Atmospheric methane levels averaged 1,895.7 ppb (parts per billion) during 2021, or around 162% greater than pre-industrial levels. It is a much stronger greenhouse gas by itself, unlike CO2 because its absorption is not saturated in the atmosphere. On the other hand the lifetime of Methane in the atmosphere is 10 to 15 years so some of the Methane eating bacteria will do its job. There is only one significant frequency band that absorbs, at 7.6 microns.
The picture shows a much smaller peak at 8.1micron. This is because at lower wavelengths absorption from water vapor has nearly eliminated the CH4 contribution. Remember that total absorption can never exceed 100 %, so the maximum absorption from CH4 occurs at 8.1 micron, At 1.8 ppm it amounts to a greenhouse effect of 0.01 C. Before industrialization the CH4 concentration was 0.725 ppm which results in an increase of the greenhouse effect of 0.0072 C from rising levels of Methane since before industrialization .
So much for cow farts, rice fields, landfills and termites eating tree roots. Methane is the “do not care” gas.
Len Bilén's blog, a blog about faith, politics and the environment. 