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

Abstract This paper explains how the European Commission exercises climate leadership in a transnational, highly mobile sector when multilateral institutions cannot yet provide a binding market-based anchor. It examines the EU’s inclusion of maritime transport in the EU Emissions Trading System (2018-2025), a case in external climate governance because the EU introduced a legally binding carbon-pricing obligation linked to EU ports while global carbon pricing at the International Maritime Organization (IMO) remained uncertain. The paper asks how the Commission can lead in global shipping when the multilateral arena cannot reliably anchor convergence through a global pricing instrument. I argue that under low external opportunity at Level I (a slow and politically contested IMO pathway) and politically costly internal ratification at Level II (divergent Member State exposure and institutional preferences), the Commission is more likely to adopt a “leadiator” (leader–mediator) strategy. Leadiator is treated as an observable strategy rather than a label, traced through three indicators: external signalling and leverage, conflict-avoidant positioning, and design-as-mediation. Empirically, the paper uses process tracing of EU and IMO documents alongside 18 elite interviews and one written correspondence. The findings show a clear leadiator attempt across all three indicators and a strong EU-level policy output: the core “50/50” coverage architecture largely survived, the phase-in was recalibrated, the scope was expanded to additional gases, and anti-evasion safeguards and enforcement provisions were strengthened. However, the strategic outcome is weaker. The EU did not lock in automatic convergence with a future IMO market-based measure; instead, it institutionalised a politically revisitable interface through review clauses. The result is an output–outcome asymmetry: robust EU adoption under two-level constraints, but contingent and time-lagged EU–IMO intergation.