In a historic statement, the International Court of Justice said climate change was an "urgent and existential threat" and countries had a legal duty to prevent harm from their planet-warming pollution.
Countries breaching their climate obligations were committing a "wrongful act", the court said in its advisory opinion, which is not legally binding but carries political and legal weight.
"The legal consequences resulting from the commission of an internationally wrongful act may include... full reparations to injured states in the form of restitution, compensation and satisfaction," said ICJ President Yuji Iwasawa on behalf of the 15-judge panel.
This would be on a case-by-case basis where a "sufficient direct and certain causal nexus" had been shown "between the wrongful act and the injury", the court added.
Campaigners and countries on the climate frontlines hailed a milestone moment in the fight for accountability from big polluters most responsible for global warming.
"This is a victory for our planet, for climate justice and for the power of young people to make a difference," said UN Secretary-General Antonio Guterres.
Ralph Regenvanu, the climate change minister for Vanuatu, the Pacific island nation that spearheaded the case at The Hague, was jubilant.
Speaking to AFP outside the court, Regenvanu said it was "a very strong opinion at the end" and better than hoped.
"We can use these arguments when we talk with our partners, some of the high-emitting states. We can say you have a legal obligation to help us," he said.
"This helps us in our arguments. It's going to give us a lot more leverage... in all negotiations."
- Catalyst for change -
This was the biggest case in ICJ history, and seen as the most consequential in a recent string of landmark climate moves.
The United Nations had tasked the 15 judges at the ICJ, a UN court in The Hague that adjudicates disputes between nations, to answer two fundamental questions.
First: what must states do under international law to protect the environment from greenhouse gas emissions for the future?
Second: what are the consequences for states whose emissions have caused environmental harm, especially to vulnerable low-lying island states?
In a detailed summary of the opinion, Iwasawa said the climate "must be protected for present and future generations".
The adverse effect of a warming planet "may significantly impair the enjoyment of certain human rights, including the right to life", he added.
Legal and climate experts said the opinion, while not legally binding, could have far-reaching consequences for national courts, legislation and public debate.
"The court's clear and detailed articulation of state obligations will be a catalyst for accelerated climate action and unprecedented accountability," David Boyd, a former UN Special Rapporteur on Human Rights and the Environment, told AFP.
Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research, said the ruling bound all nations by international law to prevent harm from emissions of planet-warming greenhouse gases.
The court was "pointing the direction for the entire world and making clear that every nation is legally obliged to solve the climate crisis", he told AFP.
- Classroom to court -
Courts have become a key battleground for climate action as frustration has grown over sluggish progress toward curbing planet-warming pollution from fossil fuels.
The Paris Agreement, struck through the UN Framework Convention on Climate Change (UNFCCC), has rallied a global response to the crisis, but not at the speed necessary to protect the world from dangerous overheating.
The journey to The Hague began six years ago with students from the climate-imperilled Pacific region fed up with the lack of accountability for the damage afflicting their homelands.
"Young Pacific Islanders initiated this call for humanity to the world. And the world must respond," said UN chief Guterres, praising Vanuatu's leadership.
The fight pitted major wealthy economies against the smaller, less developed states which are most at the mercy of a warming planet.
More than 100 nations and groups made submissions, many from the Pacific who gave impassioned appeals in colourful traditional dress.
"It's such a perfect ending to a campaign that started in a classroom," said Vishal Prasad, director of the student-led campaign that kicked off the case.
"We have now a very, very strong tool to hold power accountable, and we must do that now. The ICJ has given everything possible," he told AFP.
The United States, which has embraced a fossil fuel agenda under President Donald Trump, had a muted response to the ruling.
A US State Department spokesperson said it "will be reviewing the Court's advisory opinion in the coming days and weeks."
French Ecological Transition Minister Agnes Pannier-Runacher hailed the advisory opinion as a "victory for the most vulnerable states, a victory for France and a victory for the climate".
John Kerry, the former US special envoy for climate change, said "it should not take the stamp of international law to motivate countries to do what is already profoundly in their economic interests".
"We shouldn't need another reason to act and accelerate action," he told AFP.
Key points from the ICJ's historic climate decision
Paris (AFP) July 23, 2025 -
In a sweeping decision the world's top court on Wednesday declared climate change an "existential problem of planetary proportions" and said countries had a legal duty to act or face consequences.
The highly anticipated International Court of Justice advisory opinion is not legally binding but was unanimous and expected to have major legal ramifications for courts, companies and communities across the world.
The United Nations had tasked the ICJ to say what obligations countries were under to curb planet-heating emissions -- and to lay out possible consequences for failing to do so.
Here are some highlights from a summary of the opinion read by ICJ president Yuji Iwasawa on behalf of the 15-judge panel in The Hague:
- Big picture -
Iwasawa said the court could only address the questions put to it by the UN within its legal remit, but noted that the issues go beyond the law.
"They concern an existential problem of planetary proportions that imperils all forms of life, and the very health of our planet," he said.
"A complete solution to this daunting and self-inflicted problem requires the contribution of all fields of human knowledge whether law, science, economics... in order to secure a future for ourselves and those who are yet to come."
- On the right to a healthy climate -
"With regard to the duty to prevent significant harm to the environment, the court considers that it also applies to the climate system, which is an integral and vitally important part of the environment and which must be protected for present and future generations."
The court said climate impacts like sea level rise, drought, desertification and weather disasters "may significantly impair the enjoyment of certain human rights, including the right to life".
- What are countries' duties to cut emissions? -
The court said countries had binding legal obligations under the UN's climate negotiations framework as well as in customary law.
Each party to these agreements needs to produce climate plans that "represent its highest possible ambition".
And all climate plans taken together should be "capable of achieving the temperature goal of limiting global warming to 1.5 degrees Celsius above pre-industrial levels".
"Non-compliance with emission reduction commitments by a state may constitute an internationally wrongful act," the court said.
- What about fossil fuels? -
This was quite explicit: "Failure of a state to take appropriate action to protect the climate system from GHG (greenhouse gas) emissions, including through fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licences, or the provision of fossil fuel subsidies may constitute an internationally wrongful act which is attributable to that state."
- On reparations -
This is the most controversial aspect of the questions considered by the court.
It said that a state responsible for an internationally wrongful act is under an obligation to cease that act, provide assurances that it will not happen again and could include "full reparation to injured states in the form of restitution, compensation and satisfaction".
This was provided that "a sufficiently direct and certain causal nexus can be shown between the wrongful act and injury", the court added.
It said that while finding a causal link between the emissions of one country and the harm in another was "more tenuous than in the case of local sources of pollution, this does not mean that the identification of a causal link is impossible in the climate change context".
Restitution, it said "may take the form of reconstructing damaged or destroyed infrastructure, and restoring ecosystems and biodiversity".
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