A Revised, Hazy Methane Greenhouse for the Archean Earth

Abstract

Geological and biological evidence suggests that Earth was warm during most of its early history, despite the fainter young Sun. Upper bounds on the atmospheric CO2 concentration in the Late Archean/Paleoproterozoic (2.8-2.2 Ga) from paleosol data suggest that additional greenhouse gases must have been present. Methanogenic bacteria, which were arguably extant at that time, may have contributed to a high concentration of atmospheric CH4, and previous calculations had indicated that a CH4-CO2-H2O greenhouse could have produced warm Late Archean surface temperatures while still satisfying the paleosol constraints on pCO2. Here, we revisit this conclusion. Correction of an error in the CH4 absorption coefficients, combined with the predicted early onset of climatically cooling organic haze, suggest that the amount of greenhouse warming by CH4 was more limited and that pCO2 must therefore have been 0.03 bar, at or above the upper bound of the value obtained from paleosols. Enough warming from CH4 remained in the Archean, however, to explain why Earth's climate cooled and became glacial when atmospheric O2 levels rose in the Paleoproterozoic. Our new model also shows that greenhouse warming by higher hydrocarbon gases, especially ethane (C2H6), may have helped to keep the Late Archean Earth warm.

The extrasolar planet Gliese 581d: a potentially habitable planet?

“…The model surface albedo is 0.24, which is slightly higher than the value of 0.21 from von Paris et al (2008), but still compatible with surface albedos of other cloud-free models in the literature (e.g., Goldblatt et al 2009a;Haqq-Misra et al 2008, both studies using 0.23 as their surface albedo value). Note that the actual global value for Earth is approximately 0.13 (Kitzmann et al 2010;Rossow & Schiffer 1999), as stated above.…”

“…Figure A.1 shows that the agreement between the three models is indeed very good. Figure A.2 compares the calculations for set S from Table A.1 with calculations done by Haqq-Misra et al (2008) (similar to runs S3 and S4). They used an updated version (e.g., new absorption coefficients) of the 1D radiative-convective model of Kasting & Ackerman (1986).…”

Reduced albedo on early Mars does not solve the climate paradox under a faint young Sun

“…However, if we assume that the climate during the Archaean was relatively similar to present-day Earth, then global temperature would fall below the freezing point of water-just as is postulated for early Mars. The same solutions, namely additional atmospheric greenhouse effects from high partial pressures of CO 2 , NH 4 , CH 4 and C 2 H 6 , have been suggested as an explanation to the early Earth's problem (Kiehl & Dickinson 1987;Kasting 1993;Sagan & Chyba 1997;Catling et al 2001;von Paris et al 2008;Haqq-Misra et al 2008). An alternative solution has been recently proposed (Rosing et al 2010) that a lower albedo on the Earth, owing to considerably less continental area and to the lack of biologically induced cloud condensation nuclei, made an important contribution to moderating surface temperature in the Archaean eon.…”

“…Additionally, calculations for this hypothesis place an upper limit of 1600 ppmv for atmospheric CO 2 and 800 ppmv for atmospheric CH 4 , which limits the amount of warming provided by greenhouse gases. Radiative forcing in our EBM is parameterized as a function of CO 2 only, so we cannot calculate the contribution from CH 4 directly; however, we can use existing radiative-convective equilibrium model calculations for the Archaean Earth (Haqq-Misra et al 2008), which show that the total amount of warming provided by 1600 ppmv CO 2 and 800 ppmv CH 4 is equivalent to the amount of warming provided by about 10 000 ppmv of atmospheric carbon dioxide. We use this value for the partial pressure of CO 2 for our EBM calculations in Fig.…”

Hydrogen-Nitrogen Greenhouse Warming in Earth's Early Atmosphere

“…However, all of these mechanisms have subsequently been shown to suffer important defects (6,7). Increased atmospheric carbon dioxide is one plausible solution because of the climate buffer provided by the crustal carbonate-silicate cycle (8), but efficient mantle CO 2 cycling in the Hadean and Archean probably reduced the strength of this feedback (9).…”