## Calculating The Greenhouse Effect On Venus

Real Climate and others like to use the “CO2 doubling rule” to calculate climate sensitivity.  Every doubling of CO2 is supposed to produce something like 2.5C temperature rise.

That tells us that Venus is about 29 degrees warmer than Earth. Only off by 400+ degrees.

Obviously the high temperatures on Venus are not due to the greenhouse effect, yet our clueless friends (followers of Sagan) keep on insisting that it is.

Just having fun
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### 25 Responses to Calculating The Greenhouse Effect On Venus

1. mkelly says:

If IPCC formula of dF=5.35 ln(C/Co) is universal then Venus at vertually 100% CO2 could be said to have gone from 1 ppm to 1,000,000 ppm.

ln 1000000 = 13.815
13.815 * 5.35 = 73.9 W/m2

I don’t believe this amount can get anything to the temperature of Venus.

• Scott says:

Don’t use ppm, as it is relative to the atmospheric pressure. Use the partial pressure (which for Venus, just assume the total pressure and it’ll be close enough).

I’d imagine that one should make a pathlength correction for the depth of Venus’ atmosphere as well.

-Scott

• Double it a few more times and then subtract H20. It is a wash.

Are you saying that the path length is a function of the high CO2 content? ;^)

2. ChrisD says:

Would the same doubling factor apply to a planet that is 40 million kilometers closer to the sun?

That is a question, not a snide remark. I don’t know the answer.

• Venus is covered with white clouds, and it turns out that the increase in albedo at the TOA almost exactly negates the increased solar energy. Ever noticed how bright Venus is? It is because the clouds reflect the sunlight.

• Amino says:

Ever notice how dull some who persist to believe global warming are? It is because their heads reflect knowledge.

• ChrisD says:

Above, I asked if the same sensitivity applies to Earth and Venus.

So, I did some research and asked some questions, and the answer is a resounding “No.” It’s obvious when you think about it: Sensitivity is a function not just of CO2 concentration but also of feedbacks (otherwise it wouldn’t be so hard to pin down). The feedbacks on Earth and Venus are completely different.

So, the 2.5degC value for sensitivity is for Earth only and is totally irrelevant to Venus. The temp of Venus can be fully accounted for by standard radiative transfer calculations (atking the sulfur dioxode clouds into account).

Move along folks, nothing to see here.

• ChrisD says:

Oy.

“atking the sulfur dioxode clouds into account”

should be

“taking the sulfuric acid clouds into account”

3. Ted A says:

The US Venus probes indicated that at an altitude where pressure was 1 bar the temp. was within a few degrees of earth temp. So ask an engineer who designs diesel engines what the temp would be at 90x compression ratio(90 bars). His answer would be very close to the surface temp. of Venus.
Haven’t these “scientists” ever heard of adiabatic heating?

• Amino says:

Well, science goes out the window most of the time when you’re talking global warming.

4. Scarlet Pumpernickel says:

Mars is 95% CO2, pretty cold planet though 😛

Funny how Mars has no clouds and Venus does?

• Jimash says:

Percentages aside, Venus has MUSH more atmosphere than Mars, which is very thin in the atmosphere department.
The pressure on VEnus is immensely more than on Earth while that on Mars is much less.
And I was pretty sure that there were clouds of some kind of sulphur on Venus contributing to its golden color.
That the surface is a quicky pizza oven, is the next to last fact that I know about Venus.
The last fact is that some impact collision or cataclysm turned around its rotation to opposite that of the other planets.

• Jimash says:

Mush=much. lol facepalm pimf ( oh no pimf here)
Bedtime for Jimmy.

• ChrisD says:

The atmosphere of Mars is very, very thin. The atmosphere of Venus is very, very dense. Makes a big difference.

5. Dave says:

You do realize that the formula you are using is an approximation that only holds for a limited concentration range, don’t you?

Basic absorption lesson: any given absorption line results in absorption that is linear at low concentrations. However, at higher concentrations the center of the line begins to saturate, and line broadening and other effects are required for continued absorption increases: thus, absorption becomes less than linear. In the case of CO2, given the current saturation state of the existing most prominent lines, the absorption rate at 380 ppm is approximately logarithmic with increasing concentration.

However, CO2 has a number of very minor lines. The absorption of these lines grows linearly, but at 380 ppm they are tiny, so can be ignored. But as the nature of a logarithmic function results in the major lines contributing less and less with each added doubling, the minor lines eventually become major contributors… at this point, CO2 absorption as a function of concentration becomes more than logarithmic again, indeed, approaching linearity at certain concentrations.

Maybe you can play around with Modtran if you want to get some intuition for this kind of behavior. In any case, what it comes down to is that you are wrong on Venus, and standard atmospheric physical explanations that place radiative trapping by CO2 at the center of the explanation for Venus’ surface temperatures are not wrong.

• Yes, the broadening fills in some of the regions that are missing due to the lack of water vapour on Venus.

6. Amino says:

Good thing Venus has as much h2o in its atmosphere as earth’s so it makes it a fair comparison. And of course all other factors are comparable too. Using what is going on on Venus gives us a perfect example of what is going to happen on earth from fossil fuels. No chance for stopping it. It’s not a matter of “if” but “when”.

sarc off.

7. Amino says:

The core of the sun is hot. The core of the earth is hot, it’s like millions of degrees* there. So what’s going on with the sun is going to happen on earth too because we use fossil fuels.

If 10:10 had made a movie about children burning to death that would have been the best way to raise awareness while making people laugh. As it is, blowing them up was off the mark. And that’s why everyone was upset.

Note to 10:10 :

Make a movie about burning children. Good luck.

yes, sarc off—for god sakes folks, why did i have to make sure to add ‘sarc off’ at the end????

* science from Al Gore

8. papertiger says:

What would the temperature on Mars be without the greenhouse effect?

And shouldn’t the absorbtion lines be pretty freaking fat, considering that Martian atmosphere is approaching 100% co2 consentration?

9. Albert says:

I’m an engineer, and I can tell you that Venus temperatures are TOTALLY due to HIGH PRESSURES, around 92 bars, “greenhouse effect” is just a bogus theory, even for Venus.
Many people are not familiar with calculations, but let’s consider the following data (taken from NASA’s website “Venusfactsheet”
http://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html)

1) On Venus solar irradiance is 2613 W/m^2, which should give a max. “balckbody” emissivity/ temperature around 190° C, and NOT 460° C and more, as you find on Venus surface.

2) Most of solar irradiance does not reach at all Venus surface, because there’s a very high albedo, more than 60%, due to the thickness of Venus vapors on surface.

3) Venus rotates very slowly, one day/night on Venus is lasting around 120 days/nights here on Earth, so the dark emisphere does not receive any solar radiation for 120 days, however on Venus surface temperatures are the same BOTH on dark and on radiated emishpere. Moreover, on Venus surface winds are blowing very slowly, around 0.30/1 meter/sec. , and it is impossible that heat of radiated emisphere could be trasmitted to the dark emisphere by orizontal convection through the winds.
You have strong frozen winds, but JUST at 65 km. up, where temperatures are just – 30° C and pressures are very low, but those winds don’t reach at all Venus’ surface.

4) Finally, it is impossible that CO2 gases (which make 96.5% of Venus atmpshere) and “greenhouse effect” could explain that temperatures – even on solar radiated emisphere – could raise from 190° C up to 460°-480° C.
Remember, an inert body like a gas cannot increase the temperatures by “backradiation”, because a gas cannot send back more than 100% of thermal energy that is receiving, according to irradiance physical laws, and 2nd law of thermodynamics (a colder body cannot raise the temperature of an hotter body, without external work. But solar “work” is always the same, and just for 190° C max.).
Therefore, on Venus gases cannot make temperatures higher than 190° C (and on radiated emisphere only!)

5) The reason why Venus temperatures are so high is JUST the huge mass (4.8 x 10 ^20 kg) of Venus’ atmosphere, which is 96 times Earth’s mass atmosphere (around 5 x 10 ^ 18 kg.) and the huge pressures (92 bars) and density (around 67 kg/m^3) of surface atmosphere of Venus.

Whenever you increase a gas pressure, by keeping constant the Volume (V), of course temperatures are increasing, that’s phisycal UNIVERSAL law.

You can calculate that by using the state equation for perfect gases, which is good for Venus too, because there you don’t have chemical reactions, and you have just 1 gas (almost 100% CO2, plus trace gases: N, argon, etc.).

Equation is:

PV = nRT
where P is pressure in bars (92)
V is volume in liters (1000)

n is density/number of moles whish is 67000/44 (molecular mass of CO2) = 1522.7
R is the universal constant of gases = 0.082

And so, if you introduce magnitudes, you have T = 92 * 1000 = 1522.7/0.082
92000/ 124.8 = 737 K

737° K is 464° C, and so you have exactly the mean temperatures you find everywhere on Venus!

Of course, recorded temperatures, pressures, and gas densities on Venus are not just a fixed one, gases are moving (although very slowly) and ranging from 85/95 bars, 455° C/ 480° C and 62-67 Kg./m^3, but they can fully be explained JUST by huge PRESSURES, huge gas density, and huge atmospheric mass, according to the gas equation.

Those people who still are talking about “runaway greenhouse effect” on Venus, have no idea of physics.

• Hello, Albert. First of all, I’d like to thank you for making such an insightful post. I just ran your calculations myself and found they agree with your conclusions, although you have a few typos when you introduced the magnitudes into the ideal gas formula.

Anyway, I also noticed some basic assumptions that I wanted to verify myself. For instance, provided that the atmospheric volume and the number of moles contained within it are roughly constant, the only variables are pressure and temperature. However, pressure can be affected by temperature as easily as the reverse. So, the idea gas law alone does not prove the absence of a greenhouse effect.

To see how accurate the conclusion really is, I used the mass of the Venusian atmosphere, as well as the planet’s gravity and surface area to determine what the surface pressure would be solely due to gravitational forces. My result agreed completely with the observed pressure of 92 atm.

However, I also considered one other point. Venus’s gravity varies with distance, so the entire atmosphere isn’t being pulled as hard as it is at the surface. While Venus’s gravity accelerates matter at 8.87m/s^2 at the surface, the atmosphere extends 250km higher up, where gravitational acceleration is considerably less. Taking the average gravitational acceleration for the whole of Venus’s atmosphere, I reran my calculations and found that the portion of Venus’s surface atmospheric pressure attributable to the planet’s gravity is only 88 atm.

Substituting this figure into the ideal gas formula yields a surface temperature of 705 K, or 432°C, approximately 30 C° shy of the observed value. As such, I conclude that the missing 30 degrees (and the 4 atm of pressure that came from them) must be attributed to some other heat source. Whether that heat source is a greenhouse effect slowing the dissipation of heat from Venus’s atmosphere or some sort of geothermal heating, I cannot say, as I don’t have much expertise on that matter.

However, even if the missing 30 degrees is due entirely to some carbon dioxide greenhouse effect, a thirty degree increase is ridiculously small for an atmosphere composed of over ninety-five percent CO2. Therefore, if Venus is the poster child for the worst case scenario for a runaway greenhouse effect, I’d say that the trace amounts of CO2 in Earth’s atmosphere are of little consequence.

As an aside, I did not account for Venus’s increased proximity to the Sun or its high albedo. The only factor I was considering was atmospheric heating due to gravitationally induced pressure. It may be possible that those factors could account for my missing 30 degrees. If anyone would like to perform the necessary calculations, I’d love to see their results. I also welcome anyone who wishes to perform my calculations and review them for error. If I have made a mistake, I’d love to hear about it and have the opportunity to correct it.

• Whoops. Damned autocorrect. I apologize for the typos, such as “idea gas law” instead of “Ideal Gas Law”

10. golfsailor says:

Whats really funny is that it seem to be valid also when doing the same calculation for Mars and Earth. So what’s a greenhouse gas doing ? seem to be nothing at all …

11. AndyG55 says:

And here is the calc that shows that Venus’s surface temp is very much determined ONLY by the atmospheric pressure. (coutesy Albert the engineer)

start quote………
You can calculate that by using the state equation for perfect gases, which is good for Venus too, because there you don’t have chemical reactions, and you have just 1 gas (almost 100% CO2, plus trace gases: N, argon, etc.).

Equation is:

PV = nRT
where P is pressure in bars (92)
V is volume in liters (1000)

n is density/number of moles which is 67000/44 (molecular mass of CO2) = 1522.7
R is the universal constant of gases = 0.082

And so, if you introduce magnitudes, you have T = 92 * 1000 = 1522.7/0.082
92000/ 124.8 = 737 K

737° K is 464° C, and so you have EXACTLY the mean temperatures you find everywhere on Venus!

Of course, recorded temperatures, pressures, and gas densities on Venus are not just a fixed one, gases are moving (although very slowly) and ranging from 85/95 bars, 455° C/ 480° C and 62-67 Kg./m^3, but they can fully be explained JUST by huge PRESSURES, huge gas density, and huge atmospheric mass, according to the gas equation.
end quote…….

12. AndyG55 says:

silly me, I meant to copy and post to WUWT !! DOH !!