Climate Change, Human Rights, and the Law of the Sea

Recent Advisory Opinions from the International Tribunal for the Law of the Sea (ITLOS), the Inter-American Court of Human Rights (IACtHR), and the International Court of Justice (ICJ) mark a definitive shift from legal fragmentation toward a harmonized framework for state climate obligations. While the Law of the Sea and international human rights law traditionally operated on separate tracks, the climate crisis – a “common concern of humankind”– threatens marine ecosystems and human rights simultaneously, demanding an integrated legal response.

This paper analyzes this jurisprudential cross-fertilization, tracing how the courts built upon one another’s findings to construct a cohesive legal order through systemic integration. The analysis highlights a consensus built on four key pillars: the adoption of systemic interpretation to read different legal regimes together; the evolution of greenhouse gas emissions from “marine pollution” under UNCLOS to a direct violation of human rights; the elevation of the duty to protect the climate system to an erga omnes obligation, drawing on the concept of the “common heritage of mankind”; and the establishment of a stringent, unified standard of due diligence, guided by the precautionary principle. Ultimately, these opinions affirm that protecting the marine environment and safeguarding human rights are not separate tasks but interdependent imperatives – and thus, when it comes to climate change, different legal regimes ought to be interpreted systematically to guarantee an adequate protection of the climate system.

The Definitive Shift toward Systemic Interpretation

Systemic interpretation under article 31(3) of the VCLT requires treaties to be interpreted in light of “any relevant rules of international law applicable in the relations between the parties,” meaning that they should not be interpreted in a vacuum, but rather considering “the entire legal system prevailing at the time of interpretation.” (Legal Consequences for States of the Continued Presence of South Africa in Namibia, ICJ,AO, para.53) In the climate context, this means integrating the Law of the Sea, human rights law, and customary international law into a single, cohesive framework.

This systematic approach, was first advanced by the ITLOS AO, which cited Article 31(3) of the VCLT and the 2006 International Law Commission Report on the Fragmentation of International Law, to affirm that different legal norms bearing on a single issue should produce “a single set of compatible obligations” (paras. 135-136; ILC, 2006, p. 8). The IACtHR has adopted the same approach, stating that legal norms must be read “as part of a whole in light of the legal system to which they belong” (para. 35, fn. 30). Concluding this trend, the ICJ’s Advisory Opinion provides definitive confirmation, holding that obligations from climate treaties and customary law “inform each other” (paras. 309-315, 404), affirming that treaties must be interpreted within the “entire legal system,” and thereby rejecting a fragmented approach while cementing the principle that all relevant rules of international law must be read as a single legal system. (paras. 165, 310-311)

From Marine Pollution to a Universal Human Rights Paradigm

The systemic dialogue on marine pollution as a human rights obligation began with ITLOS, which recognized that anthropogenic greenhouse gas (GHG) emissions constitute pollution of the marine environment under article 1(1)(4) of UNCLOS, thereby triggering binding obligations for states under, among others, under article 194 of UNCLOS (paras. 159-179), which requires states to take “all necessary measures to prevent, reduce and control marine pollution from anthropogenic GHG emissions and to endeavor to harmonize their policies in this connection.” (para. 441 (3)(b)). In this context, UNCLOS duty to protect and preserve the marine environment under article 192 gains new significance when viewed through human rights lens. (paras. 384-400) As ITLOS recognized, the “deleterious effects” of GHG pollution include direct impacts on human communities by harming the conservation of “living resources and marine life” and hindering “fishing and other legitimate uses of the sea” including “income, livelihoods, and food security of marine resource- dependent communities”, as well as impacts on marine ecosystems which would put “key cultural dimensions of lives and livelihoods at risk” (see para 174 in connection to para.66). However, while ITLOS acknowledged that “climate change represents an existential threat and raises human rights concerns” (para. 66), it did not explore the human rights dimensions of the law of the sea in the climate change context. It was the IACtHR that built the bridge between human rights law and law of the sea, clarifying that the same GHG emissions that pollute the marine environment give rise to direct human rights responsibilities, including the duty to regulate and mitigate them (paras. 321-344; point 10, decision), in order to protect the rights to a healthy environment (as recognized in AO-23/17), food (435–440), work (442-443), health, and a “healthy climate.” (paras. 266 ff, 300). Similarly, the IACtHR noted that the loss of coastal territories and the disruption of traditional practices like fishing violate the right to culture and the right to property, particularly for indigenous and tribal peoples whose identities are deeply connected to their ancestral lands and waters. (406-407)

The ICJ then affirmed this link as a universal principle of international law, noting the protection of the environment, including the marine environment, is a “precondition for the enjoyment of human rights” (paras. 173, 193) and that states have obligations under international human rights law to protect the climate system. (paras. 371, 456 D-E) Citing the work of regional human rights courts like the IACtHR and the European Court of Human Rights (ECtHR), the ICJ confirmed a global judicial consensus that environmental protection and human rights are interdependent (paras. 144, 385). Thus, a state’s failure to protect the marine environment – particularly from sea level rise and the introduction of GHGs into the marine environment – is, therefore, not only a breach of UNCLOS but a violation of human rights obligations, as all obligations under ITLOS are essential to the protection of human rights and, thus, “should be interpreted in accordance with relevant international human rights obligations” (A/HRC/56/46, para.17).

From Global Commons to Erga Omnes Obligations

The IACtHR draws on the concept of the “common heritage of mankind,” as defined in in Part XI of UNCLOS, to extend the scope of human rights protection, noting that “the obligations arising from the right to a healthy climate are aimed at protecting the global climate system for the benefit of humanity as a whole, including both present and future generations. (…) The protection of that community [referring to ‘humanity as a whole’] has been established in international instruments such as those relating to the common heritage of mankind” (311, fn. 571).

With this framing, the Court acknowledges that the global climate system is part of the global commons and suggests that the corresponding obligations are erga omnes, invoking the ICJ’s definition from the Barcelona Traction Case (para.33) (see also, here). These obligations are not abstract: the IACtHR affirms that safeguarding global commons is essential to the effective enjoyment of a wide range of human rights, including the rights to life, health, food, and a healthy environment (302–304). In doing so, it transforms the duty to protect the climate system, mirroring the concept of “common heritage of mankind” under Part XI of UNCLOS, into a legally enforceable obligation owed erga omnes to individuals, communities, and the international community as a whole.

Elevating this concept further, the ICJ confirmed that certain obligations concerning the protection of global environmental commons, specifically the high seas and the atmosphere, are erga omnes, with the protection of the climate system from GHG emissions and environmental protection beyond national jurisdiction serving as a key example of such obligations owed to the international community as a whole. (paras. 281, 440-441). In this context, the Court considered that the UNFCCC and the Paris Agreement require a global response and, hence, the protection of the climate system in this regard is justified as an obligation erga omnes. (para. 440)

A Unified Standard of Precaution and Stringent Due Diligence

The common heritage of mankind entails a responsibility to preserve it across generations, an intertemporal dimension crucial to the application of the precautionary principle, which requires states to act even in the absence of complete scientific certainty in order to prevent grave or irreversible harm; particularly, when such harm would affect not only current populations but also future generations. The IACtHR affirms this notion by noting that states must adopt “efficacious” measures to avert serious or irreversible environmental harm that might lead to climate-related human rights violations – even where scientific certainty is lacking (paras. 228-229, art. 3.3 UNFCCC).This understanding of the precautionary principle echoes ITLOS’s finding that the precautionary approach is implicit in UNCLOS and central to regulating marine pollution from GHG emissions. (para.213; see also, ITLOS AO on Activities in the Areas, para. 135). The ICJ further elaborates on this and identifies the precautionary principle as a key component of a state’s obligations regarding climate change, functioning both as a guiding principle for legal interpretation and as an integral part of the customary duty of due diligence. (paras. 161, 172)

Crucially, all three international courts link precaution to a “stringent” standard of due diligence for climate action. ITLOS established this high standard for preventing marine pollution, “given the high risks of serious and irreversible harm” while recognizing that its implementation may vary by state capacity (paras. 242- 243). The IACtHR – in citing ITLOS – “coincides with these postures,” applying the same high due diligence standard to the obligation of states to define and implement national climate mitigation strategies (paras 335-336). In doing so, the IACtHR effectively equates this heightened standard of care required to protect the marine environment under UNCLOS with that required to safeguard human rights from the impacts of climate change.

The IACtHR further connects due diligence to the duty to guarantee human rights, which “extends beyond the direct conduct of state agents to include the duty to prevent harm caused by private actors” (para. 226).In practice, this means adopting all necessary measures to reduce both the causes of environmental harm and the vulnerability of affected populations (paras. 226–228), including the guarantee of their human rights. ITLOS reinforces this logic by noting that due diligence requires legal and institutional frameworks and ongoing monitoring of both public and private actors (para. 35).

The ICJ further affirmed a stringent standard of due diligence for the customary duty to prevent significant environmental harm, citing the ITLOS opinion and confirming that due diligence requires a state to deploy “all the means at its disposal” to protect the climate system. (paras. 291, 343, 347). Ultimately, the consensus among international courts establishes a clear, high bar for state conduct, applicable across law of the sea, environmental and human rights law.

Conclusion: From Fragmentation to a Harmonized Legal Order

The Advisory Opinions from ITLOS, the IACtHR, and finally the ICJ, mark a decisive move away from the fragmentation of international law, creating a powerful synergy where distinct legal regimes mutually reinforce one another and ought to be interpreted in light of each other. ITLOS grounded climate duties in the foundational Law of the Sea; the IACtHR built a bridge to human rights, providing a “jurisdictional anchor”; and the ICJ provided the authoritative confirmation, universalizing these principles within the core of general international law.

Rather than treating the Law of the Sea as a closed regime, the IACtHR and the ICJ situate UNCLOS within a broader legal framework that converges with human rights law in responding to the climate crisis. By recognizing the relevance of the ITLOS AO and their importance for small island states as the members of the COSIS (para. 180), the IACtHR and the ICJ thereafter affirm the intrinsic connection between marine environmental protection and the enjoyment of fundamental rights.

Importantly, these Opinions do not seek to collapse distinct legal regimes into one but reflect normative cross-fertilization and systemic integration: UNCLOS obligations are interpreted through human rights, while human rights reasoning draws increasingly on environmental law principles such as precaution and due diligence. Together, these opinions affirm that protecting the marine environment and safeguarding human rights are not separate tasks but interdependent imperatives in the era of the climate crisis.