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Firstly Mars only receives about 43% of the energy per square metre that falls on Earth. So the greenhouse effect would have to be much stronger before temperatures could 'run away'. To my mind the term 'run away' is only valid if there is a positive feedback involved (ie CO2 caused temperature increase releases more CO2 which causes a further increase).
Secondly although Mars' atmosphere contains 9 times more CO2 than Earth it only contains about 0.001 the amount of water vapour as Earth. On Earth the most important greenhouse gas, by a long long way, is water vapour. It accounts for the great majority (figures not at hand) of our 32 degree natural greenhouse effect. This is one reason (there are others) why a doubing of CO2 concentration can not result in a doubling of our greenhouse effect. A quick, nasty back-of-an-envelope calculation suggests that if CO2 were the only greenhouse gas and the response was linear then temperatures would have risen by 9 degrees since the industrial revolution! Clearly any effect is much much smaller.
BTW the greenhouse effect on Mars is 5 degrees.
Last edited by AstralTraveller; 30-10-2008 at 06:51 PM.
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