The natural greenhouse effect of N2 and O2 in the infrared

The radiative effects of the major constituents of the Earth’s atmosphere, N2 and O2 in the infrared has been quantified. The global mean reduction of the outgoing longwave radiation by N2 and O2 was determined to 15% of that caused by CH4 -reaching even up to 80% under dry Antarctic situations. This highlights the hitherto often underestimated role of N2 and O2 in Earth’s natural greenhouse effect.

The reduction of outgoing longwave radiation (OLR) through collision induced absorption bands has been quantified for the first time globally. The natural greenhouse effect of N2 and O2 in the infrared is with 0.28 W/m2 1/6th that of CH4. This effect is modulated mainly by the atmospheric water vapor content. Over Antarctic regions average values of 38% of the OLR reduction of CH4 are reached. This work concerns only the contribution of N2 and O2 to the natural greenhouse effect. In no way does it affect the importance of CH4 and other anthropogenically affected gases with respect to global climate change. For details see: www.agu.org/pubs/crossref/2012/2012GL051409.shtml