EJIL: The Podcast! Episode 37: The ICJ’s Advisory Opinion on Climate Obligations: Remarkable, Radical and Robust

There were gasps in the courtroom when the ICJ delivered its advisory opinion on the obligations of States in respect of climate change on 23 July 2025. In this episode, Margaret Young (Melbourne Law School), Phoebe Okowa (Queen Mary University of London, member of the International Law Commission) and Lavanya Rajamani (Oxford) explore how, with its robust and at times radical reasoning, the Court has delivered a truly significant moment for international law.

The conversation highlights the Court’s remarkably systemic account of the sources of obligations to protect the climate system, which stem from treaties – including but not limited to the Paris Agreement – and customary international law, and the far-reaching conclusion that a breach by a State of any of these obligations constitutes an internationally wrongful act entailing the responsibility of that State. Margaret, Lavanya and Phoebe delve into the treatment of applicable law (including the Court’s assessment that the climate treaties do not displace other rules and principles as lex specialis, and handling of human rights law), the robust interpretative approach to the Paris Agreement, and the customary duty of states to prevent significant harm to the environment. That economic support for fossil fuel production might in principle constitute an internationally wrongful act is gobsmacking for some, but also necessary to address the root problem of climate change. Margaret, Lavanya and Phoebe explore how to parse the Court’s treatment of the principle of ‘common but differentiated responsibilities and respective capabilities’ (CBDR-RC), which reflects the need to distribute equitably the burdens of obligations, and the vexed question of historic emissions. They touch also on the Court’s position on state responsibility, including on obligations erga omnes; and the Court’s comments on restitution, especially with respect to statehood and sea-level rise.

The panel situates the opinion in the broader context of global climate action: its implications for ‘nationally determined contributions’ (NDCs), which States maintain under the Paris Agreement to help achieve its temperature goal of limiting warming to 1.5°C above pre-industrial levels; repercussions for negotiations in conferences of the parties (COPs) including those serving as the meeting of the Parties to the Paris Agreement (CMAs); and potential impact on litigation at the international, regional and domestic level.

(For a more general discussion of advisory proceedings in international courts and tribunals, and the challenges of formulating questions, episode 18 features Margaretha Wewerinke-Singh and Philippe Sands on these themes).

Scholarship referred to in the episode includes Phoebe N. Okowa, State Responsibility for Transboundary Air Pollution in International Law (2000); Lavanya Rajamani, ‘Interpreting the Paris Agreement in its Normative Environment’ (2024) 77 Current Legal Problems 167; Margaret A. Young, ‘Climate Change and Law: A Global Challenge for Legal Education’ (2021) 40 University of Queensland Law Journal 351; and Margaret A. Young, ‘Fragmentation’  in  Lavanya  Rajamani  and  Jacqueline  Peel  (eds), Oxford Handbook of International Environmental Law (2021) 85.