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 UN's top court on Wednesday ruled climate change an "existential problem of planetary proportions" and said countries had a legal duty to act or face consequences.

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.