TY - JOUR
T1 - Influence of Carbon Dioxide Clouds on Early Martian Climate
AU - Mischna, Michael A.
AU - Kasting, James F.
AU - Pavlov, Alex
AU - Freedman, Richard
N1 - Funding Information:
The authors thank Gary Hansen for the use of his CO2 refraction indices and Tom Ackerman for help with the radiative transfer. Funding for this work was provided by an American Meteorological Society/Space Systems Loral Graduate Fellowship, a College of Earth and Mineral Sciences, Pennsylvania State University/Wilson Graduate Fellowship, a Pennsylvania Space Grant Consortium Graduate Fellowship, and an NSF/LExEn grant (ATM-9714161).
Copyright:
Copyright 2004 Elsevier Science B.V., Amsterdam. All rights reserved.
PY - 2000/6
Y1 - 2000/6
N2 - Recent studies have shown that clouds made of carbon dioxide ice may have warmed the surface of early Mars by reflecting not only incoming solar radiation but upwelling IR radiation as well. However, these studies have not treated scattering self-consistently in the thermal IR. Our own calculations, which treat IR scattering properly, confirm these earlier calculations but show that CO2 clouds can also cool the surface, especially if they are low and optically thick. Estimating the actual effect of CO2 clouds on early martian climate will require three-dimensional models in which cloud location, height, and optical depth, as well as surface temperature and pressure, are determined self-consistently. Our calculations further confirm that CO2 clouds should extend the outer boundary of the habitable zone around a star but that there is still a finite limit beyond which above-freezing surface temperatures cannot be maintained by a CO2-H2O atmosphere. For our own Solar System, the absolute outer edge of the habitable zone is at ~2.4 AU.
AB - Recent studies have shown that clouds made of carbon dioxide ice may have warmed the surface of early Mars by reflecting not only incoming solar radiation but upwelling IR radiation as well. However, these studies have not treated scattering self-consistently in the thermal IR. Our own calculations, which treat IR scattering properly, confirm these earlier calculations but show that CO2 clouds can also cool the surface, especially if they are low and optically thick. Estimating the actual effect of CO2 clouds on early martian climate will require three-dimensional models in which cloud location, height, and optical depth, as well as surface temperature and pressure, are determined self-consistently. Our calculations further confirm that CO2 clouds should extend the outer boundary of the habitable zone around a star but that there is still a finite limit beyond which above-freezing surface temperatures cannot be maintained by a CO2-H2O atmosphere. For our own Solar System, the absolute outer edge of the habitable zone is at ~2.4 AU.
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U2 - 10.1006/icar.2000.6380
DO - 10.1006/icar.2000.6380
M3 - Article
C2 - 11543507
AN - SCOPUS:0034200546
VL - 145
SP - 546
EP - 554
JO - Icarus
JF - Icarus
SN - 0019-1035
IS - 2
ER -