate change was already having on the Arctic, and of the possibility that those effects could be framed as a threat to human rights'. 50 David Hunter, evaluating the petition, said that it raised attention to the relationship between global warming and human rights not only in judicial but also in political processes: '[a]lthough not successful legally, the Inuit petition brought substantive international attention to the plight of the Inuit and undoubtedly enhanced their influence and visibility in international climate negotiations'. 51 The claim of a connection between climate change and human rights was also increasingly defended in the late 2000s at various political fora, including the UN and regional human rights bodies 52 and also at the Conference Of the Parties (COP) of the UNFCCC. 53 A recent advisory opinion by the Inter American Court of Human Rights (IACtHR) 54 similarly recognizes such an overlap by saying that the impact of climate change affects the right to a healthy environment under the additional protocol and social and cultural rights as an autonomous right on the basis of Article 26 of the American Convention on Human Rights. 55 Despite increasing interest in linking climate change with human rights, 56 it must be noted that a 'treaty's recognition of a human right does not mean that any interference with that right by any 46 See, e.g., Öneryildiz v. Turkey, supra note 43. 47 E.g., the African Charter of Human and People's Rights recognizes the right of all peoples to 'a general satisfactory environment favourable to their development' in Art. 24. 48 Petition to the Inter-American Commission on Human Rights Seeking Relief from Violations Resulting from Global Warming Caused by Acts and Omissions of the United States (7 December 2005). actor, anywhere in the world, violates a legal duty'. 57 Given the transboundary character of climate change and the nature of its consequences, transposing an environmental claim into a human rights claim is not as simple as it seems. In fact, neither international treaties nor the jurisprudence by international human rights bodies have provided any guidance about how transboundary harms could be litigated through human rights. It has not even been clear whether the responsibility can feasibly be individualized for a state regarding damages or hazardous effects of climate change. Furthermore, climate change is not an issue that can be typically solved by a single government revising their political priorities among competing domestic interests. In this regard, it is noteworthy that the efforts to litigate climate change through the legal categories of human rights law were historically met with great reservations by states. 58 For example, Limon described the opposition from both oil-producing and oil-consuming countries during the negotiation for the Resolution 7/23 to request a study on climate change and human rights. 59 Although the UN organs were mindful of the potential overlap between protection of specific human rights and environmental issues, 60 they continued to take the position that states are not held responsible for violating human rights merely because of GHG emissions. 61 Whilst there has been reluctance by international human rights bodies to directly link climate change and human rights treaties, attempts aimed at holding a state individually responsible to act in relation to climate change come to prominence in recent practice before national courts. Among these domestic cases, the Urgenda Foundation v. the Netherlands (2019) 62 and its use of the European Convention on Human Rights (ECHR) warrants some attention here. In upholding the claim by Urgenda, the Supreme Court of the Netherlands provided that a member state has an obligation to take preventive measures against climate change. It reached this conclusion by characterizing climate change as a threat to the right to life (Article 2) and the right to health and respect for private and family life (Article 8) building upon the case law of the ECtHR to the extent that it is characterized as a national problem. 63 Then the Court, in holding against the argument by the Dutch government that reducing the adverse effects of climate change greatly depends on the other large emitters' commitments, 64 found that the Netherlands could be held individually responsible for fulfilling its own obligations. The Court referred to the UNFCCC, wherein each state owes an obligation to reduce GHG emissions regardless of its own emissions being small or large. 65 As to the content of the obligation, it ordered that the Dutch government must cut its GHG emissions by at least 25 per cent by the end of 2020 (compared to 1990 levels)  protect human rights. 66 In conclusion, the Court held the state responsible for the inadequacy of its policy under this minimum standard to be compliant with Articles 2 and 8. 67 What is remarkable about this new evolution of rights strategy is that the Supreme Court appears to be under much less constraint than international courts in determining the exact level of reduction to be achieved by the state. This requires, on the part of the Court, the balancing of legitimate national interests. However, to the extent it concerns interpretation of international law on climate change, there are issues which cannot go unnoticed in further pursuing a rights strategy. In this regard, the Urgenda case calls for a few observations. The finding of responsibility for inadequate policy measures was based on the Court's composition of 'do its part' 68 obligation, which was linked to the emissions reduction target of 25-40 per cent by Annex I countries. 69 This target is based on the global amount of carbon reduction to achieve the purpose of the UNFCCC and the 2°C target. Whilst it held that a reduction target of 25-40 per cent is not legally binding, 70 the Court deployed this standard as reflecting a scientific and political consensus which is meaningful for the Court to be able to interpret the minimum standard for the government to prevent and alleviate the adverse effect on rights under the ECHR. 71 In this reasoning, the individual obligation of a state is materialized as a part (or a share) of the necessary amount of carbon reduction on the global scale as a result of its interpretation of the international law on climate change. This represents a notable, possibly accidental, effect of the human rights litigation: redesigning the architecture of obligations set by the UNFCCC negotiation by transposing environmental claims into human rights claims to vindicate normative commitments on climate change.

Dual structure of the UNFCCC: Separable obligation and inseparable obligations
This section expounds on the dual structure of obligations under the UNFCCC following the transformation of the legal architecture of international law on climate change: from a 'top-down' approach represented by the Kyoto Protocol towards a more 'bottom-up' approach embodied in the Paris Agreement. It will be shown that this evolution was informed by an attempt to move away from imposing individually allocated, quantified reduction targets as obligations of international law.
Before the article proceeds, an important preliminary observation is warranted, with a view to contextualizing current international law on climate change and the debates thereon. Mention has been made of top-down and bottom-up approaches as well as the lack of political consensus. Solving environmental problems affects diverse interests in societies. In the specific context of climate change, drastic re-engineering of the entire energy-industrial system and consumption pattern are unavoidable if one wants to achieve a green, net-zero emissions economy, given that a high number of sectors are still deeply dependent on fossil fuels. 72 Transition to a green economy requires heavy investment to reformulate the way society is managed. The obstacle is that there are many uncertainties about the evaluation of the impact and cost of tackling climate change 66 Ibid., para. 8.3.5. 67 For the critical view on whether Art. 2 can be applied for 'less ambitious' actions see, e.g., I. depending on national circumstancesincluding the social discount rate. 73 It is in this sense that climate change is called a 'super wicked problem', 74 as we cannot simply identify the individual carbon budget that is legitimately allocated to respective states out of the global carbon budget. 75 The resulting paralysis from the uncertainty and conflict of interests is what led the move by the UNFCCC from the Kyoto Protocol to the Paris Agreement. The former embodies what is known as a 'top-down approach' characterized with a strong co-ordination, timetables and legal targets based on agreed rules at the international level. The latter is the expression of what is known as a 'bottom-up approach' or 'hybrid approach' meant to preserve the autonomy of states in determination of their contributions. 76 Hence, international law on climate change on the one hand, aims to enhance the co-operation for collective interest by setting a normative framework at the international level, and on the other hand, the concrete actions required are largely domestic, which concerns the overall re-designing of the way respective societies are managed for 197 state parties under different socio-economic situations. This relationship between international and domestic, top-down and bottom-up, is the key component of the legal architecture of international law on climate change that is embodied in the UNFCCC and related legal documents.
While earlier studies repeatedly associated the obligation and the responsibility concerning climate change with terminologies that indicate a collective nature (i.e., 'common', 77 'shared', 78 or 'integral' 79 ), both the literature and practice so far have not drawn any distinction between different types of obligations under the UNFCCC and its related legal instruments: separable and inseparable obligations. The following paragraphs explain this dual structure of the obligations and how this structure nuances allocation of responsibility to individual member states.

Separable obligation under the climate change regime
A separable obligation is, for the sake of this article, defined as a commitment, which each party to the UNFCCC is expected to be bound to individually, in spite of the collective nature of damage and the adverse effect of climate change. Article 4 of the UNFCCC imposes an obligation on all state parties to take measures to mediate climate change by addressing anthropogenic GHG emissions. In particular, Article 4.2 provides a more stringent obligation for the state parties listed under Annex I (developed countries) to limit their anthropogenic emissions of GHG, which reflects the common but differentiated responsibility under Article 3. This obligation to reduce emissions is spelled out in concrete terms by the Kyoto Protocol, which specifies the quantified target for emissions limitations under a defined timeframe. Article 3 of the Kyoto Protocol specifies the content of the obligation under Article 4 of UNFCCC, such as the overall emissions 73 The Stern Review is known for supporting policies of reducing emissions by 3% per year by using a discount rate of 1.4%. Yet other analysis, such as by Nordhaus, criticized Stern's conclusion as too optimistic, as the deployed rate was too low. See There is an attempt by a group of experts to establish the precautionary principle as the ground to hold each state legally responsible for trans-border effects. In so doing, they base the standard of wrongfulness on 'any credible and realistic worstcase scenario' with reference to 2°C. See Oslo Principles On Global Climate Change Obligations, available at globaljustice.yale. edu/sites/default/files/files/OsloPrinciples.pdf. reduction of six specified gases under Annex A by at least 5 per cent below the 1990 levels for the period 2008 to 2012. Some of the parties to the Protocol participated in the second commitment period between 2013 and 2020 with regards to seven specified gases under the Doha amendment. 80 The Kyoto Protocol framed the obligation of reducing emissions (mitigation) in the form of an individually allocated carbon budget (or the level of emissions reduction) for Annex I state parties, which are the group of developed states. This centralized and binary approach to the obligation of emissions reduction was subject to change for the post-Kyoto scheme, which is covered by the Paris Agreement. The Paris Agreement adopted 'nationally determined contributions [NDCs]' to reflect a more nuanced classification according to respective national circumstances for all member states. Article 4(2) of the Paris Agreement states that '[e]ach Party shall prepare, communicate and maintain successive nationally determined contributions that it intends to achieve. The Parties shall pursue domestic mitigation measures, with the aim of achieving the objectives of such contributions'. Under NDCs, each state can define its own commitment towards the reduction of emissions in terms of amount and means under respective national circumstances. In so doing, each state is not bound by any qualitative and quantitative targets under the UNFCCC including the 2°C under Article 2 of the Paris Agreement.
Under the UNFCCC, mitigation is ranked as the most important approach to address climate change amongst the approaches listed under Article 4. While adaptation, which is also listed under Article 4 of the UNFCCC, has been framed in the form of an obligation of conduct, 81 mitigation has followed quite a different route. Under the current international consensus reflected in the Paris Agreement, however, the primary obligation is designed to respect the parties' respective domestic policy choices in defining individual routes and scenarios in GHG reduction. The obligation is owed by each state regardless of whether its own emissions caused or will cause adverse effects, and the question of attribution is strategically kept silent.

Inseparable obligation under the climate change regime
The obligation of 'inseparable' nature under the UNFCCC and its related legal instruments poses a fundamental challenge to the current system of the law of state responsibility. For the omission of the obligation, regardless of how many parties did not implement the obligation, all parties are held responsible for this breach, together as one, hence the conduct is not attributable to an individual party. The following expounds the content of inseparable obligation under the UNFCCC and the background on why such conceptualization of obligation was necessary in the light of the negotiation history built on 'top-down' and 'bottom-up' approaches.
Acknowledging climate change as a common concern of humankind in its preamble, Article 2 of the UNFCCC defines the ultimate purpose of the Convention as being 'to achieve, in accordance with the relevant provision of the Convention, stabilization of greenhouse gas concentration in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system'. This idea of a long-term emissions ceiling is repeated in Article 2 of the Paris Agreement as the 2°C target. Throughout the decades of the UNFCCC negotiations, the nature of this longterm global ceiling has remained controversial. As to the question of whether this long-term ceiling is just an aspirational target or a general obligation under the UNFCCC, the drafting process of the UNFCCC suggests that 'the ultimate purpose' later adopted as Article 2 was treated as a 'general obligation' during the drafting process despite being adopted under the heading of 'purpose'. This ambiguity is also partly due to the uncertainty of the legal effect of climate change being classified as a 'common concern of mankind'. 83 It is well known that resolutions by the General Assembly do not confer legal rights and obligations, yet the possible legal effect attached to climate change being a common concern of mankind has been the object of much scholarly debate. 84 Arguably, the nature of common concern of mankind provides the legal justification for collective action under a specific treaty. 85 After the Kyoto Protocol, the political momentum to negotiate metrics for 'the ultimate objective' emerged following increased input from the scientific community, and European political efforts to translate it into a legal temperature target. 86 In the end, the temperature target was formally endorsed in the Paris Agreement under Article 2, which aims to strengthen the global responses to climate change by '[h]olding the increase in the global average temperature to well below 2°C above pre-industrial levels'. 87 However, despite being anchored in a legal text, the 2°C target and the sum of respective commitments by each party under Article 4 are not legally linked. 88 In terms of the NDCs, the Paris Agreement did not prescribe any obligation of result and NDCs are self-proclaimed commitments undertaken by each party. Article 4.2 only includes the obligation to 'prepare, communicate and maintain' NDCs, and only 'pursue' the domestic mitigation measures. 89 In doing so, the parties only 'aim at' reducing the emissions as soon as possible in order to achieve the 2°C target under Article 4. 90 Given this understanding, a number of scholars characterized the Paris Agreement as 'a statement of good intentions, setting forth aspirational goals' without substantive obligations. 91 On the other hand, it is also debatable that 2°C is not a mere aspirational target, as it is deeply integrated into the operation of the varied standards and roadmaps established under the UNFCCC regime. 92 To this end, some would naturally argue that '2°C' must be treated by every member state as a basis for their respective national commitment. However, these polarized claims do not reflect the The UNFCCC recognizes that commitments by the parties are not sufficient to hold the warming to 2°C. See 'Synthesis report on the aggregate effect of the intended nationally determined contributions', FCCC/CP/2015/7, available at unfccc.int/ resource/docs/2015/cop21/eng/07.pdf; updated in 2 May 2016, FCCC/CP/2016/2, available at unfccc.int/resource/docs/2016/ cop22/eng/02.pdf. See also 'Global Response to Climate Change Keeps Door Open to 2 Degree C Temperature Limit New UN Report Synthesizes National Climate Plans from 146 Countries', available at unfccc.int/files/press/press_releases_advisories/ application/pdf/20153010_indcs_embargo.pdf. 89 During the drafting process, the negotiated text put 'pursue' and 'implementation' together, the latter of which was deleted in the latest stage of negotiation: See Draft Paris outcome proposed by the President (9 December 2015) Art. 3.2, available at unfccc.int/resource/docs/2015/cop21/eng/da01.pdf; Draft Paris outcome proposal by the President (10 December 2015) Art. 3.2, available at unfccc.int/resource/docs/2015/cop21/eng/da02.pdf. history of the negotiations that led to the Paris Agreement, which was meant to uphold the necessary top-down element, while establishing the bottom-up format to allow each state to adapt to respective national circumstances.
If one does not regard 2°C as a mere aspirational target, the reading of the UNFCCC and the Paris Agreement together indicates that this objective constitutes a commitment to hold the temperature rise below 2°C. Contrary to the separable obligation, the long-term target thus comes in the form of an obligation of result. All parties are bound to achieve the collective result of the longterm target of 2°C, yet the obligation is inseparable amongst the parties. In international law it has been recognized that, in some exceptional situations, an obligation is inseparable as it is shared among multiple states. 93 For the sake of this article, an inseparable obligation refers to a single obligation shared among states. When an inseparable obligation is breached, the responsibility cannot be individually attributed to one state but to all states bound by the inseparable obligation concerned. 94 It must be acknowledged that the determination of an inseparable obligation depends on the interpretation of the content of the obligation concerned. As far as the UNFCCC is concerned, it seems that interpreting its content as providing an inseparable obligation is plausible given the history of the negotiations. As will be explained in the next section, the drafting history of the UNFCCC shows that it is not a statement of good intentions but it establishes a new form of legal obligations to withhold the necessity of universality without imposing a top-down allocation of individual ceiling to each party, which was opposed by different parties during the negotiations. 95 The following section will further expound on how the distinction of separable and inseparable play out to marginalize the role of the judiciary, by illustrating the drafting history of the Paris Agreement. It will illustrate how the UNFCCC marginalized the role of the judiciary in the light of law of state responsibility under international law for each obligation, and then how separable and inseparable obligations are carefully decoupled.

Marginalization and the fall of the obligations strategy
Suppose that the issue of admissibility 96 is cleared. As was alluded to above, the erga omnes status of the breached obligation may, arguably, provide the procedural basis for invoking the responsibility of a state in its act or omission with regards to the protection of collective interests. As far as separable obligations are concerned, the characteristic of the injury being 'collective' does not bring any additional legal consequences in attributing the international wrongful act. 97 While there can be omissions by multiple state parties that lead to the temperature rise, these omissions Nadeski refers to climate change as an example of 'shared positive obligation of result' as it is meant to be implemented by 'all duty bearers', and it is not possible for only one of the duty bearers to breach the obligation. See Nedeski,ibid.,at 142, The support for detaching the top-down approach from the individual commitments was first found among the submissions of the developed state parties ('umbrella group' parties) to the ADP before COP19 where they adopted the words 'intended nationally determined commitment' (later developed into 'nationally determined commitment' under the Paris Agreement). See, for example, submission by New Zealand (September 2013); submission by the US (17 October 2013); submission by Japan (10 September 2013); submission by Canada (12 April 2013), all available via unfccc.int/process-andmeetings/conferences/past-conferences/doha-climate-change-conference-november-2012/adp-1-2/submissions-from-partiesto-the-adp-2012-2013. are attributable to each state, which could give rise to state responsibility concurrently. 98 Under Article 2 of ARSIWA, an act or omission must (i) constitute a breach under international law, and (ii) be attributable to the states. In this regard, Crawford states that a breach of obligation is identified through the consideration 'given above all to the substance of obligation itself'. 99 This statement reflects Crawford's understanding of the law of state responsibility according to which the nature of the breach under ARSIWA is defined by the content of the obligations under the primary rules of international law. But what is the content of the obligation for individual member states of the UNFCCC prescribed at the international level?
In this regard, it must be emphasized that Article 4.2 of the Paris Agreement leaves the content of the obligation to be worked out at the domestic level under 'nationally determined contributions', which is, by its nature, self-determined by each party to the UNFCCC. Because every state has the discretion to define the content by taking into account priorities amongst different domestic interests, what is prescribed at the international level is only a procedural obligation to determine and register NDCs. In other words, the substance of the obligation is independently determined by each party as a part of domestic policy making. If, then, there is no minimum substantive standard to review the content of efforts at the international law level, how could there be an unlawfulness of international law in the sense of Article 2 of ASRIWA? As was alluded to above, invocation of a claim for state responsibility requires the content of the obligation to be identified at the international level. In this regard, the separable obligation under the Paris Agreement falls short of a standard against which the Court can assess compliance under international law. This discretion of states on the content of the obligation is a stark difference from the Kyoto Protocol, in which the content of the obligation was directly identified through international negotiations in a form of quantified emissions amounts for Annex I countries.
Contrary to separable obligations, the content of what we call an inseparable obligation is explicitly spelled out in the text of Article 2 of the UNFCCC and the Paris Agreement. Yet, as will be shown here, the justiciability of inseparable obligation is questionable, not because of the lack of a fixed substantial standard, but because of a substantive and procedural vacuum under the current law of state responsibility. It is well-known that no mechanism is provided by the ARSIWA when actors from multiple states are blamed for an act or omission that constitutes an 'inseparable' breach. 100 While such a situation is recognized by the ILC, 101 international legal literature is 'surprisingly devoid of reference to the circumstances or consequences of multiple state responsibility'. 102 Unlike the separable obligations, breach of an inseparable obligation is not a mere bundle of bilateral relationships between the harm and omission by a state, nor 'shared responsibility' where a wrongful act can be disaggregated into omissions of different obligations held by multiple states. 103 When the obligation is inseparable, the breach is attributed to all states.
All these analyses on the marginalizing effect of the judiciary are built upon the key structure of the Paris Agreement, which does not link separable obligation allocated to individual states with the shared commitment to hold the global average temperature rise below 2°C in legal terms. The following provides further clarification on this point by referring to the drafting history of the Paris Agreement. As was mentioned in the previous section, some may argue that it is possible for individual states to be held legally responsible for respective carbon budgets, which can be feasibly calculated based on the 2°C target for environmental integrity. In this regard, it is indeed 98 Nollkaemper distinguishes several categories of state responsibility in explaining the situation where multiple states have committed an internationally wrongful act that results in a single injury. As to the definition of shared responsibility, see Nollkaemper and Jacobs, ibid., at 366-8, especially at 368. the Paris Agreement's intention that its long-term goal ('global stocktake') 'informs' the state parties in terms of NDCs. 104 Yet, this linking of the 2°C target with NDCs contradicts the intention of drafters as it manifests itself in the drafting history of the Paris Agreement.
During the negotiations, the decision whether or not to have the top-down obligation of emissions reduction just as the quantified target written under the Kyoto Protocol was a point of disagreement. As a consequence of intensive negotiations, giving up the idea of establishing the substantial obligation of resultsuch as an individual carbon budget by disaggregating the 2°C targetwas the cornerstone in the adoption of the Paris Agreement. In this regard, most of the member states had already acknowledged that NDCs will fall well short of the 2°C pathway without 'some form of climate engineering'. 105 This is also the reason why the decision of the COP 21 put the emphasis on finance and technology, including mobilization of 100 billion dollars a year by 2020 in climate finance for developing states, strengthening the Technology Mechanism, and having a Green Climate Fund to support the Technology Mechanism to environmentally and economically bearable climate responses.
The disconnection of NDCs from any 'top-down' element in a legal sense was particularly evident in the text negotiation for what became Article 4 and it is worth recalling some decisive moments of the drafting history. In the light of excluding 'top-down' elements from NDCs, Article 4.3, which some construe as a commitment to progression, 106 is worth noting here. For Article 4.3, some states fought hard against the possibility that even their past ambitions be the mandatory basis for future NDCs. Article 4.3 now provides '(e)ach Party's successive nationally determined contribution will represent a progression beyond the Party's then current nationally determined contribution and reflect its highest possible ambition : : : '. In the draft of 9 December 2015, the three options [shall] -[should] - [will] were all put down in the text. 107 For a number of states, [shall] was not acceptable as an introduction of the obligation to progress because it substantially suppresses the freedom to determine NDCs according to national circumstances. As a result of overnight consultation, the proposed text used the recommended [should] to counter the binding element of the progression. 108 Yet, some member states still considered that this was not enough to ensure that states have the necessary liberty in determining the respective NDCs. In the end, the final text was adopted with the term [will], which is more commonly used in non-binding instruments. 109 As the negotiation history shows, disconnecting NDCs under Article 4 from any binding 'top-down' element was the gist of the compromise on which the Paris Agreement came to be adopted.
In short, all member states agreed to accept the 2°C target as a long-term, collective goal for all, yet adopting it as a legal threshold in defining the respective NDCs was neither intended nor technically feasible. Of course, the drafting process does not frustrate the possibility that the 2°C target constitutes a related but independent legal obligation from NDCs. Judging from the history of its formation, the 2°C target is not merely aspirational in nature, which constitutes notable development from the understanding in previous instruments such as the Cancun Agreement in 2008. 110 Yet, the drafting process implies that if such a target is not an aspirational one, the maximum that can be claimed on the nature of the 2°C target is the obligation that is inseparable among all the duty bearers, i.e., the states parties to the UNFCCC. Hence, a state is not individually held responsible for the level of its contribution being inadequate for 2°C trajectories.
Without legally disaggregating the 2°C target into individual carbon budgets to be translated into NDCs, the 2°C target should be interpreted as a single obligation by all parties to the UNFCCC. Legally speaking, such an inseparable obligation by its very nature does not allow for causal investigation into who contributes to what, or to what extent, thus there can be no individual attribution to each state. Furthermore, even when the claim for a breach of inseparable obligation is formed as several bilateral cases for each respondent, it is very unlikely that the ICJ would be able to exercise their jurisdiction because the legal interest of 'third party' will always form the very subject-matter of the decision, according to the Monetary Gold Principle. 111 Scholarly efforts have not addressed this legal vacuum. For example, the new 2019 Principles of Shared Responsibility currently being drafted by a group of experts of the law of state responsibility is of limited help with respect to an inseparable obligation. 112 References are made to sharing responsibility among multiple states for both a single action or distinct actions, 113 while responsibility in relation to the obligation of inseparable nature is not covered.
While the case law on erga omnes obligations rapidly consolidated itself over the past decade, this section has demonstrated how the UNFCCC, the comprehensive legal body on climate change with 197 member states, came to be built on the centrality of national circumstances in the determination of the obligation of states. This section illustrated that this direction is based on political and technical feasibility of measures to counter climate change, and it inevitably deprives the judiciary of a standard against which the responsibility of the parties can be appraised. 114

Strengths and pitfalls of the rights strategy
It has been submitted in this article that the current dual structure of obligations in international law on climate change expresses the transition that took place between the Kyoto Protocol and the Paris Agreement. It has been shown that the fall of the obligation strategy was accompanied by a marginalization of the judiciary, reflecting a conscious decision to preserve room for the political prioritization of states. In this context, it can be anticipated that the rights strategy, particularly at the domestic level, will continue to thrive as a serious way to vindicate normative commitments about climate change. Given its resilience, the rights strategy thus warrants some specific observations. While the deployment of the rights strategy in domestic courts would provide an innovative solution, this section argues that the rights strategy simultaneously runs the risk of simply displacing unsolvable problems from one side to the other.
While the threat of climate change can constitute a violation of human rights law, the claims made in this section are premised on the idea that human rights law and international law applicable to climate change are different in nature, thereby often preventing a claim based on the one being mechanically transposed into a claim based on the other. As is confirmed by the case law, human rights law can impose positive obligations to prevent and alleviate environmental harms. These obligations are associated with the idea of a minimum substantial standard, which sets the threshold of lawfulness and unlawfulness. While the concept of standard is also found in international law on climate change, the current consensus under the UNFCCC is not to have it as a threshold of unlawfulness, but to encourage states to revise ambitions towards what is ideal. The 'standard' here is something to be aimed at, but no state is individually bound by it.
When turning claims about climate change into human rights claims, the courts are confronted with standards of a very different nature. 115 This is well illustrated in the judgment of the Dutch Supreme Court in the Urgenda case, where, in transposing a climate change claim into a human rights claim, the Court held that the Netherlands is individually responsible ('partial responsibility'), building upon its own construction of the individual obligation of the state to 'do its part' through its interpretation of international law on climate change. 116 In so doing, the Court transformed the nature of the standard under the UNFCCC into a legal threshold of unlawfulness in order to assess the conduct of states under the ECHR by way of interpretation. This is the point of fragmentation created by the Urgenda case. As was alluded to in the previous section, the specific feature of the separable obligation under the UNFCCC was to suspend the question of the allocation of burden in a 'top-down' way. Under the current architecture of obligations under the UNFCCC, no state is held responsible for their contribution being evaluated against a minimum threshold set under international law. In this light, the 2°C target under the UNFCCC is, at most, materialized as a collective obligation, which is detached from the quality of lawfulness for the individual conduct. The previous section showed that this architecture reflects the lack of global consensus as to the way to turn our normative commitments into concrete actions.
It must be acknowledged that, to the extent that a right-based claim is explicitly made through the discretion recognized by the case law of human rights courts as well as under international law on climate change, the application of a rights strategy in domestic courts can be an innovative solution to turn a normative commitment into concrete action by the government concerned. 117 As was alluded to in Section 2, the case law of the ECtHR is built in such a way as to preserve the discretion of states to work out the protection of human rights in the light of other social interests. As was sketched out in Section 3, states have considerable liberty under the UNFCCC to determine what would be the most ambitious action possible to counter climate change while keeping a fair balance between environmental interests and competing interests. This means, in assessing adequacy of such action, that the courts in each state are also free to turn technical and ambitious standards into a legal threshold in order to strengthen the protection of human rights within their own jurisdiction.
In this regard it can be argued that, had the Supreme Court of the Netherlands in the Urgenda case limited itself to this discretion, its judgment would not have proved polemical. Instead, in its December 2019 judgment, the Court identified the individual responsibility of the Netherlands by construing the corresponding individual obligation as reflecting 'the part of the cause of damage', 118 drawing upon its interpretation of international law on climate change. Then, it applied a 25-40 per cent target as its threshold of lawful protection under Articles 2 and 8 ECHR. By constructing the legal reasoning in this way, the judgment brought back the pattern of legal thinking whereby a state is held responsible based on a legal threshold, which is internationally determined, rather than simply exercising its own discretion to determine what would work the best for the state within the jurisdiction. 115 Bodansky also touches upon the difference of standards for both branches of law. See Bodansky, supra note 42. 116 See Urgenda v. the Government of the Netherlands, supra note 14, para. 5.7.5. 117 E.g., see Ashgar Leghari v. Pakistan, supra note 10. 118 See Urgenda v. the Government of the Netherlands, supra note 14, para. 5.7.6. The 'unnecessary' detour to causation discussion is also pointed out by A. Nollkaemper and L. Burgers, A New Classic in Climate Change Litigation: The Dutch Supreme Court Decision in the Urgenda Case, EJIL:Talk!, 6 January 2020, available at www.ejiltalk.org/a-new-classic-inclimate-change-litigation-the-dutch-supreme-court-decision-in-the-urgenda-case/.
At the time of writing this article, there are already multiple cases based on the ECHR including some that follow the same pattern of thinking as Urgenda. 119 While the example of Urgenda is yet to be generalized and made part of ECtHR case law, 120 the risk of a generalization of such an approachwhich resuscitates a legal threshold that was explicitly left out of the international law on climate changeis not minor. Should the Urgenda approach proliferate, even if only at the domestic level, one would possibly witness the unmaking of 30 years of international law-making on climate change whereby decisions about concrete actions are left to the state without construing its obligation as a 'share' or 'part' of a global carbon budget.

Concluding remarks
Despite the shared sense of urgency to counter climate change, the global community has not yet developed a coherent understanding of how the future world should act in the face of tremendously diverse national circumstances as well as complex global supply chains. 121 The body of law on climate change, as found in the UNFCCC, will continue to develop through different channels and at multiple governance levels. 122 In this regard, climate change litigation can also be seen as 'part of the transnational regulatory dialogue over climate change'. 123 Yet, not all the dimensions of such a dialogue should be embraced enthusiastically.
This article, drawing on the structure of obligations under the UNFCCC and the lack of global consensus behind, has shed a light on some of the problems associated with specific litigation strategies based on international law. It has, particularly, been argued that the obligations under the UNFCCC regime − which have been possibly identified here as separable and inseparable obligationsare shaped in such a way in order to avoid holding states individually responsible under the current law of state responsibility and thus being apprehended by the judiciary as to the content of respective efforts of emission reduction.
Two final remarks are in order. First, a remark must be formulated on the implications of the argument made here for the litigation strategies discussed in Section 2. Whilst the obligations strategy is frustrated by the dual structure of obligation depicted above, the argument developed here shows that the rights strategyand the judicial activism that accompanies itmay be a silver bullet in terms of accountability, but it is not always so in terms of protection of the environment. Indeed, it is submitted that pursuit of the rights strategy must be done in such way as to avoid drastic fragmentation of the body of human rights and international law on climate change.
Second, the finding in this article should not be interpreted as frustrating the international legal framework and substantive international obligations to fight against climate change. Moving away from a one-size-fits-all approach, the Paris Agreement and the COP decisions acknowledge the vision of tackling climate change collectively through the various channels of institutionalized international co-operation such as providing financial resources, 124 transfer of technology, 125 119 See Peel and Osofsky, supra note 13, at 27-9. See also, supra note 15. A symbolic recent example is the gilet jaunes (yellow vests) protest in France, which was triggered by a policy to reduce carbon emissions by 75% − in part by raising taxes on fuel. Following the increasing protests, the government suspended a planned rise in taxes on petrol and diesel (4 January 2019): Announcement of PM Philippe on this emergency measures to respond to gilets jaunes, available at www.gouvernement.fr/partage/10772-discours-devant-l-assemblee-nationale. See Peel and Osofsky, supra note 13, at 27. 124 Art. 9, particularly 9.1 Paris Agreement; COP decision 1/CP/21, paras. 53-65. 125 Art. 10, particularly 10.6 Paris Agreement; COP decision 1/CP/21, paras. 66-71.