Rahmonov Muhammadali | July 12, 2026

Nyang Nyang Beach in Uluwatu, Bali. Travel Wild/Adobe Stock.

Introduction

The United Nations Convention on the Law of the Sea of 1982 (UNCLOS) establishes a comprehensive maritime legal regime that reflects existing customary international law. However, in light of developments, specifically rising sea levels, questions have risen about whether UNCLOS permits states to retain their maritime rights in the face of coastal changes. This article demonstrates why coastal States are not prohibited from freezing their baselines by interpreting UNCLOS in light of its ordinary meaning, object, and purpose, as well as the subsequent practice of its States Parties.

UNCLOS Does Not Prohibit the Concept of Fixed Baselines

Under UNCLOS, states measure their maritime zones from baselines. In the Fisheries Case, the International Court of Justice held that the delimitation of maritime zones of coastal States is opposable against third states, those that are not parties to the specific delimitation or dispute, only if they have been set lawfully. Therefore, the primary issue now before the international community is whether it is legal for coastal States to fix their baselines, so that maritime areas, such as Exclusive Economic Zones – a maritime zone extending up to 200 nautical miles from the baselines in which the coastal state enjoys sovereign rights for resource exploration and exploitation – measured from these baselines, must be recognized by other States. 

Under Article 5 of UNCLOS, a “normal baseline” is the low-water line along the coast of the State as marked on its officially recognized large-scale charts. However, Article 5 is ambiguous about whether States can fix normal baselines once they are established. Are baselines to be understood as a physical reality on the ground, or a line on the coastal State’s chart? Until recently, the dominant position was that under Article 5, baselines are ambulatory – meaning that they are the actual physical shoreline. Simply put, a baseline will recede landward if the shore erodes due to sea-level rise. This understanding is based on the proposition that the source of the coastal state’s rights over adjacent maritime zones is its actual coastline (para. 96). Yet nothing in UNCLOS prohibits a state from fixing its normal baselines.

UNCLOS, like all treaties, should be interpreted in good faith with the ordinary meaning to be given to its terms, in the light of its object and purpose. The concept of fixed baselines relies on the ordinary meaning of Article 5, which provides that the normal baseline is the line marked on the state’s official charts. In light of this, scholars of international law agree that freezing the baseline does not contravene the meaning of the “normal baselines” as used in Article 5.

This view, however, is not unanimous. The International Law Association, for example, argues that the ordinary meaning of Article 5 is that the baseline is the line on the ground, relying on the ICJ decision in Nicaragua v. Honduras, the arbitral award in Guyana v. Suriname, and the travaux preparatoires of UNCLOS. But this argument is not persuasive. First, subsequent practice has emerged since the two cases were decided in 2007. And since then, the International Law Commission has weighed in with an authoritative opinion to claim that UNCLOS does not prohibit freezing maritime baselines. Second, the drafting history of UNCLOS is inconclusive: the text itself should be the basis for interpreting a treaty. Thus, the ordinary meaning of Article 5 does not exclude the fixing of baselines. 

The Concept of Fixed Baselines Achieves the Object and Purpose of UNCLOS

The objectives and purposes of UNCLOS include equity and stability. In the event of sea-level rise, the loss of maritime zones by low-lying states would be inequitable, and preserving the rule that baselines must be ambulatory would compromise stability. After all, States that are losing maritime areas are not ones that have contributed substantially to sea-level rise, and constant change in the positions of their baselines would undermine predictability. To the contrary, fixed baselines would ensure that states retain their maritime zones drawn from initial baselines, allowing them to access maritime resources without the fear that those resources would be lost as sea level rises. 

Interpretations of UNCLOS also show that the concept of fixed baselines is consistent with the Convention. In particular, UNCLOS does not obligate states to continuously update their charts as sea levels rise. And nothing in UNCLOS (para. 104) affirmatively requires coastal states to revise their baselines as their coastlines erode. That is why the Alliance of Small Island States Leaders announced in 2021 that they were fixing their maritime baselines because there is no obligation under UNCLOS to keep them updated.

Practice of States Parties to UNCLOS Supports the Proposition that Fixed Baselines are Lawful

A proper interpretation of a treaty includes any subsequent practice of the states parties in its application, which indicates their agreement. This requires the practice of all states parties, which may be seen either in their action or in their failure to object. It follows that if states do not challenge the legality of fixed baselines, their acceptance of the practice as lawful may be presumed. For states’ inaction to support the inference of agreement, however, there must be circumstances requiring their reaction, and they must have an opportunity to react. In other words, they must be aware of, and reject, the claim of legality.

The adoption of fixed baselines by coastal states is one such circumstance. States around the world can hardly be said to have been unaware that many nations have adopted fixed maritime baselines, as they have frequently and publicly declared. For example, Pacific Island Forum leaders announced that their members had done so, contending it is consistent with the Convention. Yet the practice has not been contested. By contrast, states such as Japan and Germany have affirmatively supported the legality of fixed baselines. Also, the United States, although not a state party to UNCLOS, adopted a new policy supporting, rather than challenging, the fixed baselines of other coastal states. From this, it may properly be inferred that the United States, too, believes that freezing maritime baselines is lawful under general international law. Given that states generally do react to unlawful conduct, and have not done so in this instance, it is fair to conclude that subsequent practice has manifested an agreement of the state’s parties of UNCLOS within the meaning of Article 31(3)(b) of the Vienna Convention on the Law of Treaties of 1969. 

Conclusion

UNCLOS does not prohibit states from freezing their normal baselines once they have been consistently established under the Convention. The concept of fixed baselines is supported not only by an interpretation based on the ordinary meaning of UNCLOS, but also by subsequent state practice, which demonstrates the Parties’ agreement on the lawfulness of such baselines. Therefore, UNCLOS offers coastal States a means to preserve their maritime entitlements in response to sea-level rise caused by global climate change.