Killing the Faint Young Sun Paradox: An exploration of Eoarchean climate

Geological proxies indicate that early Archean Earth was not in a permanent snowball state. Otherwise, we have limited data on its atmospheric composition, how volatile cycling operated, its evolving land-sea mask, topography and ocean bathymetry, etc. At the same time Archean climate studies provide a relatively large and underexplored parameter space for full complexity General Circulation Models (GCMs). Here we model the climate of the Archean at 3.8Ga when the amount of exposed land is likely very small (e.g. Cawood et al. 2022). The ROCKE-3D (R3D; Way et al. 2017) GCM is used. It is a full-complexity fully coupled atmosphere, land and ocean model. In contrast to previous studies we utilize a full complexity atmosphere, a coupled fully dynamic ocean, and dynamic sea ice. R3D is a child of the Goddard Institute for Space Studies GCM Model_E that is used for climate change studies (Schmidt et al. 2013). We model day lengths of 12 and 18 hours in an aquaplanet setup. We use an N2 dominated atmosphere with differing amounts of CO2 and CH4 (being careful to avoid ratios that lead to climate cooling hydrocarbon hazes). Surface pressures of 1, 0.5 and 0.25 bar are modeled, given various Archean pressure proxy constraints (e.g. Som et al. 2016). We use a solar spectrum from 3.8Ga with a reduction of ~25% from modern day insolation. Perhaps unsurprisingly we discover that the tipping point from a temperate state (similar to modern day Earth) versus a snowball state is very sensitive to greenhouse gas amounts and total atmospheric pressure. We see differences in latitudinal ice extent dependent upon day length (12 vs 18 hours) for otherwise similar parameters, and that the dynamics of the climate is similar to recent work by Feulner et al. (2022). This work, alongside others such as Charnay et al. (2017)  and Feulner et al. (2023) provide a clear path to explaining why the Faint Young Sun paradox may finally be put to rest.

References:

Cawood et al. (2022) RG, 60, e2022RG000789; Charnay et al. (2017) EPSL 474, 97; Feulner et al. (2023) ESD 14, 533-547; Schmidt et al. (2013) JAMES, 6, 141-184; Som et al. (2016) NatGeo 9, 448; Way et al. (2017) ApJS. 231, 12.