Low simulated radiation limit for runaway greenhouse climates

Colin Goldblatt, Tyler D. Robinson, Kevin J. Zahnle, David Crisp

Research output: Contribution to journalArticlepeer-review

94 Scopus citations

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 282 W m -2 (lower than previously reported) and that 294 W m -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 with water, 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.

Original languageEnglish (US)
Pages (from-to)661-667
Number of pages7
JournalNature Geoscience
Volume6
Issue number8
DOIs
StatePublished - Aug 2013
Externally publishedYes

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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