What stands out is that night flights have a disproportionate contrail climate impact in Europe – the number of aircraft in European airspace during the night is low and still, contrail warming is significant. Around 40% of European contrail warming was caused by flights from 8 pm to 4 am (UTC) that accounted for 20% of traffic in 2019.
But why is that? During the daytime, the contrails function like an umbrella, reflecting some of the sun’s incoming solar radiation back into space, which provides a cooling effect. Simultaneously, they act like a blanket, trapping heat emitted by the Earth and preventing it from escaping into space, contributing to warming.
At night, however, when there is no incoming solar radiation, the “umbrella” effect becomes irrelevant. The contrails then serve only as a blanket, trapping the Earth’s heat and amplifying their warming impact. This dual behaviour explains why contrails have a stronger warming effect at night compared to during the day.
This suggests that targeting late-evening and night flights to do contrail avoidance yields a disproportionately large reduction in warming. Many warming contrails are produced at times when overall traffic is already lower, reducing congestion concerns.
Contrail avoidance at night is a clear opportunity, so what about the season?
The dashboard below shows air traffic and contrail warming by month across different airspaces.
