Lessons learned from the work of the United Nations International Law Commission on Sea-level rise in relation to international law

This article presents lessons learned from the activity of the International Law Commission (ILC, the Commission) focusing on ‘Sea-level rise in relation to international law’ from the perspective of the author as former Co-Chair of the Study Group on this topic, which was included on the active agenda of the ILC in 2019 and was finalized in 2025. The article undertakes a review of the progress of the topic on its three subtopics (law of the sea, statehood and protection of persons affected by sea-level rise), mainly from the perspective of the way the Commission responded promptly, in a concrete manner, to the interests and needs of the United Nations (UN) Member States concerned by the negative effects of this consequence of climate change, as well as of the way the ILC engaged in relation with States by inaugurating a new level of interaction with them. The article proposes that future topics to be included in the active agenda of ILC follow this pattern. When topics prompt urgency, the Commission should speed up their inclusion, whilst at the same time amply consulting UN Member States prior to decisions in this respect. At the same time, it should focus on concrete solutions, which, in the case of sea-level rise, are illustrated in the article by examples such as ‘freezing’ baselines and outer limits of maritime zones, non-application of the rebus sic stantibus principle for maritime delimitation agreements or the strong presumption of continuity of statehood when territory is fully submerged. The increased interaction could be facilitated by constant consultation of Member States on lists of potential new topics. Other proposals, such as the creation of more Study Groups or the appointment of Co-Special Rapporteurs for a topic, could be considered. In the view of the author, such approaches could reinforce the key role and mission of ILC for the future. The article also presents the main pronouncements of the International Court of Justice (ICJ) on sea-level rise in its recent Advisory Opinion on the Obligation of States in respect of Climate Change (23 July 2025).