Clim. Past Discuss., 9, 1509-1534, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
The faint young Sun problem revisited with a 3-D climate-carbon model – Part 1
G. Le Hir1, Y. Teitler1, F. Fluteau1, Y. Donnadieu2, and P. Philippot1
1IPGP, UMR7154, CNRS – Université Paris 7-Denis Diderot, 1 rue Cuvier, 75005 Paris, France
2LSCE, CNRS-CEA-UVSQ, 91191 Gif-sur-Yvette, France

Abstract. Considering the weak luminosity of the early Sun, it is generally inferred that high concentrations of greenhouse gases (CO2, CH4) are required to prevent the early Earth's surface temperature to drop below the freezing point of liquid water. Conversely, a new controversial assumption based on banded iron formation mineralogy hypothesizes that the Archean atmosphere was potentially characterized by low concentrations of CO2. To solve the faint young Sun problem, it was suggested that a reduced albedo associated to less reflective clouds was able to prevent the Earth to jump into a snowball state. In this very active debate, we have investigated the early Earth climate using a general circulation model to test this scenario. Our simulations include the ice albedo feedback and specific Archean climatic factors such as a different cloudiness, a faster Earth's rotation rate, and a reduced continental surface. We demonstrate that when larger cloud droplets are accounted for, clouds warm high latitudes and inhibit sea-ice formation. This process limits the ice-albedo feedback efficiency and may prevent a global glaciation. Due to this particular mechanism, low pCO2 allow maintaining a mild climate during the early Archean. This conclusion will be challenged in the second part of this paper, where the carbon cycle is considered.

Citation: Le Hir, G., Teitler, Y., Fluteau, F., Donnadieu, Y., and Philippot, P.: The faint young Sun problem revisited with a 3-D climate-carbon model – Part 1, Clim. Past Discuss., 9, 1509-1534, doi:10.5194/cpd-9-1509-2013, 2013.
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