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.

In a landmark, unanimous advisory opinion, the International Court of Justice found that a state's violation of its legal climate obligations was a 'wrongful' act, and greatly affected countries could sue for '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.