English: This chart plots the absorption coefficient of some of the principal greenhouse gases for electromagnetic radiations with wavenumber values (i.e., frequency divided by the speed of light) in the range 200-1600 cm^-1 (wavelengths in the range 6.25-50 microns). The gases considered include water vapor (H₂O), carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄).

While water vapor has the greatest overall absorption, carbon dioxide is important because it absorbs strongly around a wavelength of 15 microns, where the Earth emits much of its thermal radiation.

Results are for sea-level atmospheric pressure, a water vapor concentration of 0.25%, and a CO₂ concentration of 420 ppm, an N₂O concentration of 390 ppm, and a CH₄ concentration of 1900 ppb. These concentrations are roughly characteristic of atmospheric average values in recent years. Ozone is present in the troposphere but most significant in the upper atmosphere, so cannot readily be compared.

Results are for sea-level pressure, but vary with altitude due to pressure broadening. Concentration of water vapor declines with altitude, increasing the relative importance of other gases at higher altitudes.

The figure was generated using calculations done by the HAPI 1.2.2.0 software package available at http://hitran.org/hapi (Reference: R.V. Kochanov, I.E. Gordon, L.S. Rothman, P. Wcislo, C. Hill, J.S. Wilzewski, "HITRAN Application Programming Interface (HAPI): A comprehensive approach to working with spectroscopic data," J. Quant. Spectrosc. Radiat. Transfer 177, 15-30 (2016) DOI: 10.1016/j.jqsrt.2016.03.005), using spectroscopic data from the HITRAN database.