France, July 24 -- 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.

The International Court of Justice's (ICJ) advisory opinion is not legally binding but was unanimous and is expected to have major legal ramifications for courts, companies and communities across the world.

The United Nations had tasked the ICJ with outlining which obligations countries are under to curb planet-heating emissions - and to lay out possible consequences for failing to do so.

The global climate should be protected for both the current population but also for future generations, the court ruled, describing the climate system as "an integral...