Diminished greenhouse warming from Archean methane due to solar absorption lines

Abstract. Previous research has shown that methane may have been sustained at high concentrations in the Archean atmosphere, helping to offset lower insolation and solve the faint young sun problem. However, recent updates to the HITRAN (High-Resolution Transmission) line database have significantly increased the shortwave absorption by CH₄ in comparison to older versions of the database (e.g. HITRAN 2000). Here we investigate the climatological implications of strong shortwave CH₄ absorption in an Archean atmosphere rich in CH₄. We show that the surface warming at CH₄ abundances >10^-3 is diminished relative to the HITRAN 2000 line data. Strong shortwave absorption also results in a~warm stratosphere and lower tropopause. We discuss these results in the context of contemporary research on the Archean climate and how these results could affect the formation of stratospheric clouds and an organic haze.