Ask for someone’s opinion on something gnarly and you might get some surprisingly strong words.

That’s what happened in The Hague on Wednesday, when the International Court of Justice, established by the United Nations and also known as the World Court, issued a stinging advisory opinion saying that countries have a legal obligation to limit the emissions of planet-heating greenhouse gases and provide restitution if their specific actions caused harm.

The opinion was unanimous. One legal analyst, Thomas Burri, a professor at the University of St. Gallen in Switzerland, called it “unexpectedly bold.” It was the result of a yearslong effort led by the tiny Pacific Island nation of Vanuatu.

The court’s opinion is not legally binding, and some countries, including the United States, haven’t accepted its jurisdiction over all matters. So how does it matter?

The opinion could affect current cases, and spur more.

The court’s opinion could strengthen the case that citizens’ groups have made in their national courts, from Australia to Switzerland, accusing their governments of failing to protect their people from the harms of climate change. “Courts worldwide are likely to reference this ruling in their upcoming decisions,” said Joie Chowdhury, an attorney with the Center for International Environmental Law.

Michael Gerrard, a Columbia University Law School professor, called it “an invitation for lawsuits in many countries’ courts saying not enough is being done.”