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| Titel |
Model-dependence of the CO2 threshold for melting the hard Snowball Earth |
| VerfasserIn |
Y. Hu, J. Yang, F. Ding, W. R. Peltier |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 7, no. 1 ; Nr. 7, no. 1 (2011-01-10), S.17-25 |
| Datensatznummer |
250004392
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| Publikation (Nr.) |
 copernicus.org/cp-7-17-2011.pdf |
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| Zusammenfassung |
One of the critical issues of the Snowball Earth hypothesis is the CO2
threshold for triggering the deglaciation. Using Community Atmospheric Model
version 3.0 (CAM3), we study the problem for the CO2 threshold. Our
simulations show large differences from previous results (e.g.
Pierrehumbert, 2004, 2005; Le Hir et al., 2007). 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
difference of simulation results is mainly due to model sensitivity of
greenhouse effect and longwave cloud forcing to increasing CO2. At 0.2
bars 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 that in Pierrehumbert (2005).
Effects of pressure broadening and collision-induced absorption are also
studied using a radiative-convective model and CAM3. Both effects
substantially increase surface temperature and thus lower the CO2
threshold. The radiative-convective model yields a CO2 threshold of
about 0.21 bars with surface albedo of 0.663. Without considering the
effects of pressure broadening and collision-induced absorption, CAM3 yields
an approximate CO2 threshold of about 1.0 bar for surface albedo of
about 0.6. However, the threshold is lowered to 0.38 bars as both effects
are considered. |
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