World leaders adopted a landmark political declaration on sea-level rise at the United Nations General Assembly on Sept. 24. Not only was the declaration a political victory for the small island developing States most at risk, but it created international consensus on fundamental legal questions, including on continuing statehood for inundated States.
The negotiations on the final text were a rare but promising example of U.N. members working with common purpose on a sensitive political issue toward the goals of international peace and stability.
“Sea level rise may threaten our coasts, our homes and our ways of life. It does not threaten our legal rights, entitlements or existence as States,” said Surangel Whipps Jr., Palau’s president, speaking on behalf of the 39 members of the Alliance of Small Island States (AOSIS).
Ambassador Tania Romualdo of Cabo Verde and Ambassador James Larsen of Australia co-facilitated the negotiations, and I led negotiations on the declaration’s legal elements. Here, I analyze the declaration, offer a perspective on its contribution to law and policy, and share personal reflections arising from the negotiations. All views are my own and do not necessarily reflect those of the Australian government.
The Threat of Sea-Level Rise
Sea-level rise is a profound threat to international stability. The Intergovernmental Panel on Climate Change has predicted sea levels will rise at minimum between 11 and 22 inches (0.28 – 0.55 meters) by 2100, but those levels could be closer to 79 inches (2 meters) by 2100 due to ice sheet dynamics.
According to the U.N. Secretary-General, even lower-end scenarios would leave many significant portions of low-lying coastal zones and small island developing States uninhabitable without extraordinary adaptation. There would be catastrophic impacts on global security and economic stability resulting from States losing portions of their territory, entire economic sectors (fishing, farming, mining, tourism) vanishing, overwhelming adaptation and infrastructure repair costs, and mass migration.
The International Community’s Response
Up until very recently, the international community’s response had been limited. The Pacific Islands Forum (PIF) and AOSIS had largely driven the international legal debate, including through their landmark declarations on maritime zones and statehood (PIF declarations here and here, and AOSIS declarations here and here).
These groups jointly advanced the interpretation that a State would continue to exist under international law even if all of its territory were inundated. Its maritime zones, including its territorial sea and its exclusive economic zone, and the rights and entitlements that flow from these zones, would likewise not be impacted. Outside the landmark 2024 treaty between Australia and Tuvalu, how to practically confront and operationalize these principles was unaddressed. But at least as a matter of law, affected States would continue to be members of the U.N., to have continuing rights over large swathes of the ocean, and maintain ongoing treaty rights and obligations.
These principles started to gain serious traction internationally only in 2025, when the U.N.’s International Law Commission (ILC) backed the PIF and AOSIS interpretations. The International Court of Justice (ICJ) also confronted the issue in its 2025 climate change Advisory Opinion.
What really mattered, however, was how States outside PIF and AOSIS would react. Only their response would either affirm the positions as existing law, or as reflecting State practice, and so drive and consolidate the development of customary and treaty law.
Up until the adoption of the U.N. declaration in September, this was not clear. The General Assembly in 2025 recognized the ILC’s “valuable contribution” but stopped short of endorsing its conclusions. In response to the ICJ’s opinion, the General Assembly went further, including by affirming statehood’s continuity in the face of sea-level rise in a resolution it passed in May. However, eight states voted against the resolution, with 28 abstentions. This was progress, but it was not definitive.
The New Declaration and Its Implications
The new sea-level rise declaration changed the landscape. Not only is it normatively progressive, but it was agreed by consensus: by all 193 Member States. This has important implications politically, and for the development and consolidation of international law.
The declaration underscores deep concern about sea level rise as a “real and lived experience for many,” especially small island developing States. It foregrounds climate change as the cause, and advocates for adaptation and mitigation, based on the best available science and knowledge. It commits States to strengthen scientific observation, and to develop better interoperability between data collected by U.N. agencies.
Threats to critical infrastructure (for example, ports, energy, telecommunications) and to economic sectors (tourism, transport and insurance markets) are underlined. The declaration recognizes the impacts of sea-level rise on culture and cultural heritage. It acknowledges that, in some cases relocation – either internally or across borders – may be required where it is voluntary, preserves dignity, and is consistent with international law. For this, it enshrines a new term: “mobility with dignity.”
The declaration makes a substantial contribution to the clarification of international law on at least three levels.
First, it makes plain that international law is the foundation for responses to sea-level rise, and it affirms the need for “legal stability, certainty, and predictability.” The declaration reinforces the role of key treaties, including the U.N. Law of the Sea Convention (UNCLOS), the U.N. Framework Convention on Climate Change, and the Paris Agreement. Given the geopolitical environment, and number of non-parties participating, this is notable.
Second, the declaration advances the international community’s position on the stability of maritime zones in the face of sea-level rise. The ICJ’s opinion was that UNCLOS does not require States to update their charts or lists of geographic coordinates depicting baselines and the outer limits of their maritime zones, once established in accordance with the Convention, in the context of coastline changes caused by sea-level rise.
The declaration takes a logical, but legally significant, next step of affirming that once States establish baselines in accordance with UNCLOS, they can “accordingly maintain their maritime zones in the face of physical changes resulting from sea level rise, without prejudice to the State’s ability to update them.” This position represents a political consensus of the international community on a subject of long-running debate over the last decade.
Third, and most critically, the declaration crystallizes the international community’s position in favor of continued statehood. The ICJ said that the loss of a constituent element of a State – i.e. territory – “would not necessarily entail the loss of its statehood.” The ambiguity of its position was criticized by Judges Peter Tomka and Bogdan Aurescu – from opposite ends of the debate – in separate opinions. Judge Tomka said the Court should have been more prudent given that “territory has been indispensable to the concept of a State.” In his opinion, the Court’s statement was a “precocious leap of legal reasoning against the backdrop of silence from many, if not most, States.”
The declaration breaks the silence asserted by Judge Tomka. States affirm
the presumption in favour of continued statehood, and in this respect underscore the continuity of statehood in the face of sea level rise, as well as sovereignty, sovereign rights and responsibilities, and membership of the UN of such States, consistent with international law.
This is the first clear indication from all U.N. Member States that the concept of territory is not viewed as an essential element of continued statehood in the context of sea-level rise. Importantly, it also addresses Judge Aurescu’s criticism that the ICJ was silent on maintenance of U.N. membership.
The Declaration answers the concern put by Tuvalu to the General Assembly that “our rights under international law cannot be allowed to sink with our sinking islands.” But in the words of Timor-Leste, it “should mark not the conclusion of our effort, but the beginning of stronger international cooperation and coordinated implementation.”
Reflections
What was clear from negotiations was that all States wanted to get to a position of supporting the declaration. That included the Permanent Five members of the Security Council, as well as other States that had recently obstructed consensus on security, climate, and other topics in U.N. forums. This did not mean negotiations were easy, or that difficult compromises were not made to reach agreement. But the goodwill created an important foundation for success, especially as the mandate was for a consensus declaration.
Through the negotiations, it was also apparent many countries were working within their systems to develop and advance their legal positions so that they could support the declaration. Most States had not had to confront these legal questions until now. That States could play catch-up so quickly, given the fundamental questions of statehood and law of the sea involved, offers hope for other fast-moving global challenges, like the governance of emerging technologies.
For small low-lying island States, the Sea Level-Rise Declaration affirms their permanent membership of the international community, come what may. For all States, the declaration creates predictability – and with this, it strengthens peace and stability – as the contours of land change in the Pacific and other regions.
– Harry Aitken, Published courtesy of Just Security.