By Steve Goddard
The classic cure for hyperventilation is to put a paper bag over your head, which increases your CO2 levels and reduces the amount of Oxygen in your bloodstream. Global warmers have been hyperventilating over CO2 on Venus, ever since Carl Sagan made popular the idea of a runaway greenhouse effect. That was when he wasn’t warning about nuclear winter.
Sagan said that marijuana helped him write some of his books.
I bought off on the “runaway greenhouse” idea on Venus for several decades (without smoking pot) and only very recently have come to understand that the theory is beyond absurd. I explain below.
The first problem is that the surface of Venus receives no direct sunshine. The Venusian atmosphere is full of dense, high clouds “30–40 km thick with bases at 30–35 km altitude.” The way a greenhouse effect works is by shortwave radiation warming the ground, and greenhouse gases impeding the return of long wave radiation to space. Since there is very little sunshine reaching below 30km on Venus, it does not warm the surface much. This is further evidenced by the fact that there is almost no difference in temperature on Venus between day and night. It is just as hot during their very long (1400 hours) nights, so the 485C temperatures can not be due to solar heating and a resultant greenhouse effect. The days on Venus are dim and the nights are pitch black.
The next problem is that the albedo of Venus is very high, due to the 100% cloud cover. At least 65% of the sunshine received by Venus is immediately reflected back into space. Even the upper atmosphere doesn’t receive a lot of sunshine. The top of Venus’ atmosphere receives 1.9 times as much solar radiation as earth, but the albedo is more than double earth’s – so the net effect is that Venus’ upper atmosphere receives a lower TSI than earth.
The third problem is that Venus has almost no water vapor in the atmosphere. The concentration of water vapor is about one thousand times greater on earth.
Composition of Venus Atmosphere
0.965 CO2
0.035 N2
0.00015 SO2
0.00007 AR
0.00002 H2O
Water vapor is a much more important greenhouse gas than CO2, because it absorbs a wider spectrum of infrared light – as can be seen in the image below.
http://www.globalwarmingart.com/images/7/7c/Atmospheric_Transmission.png
The effects of increasing CO2 decay logarithmically. Each doubling of CO2 increases temperatures by 2-3C. So if earth went from .04% CO2 to 100% CO2, it would raise temperatures by less than 25-36C.
Even worse, if earth’s atmosphere had almost no water (like Venus) temperatures would be much colder – like the Arctic. The excess CO2 does not begin to compensate for the lack of H2O. Water vapour accounts for 70-95% of the greenhouse effect on earth. The whole basis of the CAGW argument is that H2O feedback will overwhelm the system, yet Venus has essentially no H2O to feed back. CAGW proponents are talking out of both sides of their mouth.
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.
http://en.wikipedia.org/wiki/File:Emagram.GIF
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.
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UPDATE: Lubos Motl has written an essay and analysis that broadly agrees with this post. See it here
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On the comparison of compressing gas in a cylindar to Venus: Space is cold and for a planet drifting in space, can act as a heat. Greenhouse gases are your insulation. They stop some solar radiation from being radiating back into space, hence insulating the planet. There is still some penetration into this thick atmosphere by solar radiation. Whether or not it reaches the surface is irrelevant. The question is, whether there is enough of a greenhouse gas blanket above the penetration level to trap some of that heat and re-emit it back into the atmosphere. The surface, with a hot atmosphere above it, would certaininly get hot.
The pressure-temperature analysis is for the static condition of Venus today, NOT Venus developing through the evolution of the solar system, which is what the runaway greenhouse model addresses.
Besides watching a Nova special, no research was presented on what goes into the Venus runaway greenhouse idea. COnsidering the author’s insistance on refusing to take scientists statements about other scientists theories at face value, I am inclined to ask the author to go back and do his homework.
Just a thought, but wouldn’t the atmosphere around Venus, thick clouds and all, act like a very good insulator and keep the temp very stable? What little leakage occurred would be made up by the 30% not reflected.
I thought Venus was hot because of SO2 clouds.
To those trying to make a comparison to Jupiter and asking why it’s not hot.
Who is saying htat it’s not hot. the upper atmospher may be cool, but deeper in, where the pressure is higher, it is extremely warm and toasty.
Zeke said:
“May 6, 2010 at 12:36 pm
Just because you don’t understand something doesn’t make it wrong… There is a wealth of literature on Venus’ atmospheric dynamics. A good starting point is here: http://www.nature.com/nature/journal/v226/n5250/abs/2261037a0.html
Also, Carl Sagan smoking pot is a bit of a cheap shot :P”
Zeke – I clicked the link, and it’s nothing but a list of references of papers from the ’50s and ’60s, which support the runaway GH theory. You have clearly done nothing to argue its case, and nothing to address the points made in this post – which we would welcome here, as most of us are all for constructive debate. Lazy, lazy post.
How did Venus get such a dense atmosphere? It heated up over time to the point where all of it’s Carbon, Oxygen and Sulfur volatilized. No magnetic field means it lost it’s Hydrogen early on.
Why didn’t Earth do that?
It has life which aids in sequestering the elements that would lead to a denser atmosphere. a magnetic field which keeps the Solar wind from blowing away the lighter elements, and vulcanism to keep it regenerated.
Mars froze out because it has no magnetic field and no vulcanism.
The question is: Why does Venus still have vulcanism?
A layman’s question:
The greenhouse effect of the CO2 does not depend on his percentage in the atmosphere (96,5% in Venus, but 95,3% in Mars) . Alone this is true if the volume of the atmosphere is constant
The greenhouse effect depends on the absolute number of molecules that exist in the atmosphere
In mars it is said that the greenhouse effect of the CO2 does not have relevancy because his atmosphere is very thin
But:
Land: atmospheric pressure: 90 kPa %CO2 0,038 %
Mars: atmospheric pressure 0,6 kPa %CO2 95 %
If for art of magic they were eliminating all the rest gases and we were remaining with the CO2 we would have a pressure of
Land: 0,03 kPa
Mars: 0,57 kPa
Then, or I have been wrong in some point or the question arises: Why there is only a weak greehouse effect in Mars?
I think the 3rd poster (Curiousgeorge ) has a good point.
An interesting corolary to this line of thinking though is that besides the raw heat associated with burning fossil fuels that act should to some degree also increase the pressure of the earths atmosphere (due to adding gas mass) which by this argument again gives some credence to actions of man causing an increase in global temps, just again not leading back to the runaway greenhouse effect that is being thrust upon us.
I also disagree that the comparison of the oft stated
“each doubling of CO2 concentration would increase temperatures by 2-3 degrees” as applied to earth is comparable to what one would expect on Venus. Volume must be as important as concentration. I am not familiar with the volume of Venus’ atmosphere as compared to Earth’s, but I think you’ve established that the atmosphere is thicker.
If you consider a model in which one atmosphere is wrapped in a second atmosphere, where the concentration of CO2 in each is allowed to vary, there is no mixing between the 2 atmospheres, and solar radiation can penetrate both atmospheres, then by simply using the concentration approach, your total temperature increase would be double that of the single atmosphere model as you applied in your analysis. However, combine those 2 atmospehres together, and via the concentration approach, you halve your temperature affect.
For comparisons on earth, we know the size of our atmosphere, but you can’t go applying earth concentration approximations to places with different sizes of atmosphere.
(For the record, I am a geologist who does not believe in significant AGW, but did get my phd at Lamont Doherty Earth Observatory, which does tow the party line in favor of AGW)
Wow.
No longer content with doubting earthly science, this group is now reinventing the field of astrophysics? I’m better off asking a sleepy 5 year old for a scientific opinion.
This website is hysterical. Keep ’em coming Steve.
For those using the filling of a gas cylinder example and the consequent cooling due to conduction/convection to the surrounding atmosphere:
Where does the heat from compression go when the entire planet is, effectively, the ‘cylinder’? Everywhere is at the same temperature, hence cooling cannot occur.
Venus’ day (243d) is about 20 Earth’s days longer than Venus’ year (224d). Odd that, but it means that surface being irradiated for that long reaches high temperature (closer to the sun too), and being covered in dense volcanic gasses, acting as a thick blanket, unable to cool during night. Simple as that.
Steve-
Interesting article. But I wonder why the pressure is so high. Is the atmosphere of Venus so much thicker than that of Earth? My calculus is a bit weak, but I think that there would have to be a much thicker atmosphere than 30-40 km (and is that from surface to the edge of space?). I believe that the size of Venus is about the same as that of Earth, so the force of gravity should be comparable.
Furthermore…..if the temperature of Venus (presumably in the atmosphere near the surface) is 485°C, and the atmosphere is nearly all CO2, and less energy is absorbed from the sun than on Earth, why does the atmosphere not just radiate away its energy to space?
I don’t see the logic of high pressure = high temperature. It could be thus following an adiabatic compression, but if the heat could escape (as by radiation), the temperature would drop, the same as happens on Earth as heat is lost from compressed gas in a cylinder (for example). It is impossible to insulate the gas perfectly.
Comments / explanation welcome!! An inquiring mind wants to know.
IanM
timheyes
Ever hiked down the Grand Canyon? Same weather, same sunshine, similar rocks, same everything – except temperatures at the bottom are much warmer.
Hot gases rise only if the vertical temperature gradient is greater than the lapse rate. I’ve seen some very hot days in Houston with almost no air circulation.
Jim Barker
The amount of radiative energy leaving Venus is (nearly) identical to the amount it receives.
“Heat flow from inside the earth is much smaller than the energy received from the sun.”
Thanks for that, but I feel the need to point out that I didn’t say otherwise.
This article:
http://www.datasync.com/~rsf1/vel/1918vpt.htm
uses measured and inferred Venusian temperature and pressure profiles (to make an unrelated point). Interestingly, it shows that temperatures on Venus at a height where the pressure matches that of the Earth’s surface are also a fairly close match, differing in tens of degrees rather than hundreds. Not much of a “runaway greenhouse effect” there despite the >95% CO2.
Following the link back to the original authors behind the temperature and pressure profiles:
http://www-star.stanford.edu/projects/mgs/profile.html
reveals something astonishing. They not only say that the high surface temperature of Venus is due to the “runaway greenhouse effect”, they say that the high pressure is due to the “runaway greenhouse effect!” This does show that scientists operating outside of their specialist areas can be remarkably dim.
Jupiter has a temperature hotter than Earth’s … with no CO2, just H and He … and a high pressure.
http://www.ilovemycarbondioxide.com/pdf/Rethinking_the_greenhouse_effect.pdf
Anders L.
I live along the Front Range in Colorado. Two days ago we had downslope winds which warmed the night time temperatures up by 30 degrees. It had nothing to do with the greenhouse effect, and everything to do with compression of atmospheric gases at the higher pressures found at lower elevations. Look up “Chinook” for reference.
Clouds also block radiation. You don’t need greenhouse gases to impede IR.
One should note that at the altitude at which Venus’s atmospheric pressure is equal to Earth’s atmospheric pressure at sea level that the temperatures are the same. This is despite the fact that the air on Venus is 96% CO2.
Steve omitted one pertinent fact – Sagan put bthe Venus greenhouse effect to counter Velikovsky’s deduction from historical data that Venus had to be hot as it appeared to be a young planet.
Venus’ surface is radiating heat, from what I can gather from the known probe data, so Velikovsky’s deduction seems correct, Venus is hot because it was recently formed. Well that is what our ancestors reckoned.
This statement will cause hyperventilation among the mainstream geological types as well as the astronomers, but that’s science.
I really HATE that graph of the incoming and outgoing radiation from globalwarming art. It tends to make people think that the amount of incoming and outgoing temps are equivalent. If you actually scaled that correctly you would see that the solar IR is a very significant fraction, of the outgoing thermal radiation during the day.
The left hand scale of spectral intensity does not accurately represent what is going on.
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 spectral absorption characteristics of CO2 are also pressure dependent. If you have an atmosphere that much more dense than the Earth, the “wings” of the absorption bands are much wider and taller.
Even more significant about water is the phase change.
Do the calculations- you will find that in a volume of atmosphere containing 1% water vapor and 500ppm CO2, the heat transported from surface to space by the water is 50,000 times more than the CO2 can do. If it gets Cirrus, multiply times 5+.
Earth is a has a heat pump and the atmopheric profile is one of a refrigerant.
Water vapor is the lightest gas of the major constituents of the air and it rises inexorably, carrying the heat of vaporization with it.
Anybody can understand that improving the heat capacity of the working gas of a heat pump just makes it do a better job – it reduces the rate of flow required to maintain equilibrium.
When a cloud comes over, you have shade. CO2 does nothing.
When a cloud parks over the tomatoes at night, you have no frost. CO2 does nothing.
The only thing CO2 does is present a straw man that draws all the attention while they dilate your colon for cap & tax.
You have to stop debating this and run these people off. They’ve already learned that ‘no’ means yes because it’s all talk and no consequences. Look how Mann was defended by those who will bear his babies.
We are still losing and will continue to lose until this topic no longer gets top billing and removal of the mystics is finally understood to be the ONLY thing that matters.
No need to hark back to Carl Sagan. Here is what James Hansen says in his recent book:
IMHO, it was a terrible, terrible mistake to put James Hansen, a Venus specialist, in charge of an institution researching the Earth’s climate way back in early the 80s. Hansen, it seems, re-imagined Earth climate system in Venusian terms. His obsession with CO2 and runaway greenhouse effect originates from his early expertise in Venusian atmosphere. This is a mere speculation, but I don’t think we would have this runaway AGW scare had a Venus specialist not been in charge of NASA GISS.