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.

In a landmark ruling, the International Court of Justice declared that failure to act on climate change can be an “internationally wrongful act”—meaning countries could face legal consequences for harming the planet.