Navigating regulatory overlap in shipping decarbonization: coordinating the EU Maritime ETS and the IMO Net-Zero Framework

The decarbonization of international shipping is entering a transitional phase in which a regional regime and an emerging global framework are developing in parallel. Since 2024, shipping companies have been subject to phased compliance obligations under the European Union (EU) Maritime Emissions Trading System (ETS), while the International Maritime Organization (IMO) Net-Zero Framework, approved at the Marine Environment Protection Committee 83 in April 2025, has faced delayed adoption and implementation. This sequencing creates a regulatory window in which the EU regime operates ahead of the prospective global framework. Once the IMO mechanism enters into force, the same voyage, vessel, and reporting year may fall within both regimes. This article examines the resulting regulatory overlap between the EU Maritime ETS and the IMO Net-Zero Framework. The article identifies three forms of overlap. Normative overlap arises from the coexistence of port-linked EU regulation and ship-based global compliance. Cost overlap results from the combined operation of allowance surrender and greenhouse gas fuel intensity compliance. Procedural overlap stems from separate reporting, verification, and registry systems. It argues that uncoordinated coexistence may fragment multilateral governance, distribute decarbonization burdens unevenly, and increase compliance uncertainty for regulated actors. To address these risks, this article proposes a two-level coordination pathway at the regional and multilateral levels. At the regional level, the EU Maritime ETS has functioned as a catalyst for multilateral action, though its catalytic effect has fundamental limits. It may be repositioned as a transitional mechanism through jurisdictional self-restraint, crediting arrangements, and data interfaces. At the multilateral level, the IMO framework may serve as the central multilateral anchor. For it to do so credibly, a set of internal institutional conditions may need to be met, covering revenue predictability, binding allocation rules, accounting standards capable of alignment with the EU ETS, monitoring, reporting, and verification procedures that allow recognition of verified data, and effective compliance monitoring. Where these conditions are not met, coordination would be confined to managed coexistence, with the EU regime continuing as an autonomous backstop.