Paper: astro-ph/0505245
Date: Thu, 12 May 2005 09:39:35 GMT (222kb)

Title: A climatic thermostat making Earth habitable

Authors: Peter D. Ditlevsen
Comments: 4 figures, Proceedings, NORDITA conf. Astrobiology 2004
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The mean surface temperature on Earth and other planets with atmospheres is
determined by the radiative balance between the non-reflected incoming solar
radiation and the outgoing long-wave black-body radiation from the atmosphere.
The surface temperature is higher than the black-body temperature due to the
greenhouse warming. Balancing the ice-albedo cooling and the greenhouse warming
gives rise to two stable climate states. A cold climate state with a
completelyice-covered planet, called Snowball Earth, and a warm state similar
to our present climate where greenhouse warming prevents the total glacition.
The warm state has dominated Earth in most of its geological history despite a
30 % fainter young Sun. The warming could have been controlled by a greenhouse
thermostat operating by temperature control of the weathering process depleting
the atmosphere from $CO_2$. This temperature control has permitted life to
evolve as early as the end of the heavy bombartment 4 billion years ago.

\\ ( http://arXiv.org/abs/astro-ph/0505245 , 222kb)