Dependence of the runaway greenhouse threshold on the surface water distribution for Earth-like planets
Abstract
Liquid water is one of the important materials that affect the climate and habitability on a terrestrial planet. Liquid water entirely vaporizes when planets receive insolation above a certain critical value, which is called the runaway greenhouse threshold. This threshold forms the inner most limit of the habitable zone. In general, it is assumed that an Earth-like planet with oceans is a potentially habitable planet. Such a planet is implicitly assumed to be a planet whose surface is covered with oceans. Thus, most of previous studies estimated the runaway greenhouse threshold for such planets. Abe et al. (2011) suggest that the runaway greenhouse threshold significantly depends on the distribution of water on the surface. The distribution of the surface water is determined by the surface topography, the surface water flow and the transport of water vapor in the atmosphere. Here, we investigate the effects of the distribution of surface water on the runaway greenhouse threshold for Earth-sized planets using a three-dimensional dynamic atmosphere model. We recognized two climate regimes: the land planet regime, which has dry low latitude and wet high latitude regions, and the aqua planet regime, which is globally wet. We showed that each regime is controlled by the width of the Hadley circulation, the amount of surface water, and the planetary topography. We found that the runaway greenhouse threshold continuously varies with the surface water distribution from about 130% (an aqua planet) to 180% (the extreme case of a land planet) of the present insolation at Earth's orbit. Our results indicate that the inner edge of the habitable zone is not a single sharp boundary, but a border whose location varies depending on planetary surface condition, such as the amount of surface water.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.P42A..08K
- Keywords:
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- 5210 Planetary atmospheres;
- clouds;
- and hazes;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 5215 Origin of life;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 5225 Early environment of Earth;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 6207 Comparative planetology;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS