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
Ryan, are you taking into account the sheer quantity of material available to become gaseous? For example, Mercury. What material exists to become gaseous and create an atmosphere? If Pluto were closer to the sun, what would its atmosphere be like? (those familiar with Science Fiction might recall an old story about someone’s rocket exhaust igniting Pluto while landing on it…)
What counts is equilibrium. Venus clearly has it, Earth obviously has it. Minor changes in gaseous content do not push an atmosphere far away from equilibrium, especially if it has been there for hundreds of millions or billions of years.
You say the pressure is a function of the applied temperature. However, the pressure is due to how much material is gaseous. If it was cooler then perhaps more of the CO2 would be stored in rocks rather than floating around the atmosphere. But it’s not cooler. Overall, higher pressure = higher volume of material = higher ability to contain energy.
Steven Goddard:
“michael hammer,
So what you are saying is that the high temperatures on Venus are the result of high pressure. I could have sworn that was the point of this article.”
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I think Michael is saying that high pressure leads to spectral broadening which enhances the greenhouse effect. But I thought your thesis is that pressure alone is responsible for the high temperatures, not spectral broadening. To help clarify this point, would you say that your thesis applies equally if Venus’s atmosphere consisted of nitrogen instead of CO2? If your answer is yes, then the greenhouse effect does not enter into the picture, and this is definately not the same as what Michael has just said.
Remember, it is not just the pressure, but also the mixing ratio.
* On Earth – 350 ppm at 1 atm
* On Venus – 965,000 ppm at 92 atm
Pressure broadening removes the spectral fine structure, but has a minimal effect on the band widths. The increase in the total number of molecules is what makes the absorption bands so wide that the Venusian atmosphere becomes IR opaque. On Earth, the amount of CO2 in the atmosphere is about 12 feet thick, on Venus, it is 312 miles thick (at 1 atm, at 92 atm it is thinner and denser).
Luboš Motl says:
May 7, 2010 at 9:27 am
Yes, I confirm the conclusions – that the greenhouse effect on Venus is just in dozens of degrees – independently, with many details about the lapse rates etc. clarified here:
Yes Lubos, but as usual you jump into something where you have little knowledge and get it wrong. Strong absorbing lines vary as the square root of the concentration ratio, which certainly applies to Venus. “A little knowledge is a dangerous thing”
Lon Hocker
So what you are saying is the high temperatures on Venus are due to high atmospheric pressure. I could have sworn that was the point of this article.
Centrifugal force would have an effect on atmospheric pressure.
One rotation as slow as Venus has will not produce much reduction
in pressure.
Vincent
About half of this article is devoted to the greenhouse effect, que no?
@ur momisugly gbaikie says: May 7, 2010 at 1:23 am
Which means that Venus’ 96.5% CO2 content is a freaking LOT of CO2. 96.5% x 90 atm = about 86 times CO2 as much as the entire composition (all elements) of Earth’s atmosphere. Would that be close to correct?
Steven Goddard says:
In the earth’s thermosphere the temperature becomes even higher than at the earth’s surface ( http://envam1.env.uea.ac.uk/images/tprofile.jpg ) and yet the pressure is down by a factor of more than a million!
Isn’t the deal there that the molecules are so far apart you essentially have no transfer between molecules?
To summarize what I have gathered from comments so far:
-Atmospheric pressure cannot in itself generate heat. If Venus’s atmosphere consisted of only nitrogen at the same pressure and temperature, it would not be able to sustain that temperature and would cool down hundreds of degrees.
-The best (and only) explaination for why Venus is so much hotter than would be expected from the amount of solar radiation it absorbs, is the greenhouse effect.
So I consider the articles claim “The greenhouse effect can not be the cause of the high temperatures on Venus” to be completely wrong.
Joel Shore
Do you think it is a perpetual coincidence that it is much warmer at the bottom of the Grand Canyon than at the top?
About half of this article is devoted to the greenhouse effect.
Venus has very little water in it’s atmosphere relative to earth – about one tenth as much.
0.00002 H2O * 90 = 0.0018
A very interesting post, this.
Steven Goddard,
I hope you understand that many of us hasnt been at school for…well, for myself it is
30 years ago this year. Difficult to accept, even for myself.
Anyway, in the mean time one has been into other thinks than thermodynamics.
Further up here Stephen Wilde led me to his article here;
http://climaterealists.com/index.php?id=1562&linkbox=true&position=4
Which is the same issue as you say in your post.
Thanks to both of you for refreshing my schooldays teaching.
hehe.
Phil.
What would be the temperature of a hypothetical place on earth, which was at low enough elevation to have 9,000 kPa atmospheric pressure? Kind of warm perhaps?
Once again, your little table of logarithmic CO2 temperature effects is WRONG WRONG WRONG. The logarithmic approximation is only applicable for a small range of concentrations (including the concentrations that are relevant for Earth). Venus is WAY outside this range, and the effect of CO2 becomes much closer to linear again.
Let me try another way of explaining why you need CO2 for a warm Venus. The lapse rate only works up to the tropopause. The height of the tropopause is, in part, determined by the optical thickness of the atmosphere. If you remove most of the CO2, the optical thickness drops, the tropopause drops, and therefore if the lapse rate stays fairly constant and the temperature of the tropopause is fairly constant, the surface temperature must drop.
Again, pressure alone does nothing. You need an external energy source (the sun). You need an IR-absorbent atmosphere (CO2 or H2O). You need to be in the troposphere. Then, and only then, can you start using pressure as a short-hand approach to calculating temperature.
I’m sure there must be good textbooks that cover Venusian atmospheres out there somewhere. I’d suggest going and finding one and actually studying it, rather than continuing to putter around with your erroneous “blog science”. 99% of the time, the consensus science is fairly close to reality, and way less than 1% of the time are there no fatal misconceptions when someone’s back-of-the-envelope calculation differs from consensus science. This is another example of those times when fatal misconceptions creep in…
-Dave
Onion : Next time you heat your coffee in your microwave remember Venus.
Dave says:
May 7, 2010 at 12:17 pm
Once again, your little table of logarithmic CO2 temperature effects is WRONG WRONG WRONG. The logarithmic approximation is only applicable for a small range of concentrations (including the concentrations that are relevant for Earth). Venus is WAY outside this range, and the effect of CO2 becomes much closer to linear again. …
Huh. Interesting….why don’t you show us that graph. Are you implying there’s a ‘tipping point’? If not, then you might just be correct – as you go along an exponential curve, it does, indeed appear to be linear, but this linear approximation has a tiny scaling factor.
Dave
I suggested replacing 90% of the CO2 with N2 (not 100%.) At 10% CO2, you are already way, way up in the linear range.
Please read the article more carefully.
Holey moley! I cannot believe anyone could say the following with a straight face! This must be a party trick or something, designed to figure out how much people have had to drink.
Dave
Also, my table of logarithmic CO2 temperature effects was for Earth, not Venus. If Earth somehow hit 100% CO2, temperatures would only increase by about 25-35C.
Alright, I think I can word the general “layman’s explanation” of this.
Let’s look at a certain amount of gas molecules, which have a certain amount of energy. If it helps, think of them in a perfect balloon that can contain them, be any size, but the material puts no pressure on the gas.
We’ll start with them being surrounded by a low pressure. So the molecules are nice and spread out at a certain temperature, where “temperature” can be thought of here as a reading of how much energy is in a fixed volume. Now we raise the pressure around those gas molecules. That amount of molecules will then squish down to a smaller volume at that higher pressure. The same amount of energy is there but in a smaller volume, thus the temperature will be higher. The process is reversible, of course, reduce the surrounding pressure and the volume goes up while the temperature goes down.
On Earth, sunlight warms the surface. The high pressure gas absorbs the heat, then moves higher in the atmosphere. The pressure gets lower, the gas expands, gets cooler. It was heated while compressed, and now gives off heat that goes off into space.
On Venus, sunlight doesn’t make it to the surface. The heating is done up high, at lower pressure. Circulation forces the gas downwards, where it is compressed and thus at a higher temperature. It gives off whatever heat it can at the surface, then it circulates upwards to continue the cycle.
Something that makes Venus so confusing is how such circulation is not a natural pattern of convection, where hot gas rises, cools off, then sinks back down to take in a fresh batch of heat. A driven system is indicated, as heated gas is being lowered into the atmosphere and compressed. Where could the energy driving this system be coming from?
For one thing, we can already see that Venus has a lot of energy in its circulation patterns, far more than in a normal atmospheric system like with Earth, as can be noted in this section of the Wikipedia “Atmosphere of Venus” entry. (Anyone got a better source?) Thus already there is an indication there possibly is another source of energy than solar.
As to what it could possibly be, well… When doing atmospheric models, things get simplified, certain “big picture” elements get overlooked. For example, planetary rotation. The pressure at the surface of Venus is 90 times that of Earth. At such densities, there is far more atmospheric drag against the surface than is found on Earth. Now look at the rotation period of Venus, seen best at the chart at the bottom of the linked source. Venus rotates very slowly, it has the slowest rotation period in the solar system. Two possibilities for this spring to mind. One, Venus could have had a rather odd formation and ended up having such a slow rotation at the start. Two, something has caused it to drastically slow down. Atmospheric drag over a long time could do it. That would represent an enormous input of energy into the atmospheric system, that could drive a cycle of compressing heated air while driving it down to the surface.
Does work exist that shows the slow rotation period is due to something else? Does anyone know of any atmospheric modeling of Venus where the energy input of such atmospheric drag has been considered? Has the possible energy gain from drag been shown to be insignificant, without resorting to claiming “it must be insignificant since CO2 and the greenhouse effect provides enough energy”? Inquiring minds want to know.
OceanTwo says:
May 7, 2010 at 12:32 pm
Dave says:
May 7, 2010 at 12:17 pm
Once again, your little table of logarithmic CO2 temperature effects is WRONG WRONG WRONG. The logarithmic approximation is only applicable for a small range of concentrations (including the concentrations that are relevant for Earth). Venus is WAY outside this range, and the effect of CO2 becomes much closer to linear again. …
Huh. Interesting….why don’t you show us that graph. Are you implying there’s a ‘tipping point’? If not, then you might just be correct – as you go along an exponential curve, it does, indeed appear to be linear, but this linear approximation has a tiny scaling factor.
Here’s what the graph shape looks like, the first portion is for weak absorbers and is ~linear, the middle portion is ~log, and the final portion is ~square root.
http://spiff.rit.edu/classes/phys440/lectures/curve/gcurve.jpg
The concepts of atmospheric thermodynamics are not always intuitively obvious. In fact it is generally not taught until the final year of undergraduate or the graduate level at university. One of the books that I “grew up” with is Atmospheric Thermodynamics by Iribarne and Godson. You do need a pretty solid background in math and physics for this book.
Steve, I believe you clearly said:
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.
Thus, you claimed Venus is hot because of it’s high atmospheric pressure. Many posts here have proved that conclusion to be incorrect. Why not admit you made a false statement?