ICJ Interprets UNCLOS, with and without ITLOS – Indian Blog of International Law

Daniel Stein

The International Court of Justice’s (ICJ) Advisory Opinion on Climate Change (AOCC) is a sweeping and forceful judgment that fully considers the variety of sources of law and the international law obligations of States. With regards to obligations related to the law of the sea and the United Nations Convention on the Law of the Sea (UNCLOS), the ICJ also took cognizance of the Climate Change Advisory Opinion issued in May, 2024, by the International Tribunal for the Law of the Sea (ITLOS). In addition to both decisions being unanimous, they complement and overlap each other in many important ways. However, the AOCC is able to go further and consider other issues of UNCLOS not found in the request to ITLOS, specifically with regards to redrawing baselines and other maritime zones because coastlines and whole islands disappear to rising sea levels.

Procedurally, the two judgments are similar in two immediate ways: the acceptance of jurisdiction and the rejection that the UNFCCC and related climate change treaties constitute lex specialis which would “displace any other rules, as those treaties reflect a series of careful compromises which strike a balance among the main sets of competing considerations. . . [and] have priority over any other rule of a conventional or customary nature and cannot be superseded or altered by other sources of law.” (ICJ para 163) Just as ITLOS declared that it “does not consider that the Paris Agreement modifies or limits the obligation under the Convention” (para 224), the ICJ agrees that there is “no indication that the climate change treaties are meant to apply while simultaneously excluding general customary international law or other treaty rules [including UNCLOS] on the protection of the environment” (para 170). Essentially, both ICJ and ITLOS agree that UNCLOS, especially Part XII related to the protection and preservation of the marine environment, contains legal obligations relevant for international legal responsibility, but only as one part of a larger body of customary and treaty law obligations.

The other preliminary overlapping question related to the due diligence standard on States to “fulfill their duties to prevent significant harm to the environment” (ICJ para 280) is about the importance of “different capabilities.” This principle first appears in the 1992 Rio Convention as ‘common but differentiated responsibilities (CBDR),’ though UNCLOS (signed in 1982, entered into force in 1994) contains two Articles (202 and 203) related to technical assistance to developing states. Echoing ITLOS’ statement that UNCLOS “requires a State with greater capabilities and sufficient resources to do more than a State not so well placed” (ITLOS para 241), ICJ specifically connects this with the “implicit” role that CBDR-RC plays in international environmental law (ICJ para 291) and says explicitly that “developed States, in the context of climate change, must take more demanding measures to prevent environmental harm and must satisfy a more demanding standard of conduct.”(ICJ para 292). After explaining the flexibility and evolving nature of the differentiation of specific circumstances of each State, the ruling concluded with a reminder that “reference to available means and capabilities cannot justify undue delay or a general exemption from the obligation to exercise due diligence.” (ICJ para 292) 

When moving on to the similar substance of the ITLOS and ICJ requests, the ICJ noted that though “there are issues common to the two requests” the questions posed to ICJ are broader than those posed to ITLOS (para 337). While the ITLOS Advisory Opinion is not binding on the ICJ even with regard to interpreting UNCLOS, the ICJ recognized that “in so far as it is called upon to interpret the Convention, it should ascribe great weight to the interpretation adopted by the Tribunal.” (para 338)

With this introduction, the two opinions are revealed to be similar in both content and structure. Both begin with the question of whether GHG emissions fall within the definition of marine pollution contained in UNCLOS Art.1.1.4, and an answer in the affirmative, though the lengthy discussion by ITLOS is reduced to one paragraph by the ICJ. (ICJ para 339,  ITLOS paras 159-179). The ICJ similarly agrees that the general obligation of environmental protection contained in Article 192 “consists of a positive obligation to take measures to protect and preserve the marine environment and a negative obligation not to degrade it” (para 342, quoting ITLOS paras 385, 387), requiring a stringent due diligence standard which are “as far-reaching and efficacious as possible” and “more severe for the riskier activities.” (ICJ para 343, quoting ITLOS paras 239, 338). 

The interpretations by ITLOS of the more specific obligations contained in UNCLOS Article 194, requiring “all measures consistent with this Convention that are necessary to prevent, reduce and control pollution of the marine environment from any source,” the prevention of trans-boundary harms, and other regulations of land-based sources, offshore installations, and vessels, (UNCLOS Art 194) are also mostly affirmed by the ICJ, including that these obligations are ones of conduct with a stringent due diligence standard (ICJ paras 344-349, quoting ITLOS paras 187, 199, 206-7, 235, 241, 380). 

Sandwiched between these two obligations is Article 193, which provides that “(s)tates have the sovereign right to exploit their natural resources pursuant to their environmental policies and in accordance with their duty to protect and preserve the marine environment.” While only ITLOS notes the second half of this provision is a “constraint” which “shows the importance the Convention attaches to the protection and preservation of the marine environment” (ITLOS para 187), ICJ simply approvingly cites that interpretation.

The other two Articles of UNCLOS related to protection of the marine environment considered by the ICJ were Article 197, requiring to States to “co-operate on a global basis and, as appropriate, on a regional basis, directly or through competent international organizations, in formulating and elaborating international rules, standards and recommended practices and procedures” and Article 206, requiring States to “assess the potential effects of such activities on the marine environment and shall communicate reports of the results of such assessments in the manner provided” when planned activities in their jurisdiction “may cause substantial pollution of or significant and harmful changes to the marine environment.” (Art. 206). In both instances, the ICJ affirmed ITLOS, declaring, with regard to Art. 197 that the obligation to co-operate requiring due diligence, is of a continuing nature, and is not released just by the adoption of the UNFCCC or Paris Agreement. (ICJ para 351, quoting ITLOS para 311)

Beyond environmental cooperation, the ICJ also agrees that UNCLOS Articles 200 and 201 require collaboration “under Articles 200 and 201 of the Convention to promote studies, undertake research programmes, encourage the exchange of information and data, and to establish appropriate scientific criteria for regulations” (ICJ para 351, quoting ITLOS para 312). Regarding the latter, the ICJ held that Art. 206 “requires States parties, as far as practicable, to conduct EIAs when there are reasonable grounds for believing that planned activities under their jurisdiction or control which emit GHGs may cause substantial pollution or significant and harmful changes to the marine environment. This obligation also extends to activities with an impact on areas beyond national jurisdiction” (ICJ para 353, quoting ITLOS Responsibilities and obligations of States with respect to activities in the Area, Advisory Opinion, 1 February 2011, paras 145-150). 

Obligations of States in relation to sea level rise

The major law of the sea question addressed by ICJ that was outside the scope of the ITLOS opinion was with regard to obligations of States in relation to sea level rise and the problems faced by States dealing with coastal recession, territorial integrity, and sovereignty over natural resources contained within maritime boundaries. This issue did not come before ITLOS because it was only mentioned in the questions presented in relation to environmental protection, not as a separate and unique problem. The Tribunal explained “that if the Commission [of Small Island States] had intended to solicit an opinion on the consequences of sea level rise for base points, baselines, claims, rights or entitlements to the maritime zones established under the Convention, or maritime boundaries, and the corresponding obligations, it would have expressly formulated the Request accordingly” (ITLOS para 150).

Despite the lack of guidance from ITLOS, the ICJ was comfortable analyzing UNCLOS Articles 16 (on baselines for the territorial sea), 75 (on limits for the exclusive economic zone [EEZ]), and 84 (on limits to the continental shelf) to determine that once those zones are publicized and deposited, “there is no provision in the Convention requiring States parties to update them” (ICJ paras 358-359). This conclusion was supported not only by the language of UNCLOS, but by several UN and regional declarations (ICJ para 360) and the final report of the ILC seventy-sixth session (2025) which “show[ed] a convergence of views among States across all regions in support of the absence of an obligation of States parties to UNCLOS to update charts or lists of geographical co-ordinates relating to their maritime zones once they have been duly established, in conformity with UNCLOS” (ICJ para 361). Essentially, if a low-lying island territory established a baseline and maritime zones, a reduction of land territory, after “a State is established, the disappearance of one of its constituent elements would not necessarily entail the loss of its statehood.” (ICJ para 363).

The other human problems related to sea-level rise then come under the obligation of States to co-operate and take appropriate measures to address these adverse effects, recognizing “the interdependence of States and the ensuing need for solidarity among peoples” (ICJ para 364). The ICJ then reiterated that this co-operation is “not a matter of choice but a legal obligation” which must take “into account the rights of affected States and those of their populations” (ICJ paras 364-365). 

(Daniel Stein is an Associate Professor, OP Jindal Global Law School and a Research Fellow, Center for ADR, Jindal Global Law School.)