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BRUSSELS - In a case, the United Nations' highest court said countries must to slash emissions or risk having to pay off nations that are hard hit by climate change.

U.N. Secretary-General Antonio Guterres hailed the advisory opinion as a that shows the "power of young people to make a difference".

Though not legally binding, the opinion has and could influence and encourage governments to uphold their treaty commitments, legal experts say.

The in the International Court of Justice's history began when Pacific Island law students sought a way to break the "deadlock" on climate action, gaining support from Vanuatu's government to seek an advisory opinion from the court.

Dubbed "climate lawfare", a growing number of activists, scientists and Indigenous people are filing lawsuits against , hoping to slow global warming by holding them to account for climate-driven impacts such as extreme weather.

What is climate change litigation and where is it happening?

Individuals or groups have taken a range of governments and companies to court to spur climate action, such as phasing out fossil fuels and reducing harmful emissions.

Climate litigation can also refer to the growing number of legal disputes between investors and states that arise because international treaty provisions allow energy firms to sue governments when their carbon-cutting programmes affect profits.

In 2024, at least were filed, bringing the total to nearly 3,000 across nearly 60 countries.

Most were in the United States, but more and more cases are being , according to the Grantham Research Institute on Climate Change and the Environment.

The majority of them are brought by NGOs and concern environmental impact assessments, often for the construction of coal-fired power plants, but also include cases addressing issues such as the right to clean air and water.

Which cases have marked legal milestones in recent years?

In May, a German court a Peruvian farmer's appeal for damages against RWE - a German energy utility he accused of putting his home at risk through climate change - but ruled that companies were liable for emissions: a key legal precedent.

More than 2,000 Swiss women aged over 64 brought a case in 2023 accusing their government of violating their human rights by putting them at risk of dying during heatwaves.

Last year, the European Court of Human Rights , a decision likely to set a legal precedent.

In March, the Council of Europe, the court's oversight body, said Switzerland had it was meeting its climate obligations.

In May 2024, the International Tribunal on the Law of the Sea ruled greenhouse gas emissions are a form of marine pollution, subject to international controls.

In the first U.S. youth-led , 16 plaintiffs, aged from 2 to 18, filed a lawsuit against Montana over policies prohibiting state agencies from considering climate impacts when approving fossil-fuel projects.

A judge ruled in the plaintiffs' favour in 2023, citing a provision in the state constitution requiring it to The decision was upheld by Montana's top court in December 2024.

Can climate litigation drive change?

Court victories for campaigners are likely to spur more cases, and the legal precedents already set make it more likely that similar lawsuits will prevail.

A group of NGOs have also brought a case against French energy giant TotalEnergies alleging a company rebrand amounted to "greenwashing" with misleading environmental claims.

It builds on a successful 2024 case over misleading consumers about the environmental impact of air travel.

Environmentalists are also pushing for ecocide - large-scale environmental destruction - to be a crime that could be prosecuted by the International Criminal Court, alongside offences such as war crimes and genocide.

But testing legal arguments demands time and money, with some cases taking up to a decade to come to trial.

This article was updated on July 24, 2025, to include the details of the United Nations' advisory opinion. 

(Reporting by Joanna Gill with additional reporting from Nita Bhalla, David Sherfinski and Andre Cabette Fabio and Anastasia Moloney; Editing by Lyndsay Griffiths and Jon Hemming.)