On July 23 the International Court of Justice (ICJ) issued a historic advisory opinion on states’ legal obligations to address climate change. This powerful legal statement, requested by the UN General Assembly and led by Vanuatu and a group of small island states, comes at a moment of escalating climate impacts and growing calls for justice.
While the ruling is advisory in nature and not legally binding, it carries significant weight and will shape international law, national policymaking, and courtroom strategy for years to come.
Here are five reasons I think this ruling matters:
1. The ICJ makes clear that climate inaction is a violation of international law
For the first time, the world’s highest court has affirmed that states have concrete legal obligations under international law to protect the climate. These duties are not merely optional goals or political aspirations: they are grounded in existing treaties, human rights law, and long-standing legal principles. Governments must take meaningful action to prevent serious harm to the environment, work together to address the climate crisis, and act with care and urgency to reduce emissions and protect people from climate impacts.
The 140-page opinion says that countries have a duty “to prevent significant environmental harm,” “to cooperate,” and to fulfill obligations with “due diligence,” using the best available science.
This is an important reframing. Climate inaction is not just a policy failure, it’s a legal breach.
2. The Court recognizes climate change as a human rights issue
The ICJ’s opinion decisively connects climate change to international human rights law. It affirms that the escalating impacts of climate change such as rising seas, deadly heat, water scarcity, and food insecurity, pose direct threats to a range of fundamental rights, including the rights to life, health, housing, food, and water.
The Court’s recognition of the right to a healthy environment adds to a growing legal consensus and echoes a powerful opinion issued by the Inter-American Court of Human Rights earlier this month, which underscored that protecting the climate system is essential to safeguarding human rights.
Understanding climate change in the context of human rights puts people, not just emissions, at the center of climate law and shows that climate obligations are not only environmental but also social, legal, and moral. Here the Court reinforced what so many of us know, that protecting the climate is inseparable from protecting dignity, equity, and justice. These connections were powerfully made by countries, often those most impacted by climate change, in their written statements and oral testimonies.
3. It underscores that science can guide legal accountability
For me, one of the most powerful aspects of the opinion is its reliance on science. During the reading of the opinion, the ICJ recognized the findings of the Intergovernmental Panel on Climate Change (IPCC) as the best available science and accepted, without hesitation, that “anthropogenic emissions of greenhouses gases are unequivocally the dominant cause of the global warming.” While this is well established, its affirmation by the world’s highest court sends a strong message that science belongs in the courtroom.
The Court emphasized that states must act based on scientific evidence. It recognized the importance of cumulative and historical emissions in assessing harm. The opinion also specifically highlighted attribution science and affirmed the role it can play in helping courts to assess causation while identifying sources of harm.
This validation of attribution science will be critical in future litigation, particularly when assessing responsibility and proving harm. Attribution science has emerged as a key bridge between climate science and the law, enabling experts to connect specific harms like sea level rise, heatwaves, or area burned in wildfires to emissions from specific actors such as the fossil fuel industry.
4. The ICJ clarifies that states must regulate fossil fuel companies
States cannot dodge responsibility by just pointing to the private sector and shrugging off corporate emissions. The Court was very clear that governments are obligated to protect the climate system by regulating activities within their jurisdiction, including those from private companies like fossil fuel producers. Once again, this is not new or optional: these duties are grounded in both climate-specific treaties and broader international law.
This reinforces the fact that governments must take concrete, effective steps to oversee and constrain the activities of private companies that contribute to climate harms. This includes not only direct emissions, but also emissions embedded in exports, supply chains, and investments, as well as emissions from both production and consumption activities.
This finding will inform ongoing climate litigation efforts and affirms that states can be held liable for the actions of industry under their jurisdiction or control. And, the Court was careful to specify that such actions goes beyond the emissions themselves, including the production, consumption, exploration for, and subsidization of, fossil fuels.
5. It provides legal leverage for those on the frontlines of climate harm
Perhaps most importantly, the ruling affirms that small island states, developing countries, and affected communities have the right to demand action and justice. The ICJ recognized that climate change imposes disproportionate burdens on vulnerable countries and populations and that these groups and individuals, including future generations, are entitled to protection and redress.
The Court also confirmed that the obligations to protect the climate are erga omnes, meaning owed to the international community as a whole. That means any state, even if not directly injured, can raise legal challenges when other states fail to meet their climate duties. This opens new doors for legal strategies and advocacy, particularly in securing compensation, remediation, and strengthened climate action.
This point carries deep significance given where the case began. It was Pacific youth from nations already losing land and culture to rising seas who brought this question forward for the court. With this response, the Court answers clearly that climate harm is a legal wrong and those most affected have the right to protection, to justice, and to a future.
The bottom line
The ICJ advisory opinion is a milestone for international climate law. The Court has made clear that countries must act, must protect people, and must regulate industries that are driving climate change.
This opinion is powerful because it provides clarity. It makes it clear that human rights are at stake. That scientific evidence must guide decision-making. That governments cannot turn a blind eye to corporate emissions. And that those on the frontlines, youth, island nations, or communities living with loss, are able to seek justice.
That clarity must now ripple outward. It must strengthen lawsuits, shape national laws, and embolden negotiators in international climate spaces. It must remind decision makers everywhere that climate delay is not neutral, it is unlawful.
This moment is particularly urgent for the United States. As the Trump administration works to expand fossil fuel development, dismantle environmental protections, and shield polluters from legal accountability, the ICJ opinion makes it clear that no single administration can opt out of international law and that the obligation to act on climate is a binding duty to current and future generations.
Bearing witness to the leadership of core small island nations that made this possible is a reminder of how powerful international collaboration can be. Now it is up to us to carry this momentum forward, to use this ruling not as a final word, but as a foundation for real accountability and lasting change.