Most long-lived contrails form within cirrus clouds
Analysis of seven years of humidity observations by instrumented passenger aircraft shows that conditions promoting long-lived contrails are fulfilled most often in regions already covered by subvisible or visible cirrus: ~90% over the Northern midlatitudes and almost 100% in the Southeast Asian subtropics, approximately equally distributed among visible and subvisible cirrus clouds.
Most long-lived contrails form within cirrus clouds
https://www.nature.com/articles/s41467-025-65532-2
Aviation effects on already-existing cirrus clouds
Here we quantify the effect of aircraft on the optical thickness of already-existing cirrus clouds by matching actual aircraft flight tracks to satellite lidar measurements. We show that there is a systematic, statistically significant increase in normalized cirrus cloud optical thickness inside mid-latitude flight tracks compared with adjacent areas immediately outside the tracks.
https://www.nature.com/articles/ncomms12016
A Case Study on Aircraft-Induced Clouds and Natural Cirrus
Aircraft-induced clouds (AIC), consisting of persistent contrails and contrail cirrus, contribute over half of effective radiative forcing (RF) to the aviation effect on climate.
https://ui.adsabs.harvard.edu/abs/2021AGUFM.A45M2020W/abstract
World War II Bomber Contrails Show How Aviation Affects Climate
A new study based on historical data examines Allied air raids, including one on May 11, 1944, in which 1,980 aircraft took flight into Germany. Behind the planes, witnesses described the sky turning white, and temperature records show that the air turned slightly, but significantly, cooler.
https://www.scientificamerican.com/article/contrails-aviation-affects-climate/
World War II contrails: a case study of aviation-induced cloudiness
Although one event cannot provide firm conclusions regarding the effect of contrails on climate, this study demonstrates that the wealth of observational data associated with WW2 bombing missions allows detailed investigation of meteorological perturbations because of aviation-induced cloudiness.
https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/joc.2392