[ExI] Global Temperatures to Decrease

[Lee Corbin]

Damien asks a most ingenious and relevant question:

> Spike wrote:
>
>>With warming, it appears to me there is a rock solid feedback mechanism that
>>prevents the planet from ever getting too warm: Stefan Boltzmann's law (
>>http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/stefan.html ) which causes
>>the earth to radiate heat into space as a function of the fourth power of
>>the temperature (and yes I know the earth isn't exactly a blackbody, but the
>>P = 5.67E-8eA(T^4-Tc) equation still works.)
>
> And yet, strangely, this law is apparently unknown on Venus.
>
> What am I missing? (Yeah, it's closer to the Sun; and?)

Great question. And as the sun gradually warms over the next 500 million
years (the limit at which present LAWKI can exist, and assuming nature
(sans man, of course) does not evolve to cope with the increase, would
the same fate be in store for the Earth?

Now wikipedia on Venus does say

<The principal difference between the two planets is the lack
of plate techtonics on Venus, likely due to the dry surface and
mantle. This results in reduced heat loss from the planet,
preventing it from cooling and providing a likely explanation
for its lack of an internally generated magnetic field.>

But would this really be enough to do it?  Because the
article also says

Because of the lack of any moisture on Venus, there is almost no relative humidity (no more than 1%) on the surface, creating a heat 
index of 450 °C to 480 °C. Cloud structure in Venus's atmosphere, revealed by ultraviolet observations Cloud structure in Venus's 
atmosphere, revealed by ultraviolet observations

<Studies have suggested that several billion years ago Venus's
atmosphere was much more like Earth's than it is now, and that
there were probably substantial quantities of liquid water on the
surface, but a runaway greenhouse effect was caused by the
evaporation of that original water, which generated a critical
level of greenhouse gases in its atmosphere>

Hmm, but yet further

<In the absence of the greenhouse effect caused by the carbon
dioxide in the atmosphere, the temperature at the surface of
Venus would be quite similar to that on Earth.>

But I don't have patience right now to read through the
rest of http://en.wikipedia.org/wiki/Venus

Lee