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| Titel |
3d-simulations of the Archean climate: Solutions to the ‘faint young Sun problem' demand higher greenhouse gas concentrations than previously thought |
| VerfasserIn |
Hendrik Kienert, Georg Feulner, Vladimir Petoukhov |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250075432
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| Zusammenfassung |
| During the Archean eon (3.8–2.5 billion years ago), the Sun was up to 25% less luminous
than today, yet there is convincing evidence that the Earth’s ocean surface was not
completely frozen during this time period. As the Earth’s rotation rate was higher and the
continental fraction smaller than today, the climate system and, particularly, its
response to changes in radiation were different from the present-day climate state. This
has significant implications for the effect of higher greenhouse gas concentrations
which are expected to play a crucial role in solving this ‘faint young Sun problem’.
Here, we present the first comprehensive 3-dimensional simulations of the Archean
climate using a fully coupled ocean-atmosphere-sea-ice model. Our simulations thus
include processes as the sea-ice albedo feedback and the higher rotation rate of
the Earth. We find that a CO2 partial pressure of 0.4 bar is needed to prevent the
early Archean Earth from falling into a ‘snowball state’. This value is significantly
higher than estimates of about 0.06 bar based on previous studies with 1-dimensional
radiative-convective models. Our results also suggest that currently favoured CO2/CH4
greenhouse solutions could be in conflict with geochemical constraints emerging
for the middle and late Archean. In order to gain a deeper understanding of the
underlying mechanisms determining the critical partial pressure for the early Archean,
we further present the key characteristics of three simulated climate states which
differ in their atmospheric CO2 content: one of them is ice-free, one has about the
same mean surface air temperature of 288 K as today’s Earth and the third one
is the coldest stable state in which there is still an area with liquid surface water
(i.e., the critical state at the transition to a ‘snowball Earth’). We find that the most
important aspects leading to the higher critical CO2 amount are albedo changes due to
growing sea-ice as well as a reduction of meridional heat transport which results in a
steeper latitudinal temperature profile. The dependence of the surface albedo on
global mean temperature under early Archean boundary conditions is found to be
approximately linear for partially frozen ocean surfaces. We suggest to use this relation
derived from our set of simulations as a simple parameterisation of the ice-albedo
feedback in 1-dimensional models in which the effect has so far been neglected. |
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