An Observational Constraint on Aviation‐Induced Cirrus From the COVID‐19‐Induced Flight Disruption

Global aviation dropped precipitously during the Covid‐19 pandemic, providing an unprecedented opportunity to study aviation‐induced cirrus (AIC). AIC is believed to be responsible for over half of aviation‐related radiative forcing, but until now, its radiative impact has only been estimated from simulations. Here, we show that satellite observations of cirrus cloud do not exhibit a detectable global response to the dramatic aviation reductions of spring 2020. These results indicate that previous model‐based estimates may overestimate AIC. In addition, we find no significant response of diurnal surface air temperature range to the 2020 aviation changes, reinforcing the findings of previous studies. Though aviation influences the climate through multiple pathways, our analysis suggests that its warming effect from cirrus changes may be smaller than previously estimated. Plain Language Summary Global air traffic decreased rapidly during the Covid‐19 pandemic. This perturbation provides an opportunity to test the influence of aviation on cirrus cloud cover and on the contrast between daytime and nighttime surface air temperatures. We find that, despite the very large reduction in air traffic, neither cirrus cover nor temperature ranges changed by enough to be detectable relative to the year‐to‐year variability of natural cirrus. Comparing the satellite observations to previous model‐simulated aviation cirrus, we determine that any aviation‐induced change in cirrus would have a much smaller magnitude than would be inferred from climate model simulations. These results suggest that the warming effect of cirrus clouds produced by aircraft may be smaller than previously believed. Key Points Aviation reductions during COVID‐19 provide an opportunity to test the impact of aviation on cirrus cloud and diurnal temperature range Neither variable exhibits a detectable large‐scale response in satellite observations Comparison with previous model analyses of contrail cirrus suggests that warming by aviation‐induced cirrus may have been overestimated