The top court of the United Nations on Wednesday declared that countries have an obligation to combat climate change — and that a failure to do so could constitute a violation of international law.

Judges at the International Court of Justice (ICJ) adopted an advisory opinion on the subject that emphasized the “duty” of states “to use all means at their disposal” to minimize harm to the environment.

The opinion tasked governments with cooperating on this mission, noting that “a breach by a state of any obligations” identified in the advisory “constitutes an internationally wrongful act.”

Potential consequences of such violations could include “full reparation to injured states in the form of restitution, compensation and satisfaction,” the document stated.

In remarks prior to reading out the opinion, ICJ President Yuji Iwasawa stressed that the climate questions raised in the proceedings “represent more than a legal problem.”

“They concern an existential problem of planetary proportions that imperil all forms of life and the very health of our planet,” Iwasawa said.

The judges delivered their non-binding opinion with unanimous support, marking just the fifth time the body has done so in its 80-year history, according to the UN. 

The advisory ruling followed years of lobbying from island nations, arguing that they were at the mercy of climate-induced sea-level rise. The UN General Assembly decided to ask the ICJ for its advisory opinion in 2023, in a case led by the Pacific island nation of Vanuatu.

“International law, whose authority has been invoked by the General Assembly has an important but ultimately limited role in resolving this problem,” Iwasawa said on Wednesday.

“A complete solution to this daunting and self-inflicted problem requires the contribution of all fields of human knowledge,” he added.

While the advisory opinion emphasizes the responsibility of nations to act with due diligence to combat climate change, it also recognizes that those duties are “differentiated” among countries.

When taken as a whole, however, these efforts should collectively contribute to limiting global warming by 1.5 degrees Celsius, as agreed upon in the 2015 Paris Climate Agreement, per the opinion. 

In a press conference following the ICJ’s delivery, Ralph Regenvanu, Vanuatu’s climate change minister, expressed satisfaction not only with the opinion, but also with the fact that it was unanimous.

“It really points to the critical nature of this issue, and also the consensus of most people in the world that we need to really address it as a matter of urgency,” Regenvanu said. 

Describing the ruling as “a landmark moment,” the minister added that “the evidence is clear, and we can see it everywhere, that climate change is affecting everybody, all over the world.”

Ilan Kiloe of the Melanesian Spearhead Group Secretariat — a regional government agency in Vanuatu — added that area residents have already “suffered forced relocation” and have “lost much of what defines us as Pacific Islanders.”

“And climate change has only gotten started,” Kiloe said.

Vishal Prasad, campaign director for Pacific Islands Students Fighting Climate Change, described the opinion as “a lifeline and an opportunity to protect all that we hold dear.”

“This ruling is also a testament to the resolve of people everywhere, those at the front lines who chose not to allow the decisions of a minority of countries to dictate the future of the global majority,” he said.  

The ICJ opinion, Prashad added, provides countries with a foundation to build a more sustainable and equitable future.

As far as wrongful acts and reparations are concerned, attorney Margaretha Wewerinke-Singh said she believes that “the court has made it crystal clear” that injured states could now raise “a whole range of defenses” against polluters.

“It really strengthens the legal basis for such claims going forward,” added Wewerinke-Singh, an international lawyer at Blue Ocean Law who served as legal counsel for Vanuatu’s case.

She expressed hope that many polluting states would now prefer to voluntarily pay off reparations, rather than engaging in litigation.

Responding to questions about the United States, a major polluter that does not recognize the ICJ’s legal authority, Wewerinke-Singh said that as a U.N. member, the U.S. does, however, accept the court’s advisory function.

Since the U.N. General Assembly, including the U.S., requested the ICJ’s opinion, the U.S. “is also supposed to follow this advice” as long as it remains part of the U.N., she explained.

In the aftermath of the ruling, Regenvanu — Vanuatu’s climate change minister — said that next steps will involve taking the ICJ ruling back to the General Assembly and pursuing a resolution to support its implementation.

“We hope to set a new status quo and provide the structural changes needed to give our current and future generations hope for a healthy planet and a sustainable future,” Regenvanu said.

“Let this be the moment when we see a change and the world turns its face towards climate justice, and this legal clarity provides us with the moral courage to take this forward,” the minister added.