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| Titel |
On the stability of low-latitude sea-ice edges in a comprehensive coupled climate model |
| VerfasserIn |
A. Voigt, D. S. Abbot |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250059097
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| Zusammenfassung |
| The Snowball Earth hypothesis assumes that a strong ice-albedo feedback inhibits stable
low-latitude sea-ice edges. In contrast, we recently proposed the "Jormungand" mechanism
that allows stable low-latitude ice edges in atmosphere-only climate models without
continents and ocean heat transport (Abbot et al., 2011). These low-latitude sea-ice edges are
possible by virtue of net evaporation in the subtropics and a low albedo for snow-free sea ice,
because these two factors combine such as to strongly weaken the ice-albedo feedback in the
subtropics.
Here, we show that the Jormungand mechanism in principle also works in coupled
climate simulations with ECHAM5/MPI-OM when we use a low bare sea-ice albedo and
disable sea-ice dynamics. These simulations apply Marinoan boundary conditions (635
Million years before present) and, due to the Jormungand mechanism, produce stable
low-latitude sea-ice edges at 5-10o. Nevertheless, when we take into account sea-ice
dynamics, the sea-ice edge becomes unstable once it passes 20o. This destabilizing effect of
sea-ice dynamics results from strong equatorward wind-induced sea-ice advection in the
Hadley cell region.
Moreover, we find that sea-ice dynamics promote Snowball initiation. Without sea-ice
dynamics, Snowball initiation requires a CO2 reduction to 4 ppmv, while a reduction to 204
ppmv is sufficient when sea-ice dynamics are included. Because climate models
differ in their representation of sea-ice dynamics, our results might help to explain
the reported climate model dependence of both the radiative forcing needed for
Snowball initiation and the sea-ice latitude at which the collapse to a Snowball
occurs.
References:
Abbot, D. S, A. Voigt, and D. Koll (2011), The Jormungand global climate state
and implications for Neoproterozoic glaciations, J. Geophys. Res., 116, D18103,
doi:10.1029/2011JD015927. |
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