Mounting evidence has highlighted the role of aviation non-CO2 emissions in anthropogenic climate change. Of particular importance is the impact of contrails, to which recent studies attribute over one-third of the total effective radiative forcing from aircraft operations. However, the relative importance of the aircraft-design-dependent and environmental factors that influence the formation of persistent contrails is not yet well understood. In this paper, we use ERA5 data from the 2010s to better understand the interplay between the factors on a climatological timescale. We identify ice supersaturation as the most limiting factor for all aircraft designs considered, underscoring the importance of accurately estimating ice supersaturated regions. We also develop climatological relationships that describe potential persistent contrail formation as a function of the pressure level and Schmidt-Appleman mixing line slope. We find that the influence of aircraft design on persistent contrail formation reduces with increasing altitude. Compared to a state-of-the-art conventional aircraft with an overall propulsion system efficiency of 0.37, water vapour extraction technologies envisioned for the future have the potential to reduce persistent contrail formation by up to 85.1 %. On the other hand, compared to the same reference, hydrogen combustion and fuel cell aircraft could increase globally averaged persistent contrail formation by 46.5 % and 54.7 % respectively. Due to differing contrail properties, further work is required to translate these changes into climate impacts. This study is a step towards the development of a new and computationally inexpensive method to analyse the contrail climate impact of novel aviation fuels and propulsion technologies.

A growing body of research has highlighted the major contribution of aviation non-CO2 emissions and effects to anthropogenic climate change. Regulation of these emissions, for example in the EU Emissions Trading System, requires the use of a climate metric. However, choosing a suitable climate metric is challenging due to the high uncertainties of aviation non-CO2 climate impacts, their variability in atmospheric lifetimes and their dependence on emission location and altitude. Here we use AirClim to explore alternatives to the conventional Global Warming Potential (GWP) by analysing the neutrality, temporal stability, compatibility and simplicity of existing climate metrics and perform a trade-off. We find that using the temperature-based Average Temperature Response (ATR) or using an Efficacy-weighted GWP (EGWP) would enable a more accurate assessment of existing as well as future aircraft powered by novel aviation fuels

A growing body of research has highlighted the major contribution of aviation non-CO2 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-CO2 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 CO2-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.