The European Commission and the Maritime ETS: Explaining Role Performance in a Weak International Context

This paper examines how the European Commission shaped and carried out its role in bringing maritime transport into the EU Emissions Trading System (EU ETS), a policy adopted in 2023 and the first of its kind globally. Compared with aviation, where CORSIA offered at least a basic international reference point, the maritime ETS developed in a context where the IMO moved slowly and global political attention to climate policy was uneven. This created both an opportunity and a limitation for the Commission: it could move ahead regionally, but without the international backing that usually helps anchor EU climate initiatives. Based on process tracing, policy documents, and elite interviews from EU officials, the paper shows that DG CLIMA operated in a 'leadiator' mode. Externally, it tried to show leadership by signalling that the EU was ready to act despite IMO delays, while avoiding open conflict with major partners. Internally, it had to work through clear differences among Member States, especially between more ambitious countries and those with large maritime sectors. This led the Commission to design a proposal that phased in obligations, used a half-half rule for extra-EU voyages, and introduced compliance gradually. The final trilogue agreement kept most of these elements, suggesting that the Commission managed to navigate domestic constraints effectively. The analysis points to three main conclusions. First, EU leadership without a strong international framework is possible, but its impact remains limited when the IMO process stalls. Second, the maritime case shows how the Commission relies on technical and administrative arguments to maintain ambition while addressing Member State concerns. Third, combining Two-Level Game Theory with Constructivist Role Theory helps explain why the Commission’s role shifts over time: its actions depend on both external conditions and the configuration of internal support. Overall, the maritime ETS represents a form of “compensatory” climate leadership by the EU. The Commission advanced a significant policy despite weak international momentum, but the broader global effect remains uncertain given the political and institutional limits surrounding maritime decarbonisation.