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Old 3rd July 2010, 01:14 PM   #55
Critical Thinker
Join Date: Apr 2007
Posts: 334
Originally Posted by wogoga View Post
What I consider relevant is atmospheric mass, not weight or pressure.
Originally Posted by CapelDodger View Post
Why, exactly?

Please, try to understand what I've written in my previous posts. I explain the high crust surface temperature of Venus by atmospheric insulation from a colder environment, and therefore the decisive parameter is a form of quantity (mass, thickness), and not pressure of the atmosphere.

Originally Posted by wogoga View Post
The high albedo on Venus is due to its clouds.
Originally Posted by CapelDodger View Post
Yes, and irrelevant. Solar radiation that is reflected away from Venus does not influence its temperature.

Albedo due to clouds may be irrelevant in your prejudiced, ideological thinking (see post #48).

An informative quote:
"The effect of clouds depends upon their type and the time of day. The more interesting and important type is the low thick clouds. At night the reflection effect is zero so the greenhouse effect and reflection of thermal radiation dominate and the low thick clouds have a warming effect. One can easily see that the reflection of thermal radiation is far more important than the greenhouse effect. The greenhouse effect could at most return 50 percent of the outgoing radiation back to the Earth. Reflection from the underside of clouds probably returns 90 percent of the radiation. The two effects are not in competition. Clouds could return 90 percent from reflection and half of the unreflected 10 percent. Thus it is easy to see why there is such a difference in temperature between a clear night and a cloudy night in the winter. Since the greenhouse effect from the atmospheric gases would be the same on a clear and a cloudy night one could say that the effect from greenhouse gases is negligible compared to the effect of low thick clouds."
Originally Posted by wogoga View Post
And if it were possible to cool down the whole planet Venus to zero degree Celsius, its temperature would remain near water freezing point over millions of years.
Originally Posted by Ziggurat View Post
Then you better get ready to retract that statement, because it's NOT simply a function of surface temperature, as I detailed here.

The surface of Venus does receive some heating from the sun. But if the surface is frozen, then it won't lose much heat from radiation, and it will lose NO heat from convection (which it currently does, which is why the adiabatic lapse rate matters). So it won't need a lot of heating to unfreeze it, and it won't last close to a million years at that temperature.

The blackbody temperature of Venus is around -40C (source), resulting a thermal emission of 163 W/m^2. Venus obviously also absorbs (nearly) the same amount of sun radiation.
(Solar irradiance: 2614 W/m^2, mean irradiance over the whole sphere: 1/4 * 2614 W/m2 = 653.5 W/m2, not reflected: 25% * 653.5 W/m2 = 163 W/m2)

The -40C can be seen as the temperature of an averaged thermal-emission-surface of Venus (around 70 km above crust surface). The thick atmosphere is able to insulate the more than 450C hot crust surface from this -40C cold radiation-surface.

And now you tell me, that such a -40C radiation-surface could thermally not be as well insulated from a crust surface of 0C, as from a crust surface of more than 450C!

Cheers, Wolfgang
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