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Old 18th July 2010, 10:01 AM   #79
Ziggurat
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Originally Posted by wogoga View Post
What I'm disputing, is the claim that 1) radiation from the sun has been heating up the crust surface of Venus from a significantly lower temperature to its current 470C
It doesn't matter if it heated the surface from a lower temperature or just keeps it from cooling down further: the sun still provides the surface with heat. If the sun stopped shining, the surface would cool, and if the surface was magically made cooler, it would heat up.

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, and that 2) a hypothetical ground temperature of 0C would make such a heating much faster.
Of course it would. A 0C surface temperature would drastically reduce both radiative and convective heat loss, but it would still receive the same amount of incoming heat. So there would no longer be any balance between heat in and heat out, and net heat flow in = rising temperature. Your million-year lifespan for a frozen surface is an absurdity.

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It seems that the myth of a runaway greenhouse effect on Venus can be traced back to the authority of Carl Sagan. In the meantime the myth has become a dogma.

And if I'm not completely mistaken in my thermodynamic evaluation
You are completely mistaken in your thermodynamic evaluation. And what you haven't figured out is that the reasons you're wrong have nothing to do with Sagan being right, or with runaway greenhouse effects. You have made claims which don't withstand basic scrutiny.

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From the premises
  • The lowest mean crust temperature on is at crust surface
  • The highest mean atmosphere temperature is at crust surface
I conclude:
  • There is a tiny heat flow from the crust to the atmosphere
Cheers, Wolfgang
That's correct. But that tiny heat flow comes from the fact that the surface receives some heating from solar radiation. Thermal conduction from below the surface is pretty much irrelevant. The crust itself is a FAR better insulator than the atmosphere ever could be.
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