This excellent essay not only debunks Methane as a “greenhouse gas”, but it allows you to parley your high school physics into an understanding of how the greenhouse gas thing works as a whole.
Water vapour is by far the most dominant GHG and carbon dioxide and methane are only effective to a small extent where their absorption effects extent outside the overwhelming effect of water vapour.
Methane The Irrelevant Greenhouse Gas Watts Up With That#more-107326#more-107326 http://wattsupwiththat.com/2014/04/11/methane-the-irrelevant-greenhouse-gas/#more-107326
” …CO2 has absorption bands centered around 2.5 microns, 4.3 microns, and has a broad band out beyond 13 microns. Consequently, CO2 adds a small contribution to the greenhouse effect. Notice that sometimes CO2 bands overlap with H2O bands, and with vastly more H2O present, CO2 doesn’t matter in those bands.
Looking at the second graph in the figure, methane (CH4) has narrow absorption bands at 3.3 microns and 7.5 microns (the red lines). CH4 is 20 times more effective an absorber than CO2 – in those bands. However, CH4 is only 0.00017% (1.7 parts per million) of the atmosphere. Moreover, both of its bands occur at wavelengths where H2O is already absorbing substantially. Hence, any radiation that CH4 might absorb has already been absorbed by H2O. The ratio of the percentages of water to methane is such that the effects of CH4 are completely masked by H2O. The amount of CH4 must increase 100-fold to make it comparable to H2O.
Because of that, methane is irrelevant as a greenhouse gas. The high per-molecule absorption cross section of CH4 makes no difference at all in our real atmosphere.
Unfortunately, this numerical reality is overlooked by most people. There is a lot of misinformation floating around, causing needless worry. The tiny increases in methane associated with cows may elicit a few giggles, but it absolutely cannot be the basis for sane regulations or national policy.”
NOTE – “The amount of CH4 must increase 100-fold to make it comparable to H2O.”