Pathways for including non-carbon dioxide aviation climate effects in the European Emission Trading System

Abstract Aviation emissions are responsible for climate impacts through both carbon dioxide emissions and other emissions, in particular, of nitrogen oxides, water vapour, particulates, and contrail formation. In December 2022, the European Commission, Parliament and Council agreed to revise the European Union Emission Trading System for aviation. As such, from January 1, 2025, aircraft operators must monitor non-carbon dioxide climate effects, but suitable metrics for climate impact, handling of uncertainties and practical implementation are still under discussion or at least heavily debated. In this perspective, we propose a procedure for how to include non-carbon dioxide aviation effects into political frameworks. The main goal must be to create incentives for climate change mitigation for the aviation industry. Uncertainties in atmospheric processes need to be appropriately incorporated to minimise risk, and pilot projects are required to test implementation capabilities. Analysing risk, employing consistent monitoring, and determining economic effects will provide scientific grounds for including non-carbon dioxide effects in the European Union Emission Trading System.