Andrea Longo, School of Oriental and African Studies, University of London*

On May 21^st, 2024, the International Tribunal for the Law of the Sea (ITLOS) delivered its long-awaited Advisory Opinion on State obligations regarding climate change and ocean acidification requested by the Commission on Small Island States on Climate Change and International Law (hereinafter, ‘COSIS’). The Questions before ITLOS concerned the content of the obligations of the State Parties to the United Nations Convention on the Law of the Sea (UNCLOS), including under Part XII on the protection and preservation of the marine environment, to prevent, reduce and control pollution of the marine environment, and to protect and preserve the marine environment in relation to climate change impacts and ocean acidification (on the questions before the Tribunal and of the scope of the Tribunal’s advisory jurisdiction, ex multis, Barnes, Tanaka, Marotti, Asta). In a nutshell, the Tribunal heavily relied on scientific evidence from the Intergovernmental Panel on Climate Change (IPCC) and found greenhouse gas (GHG) emissions to constitute «marine pollution» within the meaning of Article 1(1)(4) UNCLOS. Accordingly, upon establishing a link between the Convention and climate change, ITLOS concluded that UNCLOS obligations must be interpreted and applied in the light of State obligations under the existing climate change treaties.

Progressive as it sounds, such a finding was almost taken as granted. With very few exceptions – e.g. China and Indonesia – the vast majority of States and non-State actors argued in that sense in their submissions. Beyond this point, the Opinion is very dense and, predictably so, it has triggered the publication of a wealth of comments and short pieces (ex multis, the different contributions on EJIL: Talk! and the symposium co-hosted by the Verfassungsblog and the Sabin Center). Several aspects would deserve thorough investigation – inter alia, the actual implications of the Opinion for Small Island Developing States, questions of State responsibility, the notion of « continuing obligation», the reference to the precautionary approach – and, in all likelihood, it won’t take long before this happens. Furthermore, this is the first of three advisory opinions on climate change (the other two are currently pending before the International Court of Justice (ICJ) and the Inter-American Court on Human Rights (IACtHR) – and the second time in just a few months that an international court deliberates on climate change (KlimaSeniorinnen; Carême; Duarte Agostino et al; on the inadmissibility of Duarte Agostino et al see, ex multis, the contribution by Pane on this blog). Thus, climate change issues are surely to remain at the forefront of international law journals and blogs for the years to come.

With this in mind, this blogpost briefly unpacks the Tribunal’s reasoning on the applicable law, addressing the scope and content of the due diligence obligations in Part XII UNCLOS, and the role of external treaties in interpreting such obligations, especially taking a close look at the Tribunal’s arguments on the systemic integration of United Nations climate change treaties into the scope of UNCLOS obligations. After that, it offers a few more reflections on the role of biodiversity law treaties and international human rights law treaties, which the Tribunal invoked either briefly or not at all.

Applicable law – Looking beyond the Convention

The Tribunal’s stance about the applicable law is clear from the outset: after recalling the relevant procedural and substantive rules, in particular Article 293 UNCLOS, the Tribunal observes that «the Convention, the COSIS Agreement and other relevant rules of international law not incompatible with the Convention constitute the applicable law in this case» (para. 127). Leaving aside the COSIS Agreement – the COSIS’ foundational instrument – Article 293 UNCLOS has given rise to a heated debate in the literature and in the case law with regard to the exact scope of the wording «other rules of international law not incompatible with the Convention» therein contained. This debate is arguably not fully settled yet, but the dominant view considers this to be a reference to «foundational or secondary rules of general international law such as the law of treaties or the rules of State responsibility», or to «primary rules of international law other than the Convention» as necessary to interpret and apply particularly «broadly worded or general provisions […] of the Convention» (paras. 190 and 191 Arctic Sunrise Award). The Tribunal avoids such a debate – regrettably so! – instead focusing directly on the relationship between UNCLOS provisions and these other rules of international law. In this regard, the Tribunal is again crystal-clear: three mechanisms regulate such relationship, namely the principle of systemic integration, the rules of reference, and Article 237 UNCLOS (paras. 131-137).These mechanisms are briefly addressed below.

i. Systemic integration

Systemic integration is a principle or method of treaty interpretation enshrined in Article 31(3)(c) of the Vienna Convention on the Law of Treaties (‘VCLT’) and requiring that a treaty be interpreted taking into account, in addition to the context, «any relevant rules of international law applicable in the relations between parties», including both treaty and customary norms. As put by the ICJ, this method ensures that treaties are not interpreted and applied in isolation from each other, but «within the framework of the entire legal system prevailing at the time of the interpretation» (Legal Consequences for States of the Continued Presence of South Africa in Namibia (South West Africa) notwithstanding Security Council Resolution 276 (1970), para. 53).

Systemic integration is particularly relevant when addressing complex and multi-faceted challenges requiring that States comply with different obligations from multiple regimes in a consistent matter (specifically on the interpretation of the UNCLOS, ex multis, Virzo, p. 15; Papanicolopulu, p. 75). This is indeed the case with climate change and ocean acidification: the Tribunal’s express reference to systemic integration is a reminder for States of the complex nature of the questions posed before it, and anticipates that the Tribunal’s analysis of the applicable law will be informed not only by other treaty regimes, but also by customary norms of international law. However, at this stage, the Tribunal does not identify which ones are relevant in relation to climate change and ocean acidification, leaving this a rather broad reference.

ii. The rule of reference

The rule of reference (or renvois) is a provision recalling an external substantive rule, technical standard, or non-binding guidelines and procedures – also known as Generally Accepted International Rules and Standards, or GAIRS – meant to inform the interpretation and application of the obligations laid out in the referring instrument (ex multis, Redgwell, Nguyen, Georgoula). As such, it is a mechanism of progressive change, for it marks the open character of the referring instrument to society – and consequently legal – changes. Rules of references are employed very frequently in UNCLOS. Notably, Part XII of the Convention, here at stake, is full of differently formulated renvois, evidence of the complex and interconnected character of the challenges underpinning the protection and preservation of the marine environment. Differently put, the numerous rules of references scattered across Part XII UNCLOS speak to the fact that the protection and preservation of the marine environment require a coordinated effort, taking into due consideration also regimes of international law other than the law of the sea.

This is upheld in the present Advisory Opinion. Climate change and ocean acidification are an example of challenges to the marine environment which did not carry the same weight for the international community at the time of the drafting of the Convention as they do now. Accordingly, the Tribunal observed that instruments belonging to the climate change regime – primarily the United Nations Framework Conventions on Climate Change (UNFCCC) and the Paris Agreement – contain relevant GAIRS for the purpose of interpreting and applying State obligations under UNCLOS. Interestingly, the expression «in particular» in paragraph 137 hints that the Tribunal is aware that the list of external treaties may be much longer.

iii. Article 237 UNCLOS

Finally, the present Advisory Opinion provided the opportunity for the Tribunal to address for the first time the role of Article 237 UNCLOS, so far mentioned only in passing by the Arbitral Tribunal in the South China Sea Arbitration (South China Sea award, para. 942). This provision regulates the relationship between Part XII UNCLOS and other treaties on the protection and preservation of the marine environment (in this regard, see both Redgwell, p. 454, and Roland Holst, p. 261 – who excluded the applicability of Article 237 UNCLOS to the UN climate change regime). Whilst paragraph 1 of this provision gives prominence to the specific obligations undertaken under other instruments – including «special conventions and agreements concluded previously» and «agreements which may be concluded in furtherance of the general principles set forth in this Convention» – paragraph 2 clarifies that such obligations should be implemented and given effect «in a manner consistent with the general principles and objectives of this Convention».

In the light of the above, ITLOS considered Article 237 UNCLOS to reflect the need for «consistency and mutual supportiveness between the applicable rules» (paragraph 133) and upheld its applicability to the climate change regime, showing a degree of receptiveness towards the arguments of COSIS in its written submission (paras. 49 and 395) as well as of some States (e.g., Italy, paras. 12-13; the United Kingdom, para. 51) and non-State actors (inter alia, the joint submission by Our Children’s Trust and Oxfam International, p. 31; ClientEarth, para. 66). Interestingly, to the best knowledge of the author, it is the first time that an international court or tribunal employs the notion of «mutual supportiveness», mentioned by COSIS (para. 394 of its written submission and pp. 30 and 35 of the oral proceedings) and thoroughly elaborated by a non-State actor (One Ocean Hub, paras. 3-4). Defined as an interpretative tool stemming from the principle of systemic integration (Pavoni, p. 650; see generally the ILC Report on Fragmentation of International Law, para. 412), a mutually supportive interpretation serves a two-fold function: preventing and solving normative conflicts while ensuring the compatibility – and even synergies – amongst multiple regimes (Matz-Lück, p. 43; Dupuy and Viñuales, p. 393; specifically on the mutually supportive interpretation of climate change treaties and UNCLOS, see generally Morgera and Lennan).

The applicable law in practice: which treaties inform the interpretation of Articles 192 and 194 UNCLOS?

As mentioned at the outset, the Opinion is very dense, and providing a detailed account of its content would fall outside of the remit of a blog post. Instead, following the above presentation of the Tribunal’s reasoning on the applicable law, I offer some reflections on the range of external treaties expressly invoked with a view to interpreting UNCLOS provisions and clarifying the scope of the due diligence obligations therein contained – i.e. climate change treaties. Finally, I take into account obligations under international biodiversity law and international human rights law which, unlike obligations under the climate change regime, are only partially invoked or not mentioned at all.

First and foremost, in responding to the two questions the Tribunal further elaborated its jurisprudence on due diligence obligations. Already the Seabed Dispute Chamber in 2011 provided important guidance regarding the nature and content of due diligence obligations in relation to sponsorship activities in the Area. After upholding such findings in its 2015 Advisory Opinion, in the present case the Tribunal endorsed the analysis by the most recent scholarship (inter alia, Krieger, Peters and Kreuzer; Ollino) and clarified two aspects: first, given the high risks of serious and irreversible harm to the marine environment from GHG emissions and, more generally, the deleterious effects of climate change and ocean acidification, the standard of due diligence must be a stringent one (inter alia, paras. 243, 256 and 399). Second, in meeting their due diligence obligations, States cannot choose «whatever measures [they] deem necessary to that end» (para. 206). Notably, in relation to climate change and ocean acidification, States should determine the necessary measures objectively (paras. 206, 257 and 405), taking into account the best available science – i.e. the IPCC reports (para. 208) – international rules and standards, and their own means and capabilities (paras. 207 et seq).

Even though none of the three is arguably exempt from a degree of discretion, the Tribunal is very clear in construing such discretion as objectively framed. In particular, in responding to Question A, the Tribunal observed that the UNFCCC and the Paris Agreement contain rules and standards informing the scope and content of the measures to prevent, reduce and control pollution of the marine environment under Article 194 UNCLOS. Such rules and standards include, amongst others, the temperature goal and the timeline for emission pathways under the Paris Agreement, as well as the principle of common but differentiated responsibilities and respective capabilities under Article 3 UNFCCC and Articles 2(2) and 4(4) Paris Agreement (see paras. 222-231). Notably, the Tribunal clarified that the obligation to prevent, control and reduce marine pollution under Article 194 UNCLOS would not «be satisfied simply by complying with the obligations and commitments under the Paris Agreement», for the latter «complements the Convention» as opposed to superseding it (para. 223), and does not qualify as lex specialis (para. 224).

The two UN climate change treaties are not the only ones expressly featured in the Tribunal’s line of arguments, but surely occupy a significant weight compared to others mentioned in the Opinion. Amongst these, the Convention on Biological Diversity (CBD) is largely overlooked. The Tribunal’s attitude towards it appears oddly cold, in stark contrast with its approach to climate change instruments. This is especially so if one considers that the reasoning underlying the applicability of Article 237 UNCLOS to the latter set of treaties could have been equally applied to biodiversity law treaties, which arguably fall under either category of agreements provided in Article 237(1) UNCLOS («special conventions and agreements concluded previously which relate to the protection and preservation of the marine environment» and «agreements which may be concluded in furtherance of the general principles set forth in [the] Convention»). In addition, a significant number of States (ex multis, Egypt, para. 32; Mozambique para. 3.44; the UK, para. 38; the European Union, para. 62) and non-State actors (ex multis, the COSIS, para. 415; International Maritime Organisation, para. 82; International Union for the Conservation of Nature, para. 177) invoked the CBD and the CBD Decisions as external instruments containing additional rules and standards to inform UNCLOS obligations, which further raises questions on the Tribunal’s decision to selectively rely on mostly climate change treaties.

The above is not to say that international biodiversity law treaties are completely overlooked. In responding to Question B, the Tribunal gives effect to the link between the protection of the marine environment and the conservation of marine living resources already drawn in its case law (inter alia, Southern Bluefin Tuna case, para. 70) by resorting to the United Nations Fish Stocks Agreement (UNFSA) and to the Convention on International Trade in Endangered Species (CITES). Thus, the two treaties related to the conservation and management of marine living resources must inform the scope of the obligations under Article 192 UNCLOS in relation to the threats of climate change and ocean acidification. Also, the Tribunal cautiously draws attention to the future role of the newly adopted Agreement on Biodiversity Beyond National Jurisdiction (BBNJ Agreement) in advancing the conservation and sustainable use of marine biological diversity in areas beyond national jurisdiction (para. 440). However, the references to the CBD and to other biodiversity treaties appear insufficient or merely confined to definitional matters (in this regard, see paras. 166 et seq).

Finally, the Tribunal chose to avoid human rights matters, at least nominally. The only express reference to human rights appears in paragraph 66 of its Opinion where, after a cursory overview of climate change impacts on health, food security and cultural rights, the Tribunal noted «that climate change represents an existential threat and raises human rights concerns». A similar statement is replicated in paragraph 122, where it says to be «mindful of the fact that climate change is recognized internationally as a common concern of humankind». Two separate but related aspects come into play. First and foremost, assessing whether the protection of the individual falls under the scope of the Convention in relation to climate change and ocean acidification. In her separate declaration, Judge Infante Caffi argued in the affirmative, noting that the UNCLOS «can raise the question of whether human rights concerns fall under its purview, in particular Part XII», echoing the arguments of part of the growing scholarship on human rights at sea (in this regard, ex multis, Treves, Papanicolopulu, Haines). The Convention is certainly not a human rights treaty, but one cannot deny that some of its provisions do address also «traditional human rights preoccupations» (Oxman, pp. 401-402), an example in the specific context of climate change and ocean acidification being that for human health, explicitly referenced in Article 1(1)(4) UNCLOS (Judge Infante Caffi’s separate declaration, para. 2).

Once established that human rights preoccupations may fall under the scope of the Convention, the second aspect concerns the applicable law. As put it in Judge Kittichaisaree’s words, «the Tribunal sidesteps the need to construe article 293 (applicable law) of the Convention to cover human rights issues in order to answer the questions posed by the Request» (Judge Kittichasairee’s Separate Declaration, para. 28). In the author’s view this is regrettable, especially given the growing literature and case law on the interconnections between climate change, human rights and ocean governance (in particular, see the contributions to this special issue on the International Journal of Marine and Coastal Law co-edited by Morgera and Lennan), evidenced in numerous submissions by States (ex multis, the Federated States of Micronesia, para. 64; New Zealand, paras. 41-42; Nauru, paras. 53-58; the UK, para. 41) and non-State actors (ex multis, joint submission by the UN Special Rapporteurs paras. 15-26 and paras. 30-64; African Union, paras. 47; United Nations Environment Programme, paras. 71-76; Pacific Community, paras. 31-33; One Ocean Hub, paras. 33-37). However, while avoiding explicit human rights language besides the reference in paragraph 66, the Tribunal arguably left some doors open for future developments in this direction: in addressing States’ obligations to monitor and assess, it observed that «the broad wording of article 206 does not preclude the assessment from including the socio-economic impacts of the activities concerned» (para. 365; in this regard, see generally Nakamura, Diz and Morgera).

Conclusion – Passing on the baton

Overall, ITLOS provided a progressive Opinion, finally bridging the law of the sea with climate change law. This will certainly have significant implications for States in future negotiations regarding climate change, which have so far – surprisingly – overlooked the importance of the ocean in that regard. However, progressive as it is, the Opinion falls short of addressing climate change and ocean acidification in a comprehensive manner by taking into account the interconnections of the protection and preservation of the marine environment with the conservation of marine biodiversity and the enjoyment of human rights. At this stage, it is now up to the IACtHR and the ICJ to collect the baton from the ITLOS and advance the protection of biodiversity and human rights while giving effect to State obligations on climate change, including with regard to the ocean.

* The author has previously worked for the One Ocean Hub (University of Strathclyde), one of the non-State actors that submitted a written statement to ITLOS in the context of the advisory proceedings