Reflections on ICJ’s climate change advisory opinion

• Department of Law

This event features a presentation by EUI Visiting Fellow Andrej Lang.

The International Court of Justice’s 2025 Advisory Opinion on climate change has sparked widespread euphoria, hailed as a 'historic legal victory' and a 'turning point', while others have dismissed it as a 'weak opinion' with worrisome 'insufficiencies and shortcomings'. Underlying these contrasting assessments are different expectations about the role and limits of the World Court in the face of the planetary climate emergency. This paper argues that the ICJ has largely risen to the occasion – not because it set out the steps required to solve the climate crisis but because it shows an acute institutional self-reflection about its role and limits. 

In its climate change opinion, the Court defined its role as architect of systemic integration in international climate law, forging a harmonious international legal framework on climate change that integrates the diverse sources of international law and prior rulings of international courts and tribunals into a coherent legal architecture. The ICJ’s institutional position as 'the principal judicial organ of the United Nations' and the unprecedented breadth of state participation in the advisory proceedings equipped the Court with authority and legitimacy to serve as a global public forum on climate obligations. 

Rejecting arguments by major emitters that climate treaties constitute lex specialis, the Court instead pursued a holistic integration of treaty and custom, primary and secondary rules, and human rights and environmental law. This interpretive strategy – while not without limitations – is likely to produce significant legal consequences yet to be discerned in legal discourse in the following months and years. By embracing systemic integration and reaffirming its function as a judicial architect, the ICJ has, as the paper concludes, demonstrated both doctrinal ambition and institutional restraint.