On 23 July 2025, the International Court of Justice (ICJ) delivered a historic advisory opinion clarifying the legal obligations of states to address climate change. This opinion responded to a request by the United Nations General Assembly (Resolution 77/276 of 29 March 2023), which sought the ICJ’s guidance on two critical questions:
The ICJ affirmed its jurisdiction to address these questions, emphasizing the urgent and far-reaching consequences of climate change, as documented by the Intergovernmental Panel on Climate Change (IPCC). The ICJ underscored that GHG emissions, driven by human activity, adversely impact the environment, human rights, and vulnerable states, including small island nations facing existential threats.
Key legal frameworks examined included:
The opinion clarified that states are required to exercise due diligence in mitigating emissions and adapting to climate impacts, with consequences for breaches assessed under principles of state responsibility. Notably, the ICJ highlighted the erga omnes nature of these obligations—owed to the international community as a whole—and the need for equitable action reflecting common but differentiated responsibilities.
This blog unpacks the ICJ’s findings, their implications for global climate justice, and the path ahead for state accountability.
Before addressing the General Assembly’s questions on state obligations regarding climate change, the ICJ first assessed three key issues: (1) its jurisdiction to render an advisory opinion, (2) whether discretionary reasons might compel it to decline the request, and (3) the scientific and legal context underpinning the questions. The ICJ confirmed:
With these foundations established, the ICJ proceeded to define states’ climate obligations under international law.
In its advisory opinion, the ICJ provided a comprehensive analysis of the obligations states hold under international law to protect the climate system and other parts of the environment from anthropogenic greenhouse gas (GHG) emissions. The ICJ’s response to Question (a) is rooted in multiple sources of law, including treaties, customary international law, and general principles. Here are the key takeaways:
The ICJ began by clarifying that while the General Assembly had referred to a broad range of legal instruments and principles, the ICJ would focus on those rules of international law that are most directly applicable to the obligations of states in the context of climate change. This included both treaty law and customary international law, as well as general principles of law that guide interpretation.
Among the treaties identified, the ICJ highlighted three central instruments that together form the core of the international climate change legal regime: the United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol, and the Paris Agreement. These instruments are interrelated. The UNFCCC lays down foundational principles and objectives, including the ultimate goal of stabilizing greenhouse gas concentrations to avoid dangerous human-induced interference with the climate system. The Kyoto Protocol and the Paris Agreement build upon this foundation, translating general obligations into more specific commitments and mechanisms. The ICJ emphasized that although no further commitments have been made under the Kyoto Protocol beyond 2020, the instrument remains legally relevant alongside the Paris Agreement.
The ICJ also considered the Charter of the United Nations, noting its emphasis on international cooperation to solve global problems, which includes climate change. Similarly, the United Nations Convention on the Law of the Sea (UNCLOS) was included within the applicable law due to its environmental provisions that have been interpreted as engaging state obligations in relation to climate change.
Beyond these, the ICJ identified several other environmental treaties as directly relevant. These include the treaties on protection of the ozone layer (including the Montreal Protocol), the Convention on Biological Diversity, and the Convention to Combat Desertification. Although these treaties address distinct environmental challenges, the ICJ found their provisions to be closely connected to the issue of climate change, particularly where their objectives align with mitigation or adaptation efforts.
In addition to treaty law, the ICJ affirmed that certain obligations under customary international law are applicable to states in the climate context. Chief among these is the duty to prevent significant harm to the environment, which the ICJ confirmed applies to climate change. While some states had questioned its relevance to global phenomena, the ICJ found that this duty extends beyond direct cross-border harm and is fully applicable in addressing cumulative global risks like those posed by greenhouse gas emissions.
This duty is characterized as one of due diligence: States are required to act to the best of their ability, taking appropriate precautionary measures based on scientific information and their own capacities. The ICJ observed that because climate change presents a well-established, serious, and universal threat, the required standard of diligence is particularly stringent. States are required to adopt appropriate rules and ensure their effective enforcement.
The ICJ also recognized the duty to cooperate as a well-established rule of customary international law in the environmental context. In the ICJ’s view, meaningful action on climate change cannot be achieved through uncoordinated national efforts alone; cooperation among states is essential and legally required.
In its analysis, the ICJ highlighted the relationship between climate action and international human rights law. It found that the core human rights treaties, including the International Covenants on Civil and Political Rights and on Economic, Social and Cultural Rights, are relevant in understanding states’ obligations. The protection of human rights and the protection of the environment are, in the ICJ’s view, increasingly recognized as interdependent.
The ICJ also gave weight to several general principles that guide the interpretation of international environmental obligations. These include:
These principles do not, in themselves, create new obligations, but they inform how existing obligations are interpreted and implemented.
By contrast, the ICJ found that the so-called “polluter pays” principle, while referenced in some international declarations and domestic legislation, has not been incorporated into the climate change treaties and does not form part of the applicable international law for the purposes of their advisory opinion.
The ICJ rejected the argument that the climate change treaties operate to exclude or override other applicable rules of international law. It held that the principle of lex specialis—which gives priority to more specific rules—does not justify sidelining customary law or other treaty-based rules. Rather, the ICJ emphasized that the climate treaties should be interpreted harmoniously with broader principles of international law, including environmental, human rights, and law of the sea obligations.
The ICJ next addressed question (b) of the General Assembly’s request: What are the legal consequences for states whose acts or omissions have caused significant harm to the climate system and other parts of the environment? The ICJ clarified that this question concerns the consequences of breaching the obligations identified under question (a), assessed under customary international law and the rules of state responsibility.
The ICJ emphasized that breaches of climate-related obligations, whether under treaties like the UNFCCC, Kyoto Protocol, and Paris Agreement, or under customary law (e.g., the duty to prevent significant transboundary harm), trigger state responsibility. Crucially, the ICJ rejected arguments that the climate treaties displace general rules of state responsibility, noting:
Thus, the ICJ concluded that customary rules of state responsibility apply to climate-related breaches.
The ICJ acknowledged the complexities of applying state responsibility to climate change, given its global and cumulative nature, but affirmed that existing legal principles remain adaptable:
Establishing causation, a prerequisite for reparation, requires a "sufficiently direct and certain causal nexus" between a state’s wrongful act (e.g., failing to mitigate emissions) and specific harm (e.g., sea-level rise displacing populations). The ICJ noted:
The ICJ underscored that climate obligations are erga omnes (owed to the international community). All states have a legal interest in demanding compliance, even if not directly injured. However, only specially affected states may claim reparations; others may seek cessation or guarantees of non-repetition.
The ICJ’s advisory opinion marks a watershed moment in the legal fight against climate change, crystallizing states’ obligations under international law and affirming that failure to act has tangible consequences. By grounding its analysis in treaties, customary law, and human rights principles, the ICJ has unequivocally stated that climate inaction is not just a moral failing but a legal breach, one that triggers state responsibility. The opinion dismantles the notion that climate treaties exist in isolation, weaving them into a broader tapestry of environmental and human rights law, where duties like due diligence and cooperation are non-negotiable.
For vulnerable nations, this signals a powerful tool to hold high-emitting states accountable, even if challenges like causation and attribution remain complex. Crucially, the ICJ’s emphasis on erga omnes obligations underscores that climate justice is a collective imperative: every state has a stake in enforcement, and no nation can evade scrutiny by hiding behind the global scale of the crisis. While the opinion doesn’t prescribe immediate penalties, it lays the legal groundwork for future claims, turning abstract principles into actionable benchmarks. In short, the ICJ has reframed climate change from a political dilemma to a legal imperative, one where the stakes are nothing less than the survival of nations and the rights of generations to come.
Widely regarded as a milestone, the opinion advances the legal codification of states’ responsibilities in addressing climate change. While ICJ advisory opinions are not legally binding and cannot compel compliance, they carry considerable weight. The ICJ has now confirmed that governmental inaction on climate change may constitute a breach of international law—potentially triggering legal, financial, and diplomatic consequences.
The opinion may significantly impact national and international climate policy. Exposure to litigation in domestic courts could incentivize governments to accelerate emission reductions and demonstrate compliance with treaty obligations. It may also serve as precedent in future international negotiations and treaty development.
With COP30 scheduled for November in Brazil, the opinion equips smaller and climate-vulnerable states with new legal leverage in global climate diplomacy.
The ICJ has traditionally approached politically sensitive matters with caution, prioritizing judicial legitimacy over sweeping declarations. The 23 July 2025 advisory opinion follows that tradition, grounding its conclusions in existing legal norms while cautiously advancing state obligations.
This evolution reflects growing judicial confidence in addressing climate risks—enabled by stronger legal frameworks, scientific consensus, and emerging state practice reinforcing customary international law.
The ICJ finds that states’ climate obligations stem from a combination of sources: environmental and climate treaties, international human rights law, and customary international law. Key findings include:
Because these duties are customary, they apply to all states—regardless of whether they are parties to specific climate treaties.
Though non-binding, the ICJ’s opinion is legally consequential. It serves as an authoritative interpretation of international law and a tool for preventive diplomacy. It clarifies key legal principles such as attribution, causation, and the duty to prevent harm—providing a basis for aligning national policies with international obligations.
Beyond shaping future treaties, the opinion is expected to influence climate litigation. It strengthens the legal foundation for claims seeking accountability based on state conduct, rather than intent alone.
The opinion confirms that all states, irrespective of their treaty participation, bear binding obligations regarding climate control. This may have implications even for countries like the United States, despite its past withdrawal from the Paris Agreement.
While the opinion does not impose direct international legal duties on corporations, it underscores states’ responsibilities to regulate private actors more effectively.
In effect, the opinion elevates climate policy from a political aspiration to a legal obligation. Governments failing to properly regulate emissions, conduct environmental impact assessments, or align their laws with international norms may face legal claims and reputational harm. Particular legal exposure may arise from inadequate due diligence concerning fossil fuel production, subsidies, or weak climate legislation.
Footnotes
[1] Fair to note that the ICJ’s observations here were not made in the context of climate change, but are of general import, showing that the rules on State responsibility are capable of addressing situations where damage is caused by multiple states engaging in wrongful conduct. Case name, Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda),