Contrails – The Journey Towards Consensus

November 20, 2025

Aircraft contrails are the thin white lines often seen trailing behind aircraft at high altitude. Scientific studies suggest that the cirrus clouds they induce may account for a portion of aviation’s warming effect which has led to growing interest across the industry in understanding and mitigating their effects. ¹

Measurement Complexity

Depending on the prevailing weather conditions and time of day, contrails can have either a cooling or warming effect, however the overall net effect is warming.

Their formation and persistence depends on highly variable atmospheric conditions, particularly humidity at cruising altitudes which typically varies during the time of day or night. Accurately quantifying their climate impact is extremely challenging, particularly because there is a lack of data. Differentiating contrails from natural clouds is also a challenge.

Mitigation strategies

Strategies to mitigate contrail avoidance are currently trial-based. They involve identifying flights with high contrail warming potential and submitting alternative flight plans to air traffic control. This in effect means dynamic navigation. Demonstration projects and airline trials such as Satavia and Etihad have proven that contrail avoidance is operationally feasible, however scaling these strategies across the industry requires collaboration between airlines, ATC and standardisation on measurement and data accessibility. ²

Science is still evolving

While the importance of contrails is acknowledged, the underlying science remains at an early stage. There is currently no industry-wide standard for measurement or reporting defined by either IATA or ICAO.

Effective from this year under the EU ETS Monitoring Reporting and Verification (MRV) program, aircraft operators are obliged to monitor non-CO2 aviation effects for intra-EEA flights and flights to Switzerland and UK. In September the EU Commission and EUROCONTROL launched NEATS to streamline and standardise the collection of input data. Airline operators must upload data inputs such as flight trajectory, engine and fuel flow data to the platform for all routes within the EEA and flights from EEA to Switzerland or the UK. This is expected to be further expanded in 2027 to include all flights departing or arriving at the EEA. ³

Subsequent iterations of NEATS will include interfaces for other stakeholders, providing a streamlined reporting process and centralisation of data, ultimately leading to automation of monitoring and reporting of non-co2 effects at least within Europe.

For now, the PACE team will continue to monitor scientific developments and regulatory progress on contrails and their avoidance so that when consensus emerges, PACE will adopt agreed practices to support our customers in delivering sustainability goals.