A landmark ruling by the United Nations’ top court has found that governments, and by extension corporations, could be in breach of international law if they fail to take adequate action on climate change.

Legal experts say the decision by the International Court of Justice (ICJ) is likely to accelerate climate litigation, bolster demands for reparations from vulnerable nations and shape future lawsuits against both states and fossil fuel producers.

In its first advisory opinion on the climate crisis, issued on Wednesday, the court said that countries had a legal duty to prevent environmental harm, protect their populations from climate risks and ensure access to a clean, healthy and sustainable environment, which it recognised as a human right.

“Failure of a state to take appropriate action to protect the climate system … may constitute an internationally wrongful act,” Judge Yuji Isawa said during the hearing. He called the climate crisis “an existential problem of planetary proportions that imperils all forms of life”.

The non-binding opinion, backed unanimously by the court’s 15 judges, was hailed as a turning point in international climate law.

“Though non‑binding, this ruling carries significant legal and political weight and is poised to guide courts and governments throughout our region,” said Charles Santiago, co-chair of the Asean Parliamentarians for Human Rights and a former member of the Malaysian parliament.