The world’s highest court said polluting countries may be in breach of international law if they do not protect the planet from the “existential threat” posed by climate change, in a landmark advisory opinion issued Wednesday.

It also said countries feeling the sharp end of climate change may be entitled to reparations for the harm caused by rising temperatures.

The advisory opinion marks the first time the International Court of Justice, the UN’s top court based in the Hague, has formally addressed the climate crisis.

The court was asked to consider two fundamental questions: what legal obligations nations have under international law to address climate change, and what the consequences should be for countries that harm the climate.

Its opinion, which runs to more than 500 pages, said climate change was an “urgent and existential” threat and was unequivocally caused by human activities.