Statehood and Maritime Boundaries Under UNCLOS Amid Sea-Level Rise

As the planet warms, the sea is rising. For some very low-lying island countries, this raises a question that international law has never faced before: if all of a country's land goes under water, does that country still exist? And what happens to the huge sea areas it controls today? This concept is about how international law answers these two questions: the survival of statehood and the fate of maritime boundaries (lines at sea that mark a country's rights).

Why is this question so serious?

Countries such as Tuvalu, Kiribati, the Marshall Islands and the Maldives are made mostly of low coral islands. Many parts of them are only one or two metres above the sea. Rising seas bring flooding, salt water entering drinking water and farms, and loss of land. For these countries, the sea areas around them are also their biggest wealth.

Fishing licences, especially for tuna, give many Pacific island governments a large part of their income. If they lose their sea zones or their status as a country, they lose both money and a voice in the world.

What makes a country a country?

The most quoted test comes from the Montevideo Convention on the Rights and Duties of States, 1933. Its Article 1 lists four things a state should have:

• a permanent population
• a defined territory
• a government
• the capacity to enter into relations with other states

The same convention (Article 3) says a state's political existence does not depend on other countries recognising it. This is called the declarative theory. The Montevideo test was written for the Americas, but today it is widely treated as a statement of general international law. The problem is simple to see: if the land disappears, the "defined territory" condition seems to fail. So the question becomes whether a state that already exists can lose its statehood because it loses its land.

How does the sea get divided?

Under UNCLOS, every coastal country measures its sea zones from a baseline. Normally the baseline is the low-water line along the coast (the line the sea reaches at low tide). From this baseline:

• the territorial sea goes up to 12 nautical miles, where the country has full sovereignty
• the contiguous zone goes up to 24 nautical miles, for customs, immigration and health checks
• the Exclusive Economic Zone (EEZ) goes up to 200 nautical miles, where the country alone has rights over fish, oil, gas and other resources

Article 121 of UNCLOS also matters. A naturally formed island can have its own EEZ. But a "rock" that cannot support human habitation or economic life of its own gets only a territorial sea, not an EEZ. So if rising seas turn an island into a mere rock, or wipe it out, a country could lose a huge piece of sea.

Moving baselines or fixed baselines?

Here is the core legal worry. If a baseline moves with the coastline (this is called an ambulatory baseline, meaning a "walking" baseline), then every time the sea eats into the land, the baseline moves inward. The outer limits of the zones then move inward too. Some sea that belonged to the island state would become high seas (open ocean that belongs to no one).

Island states argue for fixed baselines: once a country has drawn its zones and informed the world, those lines should stay, whatever the sea does. UNCLOS asks countries to deposit charts or lists of coordinates of their baselines and outer limits with the UN Secretary-General (for example, under Articles 16 and 75). It does not say anywhere that countries must keep updating them later.

How has the law developed?

Island states have moved step by step to build legal certainty:

• 2019: The International Law Commission (ILC), the UN body of legal experts that helps develop international law, set up a Study Group on "sea-level rise in relation to international law". It had five co-chairs and studied three areas: the law of the sea, statehood and the protection of affected people.
• August 2021: The Pacific Islands Forum issued the Declaration on Preserving Maritime Zones in the Face of Climate Change-related Sea-Level Rise. Its members said they would keep their zones, as already notified to the UN, without any reduction. More than 100 states and groups later supported it.
• 2023: The Pacific Islands Forum issued a second declaration, on the Continuity of Statehood and the protection of people affected by sea-level rise. It said the statehood and sovereignty of its members will continue despite sea-level rise.
• 2023: Tuvalu changed its constitution to say that its statehood continues even if it loses physical territory because of climate change, and to fix its maritime boundaries permanently.
• 2025: The ILC adopted the Study Group's final report and sent it to the General Assembly.
• 23 July 2025: The International Court of Justice (ICJ) gave its advisory opinion on the Obligations of States in respect of Climate Change. The General Assembly had asked for it through resolution 77/276 of 29 March 2023, a move led by Vanuatu and adopted by consensus.

What did the ICJ say?

The Court gave the island states strong support on both questions:

• On sea zones, it said UNCLOS does not require countries to update their charts or coordinates once their baselines and outer limits have been properly set and deposited. So existing zones stay valid even when the sea rises.
• On statehood, it said that once a state is established, the disappearance of one of its elements (such as territory) would not necessarily mean the loss of its statehood.
• It also said states have a duty under customary international law to cooperate in dealing with sea-level rise.

An advisory opinion is not a binding judgment between two parties. But it is the most authoritative statement of what the law is, and countries and courts give it great weight.

What is "continuity of statehood"?

Lawyers call this a presumption of continuity. It means: once a state exists, the law assumes it goes on existing unless something clear and deliberate ends it (for example, it merges with another country by choice). History supports this. Some governments continued to be treated as states even while they did not control their land, for example during foreign occupation. Island states argue that losing land to the sea because of other countries' emissions should not be treated more harshly.

What about the people?

Statehood on paper does not help if people cannot live on the islands. So countries are also planning for movement. In the Falepili Union treaty between Australia and Tuvalu (signed November 2023, in force from 28 August 2024), Australia offers a special pathway for Tuvaluans to live, work and study in Australia, and a route for migration if climate change makes the islands unlivable.

India's position and interest

India has a very long coastline, the Lakshadweep islands in the Arabian Sea, and the Andaman and Nicobar Islands in the Bay of Bengal. Its own EEZ depends on stable baselines. India ratified UNCLOS in 1995 and generally supports a rules-based order at sea. India also works with small island states through the Forum for India-Pacific Islands Cooperation (FIPIC) and the Infrastructure for Resilient Island States (IRIS) initiative. So legal stability for sea zones fits both India's own interests and its partnerships.

Commonly confused concepts

• Statehood vs recognition: Statehood is about whether an entity meets the conditions of a state. Recognition is a political act by other countries accepting it. Under the declarative theory, a state can exist even if some countries do not recognise it.
• Baseline vs coastline: The coastline is the physical edge of land. The baseline is a legal line, usually the low-water line, from which zones are measured. Straight baselines can cut across bays and between islands.
• Territorial sea vs EEZ: In the territorial sea (12 nm), the country has full sovereignty, subject to innocent passage of foreign ships. In the EEZ (200 nm), it only has "sovereign rights" over resources; other countries keep freedom of navigation and overflight.
• Island vs rock (Article 121): An island can have a full EEZ and continental shelf. A rock that cannot support human habitation or economic life gets only a 12 nm territorial sea.
• ICJ advisory opinion vs judgment: A judgment in a dispute between states binds those states. An advisory opinion answers a legal question from a UN body and is not binding, but it carries high legal authority.

Issues, criticism and the way forward

• Fairness vs legal change: Island states say they did little to cause climate change, so they should not lose their sea wealth because of it. Some experts point out that UNCLOS was written assuming coasts are stable, so treating fixed baselines as the rule is a new reading of the law.
• Soft law vs hard law: Declarations of the General Assembly and regional forums are political statements, not treaties. They build state practice and legal expectation, but they do not by themselves create binding rules.
• Statehood without territory is untested: No state has yet lost all its land. How a state without territory would work in practice (where its government sits, how its citizens are protected) is still open.
• People come first: Legal continuity does not stop homes from flooding. Islands need adaptation money, early warnings, sea walls, mangrove protection and fair migration pathways.
• Way forward: Island states and experts suggest that more countries formally accept fixed maritime zones, that all states deposit their charts and coordinates with the UN, that climate finance for adaptation is scaled up, and that cooperation between states (which the ICJ called a legal duty) is made practical.

Concepts to Know

• Statehood: The legal status of being a country under international law, with the rights and duties that come with it, such as a UN seat and control over its territory and sea zones.
• Nautical mile: A unit of distance used at sea. One nautical mile is 1.852 km. So 200 nautical miles is about 370 km.
• High seas: The open ocean beyond any country's EEZ. No country owns it; all countries can use it for shipping, fishing and research under shared rules.
• Advisory opinion: A legal answer given by the ICJ when a UN body, such as the General Assembly, asks it a question. It is not binding but is highly respected.
• Soft law: Statements, declarations and guidelines that are not legally binding but influence how countries behave and how law develops.
• Customary international law: Rules that become binding because countries follow them widely and consistently, believing they are legally required to do so, even without a written treaty.