HAMBURG, Germany (AP) — A U.N. tribunal on maritime law said Tuesday that countries are legally required to reduce greenhouse gas pollution, a victory for 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.