The United Nations’ top court in a landmark advisory opinion says countries could be in violation of international law if they fail to take measures to protect the planet from climate change, and nations harmed by its effects could be entitled to reparations.

The International Court of Justice called global warming an “urgent and existential threat” at a closely watched case in The Hague.

The opinion by the International Court of Justice, also known as the World Court, was immediately welcomed by environmental groups.