Encyclopedia of Paleoclimatology and Ancient Environments

2009 Edition
| Editors: Vivien Gornitz

Faint Young Sun Paradox

  • James Farquhar
Reference work entry
DOI: https://doi.org/10.1007/978-1-4020-4411-3_86

Standard models of solar evolution indicate that the intensity of solar radiation should have increased by about 25–30% over the 4.6 billion year duration of geologic time (Gilliland, 1989). The phrase “faint young Sun” was coined by Sagan and Mullen (1972) to describe the implications of these standard models for Earth’s climate, because early in the Sun’s lifetime, the radiation reaching a planet like Earth today (with both similar orbit and amount of greenhouse forcing) would not have been sufficient to prevent the planet’s average temperature from dropping below the freezing point of water. Sagan and Mullen evaluated the implications of the faint young Sun paradox in the context of geologic evidence from early in Earth’s history that rules out a long-lived frozen state. They argued that a greater amount of greenhouse gas forcing was required to offset the lower solar luminosity of the young Sun. The faint young Sun hypothesis is still being evaluated today and many hypotheses...

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© Springer-Verlag 2009

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  • James Farquhar

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