Variability of cirrus and contrails formation capability in the context of upper tropospheric conditions

Climate change, driven largely by human activities, impacts cloud formation and properties, creating complex feedback effects. High-altitude clouds, such as cirrus, influence Earth’s energy balance, while human activities, notably aviation, contribute to condensation trails, a form of anthropogenic cloud.This study evaluates long-term trends and spatio-temporal variability in conditions conducive to natural cirrus and condensation trail formation over Europe and the northeastern Atlantic from 1981–2020, using ERA5 reanalysis data at 300 and 250 hPa pressure levels. The analysis also examines trends in upper tropospheric temperature and humidity.Results show cirrus conditions vary from 2–20%, peaking in winter and over the ocean, with surface influences shaping trends. Contrails exhibit only negative trends but are also most frequent in winter (up to 14%). The findings highlight distinct behaviours between natural and anthropogenic high clouds under changing climate conditions.