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. 2009 Jun 16;106(24):9576-9.
doi: 10.1073/pnas.0809436106. Epub 2009 Jun 1.

Atmospheric pressure as a natural climate regulator for a terrestrial planet with a biosphere

King-Fai Li  1 , Kaveh Pahlevan, Joseph L Kirschvink, Yuk L Yung
Affiliations

Atmospheric pressure as a natural climate regulator for a terrestrial planet with a biosphere

King-Fai Li et al. Proc Natl Acad Sci U S A. .

Abstract

Lovelock and Whitfield suggested in 1982 that, as the luminosity of the Sun increases over its life cycle, biologically enhanced silicate weathering is able to reduce the concentration of atmospheric carbon dioxide (CO(2)) so that the Earth's surface temperature is maintained within an inhabitable range. As this process continues, however, between 100 and 900 million years (Ma) from now the CO(2) concentration will reach levels too low for C(3) and C(4) photosynthesis, signaling the end of the solar-powered biosphere. Here, we show that atmospheric pressure is another factor that adjusts the global temperature by broadening infrared absorption lines of greenhouse gases. A simple model including the reduction of atmospheric pressure suggests that the life span of the biosphere can be extended at least 2.3 Ga into the future, more than doubling previous estimates. This has important implications for seeking extraterrestrial life in the Universe. Space observations in the infrared region could test the hypothesis that atmospheric pressure regulates the surface temperature on extrasolar planets.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
U.S. Standard Tropical Atmosphere profiles used in this work. Note that 1 mb = 100 Pa.
Fig. 2.
Fig. 2.
Absorption spectra at the top of the atmosphere in the present-day Earth for β = 1 (blue) and 0.2 atm (orange), showing the effect of pressure broadening. The spectral resolution is 20 cm−1. The major species responsible for absorption are labeled. (Inset) The total radiative forcing due to the absorption by greenhouse gases as a function of β.
Fig. 3.
Fig. 3.
The evolution of surface pressure and temperature and the partial pressure of CO2 in the model as the solar luminosity evolves in the next 2.8 Ga from present. Before 0.9 Ga (dashed line), the quantities evolve as described in Caldeira and Kasting (8). After 0.9 Ga, the surface temperature and the partial pressure of CO2 at the surface (PCO2) are kept constant while the atmospheric pressure is lowered to compensate the temperature increase due to the increase in solar luminosity (see Models and Results). At ≈2.3 Ga (dash-dotted line), runaway greenhouse occurs, signaling the ultimate fate of the biosphere.
Fig. 4.
Fig. 4.
The emission spectra of the Earth's atmosphere corresponding to the 3 stages shown in Fig. 3. Blue: Stage A with 330 ppm CO2 under 1 atmospheric pressure; red: Stage B with 10 ppm CO2 under 1 atmospheric pressure; and, green: Stage C with 10 ppm CO2 under 0.08 atmospheric pressure.
See this image and copyright information in PMC

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