Different simulations of the climate effects of flights can suggest different actions needed to reduce aviation's impact. We investigate whether combining information from multiple simulations leads to better decisions than relying on one alone. We find that combining predictions can achieve greater climate benefits than using a single prediction. We also find that using multiple predictions can make efforts to reduce aviation's climate impact more robust under uncertainty.

A novel reduced-order model for assessing the climate impact of aircraft engines during the engine cycle design stage, called Climate Functions for Engine Design (CFED 1.0), is presented. The model comprises mathematical expressions correlating aviation-related species’ climate metrics with fuel burn and emissions from an engine at a given altitude. The model captures climate effects of a globally operating fleet, and is suitable for climate assessment during the iterative engine design process.

Flying a few hundred feet higher or lower can turn a warming contrail into a cooling one, or avoid it entirely, but testing this for every flight by trial and error is too costly. We built a tool that computes, in one pass, how a flight's contrail warming would change with its altitude, the surrounding humidity, and the model's own assumptions. This pinpoints promising altitude changes, shows which weather data matters, and reveals which modelling assumptions most affect predicted warming.

Contrails contribution to the climate impact of aviation could be significant, but remains uncertain. Their formation results from the interaction between microphysical processes and aircraft wake dynamics. This study combines model simulations to examine the impact of accounting for aircraft-induced dilution dynamics on contrail ice crystals formation. The results highlight the influence of the aircraft dynamics on ice crystal characteristics, upon which contrail radiative forcing depends.

We study contrail formation behind future fuel cell-based aircraft fueled by hydrogen. Simulations show that, under certain conditions, small droplets can form via a process not occurring in current plumes. This can increase ice crystal numbers in contrails, boosting their climate impact. The effect is strongest in cold air and for high plume mixing rates with air. We suggest to decrease the mixing rate and exhaust humidity by technical design to reduce the climate impact of such aircraft.

Model simulations were used to study all air traffic over Northern Europe during 16 days in 2023, following the European Union's planned framework (using CoCiP and aCCFs) for monitoring aviation’s non-CO₂ climate effects. Small changes in flight altitude reduced the climate impact of contrails by 48 % while increasing the fleet-wide fuel use by only 0.4 %. The changes had only limited effects on air traffic density and aircraft spacing, showing that climate-optimized flight planning is feasible.

Sustainable aviation fuels (SAFs) reduce the climate effect of contrail-induced cirrus cloudiness (CiC). We assess the climate-optimal SAF distribution for flights departing from Copenhagen Airport in 2030. We determine the potential climate benefit of 6 % available SAF by allocating it to flights with climatologically largest CiC climate effect to fuel use ratio. Targeted SAF use can here increase the CO2e benefit by 60 kt and enhance the CiC share in climate benefit from 20 % to almost 50 %.

This study presents a multi-physics Eulerian framework for simulating the long-term evolution of aircraft contrails, a major contributor to aviation-induced warming. The model integrates advection, diffusion, ice-particle growth, turbulent settling, and habit evolution through a system of PDEs. Computationally efficient and calibratable against observations, it is well suited for large-scale contrail and radiative forcing simulations.

Commercial flights usually follow routes that minimise travel time and fuel use, but these routes are not always best for the climate. Using simulations of 4,000 flights forming condensation trails over northern Europe in 2023, we show that small altitude changes can reduce climate impact by 11 to 16% for only 1.2% more fuel. The benefits of avoiding warming from condensation trails outweigh the additional climate effect from nitrogen oxides and water vapour emissions.