National climate litigation and the international rule of law

Abstract This article assesses the implications of national climate litigation for what is termed ‘the international rule of law’. Starting from the finding that the current international climate treaty regime lacks several elements of an international rule of law, such as legal bindingness, clarity, and justiciability, the author explores what national courts contribute to filling these gaps. Deviating from a linear progression narrative, which is prevalent in existing literature, this article provides a more nuanced and complex picture. Whereas successful climate litigation is hardly imaginable without reliance on internationally agreed-upon facts – such as reports by the Intergovernmental Panel on Climate Change and global average temperature levels deemed ‘dangerous’ – doctrinally decisions do not represent a turn toward a stricter rule of international climate law. Instead of applying and progressively developing climate treaties, courts thus far have primarily used these provisions only to develop national constitutional law and regional human rights law. The created system of highly contextual national rule(s) of climate law is a fragmented one which is regionally limited to a few states predominantly located in Western Europe. Consequently, it is a far cry from a truly global rule of international climate law.


Introduction
The pros and cons of climate litigation as a broad phenomenon remain hotly debated. Proponents of such litigation applaud court decisions in favour of litigants as a means of strengthening democracy and the rule of law in climate matters. 1 In terms of effectiveness, they stress the symbolic value of caseseven the lost onesand depict litigation as a last resort in the face of the failure of governments to provide adequate protection. 2 Opponents are not convinced by doctrinal symptoms of a legal crisis are not unrelated to the factual climate crisis. As Voigt warns, catastrophic climate impacts 'could set an end to the order as we know it and give rise to unilateralism, instability, insecurity and the use of might (if not chaos and anarchy)'. 16 Starting from this narrative, climate litigation could be a measure of crisis prevention. However, from a more pessimistic point of view, climate litigation could also be read as a challenge to the universal ambition of international (climate) law. 17 Legally dubious and overly ambitious findings by national judges about the content of international climate law could frustrate governments and lead them to withdraw or limit obligations through national reform. 18 This article promotes a nuanced reading of climate litigation repercussions for what I characterize as the international rule of climate law. It finds that national courts regularly engage with international climate law, with courts being receptive to international climate treaties as 'a setting'. 19 Some courts partially developed individual obligations of governments to contribute to the objective of international climate law. However, by predominantly relying on national laws, constitutional law, and regional human rights, courts do not promote accountability and compliance with international climate law as much as uphold national or regional rule of law. Whereas the juridification of soft law and 'international facts' 20 via regional human rights lawas practiced mostly by Dutch courtscould be seen to complement the United Nations' climate treaty regime, the so-created order at present is geographically limited to Western Europe. Thus, climate litigation is far removed from establishing a truly global rule of climate law which would be required to legally tackle the 'super-wicket' 21 common action problem of climate change.
To substantiate this argument, I proceed as follows: First, I introduce what I mean when referring to the 'international rule of law'. Second, I briefly recap the rise and decline of the idea of an international rule of law through the evolution of the international climate treaty regime. This situates the recent post-Paris Agreement phasecharacterized by the turn to climate litigationwithin the broader and non-linear evolution of the international rule of law in climate matters. In the article's main part, I provide a detailed analysis of national court decisions in climate mitigation cases and their repercussions for the international climate treaty regime.

The rule of international law and the role of national courts
The notion of an international rule of law is old and has experienced ups and downs but no linear development. 22 In the past three decades, the very idea that there could be something like an international rule of law may have arisen from the 1990s onwards but by now seems to have given way 16 See Voigt, supra note 13, at 3. 17 See, generally, A. Nollkaemper, National Courts and the International Rule of Law (2011), Ch. 9 ('Fragmentation'). 18 On national resistance and backlash to pro-climate litigation see Peel and Osofsky, supra note 2, at 300-7; M. Miller, 'The Right Issue, the Wrong Branch: Arguments Against Adjudicating Climate Change Nuisance Claims', (2010) 109(2) Michigan Law Review 257. 19 'Setting' in this context means that courts reference international climate treaties mostly in introductory statements or the facts of the case to highlight the relevance of climate change and the associated threats but without substantially engaging with these treaties' content and interpretation. See on the term in this context also C. Franzius and A. Kling, 'The Paris Climate Agreement and Liability Issues', in Kahl and Weller, supra note 13, at 197. 20 The term international fact is used here to refer to scientific findings on climate change restated in IPCC reports or other non-binding documents on which wide consensus exists at the international level. to disillusionment. 23 Nonetheless, the concept remains important for practice as an aspiration and for research as an analytical tool.

Core requirements of an international rule of law
States of diverse backgrounds and agendas embrace, in principle, the concept of the rule of law among states. 24 Arguably, this consensus is possible only because of the vagueness of the concept. 25 Still, an analysis of statements made by member states at the UN level reveals some core requirements of an international rule of law, namely, non-arbitrariness (as opposed to 'might makes right'), consistency (as opposed to selectivity), and predictability (of which clarity of substantial rules and the availability of general rules on sources and interpretation are elements). 26 Numerous differing concepts of the international rule of law exist within literature, but some core requirements can be identified on which consensus exists. Most scholars agree that elements of national rules of law must not simply be transplanted to the international level because of structural differences and for cultural and historic reasons. 27 This said, most conceptions of the international rule of law rely on national rule of law elements that are deemed appropriate for international relations. 28 Most scholars also agreealthough details are disputedthat the rule of law has not been fully realized in international relations. 29 Thus, the rule of law is an external standard rather than a reality at the international level. Whether the full realization of this standard is normatively desirable is another story. Put in simplistic terms, for classicists, the rule of law over power is the raison d'etre of international law, whereas for critical scholars, law is simply the pursuit of politics and power by other means, and scholarly conceptions of a liberal rule of international law are nothing 23 See Krieger and Nolte, supra note 15, at 5-7; A. Orford, 'A Global Rule of Law', in J. Meierhenrich  more than 'ruling-class chatter'. 30 Notions of an international rule of law on north-south lines may be perceived as another tool to perpetuate unequal distribution of wealth and patterns of exploitation. 31 Thus, efforts to strengthen the rule of climate law on mitigation may be seen as an instrument to slow non-Western economic development. Conversely, many developing states support the rule of international law on loss and damage to obtain financial compensation from states with high historic greenhouse gas (GHG) emissions. 32 For these reasons, the international rule of law here is neither understood as a reality nor as an ideal, 33 but as a descriptive category and analytical tool. The concept may well stand in a liberal tradition and not all of its elements may have universal appeal. 34 Nonetheless, it helps to understand where current developments in international law are heading and whether they depart from current understandings of the international rule of law. To display nuances, the international rule of law is conceptualized as a matter of degree rather than an all-or-nothing concept. 35 To provide for such nuances, it is also helpful to distinguish between a thin and a thicker rule of international law. 36 The thin approach conceptualizes the international rule of law in a formal, procedural and functional sense, all of which are interrelated. 37 In a formal and functional sense, the rule of law first demands that laws are prospective, accessible and clear to provide for foreseeability and stability as well as at least some limits to arbitrary exercise of power. 38 Clarity is not unrealistically imagined as absolute here; 39 rather, the rule of law is conceptualized in a functional and procedural sense as relying on a particular form of argument, including a limited set of sources and interpretative tools, that tends to restrict the open pursuit of self-interest. 40 This functional understanding, which is closely connected to interactional accounts of the rule of international law, provides for predictability while at the same time accommodating and guiding change. 41 For various reasons other forms of norms such as 'soft law' may, at times, be preferable to legal rules and principles. 42 However, in my understanding, a trend towards informality is a symptom  37 See Tamanaha, ibid., at 91; McCorquodale, supra note 27, at 281-2; see also but ultimately also taking in substantial criteria: Watts, supra note 25, at 16, 22. 38 See Chesterman, supra note 28, at 342; Beaulac, supra note 29, at 209, drawing on Dicey, Hayek and Raz; see also Watts, ibid., at 26-8. 39 See Watts, ibid., at 28; Beaulac, ibid., at 206. towards the decline of the rule of law, at least if soft law does not develop into hard law. 43 If soft law elements characterize a treaty, what looks like law is actually an empty formality. 44 Further elements of the international rule of law which are strongly supported in the literature are non-arbitrariness and equality before the law. 45 Equality before the law in the international setting would be provided if international law were generally applicable. Non-arbitrariness requires a minimum of consistency in the application of international law to comparable cases. 46 Thus, this conception of the international rule of law favours non-arbitrariness in terms of application and universality in terms of norm addressees. 47 Four caveats are necessary: First, equality must not be absolute but allows for differentiation on objective grounds. 48 Second, equality under the thin dimension of an international rule of law refers to relations between states, not between states and individuals, but the latter is captured by the thick rule of international law. 49 Third, compliance must not be mistaken for the sole element of an international rule of law. 50 Such a view confuses the rule of international law with the rules of international law 51 and overemphasizes stability over adaptability. Otherwise, developing customary law through non-compliance would be incompatible with the rule of law.
Fourth, there may exist a trilemma insofar as it is often complicated to synchronously achieve ambitious and clear content, widespread participation and compliance. 52 For example, it may well be that a 'rule of negotiation' paradigm, 53 a complex mostly procedural structure of 'hard, soft and non-obligations' 54 and 'constructive ambiguity', 55 was necessary to accommodate competing interests of the parties to the Paris Agreement. However, it is not impossible to achieve widespread participation, ambitious and clear content as well as complianceor at least a reasonable level of eachfor which one may point to the UN Charter and the World Trade Organization agreements.
A procedural thin notion of the rule of law could further include some form of accountability of states, ideally to be upheld by independent judicial dispute settlement mechanisms. 56 As accountability hinges on independent courts, it is this element of an international rule of law that is often deemed to be lacking. 57 Nevertheless, states' approaches towards international dispute settlement and the role of courts within states, particularly when it comes to applying international law, differ significantly. At the UN level, state support for accountability as an element of the international rule of law is strong, but supporters do not form a majority. 58 Moreover, international judicial dispute settlement, which has been on the rise since 1990, has faced considerable opposition 43 In that direction see Krieger 57 See, e.g., Nollkaemper, ibid., at 5; but see on the increased role of international judicial dispute settlement K. J. Alter, The New Terrain of International Law: Courts, Politics, Rights (2014). in recent years. 59 Therefore, accountability and the availability of mandatory judicial dispute settlement are treated here only as an element of a thicker notion of the international rule of law.
The second element of a thicker conception is a substantial one, namely, the compatibility of international legal norms with human rights. 60 Despite many contestations, human rights, at present, remain the central normative standard of our age. 61 The understanding here is not that the establishment of human rights at the international level suffices to speak of a thick international rule of law. Rather, human rights are taken as an internal-external standard to normatively evaluate the very content of different areas of international law. 62

National courts and the international rule of law
In the absence of compulsory dispute settlement in many areas of international law, scholars long ago began to look at national courts as guardians of an international rule of law. 63 This role does not fall naturally to domestic courts. From an international law perspective, courts are mere organs of the state whose compliance with international law is in question; thus, they appear as judges in their own matters. 64 The fact that national courts perform judicial as well as legislative functions further complicates their role from an international law perspective. 65 As court decisions qualify as state practice, they contribute to the formation, consolidation and reinforcement of customary law and general principles, and as subsidiary practice, they may influence the content of treaty law. 66 Although states in international relations mostly act through their governments the International Law Commission (ILC) clarified that there is no predetermined hierarchy among the various forms of practice. 67 Still, court decision (especially final ones by higher courts) often appear to be the last word of a state, if it is not undermined by succeeding actions of other state organs. 68 This dual role of enforcement and development of international law by domestic courts is also present in the practice of interpreting international norms. Whereas some would say that 59 Examples include the current dysfunctionality of the WTO Appellate Body Mechanism; apparent disregard of many States for decisions of human rights courts (e.g., Russia and the ECrHR) or other decisions (e.g., South China Sea Arbitration); for more examples see Orford, supra note 23, at 559-60. 60 According to Arajärvi, supra note 26, at 189, 57 states at the UN supported human rights as an element of the international rule of law; on human rights as an element of an international rule of law also see Pavel, supra note 33, Ch. 3; and more limited see also McCorquodale, supra note 27, at 293. interpretation is a mere form of application, the line to creation and destruction is thin. 69 Such law creation 70 is not formally binding on other states, except when thresholds of customary law or subsequent practice are met, but to correctly assess the contents of law, other courts must consider judgements as an expression of state practice and often engage with other courts through some form of judicial dialogue. 71 Despite all complexity, it is clear that the dual role of national courts is strongly connected to debates on the international rule of law. 72 National courts are often the only forum in which states can be held accountable for violations of international law. In applying and interpreting international law, national courts may increase consistency and clarity and expand the scope of international law. In that regard, uniformity must not necessarily be seen as the ideal, as national judges may be required to adjust international law to local circumstances. 73 Still, I take a common direction of various interpretationsfor example, whether particular provisions of a treaty are bindingas a sign for a rise in international rule of law. This is because legal bindingness stands for juridification, which enables accountability. Apparently, this also matters for statesotherwise, treaty language would not be such a central element of climate negotiations.

The rise and decline of the international rule of climate law
In the following part, I capture the rise and decline of the rule of international law through the evolutionary phases of global climate treaty law. 74 Only by evaluating where international climate law stands is it possible to analyse in which direction climate litigationwhich, in my view, is the characteristic feature of the latest post-Paris Agreement phaseleads the system. Particular emphasis is put on legal bindingness, clarity, membership and scope of obligations, the availability of international judicial dispute settlement, and the relevance of human rights.

UNFCCC
Based on these criteria, the United Nations Framework Convention on Climate Change (UNFCCC) can be seen as a first step, albeit a small one, in the establishment of a thin rule of law in climate matters. Notably, the UNFCCC introduced the essential objective of the climate regime, namely, the 'stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system' and important principles, such as 'common but differentiated responsibilities'. 75 The UNFCCC also established a procedural regime according to which parties are required to formulate, implement, publish and regularly update national programs, and in terms of substance set the soft ('with the aim of'  Explicitly, see Nollkaemper, supra note 17; Kumm, supra note 33. 73 See, for an overview of positions taken, H. P. Aust, 'Between Universal Aspiration and Local Application: Concluding Observations', in Aust and Nolte, supra note 71, at 336-8. 74 For the sake of brevity the analysis focuses on the three central climate treaties, but it is noted that international climate law in a broader sense may include further treaty regimes and customary law, see, e.g., D. Bodansky  Regarding judicial dispute settlement, the UNFCCC contains no mandatory mechanism, only a rarely used option for parties to accept the jurisdiction of the International Court of Justice in advance. 77 Relevant for the human rights element is that the treaty text acknowledges that climate change may, on the one hand, 'adversely affect natural ecosystems and humankind' and, on the other hand, that the growing share of GHG emissions in developing countries may be necessary 'to meet their social and development needs'. 78 However, as the mitigation goal was decent, soft and limited to Annex I parties, the UNFCCC, in legal terms, did little to protect rights to physical integrity and others. Conversely, there was no real danger of conflict between mitigation commitments and states' requirements under economic, social and cultural rights.

Kyoto Protocol
Based on the criteria of clarity, compliance and enforceability, the Kyoto era was the climax of the rule of international climate lawat least for industrialized states (so-called Annex I parties). The Kyoto Protocol contains multilaterally negotiated and legally binding quantitative emission caps. 79 These quantitative caps were meant to collectively reduce emissions by Annex I parties by at least 5 per cent below 1990 levels in the period 2008-2012. The Kyoto Protocol's dispute settlement mechanism came closest to being a judicial one. Individual mitigation targets were subject to a mandatory compliance system, described by commentators as 'the most ambitious and elaborate of the multilateral environmental agreements' compliance regimes in operation today'. 80 Both expert review teams and other parties could initiate review procedures, which they did in at least 12 cases. 81 Parties even installed an appeal mechanism. 82 As legal remedies, they foresaw the subtraction of excess emissions (multiplied by a rate of 1.3) from national GHG budgets, among other actions. 83 In terms of compliance, it bears notice that Annex I parties together surpassed the mitigation goal by approximately 17 per cent. 84 Other elements of the international rule of law were less developed. First, the protocol's mitigation commitments addressed only Annex I parties, ignoring China and other huge GHG emitters and thus scoring badly on generality and universality. 85 Although historical emissions can be considered a legitimate reason for differentiation, they may not justify a complete exemption. With the decision of the United States in 2001 not to ratify the Kyoto Protocol, another major gap opened, which is not justifiable on reasonable grounds. In the end, the Kyoto Protocol's mitigation commitments governed only an estimated 24 per cent of global GHG emissions. 86 Additionally, the temporal limitation to five-year commitment periods meant that the Kyoto Protocol was incapable of providing much foreseeability. 87 Although a second commitment period was adopted in 2012 to cover the years 2013-2020, its coverage was even more limited, as Canada had withdrawn from the Kyoto Protocol in 2012 and Japan, New Zealand and 77 Only the Netherlands, the Salomon Islands, and Tuvalu issued acceptances under Art. 14(2) UNFCCC (www.unfccc.int/ process/the-convention/status-of-ratification); other practically irrelevant provisions are: Art. 7(2) and Art. 13 ('multilateral consultative process'; which was never established).  Dec. 27/CMP.1, Ann., Section VII, para. 1; for an overview of cases see www.unfccc.int/process/the-kyoto-protocol/ compliance-under-the-kyoto-protocol. 82 Dec. 27/CMP.1, Ann., Section II, paras. 2-3; V, para. 4. 83 Dec. 27/CMP.1, Section XV, paras. 5(a)-(c), 6, 7. 84 UNFCCC 2015, Kyoto Protocol 10th Anniversary: Timely Reminder Climate Agreements Work, UN Climate Change News Room, available at www.unfccc.int/news/kyoto-protocol-10th-anniversary-timely-reminder-climate-agreements-work. 85 See Brunnée, supra note 21, at 231. 86 See Bodansky et al., supra note 74, at 173. 87 See Brunnée, supra note 21, at 230. Russia refused to accept new emission targets. 88 Consequently, the second commitment period covered less than 12 per cent of global GHG emissions and, due to initially low number of acceptances, entered into force only late in 2020 when the period it aimed to govern ended. 89

Paris Agreement
The Paris Agreement differs remarkably from the Kyoto Protocol in two respects, both of which are relevant for the international rule of law but that contradict each other. In terms of generality, the Paris Agreement must be seen as a huge success, as negotiators abandoned the distinction between Annex I parties and others. With the US ratification of the Paris Agreement as of 20 January 2021, all of the world's largest emitters are parties to the treaty, including China, the United States, the European Union and its member states, India and Russia. 90 Thus, the agreement in principle governs approximately 99 per cent of global GHG emissions. 91 The central cause for this success is the adoption of the so-called bottom-up approach. In essence, states discarded internationally negotiated and binding individual GHG reduction commitments in favour of a more flexible approach, entrusting governments to set nationally determined contributions (NDCs). This flexible approach resulted in considerable confusion about the legal nature of the agreement's substantial contents, which is why the Paris Agreement, in terms of legal quality and clarity, represents a decline of the rule of international climate law compared to the Kyoto Protocol.
Vagueness permeating the Paris Agreement and undermining the rule of law begins with the global temperature objective. 92 The temperature target certainly is an important step towards clarifying parties' understanding of what constitutes 'dangerous climate change' and, therefore, could be seen as an increase in the rule of law in climate matters. Nevertheless, the legal quality, if any, of the temperature target remains strongly disputed. First, the content of the objective remains dubious, as the meaning of 'well below' 2°C remains unsettled. 93 Second, the targets of the objective are unclear, since the wording neither directly addresses individual parties nor the parties as a collective. Nonetheless, some scholars have interpreted the objective as being legally binding on individual states. 94 More common is the qualification of the objective as a collective obligation. 95 Others oppose the notion of a collective obligation and qualify it as a merely aspirational nonlegal commitment. 96 In any case, it remains unclear exactly when GHG emissions are expected to peak and when net zerothe balance between the amount of GHGs produced and the amount removed from the atmosphereis to be achieved. Notably, parties only stress their intention ('aim to') to reach 88 Canada's withdrawal took effect on 15 December 2012, available at treaties.un.org/Pages/ViewDetails.aspx?src=IND& mtdsg_no=XXVII-7-a&chapter=27&clang=_en#2. 89 UN Climate Press Release of 2 October 2020, available at www.unfccc.int/news/ratification-of-multilateral-climateagreement-gives-boost-to-delivering-agreed-climate-pledges-and. the global peak of GHG emissions 'as soon as possible' and to achieve net zero 'in the second half of this century'. 97 Moreover, the Paris Agreement does not clarify whether these objectives must inform individual states' NDCs. Given that the objective is vague and that no agreement has been reached regarding the distribution method of the allowable global GHG budgetwith the principles of common but differentiated responsibility and equity providing only vague guidanceseveral scholars argue that individual parties enjoy vast (if not full) discretion in setting their NDCs. 98 Others assume that Article 4, paragraph 3, of the agreement at least establishes an 'obligation' of non-regression. 99 Accordingly, states would not be allowed to reduce their ambitions in subsequent NDCs compared to their initial pledge. However, others characterize non-regression as a mere 'normative expectation' rather than a legal obligation. 100 This lack of clarity continues when it comes to the legal bindingness of NDCs after their establishment. Depending on their content, NDCs may qualify as binding unilateral declarations, and the Paris Agreement may impose an obligation of conduct to pursue domestic measures with the aim of achieving targets listed in the NDCs. 101 Others characterize NDCs as an 'expectation of good faith'. 102 The problem is exacerbated by the fact that no clear standards exist as to the contents of NDCs. Whereas some NDCs are worded in obligatory language, 103 most refrain from establishing clear judiciable targets. 104 No clarification of these disputed issues is expected at the international level, given the rather weak compliance mechanism foreseen in the Paris Agreement. Moving away from the rather strong judicial enforcement mechanism of the Kyoto Protocol, the Paris Agreement only establishes a Facilitation and Compliance Committee, which is not a judicial body in a narrow sense. 105 The so-called global stocktake, which is due to take place in 2023, may officially reveal whether parties are on track to meet the collective objective, but it is unlikely that this mechanism will contribute to further clarification of disputed legal questions. 106 Notably, this process is not meant to assess individual countries' progress in a naming-and-shaming manner but only the collective progress of parties. 107 This does not mean that no paths exist to bring a climate case before an international judicial body with repercussions for international climate law. 108 In particular, the notion of requesting an advisory opinion from the International Court of Justice or the International Tribunal of the Law 97 Paris Agreement, Art. 4 para. 1. 98 See Franzius and Kling, supra note 19, at 201; Meguro, supra note 95, at 943-4. 99 of the Sea has recently gained traction. 109 In addition, human rights bodies already play a role in developing international climate law, although so far, a limited one.
The Inter-American Court of Human Rights in its Advisory Opinion on human rights and the environment already accepted that climate change impacts human rights. 110 Further, the Court referenced the UNFCCC several times, inter alia in establishing a human rights obligation of States to prevent 'significant environmental damage' within and outside their territories and in finding that the precautionary principle applies in human rights law. 111 However, given its limited mandate under questions raised, the Court did not address any of the more specific and controversial questions raised above and cited the Paris Agreement only once without interpreting its content. 112 Other human rights bodies cursorily addressed climate change in human rights terms in public statements, 113 general comments, 114 and concluding observations on parties' periodic reports. 115 Several individual complaints that rely partially on international climate law are pending before the European Court of Human Rights. 116 In two cases, UN human rights bodies decided individual complaints dealing explicitly with climate mitigation. 117 In Sacchi et al., the Committee on the Rights of the Child progressively affirmed its jurisdiction and accepted that '[f]ailure to take measures to prevent foreseeable human rights harm caused by climate change, or to regulate activities contributing to such harm, could constitute a violation of States' human rights obligations'. 118 The Committee also referred to the principle of common but differentiated responsibility to rebut the argument that the general nature of the causation of climate change would absolve state parties of individual responsibility. 119 However, it had not had the chance to further develop these arguments as it found the complaint to be inadmissible for failure to exhaust domestic remedies. 120 117 See, for another decision in which climate change played a major role but which did not concern climate mitigation in a narrower sense, UN Human Rights Committee (HRC), Ioane Teitiota v. New Zealand, CCPR/C/127/D/2728/2016, Decision of 7 January 2020. Ibid., at 13, para. 9.10. 120 Ibid., at 15, paras. 9.15-9.20. climate adaption. 121 Accordingly, international climate law played no role in finding a violation of the rights of complainants. 122 Regarding human rights as an element of the international rule of climate law, it is also notable that the Paris Agreement is the first climate treaty that references human rights. Many commentators thus hailed the treaty for breaking new ground on the connection between climate change and human rights. 123 Nevertheless, a more careful evaluation is due. 124 The human rights provision was not included in the operative part of the agreement and is also worded in soft-law language ('parties should'). It is also unclear whether the formulation 'when taking action to address climate change' only reaffirms the rather uncontroversial finding that climate change mitigation measures must respect fundamental rights (e.g., the right to property) or whether it also addresses the question of whether states need to protect human rights by implementing adequate mitigation policies. 125 Although the text of the preamble appears to be open to a broader interpretation and, in principle, should inform interpretation of the treaty's operative part, 126 many states continue to appear reluctant to frame climate change mitigation as a human rights issue. Negotiations after 2015 concerning the inclusion of a human rights reference into the so-called rulebook proved to be controversial. Advocates of a human rights approach to mitigation had argued that human rights should inform the design and ambition of NDCs and that state parties should be required to provide information on how human rights informed their NDCs. 127 However, parties tellingly opted to omit such an explicit reference. 128 Thus, the reference to human rights in the preamble has not led to any practical outcomes and, in terms of a rise of a thicker human rights conception of the international rule of law in climate matters, it may be seen as only a very small step. More important is the work by UN human rights bodies and regional human rights courts but much depends on how future 'case law' unfolds.

Domestic climate litigationa new era for the international rule of climate law?
For those activists who are frustrated by the outcomes of various Conferences of the Parties in recent years as well as states' insufficient NDCs, the turn to climate litigation is, first and foremost, a continuation of their struggle with other means. According to this logic, every case won is a win for the climate and, thus, for the objective of international climate law. In a similar vein, some scholars appear to be of the view that every reference to an international climate treaty in a national court's decision is a sign of the relevance of international law. I argue that the situation is more complicated; accordingly, this section focuses on cases related to international climate law, in particular, those that seek to require governments to raise their climate mitigation ambitions and/or to fulfil their self-established goals. 129 The latter comprises cases aimed at holding states accountable for fulfilling set reduction targets as well as cases challenging infrastructure projects. Cases dismissed for procedural reasons are not covered in the following. 130

Juridification, clarity, and compliance
The focus of the following analysis is on whether national courts can be said to hold states accountable for internationally agreed-upon obligations (compliance), whether they have improved clarity in a concise manner and whether they have further juridified 'soft' treaty provisions. Moreover, I highlight how courts have established constitutional rights and human rights as the predominant standard according to which climate policy and international climate law are to be assessed.

Towards individual responsibility for temperature goals?
Early after the conclusion of the Paris Agreement, the New Zealand High Court was rather reluctant to hold the government accountable for meeting internationally agreed-upon temperature goals. In Thomson v. Minister for Climate Change Issues, the court, without much ado, found that under the Paris Agreement, '[t]here is no requirement for countries to adopt a target, that if adopted by all, would achieve this goal' of keeping the global average temperature increase well below 2.0°C. 131 In other words, states are free to establish their domestic targets at a level they deem appropriate and cannot be individually held accountable. 132 At first glance several later decisions point in the opposite direction. The Supreme Court of the Netherlands, the Hoge Raad, in the much-cited Urgenda case, explicitly accepted 'partial responsibility' by the Netherlands. 133 Although the court grounded its argument primarily on the European Convention on the Protection of Human Rights and Fundamental Freedoms (ECHR), it went so far as to state that 'the UNFCC and the Paris Agreement are both based on the individual responsibility of states'. 134 To support individual responsibility, the court primarily referred to Article 47, paragraph 1, of the International Law Commission's Articles on State Responsibility, including a direct quote from the commission's commentary therein. 135 Unfortunately, the court does not engage with these legal provisions in more depth. With regard to Article 47 of the Articles of State Responsibility, it is disputed whether the clause addresses only situations in which an act qualifies as a wrongful act for each state 136 or whether it covers situations in which several acts of states together become wrongful (e.g., under a collective obligation, 129 This approach must not be mistaken as an argument against the importance of other forms of climate litigation in achieving the overall goal of protecting the planet and its inhabitants.  134 Ibid., para. 7.3.2; see also para. 5.7.3 with reference to Art. 3(1) and Art. 3(3) UNFCCC. 135 Ibid., paras. 5.7.1-5.7.7. 136 See Mayer, supra note 5, at 430. or when emissions by several states together cause harm). 137 Under the first interpretation, no individual responsibility arises for climate change, as it is difficult to conceive of each and every GHG emission as illegal. This is glossed over by the finding that partial responsibility cannot be evaded by simply pointing to other states or to a state's minor contribution to global warming ('no reduction is negligible'). 138 The court then concretized the content of this responsibility by using the so-called common ground method established by the European Court of Human Rights (ECtHR). 139 By referring to a plethora of international documents and the Paris Agreement's temperature targets, the Hoge Raad established the 2°C target as the 'maximum target to be deemed responsible'. 140 Doctrinally, this could be read to mean that states under international climate treaty law are individually responsible for fulfilling this 'maximum target'. Accordingly, commentators suggest that human rights in this case were misused as a 'Trojan horse' enabling the Hoge Raad to enforce international climate law. 141 However, the Hoge Raad refers to 'consensus in the international community and climate science'not international law as suchto establish its 'absolute minimum'. 142 Consensus in that regard must not be read as a reference to customary international law or subsequent practice. The Hoge Raad's reference to an absolute minimum is not so much a representation of international climate law but an appraisal of consented scientific evidence of what is tolerable in terms of temperature increase to adequately protect human rights to life and physical integrity. Accordingly, the court does not make an argument about the legal bindingness and content of international climate law but regards these documents as 'international facts'. This view is more explicitly promoted in the judgement of the Hague District Court in Milieudefensie v. Royal Dutch Shell (RDS). Here, judges dismissed the Paris Agreement as 'non-binding on the signatories and : : : non-binding for RDS'. 143 Instead, the court used reports from the Intergovernmental Panel on Climate Change (IPCC) as 'international facts' based on which it concludes that 'the goals of the Paris Agreement represent the best available scientific findings in climate science' and that these 'non-binding goals of the Paris Agreement represent a universally endorsed and accepted standard that protects the common interest of preventing dangerous climate change'. 144 The climate decision by the German Federal Constitutional Court (Bundesverfassungsgericht) points in a similar direction. This court followed the Hoge Raad on individual responsibility, albeit with slightly different reasoning. 145 According to the court, constitutional rights and the basic law's (Grundgesetz) environmental clause have an international dimension. 146 Thus, the government, in principle, must seek international solutions when its own means are limited. This international dimension, however, does not lead to a primacy of international climate law and is not meant to dismiss individual accountability. Rather, 'state organs are obliged to take climate action irrespective of any such agreement', for example, when 'it proves impossible for international 137 See for such an interpretation, Wewerinke-Singh, supra note 5, at 93. 138 See Urgenda v. Netherlands, supra note 133, paras. 5.7.7-5.7.8. 139 See, on the common ground method, e.g., K. Dzehtsiarou, European Consensus and the Legitimacy of the European Court of Human Rights (2015). cooperation to be legally formalized in an agreement'. 147 The need to unilaterally adopt strong climate policydespite the fact that this alone may not prevent climate crisisis justified by the argument that, to achieve effective climate action, Germany must 'avoid creating incentives for other states to undermine : : : cooperation'. Here, the Paris Agreement comes in but only to illustrate the court's argument that the international climate regime is not based on hard legal obligations but on mutual trust. 148 To nurture that trust, the court requires the government to pursue climate policies aimed at the Paris temperature objectives. Factually, this finding elevates international collective objectives between states to an individual obligation towards individuals. 149 Nevertheless, the court did not engage with the legal quality of the Paris Agreement as such. Rather, the judges argued that the legislators' reference to the Paris objectives in the Federal Climate Protection Act (Klimaschutzgesetz, KSG) is the 'constitutionally relevant specification of the climate goal contained in the basic law' 150 that 'goes beyond the consent given by the German legislator to the Paris Agreement in passing the act of approval'. 151 From that perspective, the Paris Agreement is only a tool through which the German state is fulfilling its obligations stemming from constitutional rights and the basic law's environmental clause. 152 Again, this is evidence of the court's understanding regarding hierarchy between the basic law and international obligations. 153 Notably, the court even feels the need to briefly acknowledge that the so-specified temperature objective appears sufficient from a constitutional perspective at present but also that, in the case of new scientific evidence, the objective would have to be adjusted; depending on the evidence, both upward as well as downward corrections appear possible. 154 Thus, the court upholds a thick (national) rule of law, with constitutional rights as an external standard to evaluate the content of international climate law.
Interpreting the 'constitutionally relevant specification of the climate goal', the court allowed state authorities much discretion. The closest the court could get to a numerical climate objective was in stating that a 1.75°C degree limit 'is certainly within the range of what is legally permissible'. 155 Thereby the court rejected the plaintiff's argument that state action must be sufficient to achieve the 1.5°C objective.
What the Dutch and German cases have in common is that courts found respondents to be individually responsible for contributing to international climate objectives. Doctrinally, this must not be mistaken for an interpretation of climate objectives to be legally binding as such. As indicated, the Hoge Raad relied primarily on 'international facts' and the German Constitutional Court on the climate protection act's reference to the Paris temperature goal. These approaches are replicable in states that either adopted climate protection acts with respective references or that are parties to the ECHR. However, these findings are highly context-specific and do not support the view that all parties to the Paris Agreement are individually responsible for realizing the temperature goals. 147 Ibid., para. 201. 148 Ibid., para. 203. Ibid., paras. 209-10 with reference to § 1 para. 1 KSG. 152 Ibid., para. 210. 153 Ibid., para. 211. 154 Ibid., para. 212. 155 Ibid., para. 242.

Clarifying the fair share of industrialized states
Based on the finding that their home states can be held accountable under constitutional law and human rights law, respectively, courts next had to establish the 'fair share' of GHG reductions due by individual states. Both the Hoge Raad and the Brussels Court applied the common ground method to derive an international minimum standard of required reductions to protect human rights under the ECHR but came to different conclusions. 156 According to the Hoge Raad, there is an international consensus that, for an Annex I party such as the Netherlands, a reduction of 25 per cent by 2020 compared to 1990 levels presents 'an absolute minimum' of appropriate protection under Articles 2 and 8 of the ECHR, as it 'offers a good chance of not exceeding the limit of warming of more than 2°C'. 157 In particular, this goal was taken from the non-binding Fourth IPCC Assessment Report from 2004 and several non-binding Conference of the Parties resolutions. 158 In contrast, the Brussels Court refused to rely on non-binding documents such as IPCC reports or conference outcome documents. 159 In essence, the only binding obligation for Belgium that the court found was a 20 per cent reduction commitment for 2020 stemming from the second commitment period of the Kyoto Protocol. 160 Thus, the court dismissed applicants' claims for more ambitious targets for 2025, 2030 and 2050 (net zero), as it found no support for such quantified targets in the Paris Agreement or elsewhere. 161 This did not stop the court from finding that the government was failing to take 'all necessary measures' to protect fundamental rights to life and privacy, but it refrained from establishing numerical targets. 162 The German Federal Constitutional Court took a different pathas it had earlier dismissed ECHR rights as not going beyond requirements under constitutional fundamental rightsand therefore did not apply the common ground method. 163 Rather, the court attempted to derive and concretize the national GHG budget based on the Paris temperature goals established as specified constitutional law. The court noted that the 'Paris Agreement does not specify any greenhouse gas reduction quotas or emission ceilings that would have to be met in order to achieve the targets'. 164 Therefore, it first relied on IPCC estimates regarding the global GHG budget allowable to achieve the 1.5°C and the 2.0°C goals, respectively. The problem that remained was that the target, in itself, is rather vague, and scientific estimates of the global budget remaining to achieve certain levels of global average temperatures differ. 165 Further, the court struggled to estimate the national budget for Germany, but it is noteworthy that it did not dismiss such an undertaking upfront: Germany's contribution in this regard must be determined in a way that promotes mutual trust in the willingness of the Parties to take action, and does not create incentives to undermine it (see para. 203 above). Certain indications regarding the distribution method can be derived from international law, such as from Art. 2(2) and Art. 4(4) PA (on the principle of common but differentiated responsibilities, see also Art. Even with these 'indications', the court refrained from taking the carbon budget calculated for Germany by the national German Climate Councilbased on a per-capita share and a 1.75°C temperature goalas an 'exact numerical benchmark'. 167 Nonetheless, the court required the government to 'take into account' the budget so calculated in devising its climate policy. 168 What this means more precisely remains an open debate. 169 In that sense the Bundesverfassungsgericht does not develop a clear numerical reduction commitment but only a 'due diligence obligation'. 170 In contrast, the Hoge Raad establishes a clear numerical goal comparable to the 'Kyoto approach'. 171 However, all courts refrain from strengthening clarity or developing legal bindingness of the Paris Agreement. According to the Bundesverfassungsgericht, Germany is constitutionally obliged to protect the climate irrespective of international climate treaties. While the German court cites a plethora of climate treaty provisions to concretize constitutional law, it does not make claims about the legal character of the former or even their precise legal meaning. As noted, the Hoge Raad relies on regional human rights law concretized by international facts rather than on international climate law as such. It is also doubtful whether Dutch courts are willing to develop further numerical goals for the post-2020 phase, given the lack of inter-governmental consent in that regard. 172 So the Urgenda decision did not establish clarity and foreseeability as its applicability is temporally limited. Therefore, both decisions establish only limited national rule(s) of law in climate matters but do not represent a rise of the international rule of climate law.

Compliance strictu sensu
The foregoing parts only partially addressed 'compliance' with the Paris Agreements temperature objective as the focus was on creative development and juridification. In the following, I address compliance in a stricter sense, namely via efforts to enforce goals set in Nationally Determined Contributions (NDCs) including lawsuits brought against individual projects. 4.1.3.1 Nationally determined contributions. Some scholars portray climate litigation as an instrument to hold states accountable for their NDCs and thereby to increase compliance with international climate law. 173 Practical support for that finding is slim and not concise. The New Zealand High Court qualified NDCs as non-binding in international law, 174 and both the Brussels Court and the German Federal Constitutional Court characterize the mechanism to establish NDCs as 'voluntary'. 175 A more differentiated approach is apparently pursued by the UK Supreme Court, which qualifies the European Union's NDC as binding but suggests that the Paris Agreement does 'not impose an obligation on any state to adopt a binding domestic target'. 176 Under that reading the bindingness of NDCs depends on their content.
Another court that may have taken an NDC as legally binding is the Colombian Supreme Court. In Future Generations v. Ministry of the Environment, the court seems to argue that 167 Ibid., para. 236. 168 Ibid., para. 247. 169 the pledge to stop deforestation, as included in its NDCs, is a binding commitment of the state. 177 However, one must be cautious here, as the decision's wording is not entirely clear and the findings on international climate law are only a brief obiter dictum after the court established a violation of national law.
One pending case that could shed further light on the bindingness of NDCs and the legal implications of 'progression' is a case brought by several youths against the government of Brazil. 178 However, it remains to be seen whether the court accepts the standing of individuals to bring such a case. 179 Apart from these direct invocations of NDCs, a broader range of cases is relevant here for factual reasons. These cases seek to hold states accountable for self-established policy objectives or legal targets. In states where these commitments are synchronous to the content of NDCsor even more strictthese cases qualify as 'factual' enforcement of NDCs. 180 Such an approach apparently is less likely to succeed in states where no legally binding national targets exist 181 or where individuals do not have legal standing to hold governments accountable for national climate acts. However, in jurisdictions where climate laws fall together with broad interest-based standing requirements, such as France, enforcement cases play an important role. Notably, the Paris Administrative Court, in L'Affaire du Ciecle, held France accountable for fulfilling its nationally established objectives, as well as EU objectives, and ordered the state to take actions to reduce GHG emissions. 182 In a similar way, the Conseil d'État in Grand Synthe required the government to take all necessary measures to achieve the self-determined goal to achieve a 40 per cent reduction in GHG emissions by 2030 compared to 1990 levels. 183 In these cases, international climate law played a role but only a marginal one. Notably, the Conseil d'État denied the direct effect of the UNFCCC and the Paris Agreement, but nonetheless argued that national laws must be interpreted in light of international mitigation goals. 184 This statement, however, did not extend beyond mere lip service, as national laws were sufficiently clear, and the court did not further specify how international climate law influenced its decision. 4.1.3.4 Challenging individual projects. In a final set of cases, plaintiffs relied on international climate law to challenge individual projects or policies. This group of cases is related to international climate law insofar as plaintiffs argue that it is necessary to stop certain GHG-intensive projects to comply with the Paris Agreement.
These cases overwhelmingly face the obstacle that individual projects and policies contribute little to climate change in relative terms. Thus, the Norwegian Supreme Court dismissed a case on the grounds that the individual project posed no 'real and immediate' threat to the right to private 177 life and family and the right to life. 185 Similarly, the UK Supreme Court concluded that, given remaining uncertainty as to future policies and the availability of climate-neutral technologies, a permit for another terminal at Heathrow Airport was not 'unreasonable' even if it covered the period after 2050, when, according to UK policy, the country should achieve 'net-zero' GHG emissions. 186 Most recently, the Australian Federal Court inter alia found that the approval of a coal mine extension would not cause 'personal injury' to the plaintiffs. 187 The New South Wales Land and Environment Court, in Gloucester Resources Limited v. Minister for Planning, went further in at least considering whether GHG emissions stemming from an individual project could create emissions beyond the global budget required to achieve the long-term objective of net neutrality and the global average temperature goal under the Paris Agreement. 188 However, the court did not provide further guidance on how to determine the national budget and the concrete meaning of cited provisions of the climate change accord. As the court considered the poor visual, environmental and social impacts of the project as sufficient to justify refusal of the permit, GHG emissions only presented a 'further reason for refusal'. 189 Only a few cases can be found that seem to promote more comprehensive prohibitions of GHG-intensive projects. One case in point is the deforestation matter before the Supreme Court of Colombia referred to above. 190 Another is the case of the Society for Protection of Environment and Biodiversity in front of the Indian Green Tribunal. In this case, the tribunal found an exemption for the Indian construction industry from an environmental approval process to be incompatible with the government's commitments under the Paris Agreement. 191 However, the decision lacked a justification of that view going beyond mere 'cursory reference to the need to reduce carbon emissions'. 192 In that regard, the decision connects to a number of cases in which courts referred to international climate law to justify the notion that climate mitigation is a public interest.
One of these cases is Earth Life Africa v. Minister of Environmental Affairs et al. In this case, the court interpreted national environmental law 'consistently with international law'citing the precautionary principle and Article 4(1)(f) of the UNFCCCto justify its finding that environmental impact assessments must take into account GHG emissions and even 'the decline trajectory as outlined in the NDC'. 193 Such a reading does not predetermine the outcome of the approval process 194 but at least requires national agencies to take the objectives of international climate law into consideration when granting permits for GHG-intensive projects. However, as emphasized by the High Court, the question raised by the case was 'not whether new coal-fired power stations are permitted under the Paris Agreement and the NDC'. 195 185 In a similar way, the Federal Administrative Court of Austria considered commitments stemming from the national climate protection act, the Kyoto Protocol and unspecified 'obligations' from the Paris Agreement as part of the public concerns that outweighed competing public interests in the construction of a third runway at the Vienna International Airport. 196 However, the Austrian Constitutional Court overturned the decision in 2017 as it held that international obligations stemming from the Kyoto Protocol and the Paris Agreement were not directly applicable. 197 Taken together, these cases are evidence of an increased awareness for the contribution of individual projects to climate change. In the analysed cases, international climate agreements played a role in establishing climate change as a public concern to be considered in balancing decisions. Nonetheless, in terms of enforcing international climate lawand, thus, for the international rule of law in climate mattersthese cases are negligible.
4.2 Generality: Towards a universal rule of (international) climate law?
Even if one accepts for a moment that courts in cited cases developed and enforced international climate law, to speak of an international rule of climate law would require some degree of generality and widespread participation. As seen, climate litigation, even in the narrow sense as defined here, is not merely a Western phenomenon. Nonetheless, justiciable individual responsibility for meeting international targets is limited thus far to a handful of states. Although Peel and Lin highlight the more subtle contributions of cases in the Global South for the overall objective of mitigating climate change, 198 I tend to see rather limited impact of these cases on an international rule of climate law. As demonstrated, international climate law has little to say about infrastructure projects, and courts have refrained from developing international law in that regard. Although the lack of national climate laws in many states of the Global South could induce plaintiffs to base arguments on international climate law and human rights law, the concept of common but differentiated responsibility and the lack of a clear minimum standard for developing states in terms of national budgets could prove to be major obstacles. 199 That said, several important cases are pending in major GHG emitters such as Brazil and India, and, despite initial setbacks, 200 additional cases could follow. 201 However, generality and universality may remain an elusive goal, as many important states are likely to remain outside the climate regime established by national courts. No ambitious climate litigation relevant for the international rule of climate law is known to have been decided or to be pending in Russia, the fourth-largest GHG emitter, or in China, currently the largest GHG emitter. 202 Commentators emphasize the lack of academic discussion, scepticism among public and political elites, and formal legal hurdles, such as the lack of climate laws, to explain these gaps. 203 In China, domestic climate policies increasingly seem to influence the outcome of civil actions between individuals 196 and public interest actions by state prosecutors, but these cases are based exclusively on domestic law and climate policies without formal regard for international climate law. 204 Finally, it is questionable whether a case comparable to those in Belgium, France, Germany and the Netherlands could be successful in the United States, the second-largest GHG emitter at present. In absolute terms, the United States is the jurisdiction with the greatest number of climate cases. 205 However, there is only one case that is comparable in terms of ambition to Urgenda and Neubauer et al., and it was recently dismissed. 206 Even if a case would reach the US Supreme Court its current composition most likely would not allow progressive findings that could contribute towards achieving the Paris Agreement's climate objectives.

Conclusion
It has become fashionable to describe climate law as 'multi-layered' 207 and characterized by 'crosslevel' 208 or 'transnational interactions'. 209 Multiple layers certainly exist, but this article found that doctrinal interactions among different levels are limited and work in only one direction. 210 Some courts, such as the New Zealand High Court, simply dismissed the Paris Agreement climate objectives as non-binding. Others, such as the Hoge Raad, primarily relied on 'international facts' rather than international climate law to specify a government's fair share of responsibility. Even courts that extensively cited climate treaty provisions to concretize constitutional law, such as the Bundesverfassungsgericht, refrained from comprehensively engaging with their content and legal quality. On clarifying disputed questions under the Paris Agreement and, more generally, in juridifying its content, court decisions thus far have provided little help.
The few court decisions that have allowed nongovernmental organizations and individuals to hold governments accountable for implementing national climate laws arguably support the objectives of international climate law and, in some instances, must be conceptualized as factual enforcement of NDCs. Thus far, however, such cases are a particular feature of the French jurisdiction where interest-based litigation falls together with specific climate protection laws andalbeit less clearof the Colombian deforestation case. Whereas manifest failure to fulfil national targets may also be justiciable in Germany 211 and the Netherlands 212 under regional human rights law and constitutional law, it remains to be seen whether courts in other jurisdictions will follow such an approach.
At present, only a few courtsprimarily located in Europehold their governments accountable for maintaining national GHG budgets derived from constitutional and regional human rights law, thus promoting a thick rule of national and regional law on climate mitigation. The reach of this order may expand towards some states of the Global South, but important actors such as China, Russia and the United States are likely to remain outside. Consequently, one may speak of national rules of climate law or even a hybrid rule of climate law, but not a truly international or even global rule of climate law.