In a landmark case, judges at the International Court of Justice in The Hague have found that if countries fail to take measures to protect the planet and its people from climate change, they could be violating international law.

The judges were addressing a request from the UN’s General Assembly—led by Pacific Island nations—to give an advisory opinion on the legal rights and responsibilities of nations regarding climate change.

International law is important, said court President Yuji Iwasawa, but it’s limited when it comes to the “daunting and self-inflicted problems” posed by climate change.

“They concern an existential problem of planetary proportions that imperil all forms of life and the very health of our planet,” he read out to a packed courtroom. “We must change our habits, comfort and current way of life in order to secure a future for ourselves and all who are yet to come.”

Taking the world’s three climate treaties as the main basis for its non-binding opinion—including the Paris Agreement—judges found that when it comes to climate change, states are under stringent obligations to adhere to the treaties they’ve signed.

Any breech of them can lead them back to this court–or to national and local jurisdictions–on a case-by-case basis. The climate minister of Vanuatu, one of the small, sinking Pacific Island nations that instigated this case, hailed the opinion.

“Today’s ruling is a landmark moment confirming what vulnerable nations have been saying for so long,” said minister Ralph Regenvanu. “States have legal obligations to act on climate change ground in international and human rights law.”

Judges say they hope their legal clarification helps guide future social and political action on climate change. Some 3,000 climate-related cases have been filed across almost 60 countries as 2024 proved to be the hottest year on record.

Climate minister Regenvanu says Wednesday’s opinion will no doubt inspire new cases as the world gears up for the next climate change conference in Brazil in November.