Eric T. Wolf
climate + planets + computer models
The Early Earth
Climate of the Archean and the Faint Young Sun Paradox
Evidence from ancient sediments indicates that liquid water and primitive life were present during the Archean despite the faint young Sun. I used an atmospheric general circulation model coupled to a mixed layer ocean model to simulate the climate of the Archean Earth. Our results indicate that a weak version of the faint young Sun paradox, requiring only that some portion of the planet’s surface maintain liquid water, may be resolved with moderate greenhouse gas inventories. Thus, hospitable late Archean climates are easily obtained in our climate model.
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Furthermore, numerous changes to the Archean climate system have been suggested that may have yielded additional warming, further easing the required greenhouse gas burden. Plausible changes to the surface albedo, cloud droplet number concentrations, and atmospheric nitrogen inventory may each impart global mean warming of 3–7 K. While none of these changes present a singular solution to the faint young Sun paradox, a combination can have a large impact on climate. Global mean surface temperatures at or above 288 K could easily have been maintained throughout the entirety of the Archean if plausible changes to clouds, surface albedo, and nitrogen content occurred.
Global mean and seasonal maximum ocean temperatures from simulations of the Archean Earth. Habitable temperatures can be met within geochemical constraints on carbon dioxide, provided there is some methane. Excessively hot temperatures are probably not realistic for the Archean.
Fractal Organic Hazes
I have also studied the properties and effects of Titan-like fractal aggregate photochemical hazes and their effect on the early Earth. The fractal aggregate structure of these aerosols allows them to efficiently absorb ultraviolet radiation while remaining relatively optically thin in the visible wavelengths. This minimized so-called antigreenhouse cooling while also providing for means to protect early surface life from harmful UV (sans ozone). See also the work of Arney et al. (2016,2017) for expanded studies of the effects of fractal hazes. Finally, a fortran code to calculate fractal aggregate optical properties is available under the "Code" tab.
