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Old 17th July 2010, 03:45 AM   #76
Critical Thinker
Join Date: Apr 2007
Posts: 334
Originally Posted by Ziggurat View Post
You overlooked the fact that the cloud layer also emits/reflects radiation downward.

As to your "cloud layer emits":
The temperature of the cloud layer (at a height of 60 to 70 km) is in the order of 30C below zero, yet ground temperature is 470C. A heat transfer from the colder to the hotter is thermodynamically impossible, also in the case of thermal radiation.

By the way, if the atmosphere under the cloud deck were transparent for thermal radiation, as you suggest, then the ground would lose substantial heat to the clouds (i.e. there would be a strong thermal radiation flow from 470C to -30C). This would entail a significant increase in the thermal-emission-surface temperature (see #55) of Venus. As higher thermal-emission-surface temperature (corresponding to higher blackbody temperature) leads to higher thermal emissions of the planet, significant cooling of the crust surface would be an inevitable outcome.
As to your "cloud layer refects":
If only 1% of the 17,000 W/m2 blackbody radiation (i.e. 170 W/m2) were emitted by the ground to the clouds, and as much as 90% of this emitted thermal radiation came back to the surface, then the resulting heat loss of 17 W/m^2 would already be as high as solar radiation reaching the ground on average.

We conclude: In the same way as a sea bed below tens or hundreds of meters of water does not significantly interact via thermal radiation with the atmosphere, the crust surface of Venus does not significantly interact via thermal radiation with its higher atmosphere.
(The pressure found on Venus's surface is high enough that the carbon dioxide is technically no longer a gas, but a supercritical fluid. The density of the air at the surface is 67 kg/m3, which is 6.5% that of liquid water on Earth.)
That 17 W/m is not the total amount of power that gets absorbed by the ground, and it's not the total power that gets emitted from the ground, it's the difference in the power the ground emits (through radiation and conduction/convection) and the power the ground absorbs from the atmosphere.

If the dogma of a runaway greenhouse effect on Venus had something to do with reality and science, then something similar to what you write here were actually a correct scientific conclusion.

Cheers, Wolfgang

If greenhouse-effect science concerning Earth is as catastrophically biased, unscientific, and illogical as the one concerning Venus, then we should remain very skeptical.
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