Articles | Volume 11, issue 3
Clim. Past, 11, 559–570, 2015
Clim. Past, 11, 559–570, 2015

Research article 27 Mar 2015

Research article | 27 Mar 2015

Diminished greenhouse warming from Archean methane due to solar absorption lines

B. Byrne1,* and C. Goldblatt1 B. Byrne and C. Goldblatt
  • 1School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada
  • *now at: Department of Physics, University of Toronto, Toronto, ON, Canada

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.

Short summary
High methane concentrations are thought to have helped sustain warm surface temperatures on the early Earth (~3 billion years ago) when the sun was only 80% as luminous as today. However, radiative transfer calculations with updated spectral data show that methane is a stronger absorber of solar radiation than previously thought. In this paper we show that the increased solar absorption causes a redcution in the warming ability of methane in the Archaean atmosphere.