A UN TRIBUNAL on maritime law said today 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.