The faint young Sun problem revisited with a 3-D climate–carbon model – Part 1
During the Archaean, the Sun's luminosity was 18 to 25% lower than the present day. One-dimensional radiative convective models (RCM) generally infer that high concentrations of greenhouse gases (CO<sub>2</sub>, CH<sub>4</sub>) are required to prevent the early Earth...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-04-01
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| Series: | Climate of the Past |
| Online Access: | http://www.clim-past.net/10/697/2014/cp-10-697-2014.pdf |
| Summary: | During the Archaean, the
Sun's luminosity was 18 to 25% lower than the present day. One-dimensional
radiative convective models (RCM) generally infer that high concentrations of
greenhouse gases (CO<sub>2</sub>, CH<sub>4</sub>) are required to prevent the early Earth's
surface temperature from dropping below the freezing point of liquid water
and satisfying the faint young Sun paradox (FYSP, an Earth temperature at
least as warm as today). Using a one-dimensional (1-D) model, it was proposed
in 2010 that the association of a reduced albedo and less reflective clouds
may have been responsible for the maintenance of a warm climate during the
Archaean without requiring high concentrations of atmospheric CO<sub>2</sub>
(<i>p</i>CO<sub>2</sub>). More recently, 3-D climate simulations have been performed using
atmospheric general circulation models (AGCM) and Earth system models of
intermediate complexity (EMIC). These studies were able to solve the FYSP
through a large range of carbon dioxide concentrations, from 0.6 bar with an
EMIC to several millibars with AGCMs. To better understand this wide range in
<i>p</i>CO<sub>2</sub>, we investigated the early Earth climate using an atmospheric GCM
coupled to a slab ocean. Our simulations include the ice-albedo feedback and
specific Archaean climatic factors such as a faster Earth rotation rate, high
atmospheric concentrations of CO<sub>2</sub> and/or CH<sub>4</sub>, a reduced continental
surface, a saltier ocean, and different cloudiness. We estimated full
glaciation thresholds for the early Archaean and quantified positive
radiative forcing required to solve the FYSP. We also demonstrated why RCM
and EMIC tend to overestimate greenhouse gas concentrations required to avoid
full glaciations or solve the FYSP. Carbon cycle–climate interplays and
conditions for sustaining <i>p</i>CO<sub>2</sub> will be discussed in a companion
paper. |
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| ISSN: | 1814-9324 1814-9332 |