New ‘World Court’ ruling opens the door for ambitious climate action

In a historic win for climate justice, the world’s highest court delivered an advisory opinion setting out States’ legal obligations in respect to climate change. From grassroots beginnings to the International Court of Justice, the ruling marks a pivotal moment in the global fight for climate action which centres human rights and justice for climate vulnerable nations. August 8, 2025
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This outcome follows six years of campaigning by law students from the Pacific Islands, and lobbying led by the government of Vanuatu

Written by Lila Stewart-Roberts

On 23rd July 2025, the International Court of Justice (ICJ) unanimously adopted an advisory opinion on States’ legal obligations to address climate change. The opinion provides long-awaited clarity: States are now legally required to implement ambitious climate action under international law, and failure to do so could result in legal consequences. Critically, the ruling provides a tool to operate climate justice and demand accountability and action from the countries, corporations and governments causing climate harm.

Delivering the ruling, ICJ President Judge Iwasawa Yuji expressed the immense scale of the challenge, calling climate change: “an existential problem of planetary proportions that imperils all forms of life and the very health of our planet.”

From grassroots beginnings to the UN’s top court

The road to this global milestone began six years ago when 27 law students from the Pacific Islands set out to bring climate change before the world’s top court. What started as a grassroots campaign grew into an international effort, led by Vanuatu, culminating in the UN General Assembly formally requesting an advisory opinion from the ICJ in March 2023. This was the first climate case and the largest case ever put before the Court.

The Court was asked to address two critical questions:

1) What are the obligations of States under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic emissions of greenhouse gases for States and for present and future generations?

2) What are the legal consequences under these obligations for States where they, by their acts and omissions, have caused significant harm to the climate system and other parts of the environment, with respect to:

(i) States, including, in particular, small island developing States, which due to their geographical circumstances and level of development, are injured or specially affected by or are particularly vulnerable to the adverse effects of climate change?

(ii) Peoples and individuals of the present and future generations affected by the adverse effects of climate change?

 

The advisory opinion provides clarity on the legal obligations of States, including:

  • A healthy environment is a human right: States are obliged to act on climate change to protect the human rights of present and future generations. “The right to a clean, healthy and sustainable environment results from the interdependence between human rights and the protection of the environment… The court therefore concludes that under international law, the human right to a clean, healthy and sustainable environment is essential for the enjoyment of other human rights.”
  • Ambitious climate action is a legal duty: States are bound under customary international law to reduce their emissions, even if they have withdrawn from the Paris Agreement. Nationally Determined Contributions (NDCs) must reflect their “highest possible ambition” to collectively limit global warming to 1.5 °C above pre-industrial levels.
  • Failure to act on fossil fuels has legal consequences: States must take appropriate action to achieve “deep, rapid, and sustained reductions of GHG emissions that are necessary for the prevention of significant harm to the climate system” – failure to do so, including through “fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licenses or the provision of fossil fuel subsidies”, may violate international law.
  • Regulation of private actors: States are bound by international law to regulate the climate impacts of private actors under due diligence.
  • Scientific evidence for climate justice: A clear route to reparations for States facing the worst climate impacts, from high-emitting States and those with the greatest historical responsibility, observing that: “it is scientifically possible to determine each State’s total contribution to global emissions, taking into account both historical and current emissions.” States could be required to compensate or remedy the climate harm caused by their emissions, and injured States can hold polluters to account.
  • Right to statehood: Sea-level rise and climate change-induced displacement do not legally affect the maritime borders of States or their right to statehood.

A win for climate justice

For Small Island Developing States – bearing the worst of the climate impacts that they played no part in causing – the ruling marks a long-awaited step towards global accountability. The ICJ made clear that highest-polluting countries have the greatest responsibility for addressing the climate crisis.

The Court rejected counterarguments from high-emitting States, who claimed their climate obligations were limited to specific treaties such as the Paris Agreement (under the principle of lex specialis), affirming that a wide range of obligations of treaty and customary law apply. This means States are legally bound to reduce their emissions even if they have withdrawn from the Paris Agreement.

Providing a route to reparations, the Court affirmed that injured States can act against any State that has breached its obligations and caused injury through climate change – of immense significance for countries experiencing existential threats from climate change for which they hold no responsibility.

What this means for climate action now…

While the advisory opinion is not legally binding, it carries significant legal and moral weight. It clarifies the obligations of States to act on climate change, and, significantly, the legal consequences if they fail to do so.

Citizens and frontline communities now have a tool to hold governments and corporations accountable for continuing to pollute. The ruling is expected to trigger a new wave of climate litigation. The principles can be used in local and national courts across the world to demand the maximum ambition in climate action.

The ICJ linked its decision to a broad range of international law – including international human rights law, the Law of the Sea, the Kyoto Protocol, the Paris Agreement, and even international customary law – providing unequivocal clarity that climate change touches every corner of global legal frameworks.

Governments – especially the highest-emitters – now face greater pressure and responsibility to curb emissions and implement strong and ambitious climate action.

Perhaps most significantly, the ruling symbolises the collective power of youth and communities on the frontlines of climate change to hold those threatening their futures to account.

The ruling alone will not solve the climate crisis but rather provides a powerful lever with which to fight for a safer, more just, and sustainable future. As the court concluded:

“Above all, a lasting and satisfactory solution requires human will and wisdom — at the individual, social and political levels — to change our habits, comforts and current way of life in order to secure a future for ourselves and those who are yet to come.”

Read the official Advisory Opinion: Obligations of States in respect to Climate Change

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