Between Brussels and Montreal: The European Commission’s Leadership and Mediation in Integrating CORSIA with the EU ETS for Aviation

This paper analyses how the European Commission steered the interface between ICAO’s Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) and the EU Emissions Trading System (EU ETS) from 2013 to 2024. Combining two-level game theory with constructivist role theory, it conceptualises the Commission as a “leadiator”: an actor that must lead on ambition while mediating heterogeneous coalitions across international (Level I) and intra-EU (Level II) arenas. Empirically, the study process-traces the sequence from the Fit for 55 proposal (July 2021), through Council–Parliament trilogues (2022–2023), to Directive (EU) 2023/958, while situating these choices against the 2013 “stop-the-clock” episode and the 2016 launch of CORSIA. Evidence comes from 18 elite interviews with Commission, Member-State and Parliament officials, triangulated with legal texts, Council ST documents and ICAO records. The analysis shows that DG CLIMA deliberately sequenced the EU and ICAO tracks: preserving a clean-cut jurisdictional split (intra-EEA flights under ETS; extra-EEA under CORSIA) while tightening internal ambition via the early phase-out of free allowances, SAF-oriented funding through EU instruments, and a review clause explicitly linking future EU scope to global progress. This strategy maximised the Commission’s autonomy under domestic constraints, expanded its win-set and projected an EU identity of credible climate leadership without fracturing internal consent. The findings contribute to debates on EU climate diplomacy and regime overlap by specifying the conditions under which bureaucratic entrepreneurship inside the Commission can reconcile leadership with mediation, and by showing how role expectations are managed to align internal ratifiability with external effectiveness. Keywords: EU ETS, CORSIA, Aviation decarbonisation, European Commission, two-level games, constructivist role theory, leadership