In July 2025, the International Court of Justice issued a historic advisory opinion declaring that states have legal obligations under international law to prevent and remedy harm caused by climate change.
Lea Main-Klingst, Public International Lawyer, ClientEarth
Though not legally binding, the opinion is already being hailed as a turning point for climate litigation and diplomacy, clarifying that states can be held responsible for failing to reduce emissions and protect vulnerable communities. Moreover, they stated that these duties stem not just from treaties like the Paris Agreement, but from human rights law, customary international law, and core environmental principles.
To understand what this means in practice, we spoke with ClientEarth lawyer Lea Main-Klingst about why the opinion matters, how it might shape courtrooms and climate summits alike, and what its global reach could mean for governments around the world—including that of the United States.
If the ICJ's advisory opinion is not binding for national governments, what makes it so significant?
What makes decisions like these so significant is that they are some of the strongest litigation and advocacy tools available to us in the climate movement. They are an authoritative statement of the law and therefore tell governments how to implement and apply international agreements and rules. On the advocacy front, we now have the weight of the world’s highest court behind our demands for urgent climate action, which will be invaluable to campaigners all around the world.
Outcomes like these also signal the direction of travel on an issue for national governments. For example, in the UK, the freedoms guaranteed under the Human Rights Act of 1998 are derived from international law.
When it comes to its impact in the courtroom, this decision has cemented what impacted communities have demanded for decades: countries must address climate change to protect our human rights. That means judges in every corner of the globe can consult this decision when faced when making judgments of their own on landmark climate cases—both now and in the future.
What legal precedents exist for holding states or actors accountable for environmental harm through international courts or tribunals, and how might this opinion build on or shift that precedent?
For many of us working in the climate movement, this ICJ decision felt like a legal capstone. The court confirmed that there is a clear link between the climate crisis and human rights, affirming what courts like the European Court of Human Rights (ECHR) have already said.
In April 2024, the ECHR set a European precedent by finding the Swiss government had not done enough on climate change to protect a group of elderly women’s human rights. That set a precedent for over 40 countries within the court’s jurisdiction, and now we have the world’s highest court affirming a similar principle to every country in the world, whether they signed onto the Paris Agreement or not.
The group KlimaSeniorinnen took Switzerland to court for falling short on climate action... and won.
What kinds of legal, diplomatic, or political repercussions might we expect to see from this opinion in the coming months or years? Are there specific venues or cases where it’s likely to be invoked?
One of the first big global tests of this decision will be at COP30 in Brazil later this year. Campaigners will likely—and rightly—be saying their demands for more ambitious climate plans now have indisputable backing from the ICJ, and we’ll be following closely to see how governments respond to these arguments throughout the negotiations.
In terms of legal repercussions, as well as providing aforementioned definitive guidance, the court said that countries will be subject to this decision as a matter of customary international law. So, because there are so many rulings already in existence saying one country cannot bring harm to another, it has become a universal principle that applies to everyone, whether or not they’ve signed up to specific climate agreements like Paris. We’ll be keeping a close eye on national parliaments and courts to see how that part of the decision plays out in the coming years.
The opinion emphasizes that states’ climate ambitions must be consistent with limiting global warming to 1.5ºC. How can it be determined whether a country’s NDC meets that requirement, and who has the authority to make that judgment?
I’m afraid we’re not experts on the science behind determining whether or not an NDC meets the court’s requirement—that’s something we depend on academics and organizations like Climate Analytics for.
However, when it comes to what happens legally if an NDC is viewed to be insufficient, the ICJ was very clear in its decision: if you set an inadequate NDC, you can be ordered by a court to go back to the drawing board and come back with a plan that aligns with the Paris Agreement.
The ICJ makes clear that climate obligations apply universally, even outside treaty frameworks like the Paris Agreement. Given the United States’ current posture toward climate and international cooperation generally, what legal or political consequences might this opinion have for U.S. policy, and through what mechanisms could that pressure be applied?
While the United States has participated in cases before the ICJ, it does not formally accept its jurisdiction. Given this complicated relationship, it’s fair to say the influence of this decision is weaker in US domestic courts compared to other countries that give results like these more legal weight. However, this decision could still influence ongoing climate-related lawsuits in the US, and we’ll be keeping a close eye on these cases as they continue to make their way through state courts.
The other thing that’s important to note is that US companies could see the impact of this decision as many countries recognize and abide by international law where they operate. That means that overseas countries where US companies operate will now have clearer legal justification to establish and enforce standards that protect the climate. This would likely affect US companies’ operations overseas or potentially their operations in the US if they are export-oriented or reliant on overseas finance, so it’s definitely something to follow in our opinion.
The U.S. and EU recently agreed to an energy deal that could be scrutinized under the framework of the ICJ opinion.
