The Venus CO2 "runaway warming" fallacy

There is a good post by Steve Goddard over at WUWT on the Venus CO2 “runaway” warming fallacy.  Check it out.  Conclusion:

“So why is Venus hot?  Because it has an extremely high atmospheric pressure.  The atmospheric pressure on Venus is 92X greater than earth.  Temperatures in Earth’s atmosphere warm over 80C going from 20 kPa (altitude 15km) to 100 kPa (sea level.)  That is why mountains are much colder than the deserts which lie at their base.

The atmospheric pressure on Venus is greater than 9,000 kPa.  At those pressures, we would expect Venus to be very hot. Much, much hotter than Death Valley.

Wikipedia typifies the illogical “runaway greenhouse” argument with this statement.

Without 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.

No it wouldn’t. 9000 kPa atmospheric pressure would occur on earth at an altitude many miles below sea level.  No such place exists, but if it did – it would be extremely hot, like Venus. A back of the envelope estimate – temperatures on earth increase by about 80C going from 20 to 100 kPa, so at 9,000 kPa we would expect temperatures to be in the ballpark  of :

20C + ln(9000/(100-20)) *80C = 400C

This is very close to what we see on Venus.  The high temperatures there can be almost completely explained by atmospheric pressure – not composition. If 90% of the CO2 in Venus atmosphere was replaced by Nitrogen, it would change temperatures there by only a few tens of degrees.

How did such bad science become “common knowledge?” The greenhouse effect can not be the cause of the high temperatures on Venus. “Group Think” at it’s worst, and I am embarrassed to admit that I blindly accepted it for decades.

Blame CO2 first – ask questions later.”  “Hyperventilating on Venus


2 Responses to “The Venus CO2 "runaway warming" fallacy”

  1. litesong Says:

    A back of the envelope estimate – temperatures on earth increase by about 80C going from 20 to 100 kPa, so at 9,000 kPa we would expect temperatures to be in the ballpark of :

    20C + ln(9000/(100-20)) *80C = 400C
    litesong wrote:
    Since you are extrapolating from earth climatology, your calculations include infra-red energy absorbing water vapor effects. Venus has almost no water.
    Even including water vapor in your back of the envelop calcs still leave you very short of Venus actual temperatures which are a maximum of 477 degC & minimum of 447 degC.
    Also, unlike Earth, these max-min temperatures do not come from the dayside of Venus vs. nightside of Venus or equatorial vs. polar Venus temperatures. which are the same in all cases. The max-min temperatures are due only to elevation differences.
    Your oil industry based bias shows major & continuous errors.

  2. Albert Says:

    If you make a calculation by using the general equation of gases, it is clear that Venus’ temperatures come from the very high pressure of atmosphere on surface.

    General equation is:
    PV = nRT

    where P is pressure in atm. which is 92 bars on Venus surface
    V is volume in liters* m^3, which is 1,000
    n is number of moles* cubic meter, and it is calculated as M (real mass) /atomic mass,
    on Venus you have a real mass of 67,000 gr CO2*cubic meter, and – as atomic mass of CO2 is 44 – you have 67,000/44 = 1522 moles * cubic meter.
    R is the universal constant of gases, which is 0.082

    Therefore, by introducing magnitudes, you have
    T = 92 * 1000/ 1522 * 0.082
    T= 92,000/124 = 737°Kelvin which is 464 ° C and is is exactly the temperature you find on the Venus surface.

    But this means that the temperature on Venus surface is so high JUST for the pressure of 92 atmosphere, forget “greeenhouse effect”!
    It is neither greenhouse effect nor CO2, it is just for the pressure….

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