Observed changes in stratospheric circulation: decreasing lifetime of N2 O, 2005–2021

Using Aura Microwave Limb Sounder satellite observations of stratospheric nitrous oxide (N2 O), ozone, and temperature from 2005 through 2021, we calculate the atmospheric lifetime of N2 O to be decreasing at a rate of −2.1 ± 1.2 %/decade. This decrease is occurring because the N2 O abundances in the middle tropical stratosphere, where N2 O is photochemically destroyed, are increasing at a faster rate than the bulk N2 O in the lower atmosphere. The cause appears to be a more vigorous stratospheric circulation, which models predict to be a result of climate change. If the observed trends in lifetime and implied emissions continue, then the change in N2 O over the 21st century will be 27 % less than those projected with a fixed lifetime, and the impact on global warming and ozone depletion will be proportionately lessened. Because global warming is caused in part by N2 O, this finding is an example of a negative climate–chemistry feedback.