Methane (CH4), originally known by the names of "swamp gas" or "marsh gas", is another important player in regulating earth's radiation balance. Over the past 250 years of human industrialization, the atmospheric concentration of this greenhouse gas has more than doubled, increasing from around 0.7 ppm to close to 1.7 ppm.
Open the IR Windows learning tool and click on methane's infrared (IR) absorption spectrum. Now turn on the IR absorption spectra for water vapour and carbon dioxide. Does methane absorb in the regions where water vapour and carbon dioxide do not absorb IR?
Recall that the region of the IR spectrum in which a greenhouse gas absorbs is an important factor in determining the global warming potential (GWP) of the gas. The atmospheric lifetime of a gas is also important in determining its GWP.