Concluding the Normative Synergy on State Continuity: The ILC, the General Assembly and the Climate Advisory Opinion

A month ago, the United Nations General Assembly took a position significantly less ambiguous than the ICJ on a question of existential importance to island States threatened by climate-induced sea-level rise. Referring to the Climate Change Advisory Opinion, it recalls that the Court “found that, once a State is established, the disappearance of one of its constituent elements would not necessarily entail the loss of its statehood” (Resolution 80/263, § 7, quoting § 363 of the advisory opinion). Departing from the Court’s cautious and conditional language, the General Assembly then states unequivocally, in the present indicative, that it “affirms the continuity of statehood in the face of sea level rise”. Given that 141 States voted in favour of the resolution, should it now be taken for granted that the progressive submersion of their territory no longer threatens the statehood of island States?

As we have previously argued, this positive development challenges some of the most fundamental principles of international law—not only State continuity but also sovereignty and territorial integrity. However, the broad support expressed by States pertains only to the desired outcome—the survival of island States—and not to the legal means of securing it. The Court’s caution arguably reflects the need to delimit the implications of recognising State continuity in such circumstances before that proposition can crystallise into lex lata. This is precisely where the work undertaken by the International Law Commission (ILC) and its Study Group on sea-level rise becomes crucial. Since 2019, a normative synergy has gradually taken shape: the ILC frames a possible legal development, States progressively endorse it, and international institutions such as the General Assembly lend it further authority. Yet this normative synergy will not come full circle until State practice clarifies the scope and implications of the proposed (r)evolution. This post argues that the General Assembly’s resolution brings this normative synergy close to completion, while leaving the legal conditions and consequences of continuity largely unresolved. In our view, these unresolved issues constitute precisely the obstacle to the full realization of this paradigm shift within the international community.

Strengthening island States’ diplomatic efforts through the ILC

Following the Truman Proclamation, it is well known that the United States of America was able to generate an almost immediate “snowball effect” in the development of the customary rules governing the continental shelf (see R. Müllerson, Ordering Anarchy, Martinus Nijhoff, 2000, p. 224). A comparable initiative by a single island State, or even by a broader regional group, would have faced considerably greater obstacles in generating the same snowball effect. Given the structural disadvantages they face in influencing the development of positive international law, they have shown considerable ingenuity in strengthening their diplomatic response to climate change. Beyond amending their constitutions, and concluding joint communiqués and treaties to secure recognition of their continued statehood, they also used the ILC to promote an emerging regional practice. As ILC member Mathias Forteau explained in a lecture at the Collège de France, the Commission can act as a catalyst through an “institutionalised dialogue between the ILC and States” (from around the 35-minute mark).

Indeed, once the Commission brings its proposals to the attention of the General Assembly’s Sixth Committee, silence is no longer an option. States are compelled to take a position on an issue that might otherwise appear remote or unlikely to affect their interests. A brief look at the chronology of the practice developed by island States illustrates this normative synergy. The first issue paper addressing State continuity, published in 2022, cautiously suggested that a “strong presumption in favour of continuing statehood should be considered” (§ 194). Continuity therefore remained no more than a rebuttable presumption, however strong, and its application to sea-level rise was introduced merely as a possibility. Yet, the following year, the Pacific Islands Forum adopted a declaration that invoked this presumption and applied it, without qualification, “in the context of climate change-related sea-level rise” (§ 12). Around the same time, the Falepili Union treaty was signed with Australia, which recognised Tuvalu’s permanent continuity (art. 2(b)). Drawing on this subsequent practice, the ILC Study Group’s final report moved beyond the language of rebuttable presumption and treated continuity as the definitive answer to the question (§§ 35-41). To clarify whether this emerging practice had become lex lata, island States turned to the ICJ.

Seeking clarity on state continuity before the ICJ

Until the advisory opinion was delivered in July 2025, the completion of this normative synergy appeared within reach. Once again driven by the diplomatic efforts of island States, the request invited the Court to determine States’ obligations in relation to climate change, while paying particular attention to their vulnerability. Several of them detailed original arguments in the hope to secure judicial recognition of their continued existence despite sea-level rise. They sometimes linked the principle of State continuity to the “fundamental right of every State to survival”, referring to the controversial paragraph 96 of the Court’s 1996 advisory opinion on the Legality of the Threat or Use of Nuclear Weapons (for El Salvador, see p. 74, § 17 ; for the Comoros, see p. 70, § 9). The Dominican Republic likewise relied on that fundamental right to infer an “obligation of other States to comply with their mitigation commitments under the Climate Change Convention and the Paris Agreement” (§ 4.42). The Cook Islands also invoked the Court’s 1996 dictum in support of “[d]eclaratory relief in the form of recognition of the sovereignty, statehood, territory and maritime boundaries of States despite the impacts of sea-level rise” (§ 111(c)).

The Court not only refused to engage with these arguments, but it also refrained from examining the ILC’s conclusions to assess their status under international law. Admittedly, few States expressly relied on those conclusions before the Court. Many submissions nevertheless reflected its findings or its underlying logic. The Court likewise appears to have echoed that logic without expressly relying on the Study Group’s conclusions. Although it referred to the ILC on other issues, including the law of treaties and State responsibility, it cited its work only once in relation to sea-level rise. When considering the fate of coastal States’ maritime areas, the Court stated that it was “aware of the work undertaken by the ILC”, which “shows a convergence of views among States across all regions” in support of maintaining established baselines—in other words, in support of the permanence of maritime zones (§ 361). By contrast, the Court appears deeply uncertain when addressing State continuity. The issue is confined to a single statement, itself incidental—it was inserted into the section dealing with the law of the sea (§ 363). As Judge Tomka observed, the wording leaves it unclear whether the Court merely accepted that continuity remains possible in the specific context of sea-level rise, or that it went further by implicitly endorsing “the deconstruction of the conditions of statehood as such” (§ 2 of Judge Tomka’s Declaration).

We believe that the Court’s cautious wording was, in fact, an invitation to the international community to settle the matter by indicating which of the possible readings of paragraph 363 it endorsed. The General Assembly’s resolution should be understood as a response to that invitation.

Completing the normative synergy through a General Assembly resolution?

When outlining “possible ways forward”, the Study Group suggested that its conclusions might eventually crystallise into lex lata if States and international organisations adopted “binding or non-binding instruments and develop mechanisms that specifically address the legal issues arising from sea-level rise” (§ 59 of the Final Report). In particular, it noted that the UN General Assembly “may adopt resolutions (…) in relation to the continuity of statehood” (§ 59(a)). This suggestion is significant considering the scepticism expressed by some States towards the Study Group’s findings. The United Kingdom, for example, stressed that many States were still developing their positions, that silence or abstention should not be overread (§ 9), and that the Study Group had to distinguish clearly between lex lata and lex ferenda. Its concern was therefore not that every affected States must consent to an evolution of customary international law, but that a development touching upon the fundamental category of statehood should not prematurely be presented as existing law. In that context, the United Kingdom recalled that “it is States who remain the principal law makers in international law with respect to its progressive development” (§ 12).

That assertion is undoubtedly correct, but it is also something of a caricature. The General Assembly’s recent resolution shows that States do not make international law in a vacuum. It emerged from the cumulative interaction between island States’ practice, the work of the ILC and the limited judicial opening provided by the ICJ. Island States are thus close to securing their continued statehood despite sea-level rise. The resolution indeed provides particularly strong evidence of a growing opinio juris in favour of continuity in these exceptional circumstances alone. The strategy is legally sound: rather than fundamentally changing the definition of the State, it introduces a degree of flexibility for States facing an existential threat. It does not, however, resolve all the legal conditions and consequences of continuity. In explaining its vote in favour of the resolution, the United Kingdom sought to limit its legal implications, stating that “this resolution is intended to reflect, not develop or interpret, the Court’s Advisory Opinion”. In other words, it made clear that the resolution did not definitively settle the matter—even though the wording suggests otherwise. States may endure, but the legal architecture of their continuity remains to be built.

Jean-Baptiste Dudant served on the ILC as an assistant to the co-chair responsible for the question of State continuity in the face of sea-level rise; the views expressed here are his own.

Image credit: Stefan Lins CC BY-SA 2.0