Paratus
Lifer
- Jun 4, 2004
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Look, its quite simple when comparing Venus to Earth. Just ask yourself a simple question. What would it be like on Earth if tomorrow the atmospheric pressure increased 90X. Hint: the answer is with a formula already mentioned more than once in recent posts. No convection required, no more CO2 required. This should make it clear why Venus' temperature is the way it is and why it is so hot compared to Earth.
Yes let's take a look at that thought experiment. I agree that if we magically increased the pressure 90X the temperature would roughly be equivalent to the temperature on Venus. So again I agree with you in this point.
Here's my point and it's one you and dphantom continually miss.
What's the temperature and pressure of the Earth in this thought experiment the next day? Next year? Next Millenia?
Here's a hint. This thought experiment is not in thermal equilibrium.
Compare:
The Earth receives ~340W/m^2 (Watts per Meter squared - a watt is a unit of energy or heat over a length of time) over the entire surface of the Earth facing the sun. The Earths average temperature is about 16C. At this temperature the Earth radiates back into space at about 339.4W/m^2. Basically in equilibrium.
Now our thought experiment.
The Earth still receives 340W/m^2 from the sun, but due to our magic increase in pressure the average temperature is now 450C. The Stefan-Boltzmann equation gives the power at which a body radiates to space. :
Power/Area=Stefan-Boltzmann Constant x Temperature ^ 4.
For our example earth it's now radiating away over 17000 W/m^2. This is more than the 340 it receives. Our hot dense atmosphere is losing heat at a prodigious rate.
When matter radiates away heat it loses temperature. When that matter is a hot gas it looses pressure by PV=nRT as it loses heat. Unless our thought experiment includes an excellent insulator our hot high pressure atmosphere will shortly be a cold low pressure atmosphere.
Do you get it now? Venus cannot maintain a hot high pressure atmosphere without a massively good insulator between it and space. The only thing that's is between the atmosphere and space is the atmosphere - the atmosphere that is 97% CO2.
This is why you are wrong and so is the guy on watts up with that where you got this from.
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