Enhanced CO2 greenhouse to compensate for reduced solar luminosity on early Earth

CURRENT models for the evolution of the Sun require an increase in solar luminosity by 25% since the formation of the Solar System¹. Such an increase in the solar constant should have profound effects on the terrestrial climate, but there is no evidence from the fossil record of a corresponding change in the Earth's global mean temperature². This apparent conflict cannot be explained by the apparent inability of solar models to account for the low observed neutrino flux³. Even models that are forced to fit the neutrino data require a similar increase in the solar luminosity. As Newman and Rood¹ state: ``a faint young Sun is one of the most unavoidable consequences of stellar structure considerations''. We discuss here whether CO₂-H₂O in a weakly reducing atmosphere could have caused this change in the early Earth's temperature by the so-called greenhouse effect.