On 21st May 2024, the International Tribunal for the Law of the Sea (ITLOS) issued its first advisory opinion on climate change, clarifying States’ obligations under the United Nations Convention on the Law of the Sea (UNCLOS) but offering limited guidance on marine geoengineering – an increasingly relevant set of ocean-based interventions for carbon dioxide removal (CDR). As concerns grow that emission reductions alone may be insufficient to meet the Paris Agreement goals, ocean-based CDR techniques such as ocean fertilization and alkalinization are attracting growing interest, yet they remain largely unregulated under binding international law. Until now research on ocean-related CDR proposals concentrated its attention on the possible application of UNCLOS, the 1972 London Convention on the prevention of marine pollution by dumping of wastes, the 1996 Protocol to the Convention and its amendments. This article examines these instruments arguing that their sectoral scope and risk-averse orientation provide only a limited foundation for governing marine geoengineering. It then considers the Agreement on Marine Biodiversity of Areas Beyond National Jurisdiction (BBNJ), not merely as a gap-filling tool but as a framework offering complementary procedural and institutional mechanisms that could support the effective governance of further research and implementation of CDR projects in areas beyond national jurisdiction. The article argues that international law should evolve to ensure that marine geoengineering is regulated in a way that supports both ocean protection and climate mitigation, while fostering transparency, scientific integrity, knowledge pluralism, and advancing systemic integration between the law of the sea and the climate regime.
