The ICT advisory opinions: The ocean, harm prevention and the disciplining of the climate regime

The three climate treaties [UNFCCC, Kyoto Protocol and Paris Agreement] treat the ocean as a carbon sink, a service provider to the climate system whose absorptive capacity is to be conserved and enhanced. The advisory opinions delivered by the International Tribunal for the Law of the Sea [ITLOS] in 2024 and the International Court of Justice [ICJ] in 2025 replace that instrumental frame with a legal one. Reading the two opinions together, and alongside the Inter-American Court of Human Rights' [IACtHR] opinion of 2025, this article traces three converging threads. First, the ocean is recognised as more than a sink: an inherently valuable part of the environment whose protection and preservation are ends in themselves under the law of the sea. Second, the centre of gravity of climate law shifts from managing permitted harm to prohibiting significant harm, policed by a stringent, science-referenced standard of due diligence and enforced through the ordinary law of State responsibility. Third, the climate regime, mired for years in overly permissive readings, is re-embedded in general international law, its cooperative machinery re-read as obligation rather than aspiration. The article examines what this turn means for ocean governance, for the negotiations and for the litigation now unfolding.