By Patrícia Galvão Teles and Dave-Inder Comar

In 2019, the UN International Law Commission (ILC) established an open-ended Study Group to assess the implications of sea-level rise on a variety of international legal issues. Through 2025, the Study Group focused on three sub-topics: the law of the sea; statehood; and the protection of persons.

As discussed in the final report of the Co-Chairs of the Study Group, a large number of States made comments on the sub-topic of statehood before the Sixth Committee in 2024. Several States took the view that the Convention on Rights and Duties of States (Montevideo, 26 December 1933) (the “Montevideo Convention”) did not directly discuss the issue, permitting additional interpretations of international law.

Other States took a more explicit perspective that a State subject to loss of territory as a result of sea-level rise would remain a subject of international law. Support for the continuity of statehood was expressed not only by specially affected or vulnerable States. The US, for example, commented that sea-level rise driven by climate change should not cause any country to lose its statehood or its membership in the UN, its specialized agencies, or other international organizations. Brazil and Germany expressed similar views. Some States, including India and the Czech Republic, expressed caution on the issue. Generally speaking, however, there was strong support for the presumption of continuity of statehood and international legal personality from States.

Many States, including the Netherlands, Germany, Singapore, Portugal, Liechtenstein, and Chile, further highlighted the connection between continuity of statehood with self-determination during the 2024 debate in the Sixth Committee of the UN General Assembly (UNGA). These comments reflect a growing understanding from States that self-determination is an ongoing, perpetual right of a people to continue to maintain a preferred political status and may therefore provide legal protection in the context of sea-level rise.

This interpretation of the right to self-determination has also been set forth by regional bodies representing the interests of States. For example, the 2023 Declaration on the Continuity of Statehood and the Protection of Persons in the Face of Climate Change-related Sea-Level Rise from the Pacific Islands Forum (PIF) refers to self-determination, along with other international principles, as being “consistent” with the continuity of statehood in the face of climate change-related sea-level rise. The 2024 Declaration on Sea-Level Rise and Statehood from the Alliance of Small Island States (AOSIS), issued one year later, goes a step further by declaring that “consistent with the right to self-determination,” the statehood and sovereignty of SIDS will only cease “if another form of expression of the right to self-determination of a SIDS population is explicitly sought and freely exercised by that population.” Read together, the PIF and AOSIS declarations reflect that self-determination is not only a guiding principle for at-risk States, but also a substantive right in ensuring continued participation in the international legal order. The AOSIS declaration’s emphasis on the affirmative consent of an affected population also suggests a critical procedural protection rooted in self-determination.

The Falepili Union Agreement between Australia and Tuvalu also presents an example of State practice on the continuity of statehood in the context of sea-level rise. The agreement recognizes both “the desire of Tuvalu’s people to continue to live in their territory where possible and Tuvalu’s deep, ancestral connections to land and sea” and that “the statehood and sovereignty of Tuvalu will continue, and the rights and duties inherent thereto will be maintained, notwithstanding the impact of climate change-related sea-level rise.”

The ILC Study Group’s conclusions on statehood and self-determination

In its final report, the ILC Study Group concluded that there was “strong support” among States for the continuity of statehood and sovereignty in the face of climate change-related sea-level rise. The ILC Study Group also concluded that the Montevideo Convention “does not address the question of the continuity of statehood in the context of climate change-related sea-level rise.” Continuity of statehood was linked to a variety of other international legal principles including the right of States to preserve their existence, territorial integrity, and self-determination. Therefore, preservation of statehood “correlates with the right of peoples, including Indigenous Peoples, to self-determination, as they cannot be deprived of the continuity of statehood without their consent.” Respect for the right to self-determination also requires “consultation in good faith as to alternatives that may be applied to preserve their identities and international legal personality.” These conclusions make clear that self-determination should be treated as a guiding principle in the context of existential climate change impacts such as sea-level rise.

The ICJ’s nod to self-determination and to statehood

The recent Advisory Opinion from the International Court of Justice (ICJ), Obligations of States in Respect of Climate Change, also contains important pronouncements on statehood and self-determination in the context of existential climate change impacts. The Court clarified that “once a State is established, the disappearance of one of its constituent elements would not necessarily entail the loss of its statehood,” affirming the view that the Montevideo Convention criteria were not wholly dispositive on the question of continuity of statehood and disappearing territory from sea-level rise. The Court also observed the possibility of “adverse consequences” on vulnerable States from sea-level rise, including forced displacement and impacts on territorial integrity and permanent sovereignty over natural resources. “[S]ince these principles are closely connected with the right to self-determination, sea level rise is not without consequences for the exercise of this right.”

The ICJ’s discussion, while brief, is significant in that, though a bit more nuanced, it broadly aligns with the work of the ILC as well as the PIF and AOSIS declarations. In the context of statehood, the Court unanimously considered that the Montevideo criteria in relation to the creation of States are not to be applied point-for-point in discussions of State continuity and sea-level rise, and that room for interpretation exists. Similarly, the Court’s conclusion that self-determination will be implicated by sea-level rise represents a major extension of its jurisprudence related to self-determination beyond the contexts of decolonization and occupation.

Judge Tomka, in his separate declaration, expressed doubts that there was sufficient acceptance from the international community on the question of statehood, self-determination, and sea-level rise, and suggested that the inexistence of land as a result of climate change impacts “would tend to result in the demise of that [impacted] State as a subject of international law.” Vice-President Sebutinde and Judge Aurescu, on the other hand, separately opined that the Court should have engaged in further analysis on the topic of self-determination, particularly on issues of statehood and the law of the sea. Taken together, these separate declarations reflect that in the context of climate change impacts, questions of statehood, maritime entitlements, territorial integrity, and permanent sovereignty over natural resources will need to be reconciled with the right to self-determination and the protections it affords to affected peoples and States.

As noted in the final report of the ILC Study Group, adopted unanimously by the ILC, further declarations or statements from States – for example, in the UNGA, or through other binding or non-binding instruments – may provide further legal certainty on the continuity of statehood and the preservation of self-determination for impacted peoples and States.

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Patrícia Galvão Teles is a member of the International Law Commission and Co-Chair of the Study Group on Sea-Level Rise in relation to International Law. She represented Portugal at the ICJ Advisory Proceedings on Obligations of States in Respect of Climate Change. The views expressed are in a personal capacity.

Dave-Inder Comar is a PhD Candidate at the Grotius Centre for International Legal Studies at Leiden University, and Executive Director of Just Atonement Inc.

This Guest Article is part of a project that seeks to raise awareness and build momentum and knowledge around the ICJ advisory opinion on obligations of States in respect of climate change and to promote a better understanding of the implications of the advisory opinion among sustainable development decision makers.