Tejaswinee Burumdoyal, Second Secretary, Ministry of Foreign Affairs, Regional Integration and International Trade
Small Island Developing States (SIDS) are a group of thirty-nine States recognised by the United Nations. For many SIDS, the ocean represents a major source of natural resources. However, climate change impacts the lives, livelihoods, food security, ecosystem as well as the wellbeing of people and communities in SIDS. They are also likely to be the most affected due to their geographical circumstances and level of development. While the Intergovernmental Panel on Climate Change (IPCC) projects that the global mean sea-level is expected to rise between 0.61 and 1 metre by 2100, in Mauritius, climate-induced sea-level is expected to be between 24 and 40 cm by 2050 and up to 1 m 84 cm by 2100. From a geological and geophysical perspective, sea-level rise causes shoreline migration, changes in ocean area, and vertical land movements. This issue is even more pertinent for islands as sea-level rise is also like to cause islands to submerge. No thought had been given to this issue prior to the 1989 Malé Declaration on Global Warming and Sea Level rise, meeting organised by SIDS. This is also the primary reason why the 1982 United Nations Convention on the Law of the Sea (UNCLOS) has no relevant provisions concerning sea-level rise. Following the 1989 Conference in Malé, SIDS, including Mauritius, created the Alliance of Small Island States (AOSIS). This blog will look at the legal implication of a rise in sea level on islands and their maritime entitlements.
Article 121 of UNCLOS1 defines an island as a naturally formed area of land, surrounded by water, which is above water at high tide. Such island generates maritime zones, territorial sea, contiguous zone, an Exclusive Economic Zone (EEZ) and Continental Shelf, like other land territory. The EEZ of SIDS is estimated to be, on average, 28 times the country’s land mass. These entitlements are measured using baselines2 under the provisions of UNCLOS. The baseline is the line along the coast from which the breadth of the territorial sea (12 nautical miles) from the land and the outer maritime zones are calculated3. In Mauritius, the baselines are regulated, in line with the provisions of UNCLOS, by the Maritime Zones Act 2005 and the Maritime Zones (Baselines and Closing Lines) Regulations 2024.
In physical terms, sea-level rise causes the water body to shift inwards and makes coasts retreat. This challenges existing maritime boundaries and entitlements. For islands, an inward shift in the baseline as a result of sea-level rise could mean that the territorial sea and other maritime entitlements would grow inwards. This could cause major economic losses to islands whose economies depend on the resources of the oceans. A rise in sea-level, thus, challenges the maritime entitlements, statehood, and SIDS’ continued enjoyment of permanent sovereignty over natural resources4.
In 1969, the ICJ, in its judgement of the North Sea Continental Shelf Case stated the principle of ‘land dominates sea’. This is because maritime entitlements are derived from the land territory. Sea-level rise tests that assumption directly.
Conversely, in July 2025, the International Court of Justice (ICJ), in its Advisory Opinion on Climate Change and States’ Obligations, stated that: the provisions of UNCLOS do not require States parties, in the context of physical changes resulting from climate-change related sea level rise, to update their charts or lists of geographical co-ordinates that show the baselines and outer limit lines of ’. Such assertion backs the statements of the Alliance of Small Islands States (AOSIS), the Commonwealth and the Pacific Islands Forum., that there is no obligation under UNCLOS to review or update baselines and outer limits of maritime zones, once they have ben deposited with the Secretary-General of the United Nations, and that notwithstanding any physical changes related to climate change-related sea-level rise, there shall be no change in the maritime zones and the rights and entitlements that flow from them.
Prior to the Advisory Opinion, in early 2025, the International Law Commission (ILC) highlighted the importance of maintaining existing baselines and maritime boundaries in the wake of sea-level rise in order to preserve the legality, certainty, and stability of the regime.
But what will happen in real terms if an island is submerged and /or covered with water? Does the State cease to exist?
The 1933 Montevideo Convention on the Rights and Duties of States defines statehood as comprising four elements namely, (a) a permanent population, (b) a defined territory, (c) government, and (d) capacity to enter into relations with other states. The ICJ’s Advisory Opinion informed that once a State is established, the disappearance of one of its constituent elements would not necessarily entail the loss of its statehood. This supports the advocacy by Pacific Islands Forum, the Commonwealth and the AOSIS that statehood remains even in the context of climate change-induced sea level rise.
Rhetorically, this may make sense. However, what happens in real terms?
If the physical territory of an island ceases to exist, then it cannot sustain human habitation or economic life. Article 121 (3) of UNCLOS regards a feature without these two defining criteria as a rock. Consequently, as per UNCLOS a rock only generates a territorial sea and a contiguous zone. In such situation, does a State lose its maritime entitlements as regard the resources in its Exclusive Economic Zone and Continental Shelf?
One of the most prominent cases on ‘rocks’ is the South China Sea Arbitration. The Tribunal, inter alia, considered that ‘it will be difficult, if not impossible, to determine from the physical characteristics of a feature alone where the capacity merely to keep people alive ends and the capacity to sustain settled habitation by a human community begins’.
The Tribunal stated that there should be evidence that human habitation has been prevented or ended by forces that are distinct from the intrinsic capacity of the feature, such as war, pollution and environmental harm which could lead to depopulation. As regard environmental harm, it is worth noting that SIDS contribute less than 1% of global greenhouse emissions. This argument could later be used by SIDS to secure their maritime entitlements.
However, it may be noted that during the proceedings of the Advisory Opinion on Climate Change, the Court only noted States’ arguments that the complete submergence of their territory should not deprive them of their maritime entitlements.
Conclusion
The Advisory Opinion of the ICJ, while not binding, is of authoritative nature and carries moral obligation. The 2025 Advisory Opinion on Climate Change and States’ Obligations marks a significant achivement for SIDS which have long argued that baselines are non-ambulatory. It affirmed that a State’s legal personality remains, even if one of the constituent elements defining it is lost. These offer a certain comfort to SIDS on the legal stability and certainty of the regime, whose importance has been highlighted by the ILC.
However, the Advisory Opinion leaves important questions unresolved. It does not conclusively determine whether a State’s maritime entitlements remains if its territory is submerged and whether or not that feature becomes a rock. Such situation raises several legal and political questions as regard the permanent sovereignty over natural resources, continued Statehood, and the protection of self-determination.
The ICJ's Advisory Opinion is a foundation, not an end in itself. Continued work with regard to sea-level rise in the years to come is likely to determine whether that foundation proves durable enough.
Charles Telfair Centre is an independent nonpartisan not for profit organisation and does not take specific positions. All views, positions, and conclusions expressed in our publications are solely those of the author(s).
Main photo: View of the ICJ courtroom during the reading of the Advisory Opinion of the Court on Obligations of States in respect of Climate Change. 23 July 2025, The Hague.Photograph: UN Photo/ICJ-CIJ/Frank van Beek. Courtesy of the ICJ. All rights reserved.
