Assessing Contrail Mitigation Potential Through Initial Climb and Final Descent Phase Analysis: A Comparison of Short- and Medium-Range Flights Within Europe

The steady increase in global air traffic demand has led to a corresponding rise in contrail radiative forcing, contributing significantly to effective radiative forcing (ERF). Contrails, formed when hot exhaust gases from jet engines mix with cold, humid ambient air, have a warming effect that can surpass the CO₂ emissions of aviation in the short term. While contrail mitigation strategies often focus on adjustments to cruise altitudes and flight trajectories, less attention has been given to the impact of climb and descent phases, and particularly their effects on cruise phases for short- and medium-range flights. This study explores the contrail mitigation potential of these flight phases, providing a comprehensive analysis of their contribution to contrail formation, and associated operating costs.

Contrail persistence depends on atmospheric conditions within ice-supersaturated regions (ISSRs), primarily occurring at typical cruising altitudes. However, the dynamics of the initial climb and final descent phases should only occasionally allow for contrails to form, and much less for persistence to occur, primarily due to higher temperatures at low altitudes. When transitioning through vertical layers of ISSRs, some contrails may however still form, though a quantification of this phenomenon is lacking. Thus, by leveraging simulations conducted with an air traffic simulator embedded in a climate-chemistry model (EMAC/AirTraf), this study investigates contrail formation during these phases, narrowing this gap. By incorporating these overlooked flight segments, we aim to provide a more accurate estimate of contrail prevalence.

A critical aspect of the analysis involves quantifying the impact of climb and descent phases on contrail length and operating costs. By grouping simulations based on flight length for a set of European flights, this study elucidates differences in contrail distances and cost estimated using fuel consumption. In order to investigate this, the flights are first analysed using an airport to airport trajectory, optimised using different objectives such as contrail distance minimum, fuel optimal, and multi-objective (fuel-contrail). For airport to airport, it assumes that these flights entirely occur at cruise altitude. The next step uses more realistic trajectories, considering a cruise phase bounded by climbing and descending phases, using the same optimisation options. The direct impact of climb and descent in terms of contrail distance is observed from the difference between the original trajectory (airport-airport) and the cruise only trajectory. Next using the cruise only trajectory determined with the standard entry/exit points, also known as standard instrument departures (SID) and standard instrument arrivals (STAR), together with the separate impact of ascent/descent, the overall climate impact reduction potential can be determined for a more realistic flight path, using algorithmic climate change functions (ACCF).

By applying this method, we expect to identify the potential contribution of climb and descend to the contrail climate impact for a given flight. By extension, this would indicate the relevance of climb/descent phases in contrail mitigation potential studies, regardless of chosen optimiser, and moreover, the differences arising in the mitigation potential as a function of flight length.