A systematic approach to select a suitable climate metric for aviation policy and aircraft design

A growing body of research has highlighted the major contribution of aviation non-CO 2 emissions to anthropogenic climate change. Regulation of these emissions, for example in the EU Emissions Trading System (ETS), requires the use of a climate metric. However, choosing a suitable climate metric is challenging due to the high uncertainties of aviation non-CO 2 climate impacts, their variability in atmospheric lifetimes and their dependence on emission location and altitude. In this study, we explore the neutrality, temporal stability, compatibility and transparency of existing, physical climate metrics and find the Average Temperature Response (ATR) to be most suitable for aviation policy and aircraft design. We show that the similarities of the total CO 2 -eq emissions calculated by the ATR and the Global Warming Potential (GWP) for current aircraft would enable a timely introduction of the ATR in aviation policy, allowing for a more accurate assessment of novel aviation fuels and aircraft designs.