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Most long-lived contrails form within cirrus clouds with uncertain climate impact
Andreas Petzold1,2, Neelam F Khan3,4, Yun Li3
1Institute of Climate and Energy Systems-Troposphere (ICE-3), Forschungszentrum Jülich GmbH, Jülich, Germany. a.petzold@fz-juelich.de.
Nature Communications
|November 3, 2025
Summary
Contrail cirrus clouds, a major climate impact from aviation, are often found with existing cirrus. Flight rerouting to avoid contrails must consider cirrus cloud cover.
Area of Science:
- Atmospheric Science
- Climate Science
- Aviation Impacts
Background:
- Contrail-cirrus represents a significant component of aviation's climate impact.
- Accurate assessment necessitates a deeper understanding of contrail-cirrus radiative effects.
Purpose of the Study:
- To analyze the conditions under which long-lived contrails form.
- To investigate the interplay between contrails and existing cirrus cloud cover.
- To assess the radiative effects of contrails in different cirrus environments.
Main Methods:
- Analysis of seven years of humidity observations from instrumented passenger aircraft.
- Conceptual analysis of contrail radiative effects in relation to cirrus cloud types and coverage.
Main Results:
- Long-lived contrail formation conditions frequently coincide with pre-existing subvisible or visible cirrus.
- ~90% of Northern midlatitude and nearly 100% of Southeast Asian subtropical cruise altitudes exhibit this overlap.
- Contrails in subvisible cirrus are expected to cause additional warming, while those in thicker, visible cirrus may have a neutral or cooling effect.
Conclusions:
- Contrail formation is strongly linked to existing cirrus cloud cover.
- Flight rerouting strategies for contrail mitigation must integrate cirrus cloud information alongside ice-supersaturation levels.
- Understanding the radiative impact of contrails requires considering the background cirrus environment.
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