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Clim. Past Discuss., 7, 3577-3582, 2011
www.clim-past-discuss.net/7/3577/2011/ doi:10.5194/cpd-7-3577-2011 © Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 License. |
Comment on "Clouds and the Faint Young Sun Paradox" by Goldblatt and Zahnle (2011)
1Department of Geophysics, University of Chile, Santiago, Chile
2Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, 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 some of the criticism is not warranted. In particular, the criticism related to cirrus clouds being an "end member" case of possible clouds depends heavily on models that may have an inadequate representation of cirrus clouds. Present climate observations show that thin cirrus clouds (optical depth less than 10) can produce positive cloud radiative forcing. When this forcing is represented in models, resulting cirrus clouds are not necessarily realistic. Therefore, cirrus clouds that have a radiative forcing consistent with present climate observations, 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.
Citation: Rondanelli, R. and Lindzen, R. S.: Comment on "Clouds and the Faint Young Sun Paradox" by Goldblatt and Zahnle (2011), Clim. Past Discuss., 7, 3577-3582, doi:10.5194/cpd-7-3577-2011, 2011.