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.

The United Nations' top court has issued a landmark advisory opinion on climate change, its 15 black-robed judges weighing in for the first time on what the court's president called “an existential problem of planetary proportions that imperils all forms of life and the very health of our planet.