The world's top court will Wednesday deliver a landmark ruling laying out what legal obligations countries have to prevent climate change and whether polluters should pay up for the consequences.

It is the biggest case ever heard at the International Court of Justice and experts say the judges' opinion could reshape climate justice, with major impacts on laws around the world.

"I think it will be a game-changer for the whole climate discourse we're going through," said Ralph Regenvanu, climate change minister of Vanuatu.

The Pacific island nation spearheaded the push for a court opinion amid growing frustration at sluggish progress in UN climate negotiations.

"We've been going through this for 30 years... It'll shift the narrative, which is what we need to have," Regenvanu told AFP.

The United Nations has tasked the 15 judges at the ICJ, a UN court that adjudicates disputes between nations, to answer two fundamental questions.

First: what must states do under international law to protect the environment from greenhouse gas emissions "for present and future generations"?

Second: what are the consequences for states whose emissions have caused environmental harm, especially........

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