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The trilogy of climate advisory opinions from the <\/span>International Tribunal for the Law of the Sea (ITLOS)<\/span><\/a>, <\/span>Inter-American Court of Human Rights (IACtHR)<\/span><\/a>, and the <\/span>International Court of Justice (ICJ)<\/span><\/a> marks a watershed moment not only for climate litigation but also for understanding the evolving role of Conferences of the Parties (COPs) in international law. The opinions provide unprecedented recognition by ITLOS, the IACtHR, and ICJ of COP decisions’ legal significance.\u00a0<\/span><\/p>\n This post analyses the courts’ engagement with COPs and argues that it represents another step in clarifying their institutional role in global governance \u2013 one that elevates these treaty bodies from largely diplomatic forums to authoritative interpreters and potentially norm-creators within treaty regimes. Building on our previous analysis elsewhere of<\/span> COPs as emerging subjects of international law<\/span><\/a>, we explore the implications of this evolving governance model.<\/span><\/p>\n The three climate change advisory opinions considered the activities of COPs in their reasoning. ITLOS acknowledged the importance of the United Nations Framework Convention on Climate Change (UNFCCC) COP (para. 69), and also noted the establishment of a similar body in the context of the Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ Agreement) (para. 92). ITLOS mostly used COP decisions as documentary evidence to trace how climate commitments have evolved, particularly regarding the 1.5\u00b0C target (paras. 77, 216).\u00a0<\/span><\/p>\n The IACtHR also recognised the prominent role of the COP in the UNFCCC regime (para. 131), and footnoted its decisions several times across the opinion to support its views (eg. paras. 192, 200, 430). Furthermore, the IACtHR considered the steps of the adaptation “iterative cycle” identified by the COP serving as the Meeting of the Parties to the Paris Agreement (CMA) a \u201cuseful guide\u201d for States to comply with their human rights obligations (paras. 381, 389).\u00a0<\/span><\/p>\n Finally, as<\/span> Wewerinke-Singh noted<\/span><\/a> in her contribution to this blog series, the ICJ equally underlined the relevance of COPs to the operation of climate change treaties (paras. 63 and 184), and also engaged with the work of COPs operating outside of the climate regime (para. 328). Notably, unlike ITLOS or the IACtHR, the ICJ provided reasoning for its reference to COPs, and an explanation of two pathways available for their decisions to have certain legal effects: (1) when treaties explicitly authorize it, and (2) when the decisions constitute “subsequent agreements” interpreting treaties (para. 184).\u00a0<\/span><\/p>\n The idea that COP decisions may constitute \u201csubsequent agreements\u201d for the purposes of Article 31(3)(a) Vienna Convention on the Law of Treaties (VCLT) is not new. The International Law Commission reached this conclusion<\/span> in 2018<\/span><\/a>, indicating that a COP decision could be invoked under this provision \u201cin so far as it expresses <\/span>agreement in substance<\/span><\/i> between the parties regarding the interpretation of a treaty, regardless of the form and the procedure by which the decision was adopted, including adoption by consensus\u201d (conclusion 11.3, emphasis added). Still, it is notable that this approach has now been endorsed by the ICJ. Moreover, the ICJ put it into practice in interpreting the temperature goal of the Paris Agreement.\u00a0<\/span><\/p>\n The ICJ decision highlights both the strengths and weaknesses of viewing COP decisions as subsequent agreements. On one hand, the ICJ has provided an example of <\/span>evolutionary interpretation<\/span><\/a> based on identifying the intention of Parties. The ICJ used COP decisions to show \u201cthe 1.5\u00b0C threshold to be the parties\u2019 agreed primary temperature goal for limiting the global average temperature increase under the Paris Agreement\u201d (para. 224). On the other hand, as Stephen Humphreys has<\/span> observed<\/span><\/a>, the ICJ opinion transforms what the Paris Agreement frames as \u201cpursuing efforts\u201d into a \u201cprimary temperature goal\u201d. This, to our minds, brings to the fore the question of where treaty interpretation ends and treaty amendments begin. It also raises fundamental questions about COPs institutional mandates and competence, especially when COP decisions reflect political aspirations or forward-looking ambitions rather than present-day objectives.<\/span><\/p>\n Furthermore, the ICJ does not clarify the meaning of the expression \u201cagreement in substance\u201d. There is no guidance within the Advisory Opinion on when a COP decision constitutes such an agreement. Moreover, although there are 12 opinions and declarations appended to the main text which touch on different subject-matters, the temperature goal remains the only instance where a COP decision is utilised as a subsequent agreement.\u00a0 Lawyers can only interpret so much from its use for the temperature goal, raising a number of questions concerning the future application of the Article 31(3)(a) pathway. These concerns will not only interest legal practitioners and academics, but more importantly COP negotiators who must demand greater clarity on what constitutes a decision that qualifies as a subsequent agreement.\u00a0<\/span><\/p>\n While most commentary on the role of COP decisions in the ICJ opinion focuses on their status as \u201csubsequent agreements,\u201d other parts of the opinion raise additional potential pathways for COP decisions to produce legal effects. First, the ICJ acknowledged that COP resolutions might also play a role in the identification of customary international law, both reflecting State practice and expressing <\/span>opinio iuris<\/span><\/i> (para 288), a subject<\/span> analysed by Gehring<\/span><\/a>. Yet, unlike its treatment of General Assembly resolutions (see <\/span>Legality of the Threat or Use of Nuclear Weapons Advisory Opinion<\/span><\/a>, para. 71 and<\/span> Lepard<\/span><\/a>), the ICJ did not provide any guidance on when this <\/span>opinio iuris <\/span><\/i>may be found (or not found).\u00a0<\/span><\/p>\n Second, the ICJ seems to bring COP decisions into the \u201cgood faith\u201d framework, in the context of its discussion of the obligations of co-operation and assistance under the UNFCCC. The ICJ stated that \u201c[t]he duty to co-operate is an obligation of conduct, the fulfilment of which is assessed against a standard of due diligence (…). Good faith co-operation in this context would entail taking into account the guidance provided by the COP decisions.\u201d (para. 218).\u00a0 This raises the question of whether performing obligations in good faith, as required by Article 26 VCLT, entails giving effect to COP decisions.\u00a0<\/span><\/p>\n Finally, another less explored pathway for COP decisions to produce legal effects is found in the ICJ\u2019s discussion of relevant international rules and standards as an element to determine the content of the standard of due diligence. The ICJ considered that international standards \u201cmay arise from binding and non-binding norms,\u201d including the outcomes of COPs (para. 287). This might prove to be a particularly relevant pathway considering the significant role that ITLOS, the IACtHR, and the ICJ assigned to due diligence. All in all, these examples reveal that COP decisions can potentially produce legal effects in more than one way.\u00a0<\/span><\/p>\n The ICJ’s reasoning alters the stakes of COP negotiations across regimes. As Humphreys <\/span>noted<\/span><\/a>, the ICJ\u2019s reading \u201cpotentially increases enormously the relevant text to be taken into account as a matter of law\u201d with over 900 COP decisions from the climate regimes that might now constitute legally relevant “subsequent agreements.” As<\/span> Frydlinger showed<\/span><\/a>, the stakes are high for the UNFCCC COP30, as negotiators must now consider that consensus decisions may acquire binding force through judicial interpretation, even absent explicit treaty authorization. Could we expect future COP decisions containing preambulatory language to the effect of \u201cthe Parties declare that this instrument does not necessarily express agreement in substance\u201d?\u00a0<\/span><\/p>\n These issues are amplified when we consider that COPs exist beyond climate change agreements, and ongoing negotiations in those fields will also be affected by the findings of the ICJ regarding the legal effects of COP decisions. In this context, it is pertinent to note that the ICJ only engages with the UNFCCC COP for its reasoning, even though it provides an interpretation of obligations from other multilateral environmental agreements that have COPs (such as the Convention on Biological Diversity and the United Nations Convention to Combat Desertification in Those Countries Experiencing Serious Drought and\/or Desertification, Particularly in Africa). Furthermore, COPs also <\/span>exist outside of the multilateral environmental system<\/span><\/a>, in areas such as international health law, international disarmament, international criminal law, and international law relating to cultural heritage. Delegates who once viewed COP decisions as political compromises must now consider the possibility that their consensus language could crystallize into binding legal obligations through judicial interpretation. Expect future negotiations to feature even more protracted debates over every word and every comma, with States increasingly wary of language that might later be claimed as an \u201cagreement in substance.\u201d <\/span>\u00a0<\/span><\/p>\n As a further issue, if and when COP decisions acquire legal force through judicial interpretation, States might become bound by obligations they may not have explicitly consented to. This is because most COPs do not have a voting procedure, instead, adopting decisions by consensus. As such, sometimes, States have agreed to pass a decision they may not individually agree with in its entirety to avoid halting progress on all negotiations, providing observations on any limitations or objections during or after the adoption of the decision. Therefore, interpreting treaty obligations (which have an explicit consent mechanism) in this manner challenges traditional notions of sovereign consent, although this could be a pathway to \u201cthick stakeholder consensus\u201d, as<\/span> Pauwelyn et al argue<\/span><\/a>. In the case of climate governance, this exposes a particular variance of the <\/span>democratic deficit<\/span><\/a>. Here, the deficit operates on two levels: not only are COP decisions made through processes that do not necessarily place States on a level-playing field, but States may also find themselves legally bound by interpretations of consensus decisions they never fully endorsed, creating a double attenuation of the consent principle that underpins both democratic governance and treaty law.<\/span><\/p>\n The use of COP decisions across the climate advisory opinions, and in particular by the ICJ, \u00a0 confirm what those writing about COPs have long suspected: COPs have moved from the sidelines to center stage as playmakers in international lawmaking. They are also rapidly being endowed with a broader institutional mandate, such as in the BBNJ Agreement, <\/span>where the COP is empowered to take legally binding decisions and can request Advisory Opinions<\/span><\/a>. No longer mere diplomatic spectators, in light of this decision, COPs should be seen as directing the action, adopting decisions capable of producing legal effects and even <\/span>impacting ongoing international conflicts<\/span><\/a>. By bringing some clarity to when and how COP decisions achieve legal effects, the ICJ has validated this starring role.\u00a0<\/span><\/p>\nCOPs in the Climate Advisory Opinions\u00a0<\/b><\/h2>\n
The Legal Status of COP decisions<\/b><\/h2>\n
What\u2019s Ahead<\/b><\/h2>\n
Concluding Thoughts\u00a0<\/b><\/h2>\n