This marks a significant turning point for international law, with substantial political implications. In a highly anticipated advisory opinion, delivered unanimously on July 23, 2025, the International Court of Justice (ICJ) affirmed that states have an “obligation to prevent significant damage to the environment” and must “cooperate in good faith” to curb climate change.
This is a solemn—and scathing—reminder that inaction on climate change is no longer just a political failure: it may now constitute a violation of international law. UN Secretary-General António Guterres welcomed the ICJ’s “historic advisory opinion” in a video message. “It has made clear that all states have an obligation under international law to protect the global climate system.”
Climate change, Judge Iwasawa Yuji emphasized, constitutes an “urgent and existential threat,” whose “serious and far-reaching effects […] affect both natural ecosystems and human populations.”
The main polluters disavowed
The case dates back to March 2023, when, at the initiative of Vanuatu, the United Nations General Assembly referred two questions to the ICJ: what are the legal obligations of States to protect the climate, today and tomorrow? And what are the consequences if they fail to do so, particularly with regard to the most vulnerable countries?
Historic hearings were held in December, with an unprecedented number of 96 states and 11 international organizations presenting their submissions. The main polluting countries—China, the United States, and the European Union—had argued that the treaties in force should remain “without legal obligation” and asked the ICJ to ensure that its opinion could not “lead to a conclusion of established, or even probable, violations” on the part of States.
The court’s advisory opinion, which is commensurate with the stakes involved, marks a rejection of this position. It establishes a robust legal framework based on customary international law, human rights, the law of the sea, and several key treaties, including the 1992 United Nations Framework Convention on Climate Change, the 1997 Kyoto Protocol, and the 2015 Paris Agreement. According to the ICJ’s opinion, all these treaties are legally binding and entail obligations.
The law no longer excuses inaction
At the heart of the opinion is one certainty: the complexity of the climate crisis cannot be used as an excuse for inaction. The obligation to prevent climate change requires states to take “appropriate,” “substantial,” “rapid,” and “sustainable” measures to reduce greenhouse gas emissions. The precautionary principle applies in full: “the absence of absolute scientific certainty must not be used as an excuse” for inaction, the court ruled.
Another decisive point is that these obligations do not arise solely from multilateral treaties. They also fall under customary international law and are therefore applicable to all states, regardless of whether they are parties to major climate agreements.
The ICJ also emphasizes the duty of cooperation, particularly in terms of financing, technology transfer, and support for the most vulnerable countries.
The door is open to claims for reparations
Although the ICJ’s advisory opinion is not legally binding, it could redraw the lines of climate law. It will serve as a reference for national and international courts, with nearly 3,000 climate-related lawsuits already underway in some 60 countries.
The ICJ’s opinion strengthens climate justice by clearly opening the door to claims for reparations. It states that a violation of states’ climate obligations may justify “the award of full reparation to the injured states,” provided that “a sufficiently direct and certain causal link can be established between the wrongful act and the damage suffered.”
The Court does not name any specific state as being at fault. But its message is clear: all governments must now answer not only to their people, but also to the law.
This ONU Info article has been adapted by UNRIC.
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