CAMBRIDGE, Mass. (July 23, 2025)——The world’s highest court issued an advisory opinion today affirming that governments have legal obligations to address climate change under international law, including regulating private actors within their jurisdictions, and may bear legal responsibility if they fail to take necessary measures to limit emissions from fossil fuel companies and other sources.
The International Court of Justice (ICJ) opinion, which saw unprecedented global participation from over 190 countries, also specified that nations which have emitted the most planet-warming gases must take immediate and sustained action to prevent further climate harm and protect the environment as a precondition for the full enjoyment of human rights.
Though the ICJ’s opinion is not legally binding, it will carry significant weight in courts and negotiations around the world. For the United States, the world's largest historical emitter, this ruling adds mounting legal, scientific and moral pressure to meet its climate obligations, both at home and on the global stage. As lawsuits against governments and corporations continue to grow, today's opinion strengthens the legal foundation for holding polluters accountable.
Below is a statement by Dr. Delta Merner, a lead scientist with the Science Hub for Climate Litigation at UCS who supported submissions to the ICJ from multiple Global South countries. “The world’s highest court leaves no room for ambiguity—governments cannot ignore their legal responsibilities to prevent further climate harm. This ruling makes clear that obligations under existing international law are not voluntary or symbolic; they are enforceable duties rooted in science, human rights and intergenerational equity. The Court also affirmed that countries must rein in corporate polluters and if they fail, they’re responsible for helping to fix the damage.
“As the Trump administration takes extreme steps to prioritize corporate polluters over public health and the environment, the legal recklessness of doing so has been laid bare by the new advisory opinion. This further emphasizes what fossil fuel companies already know—failure to meaningfully address climate change risks serious legal liability for them. That’s why fossil fuel companies and their allies are urging Congress to protect them from future lawsuits and legislation for their decades of climate disinformation and the worsening climate crisis.
“This decision heralds a new frontier in the movement for climate accountability. The climate impacts felt most acutely by the Global South, women, children, low-income, Black, Indigenous and people of color are undeniably litigable.”
Below is Dr. Carly Phillips, a scientist with the Science Hub for Climate Litigation at UCS who provided scientific input to the ICJ for countries in Asia, Africa, and the South Pacific.
“The opinion underlines what attribution science makes clear—a handful of actors are responsible for the vast majority of climate harms. The Court’s strong, science-informed ruling underscores how accountability for past and ongoing emissions is a scientific and legal necessity, not a political inconvenience.
“The court emphasized the key role of science in crafting this opinion and its importance in future determinations of responsibility for climate related losses and damages. The opinion rightfully concluded that science can show historical and cumulative emissions attributable to an individual state, underscoring the responsibility that high emitting states have for driving greenhouse gas emissions and climate change.
“While the Trump administration has attempted to evade accountability by withdrawing from the Paris Agreement, the court made clear that taking climate action is an obligation under customary international law, not just climate treaties, and includes regulating fossil fuel production, consumption and exploration.
“Cases will continue to be filed against major polluters because that is what the science, and now the world’s highest court, deem necessary in the pursuit of climate justice.”
Additional Resources:
- The Cambridge Handbook on Climate Litigation, Chapter 3—Attribution Science, co-authored by Drs. Merner and Phillips
- UCS blog post on international courts and climate action
- UCS blog post on the human right to a stable climate
- UCS blog post on major moments for climate litigation in 2025
- Peer-reviewed UCS study on the lasting impacts of fossil fuel emissions on sea level rise
- Peer-reviewed UCS study on the contributions of major carbon producers to wildfire risk in the western United States
- UCS report on fossil fuel companies’ decades-long disinformation campaigns to stall climate action in the United States