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www.clim-past-discuss.net/6/1337/2010/
doi:10.5194/cpd-6-1337-2010
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Uncertainty of the CO2 threshold for melting a hard Snowball Earth
Dept. of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China
Abstract. One of the critical issues of the Snowball Earth hypothesis is how high level of CO2 is required for triggering the deglaciation. Using Community Atmospheric Model version 3 (CAM3), we study the problem for the CO2 threshold. Our simulations show large differences from previous results (Pierrehumbert, 2004, 2005). At 0.2 bars of CO2, the January maximum near-surface temperature is about 268 K, about 13 K higher than that in Pierrehumbert (2004, 2005), but lower than the value of 270 K for 0.1 bar of CO2 in Le Hir et al. (2007). It is found that the diversity of simulation results is mainly due to model sensitivity of greenhouse effect and longwave cloud forcing to increasing CO2. At 0.2 bar of CO2, CAM3 yields 117 Wm −2 of clear-sky greenhouse effect and 32 Wm−2 of longwave cloud forcing, versus only about 77 Wm−2 and 10.5 Wm−2 in Pierrehumbert (2004, 2005), respectively. CAM3 has comparable clear-sky greenhouse effect to that in Le Hir et al. (2007), but lower longwave cloud forcing. CAM3 also produces much stronger Hadley cells than in Pierrehumbert (2005).
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Notice on Discussion StatusCitation: Hu, Y. and Yang, J.: Uncertainty of the CO2 threshold for melting a hard Snowball Earth, Clim. Past Discuss., 6, 1337-1350, doi:10.5194/cpd-6-1337-2010, 2010. Bibtex EndNote Reference Manager XML
