Published on July 22, 2026
Joie Chowdhury, Climate Justice and Accountability Manager and Senior Attorney at the Center for International Environmental, Richard Harvey, formerly Legal Counsel Campaigns at Greenpeace International, and Nicole Ponce, Advocacy Lead at World Youth for Climate Justice
One year ago, on July 23, 2025, the International Court of Justice (ICJ) delivered a landmark unanimous ruling on States’ legal obligations to address climate change. Twelve months later, the Opinion is no longer simply a legal milestone; it is already shaping litigation, climate diplomacy, national policymaking, and the language of climate justice around the world.
Why Seek an Advisory Opinion?
The campaign for an ICJ Climate Advisory Opinion (ICJ AO) was deeply personal. It was born in a Pacific classroom, led by Pacific students and youth campaigners worldwide, embraced by the wider climate justice movement, and championed by Vanuatu and other Global Majority countries.
For many communities, particularly across the Pacific, climate change is a lived reality of dispossession, cultural loss, and existential threat. These experiences are echoed globally, yet they are neither borne nor experienced equally. The crisis exposes profound, structural inequalities, forcing those least responsible for emissions to face the most severe consequences — an injustice that threatens both present and future generations. This is why youth leadership is central to this story. Youth advocates refuse to inherit a heating world; their survival is the core “Why” of the case.
While international law aspires to objectivity, it cannot be detached from the power structures that shape it. Bringing climate justice before the world’s highest court is a defiant act of recentering, forcing a historically exclusive legal system to account to those on the front lines.
What Did the Court Conclude?
The ICJ rose to the urgency of the moment, clarifying that States have binding legal duties to prevent significant environmental harm, protect human rights from the impacts of climate change, and provide full reparation for climate-related harm. The Opinion rejected long-standing arguments used by major emitters to evade responsibility. The legitimacy of the ruling is reinforced by record participation in the proceedings and widespread acceptance by UNGA member States.
And now what?
Since its delivery a year ago, the Advisory Opinion (AO) has already been taken up as a source of law, offering “not a new edifice but a sturdier legal architecture.” While the opinion is advisory, the legal obligations it clarifies are not. ICJ advisory opinions are authoritative interpretations of binding international law. The implementation landscape of the AO cuts across litigation, multilateralism, norm development, and domestic governance.
Climate Litigation
The uptake of the AO in the realm of litigation has been swift. The European Court of Human Rights (ECtHR) relied on the ruling in establishing “new, binding legal obligations that will reshape how governments approach fossil fuel development.” Domestic courts have likewise relied on the ruling, including in Costa Rica, France, the Netherlands, Brazil, and Canada. The Advisory Opinion has also informed efforts to enforce legal judgments, including in relation to implementation of the European Court of Human Rights’ ruling in KlimaSeniorinnen.
Beyond judicial reasoning, litigators have increasingly drawn on the ICJ AO to strengthen legal arguments and framing across a wide range of proceedings, whether a mitigation complaint before the UN Human Rights Committee; in the transnational climate loss and damage claim brought by the Pari Islanders against Holcim in Switzerland; or in other corporate accountability litigation in South Africa, South Korea, Japan, and Malaysia. Although the AO is rarely the primary legal basis of these claims, it sharpens and reinforces legal arguments across jurisdictions.
Multilateralism and Climate Diplomacy
In a fractured multilateral landscape, the ICJ AO has underscored how legal clarity can precipitate political reckoning. The negotiations leading to the adoption of a UN General Assembly Resolution welcoming and operationalizing the Advisory Opinion moved it from the courtroom to the center of global climate governance. Despite intense contestation, the final resolution faithfully reflects the opinion’s core elements, with a strong majority determined not to allow a small number of holdout States to obstruct progress towards climate justice.
More broadly, the ICJ AO and arguments set forth in its proceedings are increasingly shaping multilateral processes, including in relation to the Human Rights Council, the UN Ocean Conference, and the work of the International Law Commission.
The ICJ AO has operated as a source of law supporting the arguments of climate negotiators. One of the most notable outcomes of COP30 came outside the formal process, with Colombia and the Netherlands announcing the first diplomatic conference in Santa Marta on fossil fuel phase-out, with the ICJ AO shaping the agenda and the outcome report.
Bridging international and domestic pathways, the impact of the AO on national climate plans under the Paris Agreement (NDCs) has been notable, with striking examples including those of Vanuatu, Mexico, and Bangladesh.
Laws and Institutional Practice
The ICJ AO is already being integrated across a range of normative settings; it is expressly referenced in the Human Rights Council’s resolution on sea-level rise, and it informed the Committee on Economic, Social and Cultural Rights’ General Comment on the environmental dimension of sustainable development. In the Philippines, a recent House Resolution called for the integration of the ICJ AO into national climate policy, domestic legislation, and international negotiations.
The long arc of law as an impetus for change
Building on Past ICJ Advisory Opinions
Advisory Opinions are instrumental in resolving highly complex, even novel, issues of law. They can establish authoritative legal baselines that shape litigation, diplomacy, and State practice over time. History also shows that the implementation of landmark advisory opinions is rarely linear or immediate. Such implementation is often contested, uneven, and politically fraught, but even so, can reshape legal norms, and lay the foundation for stronger judgments and greater accountability over time.
The Nuclear Weapons AO
In 1996, the ICJ advised on the Legality of the Threat or Use of Nuclear Weapons. Confronted by the existential threat of a nuclear conflict, the Court was sharply divided: its President cast his vote to break the 7-7 tie, holding that the Court could not conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defense, in which the very survival of a State would be at stake. The Court clarified key legal principles governing the threat or use of nuclear weapons and the constraints imposed by international law, which have informed discussions on the interpretation of the Nuclear Non-Proliferation Treaty.
The Chagos Islands Case
When Mauritius was decolonized in 1968, the UK kept the Chagos Islands and created a new colony, the British Indian Ocean Territory. In 2019, the Court held this was unlawful. The ICJ said the decolonization of Mauritius had not been lawfully completed in 1968. Of course, 40 years later, the elephant outside the room was the United States, which reportedly used Diego Garcia (a military base in the Chagos archipelago) as a blacksite and, more recently, sought to use it as a launchpad for bombing Iran. While the UK and Mauritius signed a bilateral agreement on May 22, 2025, providing for the transfer of sovereignty of the Chagos archipelago to Mauritius, which “is presented as a measure to implement the ICJ Advisory Opinion and the General Assembly resolution,” the agreement has raised human rights concerns regarding Chagossian people’s rights, and the domestic legislation to put this in place is not yet in effect due to shifting US positions.
The ICJ AO
Asked to advise on climate change, the Court faced a further concrete existential threat. No Party argued that severe climate change was unlikely. All agreed that without major changes, it was inevitable. The Court held that the UN Charter — and not exclusively the UNFCCC, Kyoto Protocol, and Paris Agreement — was the starting point from which to examine the most directly applicable law. The Judges went further, holding that breaches may give rise to the “entire panoply” of legal consequences, including obligations of cessation, non-repetition, restitution, compensation, and satisfaction. (para. 445)
On greenhouse gas (GHG) emissions, the Court expressly held: “Failure of a State to take appropriate action to protect the climate system from GHG emissions – including through fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licences or the provision of fossil fuel subsidies – may constitute an internationally wrongful act…” The Court also emphasized that the internationally wrongful act in question is not “the emission of GHGs per se, but the breach of conventional and customary obligations….” (para. 427)
These clarifications authoritatively resolve previously heavily contested legal questions, grounding them in established principles of international law, building on the Court’s past jurisprudence and the wider legal ecosystem. All Judges were in substantial agreement, and several would have gone further, but none filed a dissent.
From the examples of past ICJ advisory opinions, and drawing on lessons from other struggles for justice from anti-apartheid and anti-occupation to civil rights, and protections for LGBTQI communities, we know enforcement of legal duties and implementation of rulings is almost always messy and imperfect, but there tends to be a direction of travel. As Martin Luther King Jr. reminded us, “the arc of the moral universe is long, but it bends toward justice.” That arc does not bend on its own. It bends because people and States choose not to give up.
Looking ahead
At a moment when multilateralism is under strain, corporate and political impunity appear entrenched, climate inequities deepen, reparations remain contested, and fossil fuel expansion continues, the AO holds transformative power to advance accountability. Its power lies not only in the legal clarity it provides, but also in the extraordinary solidarity that shaped the proceedings and the expansive implementation that has followed. Together, they challenge unbridled power, resist impunity and narrow self-interest, and advance a vision of international law rooted in care and a decolonial vision of the rule of law, as well as public and planetary well-being.