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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 8, issue 2 | Copyright
Clim. Past, 8, 701-703, 2012
https://doi.org/10.5194/cp-8-701-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 Mar 2012

30 Mar 2012

Comment on "Clouds and the Faint Young Sun Paradox" by Goldblatt and Zahnle (2011)

R. Rondanelli1 and R. S. Lindzen2 R. Rondanelli and R. S. Lindzen
  • 1Department of Geophysics, University of Chile, Santiago, Chile
  • 2EAPS, MIT, Cambridge, Massachusetts, USA

Abstract. Goldblatt and Zahnle (2011) raise a number of issues related to the possibility that cirrus clouds can provide a solution to the faint young sun paradox. Here, we argue that: (1) climates having a lower than present mean surface temperature cannot be discarded as solutions to the faint young sun paradox, (2) the detrainment from deep convective clouds in the tropics is a well-established physical mechanism for the formation of high clouds that have a positive radiative forcing (even if the possible role of these clouds as a negative climate feedback remains controversial) and (3) even if some cloud properties are not mutually consistent with observations in radiative transfer parameterizations, the most relevant consistency (for the purpose of hypothesis testing) is with observations of the cloud radiative forcing. Therefore, we maintain that cirrus clouds, as observed in the current climate and covering a large region of the tropics, can provide a solution to the faint young sun paradox, or at least ease the amount of CO2 or other greenhouse substances needed to provide temperatures above freezing during the Archean.

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