Low simulated radiation limit for runaway greenhouse climates
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Title:
Low simulated radiation limit for runaway greenhouse climates
Series Title:
Nature Geoscience- Volume 6
Creator:
Colin Goldblatt
Tyler D. Robinson
Kevin J. Zahnle
David Crisp
Affiliation:
University of Victoria -- School of Earth and Ocean Sciences
University of Washington -- Astronomy Department
NASA Ames Research Center -- Space Science and Astrobiology Division
Jet Propulsion Laboratory
Publication Date:
Language:
English

Notes

Abstract:
The atmospheres of terrestrial planets are expected to be in long-term radiation balance: an increase in the absorption of solar radiation warms the surface and troposphere, which leads to a matching increase in the emission of thermal radiation. Warming a wet planet such as Earth would make the atmosphere moist and optically thick such that only thermal radiation emitted from the upper troposphere can escape to space. Hence, for a hot moist atmosphere, there is an upper limit on the thermal emission that is unrelated to surface temperature. If the solar radiation absorbed exceeds this limit, the planet will heat uncontrollably and the entire ocean will evaporate—the so-called runaway greenhouse. Here we model the solar and thermal radiative transfer in incipient and complete runaway greenhouse atmospheres at line-by-line spectral resolution using a modern spectral database.We find a thermal radiation limit of 282Wm􀀀2 (lower than previously reported) and that 294Wm􀀀2 of solar radiation is absorbed (higher than previously reported). Therefore, a steam atmosphere induced by such a runaway greenhouse may be a stable state for a planet receiving a similar amount of solar radiation as Earth today. Avoiding a runaway greenhouse on Earth requires that the atmosphere is subsaturated withwater, and that the albedo effect of clouds exceeds their greenhouse effect. A runaway greenhouse could in theory be triggered by increased greenhouse forcing, but anthropogenic emissions are probably insufficient.

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Florida International University
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