Symposium on the ICJ Climate Change Advisory Opinion: A Landmark Moment for International Law

[María José Alarcón Santillán is an international lawyer and S.J.D. candidate at GW Law, serves as Counsel in the ICJ Advisory Opinion on Climate Change, is a CISDL Fellow, and Regional Co-leader at the Sabin Center for Climate Change Law. She has advised states on cases before the ICJ, ICSID, ITLOS, and the PCA.

Erick Guapizaca is an S.J.D. candidate at the University of Michigan Law School and a lecturer at the Universidad Internacional del Ecuador.]

On 23 July 2025, the International Court of Justice (ICJ) delivered its long-awaited Advisory Opinion (AO or Opinion) on the Obligations of States in respect of Climate Change, marking a decisive moment in international law. The unanimous opinion has been described as a “historic legal victory for small island states” and extends far beyond the immediate context of the climate crisis. The Opinion signals a turning point in both international environmental law and public international law more broadly. Among other contributions, the Court clarified several concepts that had long remained unsettled in the practice of international law.

The Opinion was delivered in response to two questions posed by the UN General Assembly through Resolution 77/276, following an extraordinary campaign led by the Youth of Pacific Island nations. The request generated unprecedented global engagement, with states from both the Global North and Global South aligning into opposing blocs. However, the Court transcended these divisions, issuing an advisory opinion that, although arguably controversial in light of the Court’s traditional stance, signaled a new era and underscored the global significance of the issue at hand.

The Court’s Groundbreaking Findings

The Court’s AO articulated a unified legal baseline for climate governance, reading climate duties across treaties, customary international law, and human rights. The Court further confirmed that climate protection arises from several treaties, among others,  the United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol, the Paris Agreement, the United Nations Convention on the Law of the Sea (UNCLOS), the International Covenant on Civil and Political Rights (ICCPR), the International Covenant on Economic, Social and Cultural Rights, and related instruments such as the Convention on Biological Diversity (CBD), Agreement on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ) and the Vienna Convention for the Protection of the Ozone Layer with its Montreal Protocol on Substances that Deplete the Ozone Layer (paras. 113–130).

Building on these frameworks, the Court required every state, whether or not party to the Paris Agreement, to mitigate its emissions using the best available science; to prepare, communicate, and progressively strengthen Nationally Determined Contributions toward the 1.5°C objective as a legally binding obligation of result rather than a merely political goal (para. 224); and to exercise due diligence through domestic measures regulating private actors, particularly those in the fossil fuel industries (paras. 281–299< 409–412, 427). Because climate harms threaten, among others, the right to life, health, privacy, family, home, and an adequate standard of living (paras. 372–387), the Advisory Opinion tied mitigation and adaptation to human rights compliance and required legislation, enforcement, and supervision of private activity to protect present and future generations (paras. 155–157).

The Advisory Opinion then treated adaptation as a legal duty for all states and attached differentiated obligations to parties listed in Annex II to UNFCCC to provide finance, technology transfer, and capacity building, all within a customary duty to cooperate (paras. 301–302). The Court, echoing the ITLOS Advisory Opinion, characterized anthropogenic greenhouse gases as marine pollution under UNCLOS, which, in turn, triggers duties to prevent, reduce, and control such pollution through legislation, administration, enforcement, and environmental impact assessment for activities posing significant marine harm (paras. 339-340). The Court explained that issuing new fossil exploration licenses, maintaining subsidies for carbon-intensive industries, or failing to regulate private emissions can breach due diligence and amount to internationally wrongful acts, with injured states entitled to invoke responsibility against multiple emitters (paras. 427, 445)

Concerning reparations for climate change, the Advisory Opinion adopted a flexible causation standard (para. 436) and relied on attribution science to establish a sufficiently direct and certain causal nexus (paras. 437–438). Finally, the Court rejected reliance on compliance with the Paris Agreement as a safe harbor and confirmed that customary duties to prevent significant transboundary harm, to cooperate in good faith, and to regulate private actors remain in force for all states, guided by precaution and intergenerational equity (paras. 155, 240, 403). Accordingly, the Advisory Opinion shifts climate action from policy discretion to enforceable commitments that courts and tribunals can invoke across environmental law, human rights law, and the law of the sea.

Looking Forward: The Symposium’s Contributions

The Court has spoken with a clear, unanimous voice on one of the defining challenges of our time. Now begins the crucial work of translating these legal pronouncements into the concrete actions necessary to address the climate crisis. This symposium contributes to that vital endeavor by uncovering the legal pathways the Court has opened and the opportunities they create for enhanced climate governance. For this reason, we bring together a group of distinguished authors to reflect on the ICJ’s Advisory Opinion on Climate Change. Their contributions explore the Opinion’s broader implications, consider its potential to spur reform across different areas of international law, and trace how its reasoning may shape future developments in both doctrine and practice. This marks the beginning of what we hope will be an open, rigorous, and diverse discussion on the many normative universes opened by the recent ICJ advisory opinion; universes that are already stirring curiosity and hope in some quarters, while provoking skepticism in others. This first phase of the Symposium presents a group of those reflections; a second phase will follow, delving into further discussions sparked by the contents of the Opinion. Stay tuned! 

The first phase will run three posts per day for the rest of the week, and the second phase will, in turn, run only one post per day, to allow our readers to soak in its contents to spark further discussions. In our first phase:

Fabián Cárdenas offers a careful structural roadmap of the opinion. His contribution examines how the Court framed its jurisdiction, strategically organized the complex legal questions, and connected core legal principles of prevention, mitigation, and cooperation. Particularly valuable is his examination of how the judges linked long-standing environmental law to emerging duties toward future generations, creating a jurisprudential foundation for future climate governance. Cárdenas offers readers a clear guide to understanding both the Opinion’s internal logic and its broader doctrinal innovations.

David W. Patterson and Benjamin Mason Meier move beyond the decision to outline next steps, analyzing analyzing how the Advisory Opinion creates unprecedented opportunities for enhanced multilateral action at the United Nations Their contribution argues that the AO creates momentum for convening a special session of the General Assembly that could further consolidate state practice, clarify enforcement mechanisms, and translate the Court’s findings into a coordinated program of global climate action. Their analysis bridges the gap between legal pronouncement and political implementation, showing how the Opinion can catalyze transformative institutional action.

Monica Iyer explores the AO’s impact on migration and refugee law. Her contribution demonstrates how the Court’s recognition of climate-related harms strengthens claims to protect people from forced return and anticipates new litigation strategies to expand non-refoulement protections in climate-related displacement cases.

Digvijay Rewatkar examines the Opinion’s implications for the extractive industries. His contribution analyzes how the Court’s reasoning is applicable to terrestrial and deep-sea mining operations, exploring the tension between resource exploitation and climate obligation compliance. Rewatkar develops two possible approaches for reconciling extraction activities with the climate obligations of states.

Conclusion

Together, these contributions showcase how the ICJ’s Advisory Opinion reshapes fundamental concepts across multiple domains of international law. From doctrinal foundations to institutional mechanisms, from human rights protection to economic regulation, the Opinion’s influence extends far beyond traditional environmental law boundaries. The breadth and complexity of the Court’s findings demand continued analysis that probes unexplored dimensions, challenges conventional interpretations, and traces the Opinion’s practical impact across diverse legal and policy contexts. In this context, we remain eager to host new contributions and provide them with a platform where rigorous scholarship can influence the broader conversation. 

Contributions that push beyond the established boundaries of the Advisory Opinion, propose fresh interpretations of the Court’s reasoning, or trace its impact on concrete legal regimes are particularly welcome. Our goal is to create a dynamic intellectual space where ideas can travel beyond a single post, spark dialogue among academics and practitioners, and help shape the emerging legal and policy debates that this landmark opinion has set in motion. More information on the submission guidelines can be found here.