HAMBURG, Germany (AP) — A U.N. tribunal on maritime law said Tuesday that countries are legally required to reduce greenhouse gas pollution, delivering a long-awaited opinion sought by small island nations that are on the front lines of climate change.

The International Tribunal for the Law of the Sea found that carbon emissions qualify as marine pollution and said countries must take steps to mitigate and adapt to their adverse effects.

It was the first ruling to come in three cases in which advisory opinions have been sought from international courts about climate change.

Experts say the decision, though not legally binding, could profoundly impact international and domestic law on climate change.

“The opinion is a clarification of international legal obligations,” said Joie Chowdhury, a senior attorney at the Center for International Environmental Law.

China, Russia and India are among the 169 parties to the U.N. Convention on the Law of the Sea, the treaty that underpins the court. The United States, which is the world’s biggest historic emitter of greenhouse gases, is not a party.

“States parties to the convention have the specific obligations to take all necessary measures to prevent, reduce and control marine pollution from anthropogenic (greenhouse gas) emissions,” Judge Albert Hoffmann told a packed courtroom in Hamburg, where the tribunal is based.

The request for the opinion was made in 2022 by the Commission of Small Island States on Climate Change and International Law, a coalition of nations spearheaded by the Caribbean nation of Antigua and Barbuda and the Pacific island country of Tuvalu.

The group asked the court to specify what obligations signatories of the maritime treaty have in relation to the effects of climate change caused by human activity, and to protecting the marine environment from ocean warming and sea level rise.

Small island states are among the most vulnerable nations to climate change, facing encroaching seas, recording breaking temperatures and increasingly severe storms. Last year, Australia offered to allow residents of Tuvalu — one of the island countries involved in the proceedings — to relocate to escape the effects of climate change.

Ocean temperatures in particular have increased, worsening the impact on coastal states.

“Without rapid action, climate change may prevent my children and grandchildren from living on their ancestral home,” Gaston Alfonso Browne, the prime minister of Antigua and Barbuda, told the tribunal last year.

Climate change is on the docket of a string of international courts. Last year, the same group of island nations asked the International Court of Justice to weigh in as well.

The U.N.’s top judicial body is set to hold hearings next year and more than 80 countries have already asked to participate.

Climate change proceedings also are under way at the Inter-American Court of Human Rights. Chile and Colombia asked the regional body to give an advisory opinion on what obligations countries in the Americas have to tackle greenhouse gas emissions.

Tuesday’s decision follows a landmark ruling by the European Court of Human Rights, which found that the Council of Europe's 46 member states have a legal obligation to protect their citizens from the adverse effects of the climate crisis. The Strasbourg-based court was the first international judicial body to rule on climate change.