The International Court of Justice issued a strongly worded opinion on Wednesday saying that states must protect people from the “urgent and existential threat” of climate change, a major moment for the global environmental movement and for the countries at greatest risk of harm.

It was the first time that the court, which is the United Nations’ highest judicial body, has weighed in on climate change.

The unanimous opinion said that the failure of nations to take action to protect the climate system may constitute “an internationally wrongful act.” It also found that protection of the environment is “a precondition” for ensuring human rights and cited government support of fossil-fuel production as a potential violation of these principles.

“The environment is the foundation for human life, upon which the health and well-being of both present and future generations depend,” Judge Iwasawa Yuji, president of the court, said.