Warming the early earth—CO2 reconsidered |
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Authors: | Philip von Paris Heike Rauer J. Lee Grenfell Beate Patzer Barbara Stracke Franz Schreier |
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Affiliation: | a Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt, Rutherfordstr. 2, 12489 Berlin, Germany b Zentrum für Astronomie & Astrophysik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany c Institut für Methodik der Fernerkundung, Deutsches Zentrum für Luft- und Raumfahrt, Münchener Str. 20, 82234 Wessling, Germany |
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Abstract: | Despite a fainter Sun, the surface of the early Earth was mostly ice-free. Proposed solutions to this so-called “faint young Sun problem” have usually involved higher amounts of greenhouse gases than present in the modern-day atmosphere. However, geological evidence seemed to indicate that the atmospheric CO2 concentrations during the Archaean and Proterozoic were far too low to keep the surface from freezing. With a radiative-convective model including new, updated thermal absorption coefficients, we found that the amount of CO2 necessary to obtain 273 K at the surface is reduced up to an order of magnitude compared to previous studies. For the late Archaean and early Proterozoic period of the Earth, we calculate that CO2 partial pressures of only about 2.9 mb are required to keep its surface from freezing which is compatible with the amount inferred from sediment studies. This conclusion was not significantly changed when we varied model parameters such as relative humidity or surface albedo, obtaining CO2 partial pressures for the late Archaean between 1.5 and 5.5 mb. Thus, the contradiction between sediment data and model results disappears for the late Archaean and early proterozoic. |
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Keywords: | Faint young Sun problem Earth&mdash atmospheres Composition&mdash radiative transfer |
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