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Old 08-06-2013, 10:24 AM
Lumpy Lumpy is online now
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How hot would Venus be without the greenhouse effect?

If Venus didn't have a very thick envelope of carbon dioxide- say it had 1 standard atmosphere of nitrogen- how hot would it be?
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Old 08-06-2013, 10:44 AM
aNewLeaf aNewLeaf is offline
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About as much hotter than Earth as Earth is compared to Mars, is my first guess.
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Old 08-06-2013, 12:00 PM
leahcim leahcim is online now
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An effective temperature (assuming Venus had an albedo of zero and no atmosphere) can be derived using the Stefan-Boltzmann law, which is based on the assumption that the planet will absorb all solar radiation incident on it, and rise in temperature until the thermal radiation it emits is enough to dispose of all that power.

Using the derivation that that article uses for the Earth, but with Venus' numbers gives an effective temperature of about 329K (55.9 C). As is noted in the article, there is a downward adjustment for non-zero albedo, and and upward adjustment because of the atmosphere, but that gives a ball park estimate.
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Old 08-06-2013, 07:34 PM
ralph124c ralph124c is offline
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Why is the Venutian atmosphere so dense? The earth is a lalrger mass than Venus-and our atmosphere is much thinner. Why hasn't the Venutian atmosphere boiled off to space (and be about the same density as the earth's).
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Old 08-06-2013, 07:59 PM
njtt njtt is offline
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Quote:
Originally Posted by ralph124c View Post
Why is the Venutian atmosphere so dense? The earth is a lalrger mass than Venus-and our atmosphere is much thinner. Why hasn't the Venutian atmosphere boiled off to space (and be about the same density as the earth's).
It is largely carbon dioxide, which is a much heavier gas than the nitrogen and oxygen that make up most of Earth's atmosphere.

If it wasn't for plants eating up the CO2 and pooping out oxygen, our atmosphere would no be much different.
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Old 07-12-2014, 01:49 PM
smarter smarter is offline
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The answer

About 80 degrees celsius, or 353 degrees Kelvin.


You do this by seeing how many times further away the Earth is from the sun. Then you take that number (1.38251), and multiply it by earth's temperature if it didn't have greenhouse gasses(255k). The answer is 353 degrees kelvin, or 80 degrees celsius.

So if you are wondering the greenhouse gasses are responsible for making Venus 384 degrees warmer than it already is...now that is a hot topic
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Old 07-12-2014, 03:43 PM
Chronos Chronos is offline
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Venus actually has about the amount of atmosphere you'd expect for its mass and distance from the Sun. The better question is why Earth's (and Mars') atmosphere is so thin.
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Old 07-13-2014, 09:38 AM
MikeS MikeS is online now
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Quote:
Originally Posted by smarter View Post
About 80 degrees celsius, or 353 degrees Kelvin.


You do this by seeing how many times further away the Earth is from the sun. Then you take that number (1.38251), and multiply it by earth's temperature if it didn't have greenhouse gasses(255k). The answer is 353 degrees kelvin, or 80 degrees celsius.

So if you are wondering the greenhouse gasses are responsible for making Venus 384 degrees warmer than it already is...now that is a hot topic
This derivation doesn't work, even in the absence of greenhouse gases. According to the Stefan-Boltzmann Law (mentioned upthread), the proportionality works out to

(temperature in Kelvin)4 * (radius of the planet)2 is inversely proportional to (distance from planet to star)2

for planets orbiting around the same star (and with the same albedo). For Venus and the Earth, the sizes of the two planets are about the same, so the temperature in Kelvin on Venus will be inversely proportional to the square root of the distance to the Sun, not the distance itself.

Last edited by MikeS; 07-13-2014 at 09:38 AM..
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