Investigating the limiting aircraft design-dependent and environmental factors of persistent contrail formation

Abstract. Mounting evidence has highlighted the role of aviation non-CO₂ emissions in contributing to anthropogenic climate change. Of particular importance is the impact of aircraft contrails and induced cloudiness, which recent studies attribute to 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 and limit the formation of persistent contrails is not yet well understood. In this paper, we use ERA5 data from the 2010 decade to better understand the interplay between the factors on a climatological timescale. We identify ice supersaturation as the most limiting factor for all considered aircraft designs, 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 G, and find that the influence of aircraft design on persistent contrail formation reduces with increasing altitude. Globally-averaged persistent contrail formation could increase by 13.8 % for next generation conventional aircraft, or by 71.4 % if all aircraft were to be replaced by hydrogen combustion or fuel cell equivalents. On the other hand, water vapour extraction technologies such as the Water Enhanced Turbofan concept have the potential to reduce persistent contrail formation by 53.6 % to 85.6 %. The introduction of novel aviation fuels and propulsion technologies, therefore, present both challenges and opportunities with respect to persistent contrail formation.