Three Courts, One Ocean: a Consultative Triangle for Climate Law at Sea
By Laura Patricia Romero y Pino*
Introduction
In recent years, three international courts have been asked to answer a question that no single State—or treaty—can solve alone: what are States legally obliged to do in the face of the climate crisis? The responses came from three very different corners of international law: the International Tribunal for the Law of the Sea (ITLOS), (ii) the International Court of Justice (ICJ), and (iii) the Inter-American Court of Human Rights (IACtHR). Together, their advisory opinions form an unprecedented dialogue between regimes that have long operated separately — the law of the sea, climate law, and human rights law. Advisory opinions do not create new treaties; they interpret existing law and clarify the scope of States’ duties. Yet, when issued by three of the world’s most authoritative judicial bodies within a short span of time, their combined effect is powerful. They reveal that the protection of the oceans, the atmosphere, and human communities is part of a single legal continuum — one that binds States through obligations of diligence, cooperation, and respect for human and environmental integrity.
This blog explores that “triangle of opinions”, showing how each Court contributes a distinct perspective: ITLOS, the specialized maritime tribunal, anchors climate change within the United Nations Convention on the Law of the Sea (UNCLOS); the ICJ, as the principal judicial organ of the UN, connects it to global cooperation and legal stability; and the IACtHR, the regional human rights court, gives it a human face, linking ocean protection to human dignity, culture, and intergenerational justice.
ITLOS: the Specialist Court that Brought Climate into Part XII
ITLOS spoke first. Its 2024 Advisory Opinion anchored climate change firmly within the framework of the United Nations Convention on the Law of the Sea (UNCLOS) by defining greenhouse gas emissions (GHG) as pollution of the marine environment. Through this interpretation, the Tribunal clarified that States have concrete obligations of due diligence, cooperation, monitoring, and environmental impact assessment under Part XII of UNCLOS. This finding laid the groundwork for the later advisory opinions of the ICJ and the IACtHR, which built upon its reasoning.
These developments have been discussed in depth elsewhere, including in WYCJ’s own analyses of the Opinion — see The ITLOS Advisory Opinion: A win for the oceans, a win for the fight against climate change and Webinar: The ITLOS Advisory Opinion on Climate Change and the Law of the Sea.
ICJ: the General Court that Stabilizes in the Storm
In 2025, the ICJ delivered its Advisory Opinion on the Obligations of States in respect of Climate Change, identifying the applicable law — including UNCLOS, the UN Charter, customary law, human rights instruments, and climate treaties — as a coherent and mutually reinforcing framework (ICJ, paras. 353–354). The Court emphasized that these bodies of law do not operate in isolation: obligations to protect the marine environment under UNCLOS, to uphold human rights, and to mitigate and adapt under the Paris Agreement all form part of a single continuum of legal duties. As it stated, “States parties must therefore take their obligations under UNCLOS into account when implementing their obligations under the climate change treaties” (ICJ, para. 354). Confirming ITLOS’s findings, the ICJ adopted its view that GHG emissions constitute marine pollution and reaffirmed a stringent due-diligence standard under Article 194, requiring States to act in line with the best available science (ITLOS, paras. 193, 243; ICJ, paras. 353–354).
For the law of the sea, the ICJ’s clearest contribution concerns sea-level rise (SLR) and the stability of maritime zones. Once a State has established, publicized, and deposited its outer limits and baselines in accordance with UNCLOS, there is no obligation to update them due to physical changes caused by rising seas (ICJ, para. 362). The Court also recalled that “once a State is established, the disappearance of one of its constituent elements would not necessarily entail the loss of its statehood” (ICJ, para. 363), linking maritime stability to the preservation of statehood and the right to self-determination.
This clarification carries profound real-world implications, especially for Small Island Developing States (SIDS). Before this ruling, uncertainty lingered over whether receding coastlines could erase States’ maritime entitlements. For SIDS — whose territories and economies depend on the sea — this was existential: losing land could mean losing sovereignty, fisheries, seabed resources, and stability. By confirming that maritime zones remain valid once lawfully established, the ICJ provided long-needed legal certainty while reminding States that such protection does not excuse inaction against the causes of sea level rise (SLR).
Beyond maritime boundaries, the Court’s reasoning broadens ocean protection. By recognizing GHG emissions as environmental harm, it linked mitigation and adaptation duties under the Paris Agreement directly to marine health. Reducing emissions and restoring mangroves, wetlands, and coral reefs are not only climate measures but also ocean obligations. States must implement their nationally determined contributions (NDCs) in ways that protect marine ecosystems—including “blue-carbon” strategies and sustainable coastal management. As the ICJ observed, UNCLOS, the Paris Agreement, and customary law “inform each other” (ICJ, para. 354), meaning that fulfilling climate duties simultaneously fulfills the duty to preserve the marine environment.
Cooperation lies at the center. The ICJ declared that “co-operation in addressing SLR is not a matter of choice for States but a legal obligation” (ICJ, para. 364). States must “work together … to achieve equitable solutions, taking into account the rights of affected States and their populations” (ICJ, para. 365). This duty, founded on solidarity, may imply continuing recognition of SIDS statehood even if territory is lost. The Court, thus, gave ocean governance a human dimension: cooperation is not merely procedural but existential.
It also recognized the erga omnes character of relevant climate obligations (ICJ, para. 440). By defining climate duties as obligations owed to the international community, the Court strengthened the collective basis for protecting global commons—including the oceans, which absorb a quarter of anthropogenic CO₂ and regulate climate. Safeguarding the climate and safeguarding the seas become mutually reinforcing.
Several judges expanded these findings. Judge Aurescu affirmed that “fixed baselines” have crystallized into customary law, ensuring stability for SIDS (Separate Opinion, paras. 3–5). Vice-President Sebutinde called for stronger recognition of the jus cogens right to self-determination, urging that loss of territory not entail loss of statehood (Sebutinde, para. 8). Judge Yusuf stressed the need to articulate consequences for historically responsible States under CBDR-RC (Yusuf, paras. 3–7, 9–11). Together, these opinions emphasize that cooperation, fairness, and ocean protection are inseparable from the protection of peoples.
Methodologically, the ICJ gave weight to ITLOS’s interpretation of UNCLOS to promote coherence across adjudication while preserving its own judicial function (ICJ, para. 338). The result is a substantive judicial dialogue rather than parallel monologues.
IACtHR: Where the Ocean Becomes Human
The IACtHR, in its Advisory Opinion OC-32/25 on Climate Emergency and Human Rights, literally brought the ocean into the human rights framework. It devoted a section to the oceans (paras. 73–80), recognizing that they generate half of the planet’s oxygen and absorb a third of atmospheric CO₂, making them indispensable for life (IACtHR, para. 75). The Court underscored that ocean degradation—acidification, warming, biodiversity loss—undermines human survival (IACtHR, paras. 113–115). Citing ITLOS (paras. 148, 180, 231, 232, 305), it confirmed the global convergence between protecting the climate system and the marine environment.
The Court reaffirmed the right to a healthy environment (R2HE) as both individual and collective (IACtHR, para. 272). It held that this right belongs not only to persons but also to Nature itself: “the right … protects forests, rivers, and seas as legal rights in themselves” (IACtHR, para. 273). By recognizing the seas’ own legal protection, the Court placed the ocean within the sphere of rights once reserved for humans—a shift Judge Nancy Hernández López called historic (Dissenting Opinion, para. 20).
It further recognized the rights of Nature, describing ecosystems as “complex and interdependent systems” (IACtHR, paras. 279–281). Judge Patricia Pérez Goldberg observed that “the holders of the right are the ecosystems themselves,” requiring States to protect and restore them (Dissenting Opinion, para. 90). The Court also highlighted the planetary function of the oceans—the “lungs of the Earth” vital to climate balance (IACtHR, paras. 73–75, 315). Preserving “the integrity of ecosystems and their living and non-living components,” it held, is necessary for maintaining equilibrium and realizing the right to a healthy climate (IACtHR, para. 315). Judge Verónica Gómez called this a “roadmap for climate justice,” emphasizing that recognizing Nature’s legal status forbids irreversible harm (Concurring Opinion, para. 20).
Grounded in this reasoning, the Court and concurring judges identified a peremptory norm (jus cogens) prohibiting irreversible environmental damage (IACtHR, para. 291; Mudrovitsch, Ferrer & Pérez Manrique, Concurring Opinion, para. 80). It extended this duty beyond States, requiring corporate actors to disclose and mitigate climate impacts (IACtHR, paras. 503–506; Gómez, Concurring Opinion, para. 35). Finally, the Court grounded its reasoning in intergenerational equity, viewing the environment—and the oceans within it—as a trust linking present and future generations (IACtHR, paras. 309–310; Mudrovitsch et al., Concurring Opinion, para. 13). Through this lens, the IACtHR closes the circle: it situated ocean protection within human rights, not as a new frontier of law but as an enduring obligation toward life itself.
Triangulation: a Common Framework Without Re-Writing UNCLOS
Together, the three opinions form a shared interpretive framework that harmonizes existing law’s application to the climate crisis without altering UNCLOS. At its base lies ITLOS, embedding climate change in the Convention through its interpretation of GHG emissions as marine pollution and related duties of diligence and cooperation.
At the center stands the ICJ, which reinforces legal stability by confirming that SLR does not require States to redraw maritime charts once duly established, while linking this stability to broader obligations under international law. Its reasoning connects climate duties with human rights protections including the right to life, adequate housing, and the duty of non-refoulement where rising seas displace populations. By recognizing the erga omnes character of climate-related obligations, the ICJ placed ocean protection within humanity’s collective interest.
At the apex rises the IACtHR, translating this framework into human-rights terms. It reaffirms the right to a healthy environment, underscores the interdependence between ecosystems and human dignity, and positions intergenerational equity as a guiding principle of State action. This approach strengthens ocean protection by making environmental harm justiciable and ensuring that participation and equality guide marine governance.
This triangular construction does not decide maritime delimitation or freeze baselines but sets enforceable standards and guiding principles that ground future disputes in stability, solidarity, and a rights-based compass.
Conclusion
International law governing ocean protection is not frozen; it unfolds through interpretation and coordination across regimes. These advisory opinions demonstrate a coherent interpretive dialogue that allows existing law — without rewriting UNCLOS — to address the climate crisis by aligning environmental, human-rights, and maritime norms within a single, mutually reinforcing framework.
Through this convergence, international law now provides the tools to safeguard both the climate system and the seas it regulates. The combined jurisprudence of ITLOS, the ICJ, and the IACtHR shows that protecting the oceans is no longer only a matter of maritime management, but a question of justice — ecological, social, and intergenerational. What remains is not to reinvent the law, but to apply it with diligence, solidarity, and foresight.
From that “triangle” emerges a shared legal foundation: obligations under UNCLOS guided by science; stability of maritime zones coupled with good-faith cooperation on SLR; and a human-rights dimension requiring preventive and equitable marine policies. No new lines are drawn, but clearer rules now shape how old rules should be applied. The sea is rising; the law has begun to respond.
* Laura Patricia Romero y Pino is a law student at Universidad Panamericana in Guadalajara, Mexico. She has experience in international law and arbitration through her participation in the Philip C. Jessup International Law Moot Court Competition and the International Arbitration Competition of the UBA. She recently completed an internship at the Inter-American Court of Human Rights.