Introduction 

In May 2024, the International Tribunal for the Law of the Sea (ITLOS) published the Advisory Opinion No. 31 on climate change, recognizing that greenhouse gas (GHG) emissions absorbed by the oceans constitute marine pollution. Its peculiarities make it a valuable contribution to understanding climate litigation efforts as a way to prompt judicial systems to rule on the applicable law on the subject (PEEL; LIN, 2019; VANLOON; KLEIN; SMIT; 2025; QIAN; SUN; CHANG, 2025). Although not a litigation process, it provides an arena in which member states stand for their interpretations – an ideal locus for empirical research in Public International Law (PIL). The second reason lies on the interpretation conducted by the Tribunal itself: it reinforces the interpretation of PIL concerning international obligations regarding the sea and the climate.

This contribution aims to briefly demonstrate how the request made by the Commission on Small Island States on Climate Change and International Law (COSIS) portrays an arena of climate litigation, both in terms of the articulation of strategic legal-argumentative movements (1); and of the result arising from the provocation, with the Court’s interpretation on the recognition of marine pollution and international climate obligations (2).

1. The arena surrounding the ITLOS advisory opinion as an expression of climate litigation: the articulation of strategic legal-argumentative movements.

Understanding the Advisory Opinion as a form of climate litigation implies grasping some important elements of the political-legal context of the COSIS request for an advisory opinion, which is marked by a lack of effective enforcement mechanisms in international climate instruments, such as the Paris Agreement, which has a non-binding character regarding emission reduction targets (United Nations, 2015). On the one hand, COSIS seized a Tribunal specialized in oceans to interpret international law, which in itself is a litigation strategy. On the other hand, it draws attention to the repercussions of climate change on oceans and to its relationship with the obligations of States under international law. In this context, the opportunity for the parties to express their views is a crucial moment for understanding the strategic legal-argumentative movements regarding the hermeneutics that should prevail in the matter. All these aspects make the event an expression of climate litigation, albeit in an advisory form.

The IPCC, in its Synthesis Report (AR6, 2023), highlighted that the global average temperature has increased more rapidly since 1970 than in any other 50-year period and stated that “it is unequivocal that human influence has warmed the atmosphere, the ocean and the land” (IPCC, Summary for Policymakers, 2023, p. 5). In this context, COSIS requested the advisory opinion as a strategy to strengthen the accountability of States for climate change, since the member countries of the commission are among those most affected by the climate crisis.

However, the arena manifests itself from a procedural aspect: once an advisory opinion is requested to the Court, States Parties have the opportunity to express their views, and it is at this point that one can perceive the existence of an argumentative field, making it possible to find positions on whether they are for or against the existence of ratione materiae, as well ason what was asked.

By giving voice to island nations, COSIS highlighted the implications of the ocean as a relevant player in the climate debate, one in relation to whom, for these countries, the issue is also existential. The questions posed by COSIS regarded the obligations of States Parties to prevent, reduce, and control pollution in the marine environment in relation to climate change, including ocean warming and acidification, as well as sea-level rise caused by anthropogenic GHGs; and the obligations to protect the marine environment in relation to climate change (COSIS, 2022).

Intrinsic to the definition of international obligations is the accountability for non-compliance, and, although the international responsibility of States depends on a series of factors and is immersed in nuances and fragilities inherent to Public International Law (MALJEAN-DUBOIS, 2019), the strategic perspective here lies on perceiving the advisory opinion as a space for the possibility of defining future obligations, or their interpretations, based on which a State may be held accountable for non-compliance. In their written submissions, States presented their efforts to hermeneutically guide – based on the analysis of written submissions – the understanding of the Court. And even if it does not have this influence, it is still a source of the States’ positions, allowing a glimpse into their strategies on that issue.

To obtain a sample for this study, we sought to analyze some of the written statements from States. Given the volume of documentation, the statements were selected considering four criteria: (I) legal relevance in the ITLOS consultative process; (II) political-economic weight in the International System; (III) technical and scientific expertise in the subject matter; (IV) non or partial recognition of the ITLOS jurisdiction. The countries Brazil, China, India, and Japan are thus highlighted, as they do not recognize the consultative jurisdiction of the Tribunal for any or just for climate matters (ratione materiae). Also, these actors represent two interconnected subsets: advanced economies (Japan) and emerging economies (Brazil, China, and India) according to the World Economic Outlook ( International Monetary Fund, 2025), which are nevertheless in convergence by raising the argument against recognizing the Court’s jurisdiction in consultative and climate matters.

From the statements of the aforementioned states, we highlight their positions regarding whether the State: 1. Recognizes the ITLOS jurisdiction?; 2. Recognizes that greenhouse gases (GHGs) are subject to the obligation to protect?; 3. Recognizes that GHGs are a form of marine pollution? The answers by the States are summarized in the table below.

Table: Written manifestations to Advisory Opinion 31 from Brazil, China, India and Japan

Source: NASCIMENTO, Júlia Vargas; MORAES, Gabriela GB Lima (advisor). The responsibility of States for the analysis of advisory opinions related to climate change: TIDM. PIBIC/UnB, 2024-2025.

Japan’s position acknowledged that GHG emissions affect the marine environment. The State avoided denying the Tribunal’s jurisdiction, but requested the analysis to be conducted cautiously and to be based on the positions of other States, emphasizing that the United Nations Convention on the Law of the Sea (UNCLOS) – Montego Bay Convention – does not provide for specific obligations regarding climate change (JAPAN, 2023, p. 2).

In contrast, Brazil, China, and India found several points of convergence: firstly, these States argue that the ITLOS, in its full composition, does not have advisory jurisdiction to rule on the matter submitted by COSIS. According to their understanding, the Court has jurisdiction to judge contentious cases, not to issue advisory opinions whose purpose is not to resolve disputes. They draw a restrictive interpretation of Article 21 of the Statute of the Tribunal and – in the case of China and India – include Article 288 of UNCLOS. The advisory jurisdiction provided for in Article 138 of the Statute is not recognized because it was included in the document without prior negotiation by the States (BRAZIL, 2023, p. 7; CHINA, 2023, p. 12; INDIA, 2023, p. 5). These positions further reinforce that the Montego Bay Convention only granted advisory jurisdiction to the Seabed Chamber.

Furthermore, Brazil, China, and India reaffirmed the principle of common but differentiated responsibilities. They argued that states should adopt prevention and mitigation measures according to their capabilities (BRAZIL, 2023, p. 3; CHINA, 2023, p. 3; INDIA, 2023, p. 2), in spite of recognizing, even if indirectly, the effects of the climate emergency on the oceans. Finally, the three states seek to shift the debate to the multilateral climate regime (United Nations Framework Convention on Climate Change – UNFCCC, Kyoto Protocol, and Paris Agreement). China asserts that the UNFCCC is the primary forum for addressing climate change, while India argues that the UNFCCC and the Paris Agreement should prevail over UNCLOS, and Brazil asserts that UNCLOS should be interpreted in harmony with the climate regime (BRAZIL, 2023, p. 8; CHINA, 2023, p. 12; INDIA, 2023, p. 5).

Although they vary in style, written submissions are sources of knowledge regarding the political and legal positions of States on the issues discussed by a court. It is worth highlighting that the States mentioned, according to the Emissions Database for Global Atmospheric Research (EDGAR) – which uses international statistics and a consistent IPCC methodology – were, in 2024, among the ten countries in the world that polluted the most (EUROPEAN COMMISSION, 2025, pp. 8 and 20). In this sense, the status of these states as the largest global emitters of Greenhouse Gases as well as the strategic importance of the ocean to their economies may explain the resistance against the strengthening of the legal obligations they hold before the ITLOS. From this perspective, recognizing that the Tribunal detains advisory jurisdiction ratione materiae could pave the way for resolutions that affect their geopolitical and economic interests.

2. The interpretation of the Opinion on the recognition of marine pollution and international climate obligations as contributions to climate litigation.

According to Advisory Opinion No. 31, the Tribunal’s contributions to climate litigation include, among others: the concept of marine pollution resulting from anthropogenic GHG emissions; the definition of which of the primary obligations of the Montego Bay Convention may be violated by States’ inaction regarding GHG emissions; the role of due diligence in the systemic interpretation of the configuration of climate obligations in the Law of the Sea; and the role of general principles of international law in this effort.

Regarding the first point, GHG emissions can fall under Article 1, paragraph 1, subparagraph 4 of the Convention (ITLOS, 2024, paragraph 179, p. 66). This understanding certainly strengthens the need to comply with climate obligations. Unprecedentedly, the Tribunal interpreted UNCLOS in light of the climate crisis, recognizing that anthropogenic GHG emissions, when absorbed by the oceans, can objectively meet the criteria outlined in the aforementioned article of the Montego Bay Convention for marine pollution, namely the presence of a substance or energy, the direct or indirect introduction into the marine environment, and the existence of deleterious effects or the risk thereof (ITLOS, 2024, paragraphs 159 et seq., p. 60 et seq.).

This interpretation imposes mitigation and adaptation obligations on States, which are to be based on the best available science (ITLOS, 2024, paragraphs 198 et seq., p. 72 et seq.) in order to promote more diligent and cooperative action on a global scale. The ITLOS also highlighted that the impacts of climate change constitute a threat to planetary health and human well-being, with disproportionate effects on vulnerable communities that have historically contributed less to the climate crisis. It has further stated that the impacts of climate change constitute an existential threat to these populations and raise concerns in terms of human rights (ITLOS, 2024, paragraph 66, p. 34).

Refuting, directly or indirectly, any argument for the absence of jurisdiciton ratione materiae, the Court further clarifies which are the primary international obligations of the Montego Bay Convention that, if violated, could characterize marine climate pollution. These obligations encompass the general rules of Articles 192 and 194 on the general obligation to protect the marine environment and to prevent, reduce and control marine pollution (ITLOS, 2024, paragraph 234 et seq., p. 84 et seq.). As specific obligations, the Tribunal mentioned the obligation to monitor the risks or effects of pollution (Article 204), to publish reports (Article 205) and to conduct Environmental Impact Assessments (Article 206), all of the aforementioned Convention (ITLOS, 2024, paragraph 340 et seq., p. 117 et seq.).

It is important to highlight the systemic hermeneutics conducted by the Tribunal in interpreting the manner of fulfilling the general obligations of Articles 192 and 194 of the Montego Bay Convention (it is worth remembering: the obligations to i. protect and preserve the marine environment; and ii. prevent, reduce and control marine pollution). The decision thus explain that these obligations are connected to the international climate regime as obligations of due diligence in light of the general principles of international law (ITLOS, 2024, paragraph 234 et seq., p. 84 et seq.). In other words, that States are to comply with the obligations they have undertaken: the obligations of the climate regime are connected to the Montego Bay regime because they are obligations of due diligence.

Regarding the incorporation of international environmental principles, the Tribunal reaffirmed and reinterpreted structuring elements of international environmental law, such as the precautionary principle, the prevention principle, and intergenerational equity. The precautionary principle, according to the opinion’s understanding, is applicable whenever there is a risk of serious or irreversible damage to the marine environment (ITLOS, 2024, paragraphs 212-213, p. 77). In addition, the prevention principle was reaffirmed as the basis for states’ proactive action in preventing, reducing, and controlling marine pollution resulting from anthropogenic emissions of Greenhouse Gases (GHGs), as an application of the duty to care in a preventive manner (ITLOS, 2024, paragraphs 232 et seq., p. 83 et seq.). Finally, intergenerational equity can be understood as implicitly integrated into the Court’s reasoning, requiring States to adopt a rigorous standard of due diligencein light of the irreversible risks to the marine environment due to climate change. This links the preservation of the environment to the rights of future generations and reinforces the preventive and precautionary dimensions of state obligations. (ITLOS, 2024, paragraphs 241 et seq., p. 86 et seq.).

Thus, Advisory Opinion No. 31 constituted a significant normative development as an expression of climate litigation, since an international court objectively issued its position regarding the climate obligations under its jurisdiction while also serving as a guide for the subsequent application of international law in that matter. The Consultation stands out for both its particular procedural and material aspects – distinct from that of a lawsuit – as well as for directing the efforts of a specialized Tribunal to clarifying international obligations in this field. The opinion pioneered in interpreting UNCLOS as applied to climate change and, especially, in recognizing the possibility that ITLOS jurisdiction ratione materiae is appliedto climate matters, through systemic interpretation and in light of the conduct due diligenceobligations. In general, based on a systemic hermeneutics of international law analysis, the Tribunal objectively identified when the Montego Bay Convention would objectively be violated in the event of an omission by a state regarding international climate obligations.