Venus Envy

What disturbs me is the following;
Personally I havent given Venus much thought before reading Steven Goddards posts here at WUWT. Why should I have. I have enough other thinks to worry about on a daily basis.
But now, reading about Venus, thinking about it, the grey cells working…over at Stephen Wildes post…it stands clear to me, at least for now….that, hey, it makes sense!
And then the disturbing thought;
Surely J. Hansen must know this too? Surely? I mean, if its your job to use the grey cells on such matters?
Surely?

When you compress or decompress a gas, it either warms or cools. Due to the temperature differential to the surroundings, after some time it will cool or warm by exchanging heat with the surroundings until the temperature differential is approaching zero and hence the temperature of the gas approaches that of the surroundings.
Why should Venus behave any different?

Experiment # 1 – Atmospheric pressure on Venus’ surface is 92 times larger than earth, because the atmosphere is much thicker and thus weighs more.
I am always puzzled by the statement that the atmospheric pressure on the surface of Venus is a large multiple of that on earth.
The MW of earth’s atmosphere is about 29, and that of Venus around 44. But gravity at the surface of Venus is only 0.904 that of earth.
Atmospheric pressure is the result of the weight of a column of gas above the surface pressing down. I won’t embarrass myself by trying to calculate the effect of higher MW and lower force due gravity on Venus, and compressibility of the gas(es), but I would expect the atmosphere of Venus to extend out a large multiple of the distance that it does on earth to produce an atmospheric pressure 92X that on earth. But I have not heard that the Venusian atmosphere extends out so far…..
So, the question remains why the atmosphere is so “thick”. It is not constrained to a fixed volume, but can expand as the mass of gas is increased.
A further niggle comes from the statement: “If there were no Sun (or other external energy source) atmospheric temperature would approach absolute zero. As a result there would be almost no atmospheric pressure on any planet -> PV = nRT.”
At 0K all gases would have condensed to liquid or solid, but the mass of the gas would still be present as a layer on the surface. I would think that the liquid/solid would be as heavy (=attraction due to gravity) as the atmosphere from which it was produced, and possibly a tiny bit higher since the molecules would be concentrated at the surface instead of extending a distance above the planet and thus minutely farther from the center of attraction of the mass of the planet.

Leonard Weinstein
You are correct.
Earth already has plenty of greenhouse gases, so my point is that even if earth went to 100% CO2, the maximum temperature increase would be less than 36C – nothing like Venus. (In reality, it would get cooler because of the loss of water vapour.)

Ian l. McQueen
Liquids are not very compressible and don’t heat up much under pressure. Consider the bottom of a swimming pool.

John caten
Title is Anthony’s idea. He also added the ESA and Venera content.

In addition to pressure, Venus also has high concentrations of other greenhouse gasses such as carbon monoxide. If one of these gasses absorbs at the frequency corresponding to earths atmospheric window then it could have a significant effect on temp. I also wonder if atmospheric pressure could explain the faint sun warm earth paradox.

Willis- the lapse rate of earth’s atmosphere is NOT the lapse rate of a dry atmosphere.
In fact, the profile of earth’s atmosphere is that of a refrigerant system because of the working fluid water.
Venus has no such phase change gases in its atmosphere so it has the dry lapse rate.
The lapse rate of earth’s atmosphere is definitely not that of a dry atmosphere.
The are completely different- not similar at all.

Troels,
The atmosphere is not static and conductive heat transfer to surroundings is small. Here’s a description:
“An adiabatic temperature change occurs in a vertically displaced parcel of air due to the change in pressure and volume (refer to the gas equation in section 1.2) occurring during a short time period, with little or no heat exchange with the environment. Upward displacement and consequent expansion causes cooling; downward displacement and subsequent compression causes warming. In the troposphere, the change in temperature associated with the vertical displacement of a parcel of dry (i.e. not saturated) air is very close to 3 °C per 1000 feet, or 9.8 °C / km, of vertical motion; this is known as the dry adiabatic lapse rate [DALR]. As ascending moist air expands and cools in the adiabatic process, the excess water vapour condenses after reaching dewpoint and the latent heat of condensation is released into the parcel of air as sensible heat, thus slowing the pressure-induced cooling process.”

Another great post. I have been trying to go through similar ideas in the Climate Sceptics group for a while myself.
May I suggest a couple of interesting links:
(1) UTexas teaching notes about why there is an adiabatic lapse rate at all (hint: there is no mention of any GH effect)
(2) From the New Mexico State University a table about lapse rates in various atmospheres in the Solar System (and showing that composition might matter, alongside gravity)
In particular, the lapse rate is roughly g/Cp, where g is the acceleration due to gravity and Cp is the atmosphere’s specific heat at constant pressure (cp) divided by the molecular weight. It would be interesting to find out why exactly Cp for Venus would only be 85% of Earth’s.

Why is the atmosphere on Venus 92 times more dense than on Earth? That is the big question, that I don’t understand.
Now, if the atmosphere is denser – it means there are 92 times more molecules of gas in the same volume (or layer) of the atmosphere, therefore they would absorb 92 time more outgoing radiation (much more anyway). So, the heat on Venus’ surface is caused by the greenhouse effect after all, by the fact that the greenhouse effect is much stronger there, due to the density of the atmosphere, and not necessarily due to it’s composition (Co2).
If pressure alone could cause heating – why isn’t the bottom of the oceans very hot?

“In my last piece about Venus I laid out arguments against the claim that it is a runaway greenhouse which makes Venus hot. This generated a lot of discussion.”
The accepted view is that present day Venus is a result of a runaway greenhouse, she got too warm, her oceans boiled, the resultant water vapour created a super GH effect, which melted the planets crust, the oxygen released from ionize H2O combined with crustal carbon to create CO2. The planets surface is hot because of its present atmosphere, its atmosphere is a product of a runaway greenhouse.
“we have a sun providing energy to the periphery of the atmospheric system”
Not sure what you mean by this, the sun’s EM radiation is absorbed by atmospheric constituents throughout the depth of the Venusian atmosphere, not at the “periphery”.
“If there were no Sun (or other external energy source) atmospheric temperature would approach absolute zero. As a result there would be almost no atmospheric pressure on any planet”
The surface pressure is almost entirely independent of the temperature, assuming that all the atmospheric constituents remain suspended.

OT: One gets the distinct impression from recent posts here, at CA, and RC etc, that interest in the subject (AGW), is finally waning. Would be interesting to follow the sites statistics recently, to confirm/deny this. Basically the skeptics/deniers were right.. weather, aka climate is not changing due to AG. AGW news stories have certainly dipped. We can all go back and get a life instead of looking at graphs of temps, ice, polar bears, anxiety due to AGW, etc.. Of course a few diehards will keep banging away at it until they too, just give up, a good ol hahaha and LOL!

For anyone still believing that CO2 GHG is the fundamental reason for high surface temperatures, please consider this, (adapted from my comment in the earlier thread):
Here is an authoritative extract from the ESA, (my bold), so let’s examine it, particularly as to why Venus has a uniform average temperature everywhere. (over 117 earth days, and see link below)
“…[1] On Venus there are no day and night variations of the surface temperature. The heat is globally ‘trapped’ under the carbon-dioxide atmosphere, with pressure 90 times higher than on Earth.
[2] Instead, the main temperature variation is due to topography. Just like on Earth, mountain tops are colder, whereas the lowlands are warmer. The ‘only’ difference is that on Venus ‘cold’ means 447º Celsius, while ‘warm’ means 477º Celsius. Such high temperatures are caused by the strongest greenhouse effect found in the Solar System…”
[1a] When facing the sun, she is said to receive at the surface about 10% of sunlight. Whether this is a midday or total facing area average, or the effects of scattering, I don’t know, but whatever, the surface receives SOME solar energy. This energy amount must be lost back to space because the planet is apparently in thermal equilibrium. The fundamental process for this should be convection and conduction. Additionally, since infrared photography etc of the surface has been accomplished there is at least one window for some infrared to directly escape to space.
[1b] At nightime she no longer receives any solar energy, but has capability to lose heat in the same way as on the daylight side, over a period 117 times longer than on Earth. What is more, because the upper atmosphere is no longer heated by solar infrared, (~40% of sunlight), the temperature gradient of the atmosphere should increase, inferring increased conductive/convective cooling. Yet, there is no change in surface temperature! Such a condition would require an impossible perfect insulation layer, and no geothermal energy, but clearly, this is not the case.
[2] This part of the extract supports Steven’s hypothesis, but see also my comment in the earlier thread concerning the strange and unexplained dynamics of the atmosphere, according to the ESA. (that may have an astonishing “mixing” effect).

(kcom says:
May 8, 2010 at 2:46 pm
The mind is a powerful thing and can overwhelm logic when placed under enough stress. Ask any medical student if this has ever happened to them.)
James Hansen came to his conclusions based on observations. If you can prove him wrong you win. Do ou have a better explanation?

George Turner
Gas pressure P = nRT/V
There is no term for either mass or gravity.

Steve, I don’t see how they get the lapse rate for Venus you mention. I tried three ways and each is much lower. Assuming 740K for the surface temp per Wiki, the top graph has two possibilities:
(740K-260K)/58km = 8.3 K/km
(740K-310K)/52.5km = 8.2 K/km
The lower graph, assuming Earth’s mean surface temp at 290K, based on pressure, not temperature is:
(740K-290K)/49.5km = 9.1 K/km
All of these are between the surface and to the point where ~90% of the mass of the atmosphere is lower.
Do you think their 10.468 K/km rate is more accurate? As you were saying, if co2 has it’s hand in it then the lapse should be much higher than the lapse rate of earth and I come up lower, not higher by the equally valid graphs (they tend to mirror what you read in Wiki).

In the end there is simply the warmth given by the sun plus the warmth produced inside Venus, and the warmth radiated into space.
My opinion:
It is the heat the atmosphere gets from the planet surface that determines how far the atmosphere expands into space, not the other way around.
It is not the distance the atmosphere expands into space that determines the temperature at the surface.
The air receives heat on the planet surface, expands, rises and cools down, and falls back. As it falls back and contracts, it warms up again, but it will not gain more heat than it has lost by expanding. As it has also lost heat that is radiated out to space, it will arrive at the surface of the planet cooler than it left it.
My reasoning:
1. OK. For the moment, let’s forget the green house effect and let’s start with a very cold atmosphere, contracted very close to the surface of Venus.
2. You say: “Because we have a sun providing energy to the periphery of the atmospheric system, the atmosphere circulates vertically and horizontally to maintain equilibrium.”
The energy of the sun must go through the atmosphere and warm the surface of the planet, which then warms the lower layers of the atmosphere for circulation to start happening.
(The sun providing energy to the periphery (= outside) of the atmosphere, means the periphery warms up. The air there expands and wants to rise, not sink, thus no circulation. The word periphery is usually used for ‘outside’ and seems misplaced here.)
3. OK, when such a dense atmosphere is heated up, the resulting upward force is greater that of the thinner Earth atmosphere heated up to the same temperature. This makes the Venus atmosphere spread out further into space than Earth’s.
4. And yes, when the expanding gas has reached the outer layer, and has cooled down, it will fall and contract and heat up, but it will not gain more heat than it has lost by expanding. As it has also lost heat that is radiated out to space, it will arrive at the surface of the planet cooler than it left it. (Otherwise it would be a perpetuum mobile).
5. As Venus has no oceans and no biosphere, it has a hell of an urban heat island (UHI) effect.
The energy that the sun radiates on the surface heats up a thin layer of surface to very high temperatures. The whole planet is one big heat island.
None of it is spread over a huge body of water like our oceans or converted into plant growth.
I would expect that to be the most important reason the surface temperature of Venus is so much higher than that of the Earth.
Plus, of course, that Venus is closer to the Sun and receives more heat per square meter or foot than Earth.
6. The much denser atmosphere is much better at absorbing the heat of the planet’s surface, than Earth’s thinner atmosphere. Giving it a huge upward, expansive force, that expands it far out into space.
But the extend to which it spreads out is determined by the heat it receives on the surface, so that after the hot air has reached the cold space and – cooled down – falls back, it does warm up, but not to higher temperatures than it had when it started at the surface of the planet.
In other words, it is the heat content of the atmosphere – heat it gets from the planet surface – that determines how far the atmosphere expands into space, not the other way around.
It is not the extend to which the atmosphere expands into space, that determines the temperature at the surface.
7. The heat content of the atmosphere if Venus is so high, because of the massive UHI effect and because the dense atmosphere is so efficient at absorbing heat from the surface.
(8. I imagine that without oceans there is no thunderstorm belt that transports massive amounts of heat to the highest layers of the atmosphere, bypassing the greenhouse effect – the thermostat Earth has in the tropics.)

I’d like to suggest another experiment for Steve.
To simulate the effects of an IR blocking atmosphere on a very dim planet, build a greenhouse. The glass for the greenhouse should be selected for absolute IR opacity across the band, and it can even be triple-paned and argon-filled to limit convection losses. To best mimic the dim light on the surface of Venus, build the greenhouse deep in the forest and wait for a very dark, overcast day. Sit inside with a good thermometer and see if the temperature approaches 900 degrees F.

(http://en.wikipedia.org/wiki/Atmosphere_of_Venus#Structure_and_composition
The large amount of CO2 in the atmosphere together with water vapor and sulfur dioxide create a strong greenhouse effect, trapping solar energy and raising the surface temperature to around 740 K (467°C), hotter than any other planet in the solar system, even that of Mercury despite being located further out from the Sun and receiving only 25% of the solar energy Mercury does.[11])
Based on AGW theory if venus’s atmosphere were nitrogen, then infrared would continue back out into the space without being reactive to the nitrogen. The gas in the atmosphere does make a difference as to how much heat is held in.

Ian l. McQueen says: May 8, 2010 at 2:40 pm
“I am always puzzled by the statement that the atmospheric pressure on the surface of Venus is a large multiple of that on earth.”
If you blow away many of the lighter elements of a planet’s atmosphere with the ‘solar wind’ and continue to warm it, the heavier elements will stay there in the atmosphere to provide a greater surface pressure.
Having said that, I’m sure you realise that the heavier gasses should form a shorter altitude distance for any change in pressure. It’s curious that the lapse rate of both Venus and Earth are similar, but is this more to do with the similar orbital distance from Sol than the atmospheric makeup of these planets?
Well I think this is possible, but perhaps it’s more to do with the natural progression of (and here’s a new term) ‘nature’!
We have the ‘nature’ of Earth, and we have the ‘nature’ of Venus.
The history of Venus has led it to its current situation, and ditto for Earth. Although Venus has a lower gravity field than Earth it has lost many of its lighter elements. Thus, Venus’s troposphere contains compounds that are much heavier than those incorporated within Earth’s troposphere and this reflects in its higher surface pressure.
Best regards, Ray Dart.

The adiabatic lapse rate argument works best with heating from below. This might be caused by geothermal activity since the atmosphere of Venus, unlike earth, is opaque. I believe that a number of scientists have studied the strange geology of Venus’ “not quite plate tectonics” and no doubt have already made this same suggestion. Popular knowledge dies hard though, even among scientists, and the runaway greenhouse analogy lives on.

William Sears
Whether the source of heat is geothermal or absorbed SW, the lapse rate is the similar on both planets – indicating that greenhouse effect is less important on Venus than advertised.

Stephan says:
May 8, 2010 at 4:32 pm
OT: One gets the distinct impression from recent posts here, at CA, and RC etc, that interest in the subject (AGW), is finally waning. Would be interesting to follow the sites statistics recently, to confirm/deny this. Basically the skeptics/deniers were right.. weather, aka climate is not changing due to AG. AGW news stories have certainly dipped. We can all go back and get a life instead of looking at graphs of temps, ice, polar bears, anxiety due to AGW, etc.. Of course a few diehards will keep banging away at it until they too, just give up, a good ol hahaha and LOL!
Staphan, in an ideal world you would be right. But, unfortunately, many governments have accepted the IPCC reports as gospel truth and have enacted legislation designed to reduce CO2 emissions. They will do nothing for the climate but WILL do great harm to the economy. It is as if we were on a hill overlooking a railway line on which a train is headed at high speed for a bridge that is no longer there. We know that a trainwreck is inevitable, but there is nothing that we can do to stop it.
IanM

stevengoddard says:
May 8, 2010 at 4:48 pm
George Turner
Gas pressure P = nRT/V
There is no term for either mass or gravity.
Steven-
The term “R”, the gas constant, has units of 8.314472(15) J·K-1·mol-1

Steven,
Gravity doesn’t appear in PV=nRT, but it does appear in F=ma. The mass is the mass of the atmosphere and the acceleration is due to gravity. That gives the downward force an atmosphere exerts on the surface (minus a small error because gravitational acceleration decreases with altitude).
Given a planet’s surface area S, the average surface pressure must be F/S = mg/S.
Venus atmophere’s mass is approximately 4.8×10^20 kg and its surface gravity is 8.87 m/sec^2, so the force it exerts on the surface is 4.26×10^21 Newtons. This is spread across a surface area of 4.6×10^8 square km, or 4.6×10^14 m^2, so the pressure is 4.26×10^21 N/4.6×10^14 m^2 = 9.26×10^6 N/m^2 (Pascals), which is 1343 psi or 91.4 atmospheres.
Even if the atmosphere condenses to a liquid or freezes to a solid, the pressure on top of the rocks is still going to be 91.4 atmospheres.
🙂

Steve,
I agree with your claim about the lapse rate explaining in part why the surface of Venus is so hot, but the lapse rate does not disprove the existence of a greenhouse effect, and I believe it is only part of the story about the high surface temperature.
First, a technicality – your dry lapse rate only applies for an adiabatic process where there is no condensation or heat transfer. It is an upper limit. The actual lapse rates on both Earth and Venus are lower than their dry lapse rates.
In your previous post “Hyperventilating on Venus”, you presented this plot (http://www.globalwarmingart.com/wiki/File:Atmospheric_Transmission_png) showing the transmissivity of various gases in Earth’s atmosphere. It shows that the 380-some ppm of CO2 in Earth’s atmosphere is enough to block all infrared radiation from 13 microns to 17 microns wavelength. Combined with the infrared opacity of Earth’s water vapor, that still leaves a broad window of atmospheric transparency to infrared between 8 microns and 13 microns, enough to keep the Earth at its current comfortable temperature range.
However, on Venus, the CO2 concentration is the equivalent of 89 million ppm, relative to Earth’s atmosphere, or 234,000 times the optical thickness of CO2 on Earth. As a result, the atmospheric transmissivity to infrared on Venus is quite different from the plot linked above.
I got into this Venus argument with a friend last year and to satisfy myself of the effect of CO2, I subscribed to Spectralcalc.com for a month to run some numbers. I was able to replicate the CO2 curve in the Atmospheric Transmission plot for Earth, and I found that for Venus, the absorptive range of the gas broadens so much to other wavelengths that the Venutian atmosphere is opaque to infrared from below 2 microns up to 28 microns except for three relatively narrow windows of transparency at 2.3, 3.4, and 5.7 microns, even for only 5 kilometers of atmospheric depth (near the surface). Also, my sources indicate there is enough water vapor in the Venutian atmosphere (somewhere above 50 km altitude) to effectively block infrared emissions above 28 microns.
This shows the Venutian atmosphere is way more opaque to infrared than Earth’s atmosphere and does indeed reveal a strong greenhouse effect on Venus. Even the lower atmosphere, while efficiently passing infrared from 28 microns and higher (because there is virtually no water vapor below the clouds) is still almost opaque from 2 to 28 microns and presents a substantial impediment to radiative cooling of the surface.
As I said in the beginning, I agree with your claim that the lapse rate helps to explain partly why the Venutian surface is so very hot, but I think that lapse rate is not the whole story. With the surface receiving only 1/6th the sunlight that the Earth’s surface receives, something has to act as a barrier to slow the rate of radiation from the surface to the much cooler haze layer at 30-50km altitude, and I think that something is the CO2 infrared opacity. I’m no atmospheric scientist or physicist and I lack the tools to model this, but I suspect that if CO2 were transparent to infrared the Venutian surface would be a lot cooler than it is, but still substantially hotter than the upper atmosphere thanks to the lapse rate.
Heat from below ground cannot possibly explain the high surface temperature as some have suggested. On Earth, the heat radiating from the ground is only 1/10th of a watt per square meter, and even if it is ten or 100 times that on Venus, this is still dramatically less than the visible light reaching the surface.
[Interesting factoid: On Earth, refraction or bending of sunlight makes the horizon light during dusk and dawn even though the sun is not up. Well according to one source, on Venus the refractive effect from the thick atmosphere is so much stronger than on Earth that even the darkest region of the dark side still gets some glow from the sunlit side.]

Speaking of radiation… How much of Venus’s heat is coming from it’s own core? Given its formation closer to the Sun, I would surmise that Venus might have a greater proportion of heavier/more unstable elements at its core than Earth. ?

The whole idea of a runaway greenhouse effect causing the dense atmosphere of Venus is so silly that it could only have been as created in the minds of Marxist brainwashed pseudo-scientists with a political agenda. The Universities have been pushing the nonsense for so long that even some real scientists have been hood winked by it. It is not that Venus has an unusually high atmospheric density for its size and location, its that the Earth has an unusually low density. That density can be quite adequately be attributed by that absurdly big ball we call the Moon.
Why are so many so confused by the relationship of temperature and density. Gas is compressible so its density is highly related to pressure. Energy will distribute evenly through the mass. The more mass per volume, the more kinetic energy per volume, the higher the temperature. It is not pressure causing heating. Sheesh! Liquid is not a compressible fluid so its density is not very related to pressure. The behaviour of the Earth’s oceans tells us nothing about the behaviour of an atmosphere. So bringing up the thermal characteristics of the Ocean is meaningless.

This is, without a doubt, the most authoritative description of the planet Venus and its environment: http://www.feedbooks.com/book/2482.pdf

Nick Stokes,
“CO2 emits to space at the top, not at the bottom.”
Which side of the molecule is the TOP??
HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA
In case any one listens to you, CO2 emits to space from tropopause out to the edge of the atmosphere here on earth and a similar depth on Venus. You are being simpleton again and more confusing than informative.

DesertYote at May 8, 2010 at 6:11 pm said:

Why are so many so confused by the relationship of temperature and density. Gas is compressible so its density is highly related to pressure. Energy will distribute evenly through the mass. The more mass per volume, the more kinetic energy per volume, the higher the temperature. It is not pressure causing heating. Sheesh!

Wikipedia defines temperature as the average kinetic energy of particles in matter. You seem to be talking about energy density. While Wikipedia often contains things I disagree with, there seems to be a disconnect here.

Well Steve, I just thought it was assumed. Since Venus is totally devoid of vegetation, the idea of a greenhouse on it is rather silly. ^_^
Anyway, given the little F=ma thing, imagine if we reduced Venus’ surface gravity by a factor of 90, to about 0.01G or so (Vulcan terraformers probably do this all the time). Then we have a planet with the same amount of CO2, the same clouds, the same basic atmospheric structure (just stretched way up), but a surface pressure that’s Earth normal. If GHG completely drives Venus’ temperature then the dramatic change in surface pressure wouldn’t matter in the long term, and it would still be 700K+. If adiabatic heating is largely responsible then the change should produce a much cooler surface.

The heat MUST be created by planetary forces, see http://www.esa.int/esaSC/SEMUKVZNK7G_index_0.html .
It has long been recognised that there are simply not enough craters on Venus. Something is wiping the planet’s surface clean. That something is thought to be volcanic activity…….. and “Now we have strong evidence right at the surface for recent eruptions,” says Sue Smrekar, a scientist at NASA’s Jet Propulsion Laboratory in California. They do say They estimate that the flows are possibly as geologically recent as 2 500 000 years – and likely much less, possibly even currently active. In other words they don’t know, but something must be bringing heat from the interior of the planet to lava flow the surface. This must be the major phase change going on in ‘Her’. Recent laval surface remodelling seems to me to be the cause of the night/day hot surface temperatures, the sun’s role on the surface heat seems minor. The (relatively) waterless atmosphere without significant convective
forces seems to be keeping the heat in.
This enormous heat must be coming from the planet itself, the atmosphere is merely a blanket, the adiabatic lapse rate is too limp to explain such persistent high night /day heat.

I’ll consult with the local florist, but I’m pretty sure that huge pressure differences don’t come included in the standard greenhouse package.
Hehehehe.

Richard Sharpe
May 8, 2010 at 6:55 pm
I was under the impression that it is average kinetic energy within a volume.

Ian l. McQueen says:
May 8, 2010 at 2:40 pm
“……A further niggle comes from the statement: “If there were no Sun (or other external energy source) atmospheric temperature would approach absolute zero. As a result there would be almost no atmospheric pressure on any planet -> PV = nRT.”
At 0K all gases would have condensed to liquid or solid, but the mass of the gas would still be present as a layer on the surface. I would think that the liquid/solid would be as heavy (=attraction due to gravity) as the atmosphere from which it was produced, and possibly a tiny bit higher since the molecules would be concentrated at the surface instead of extending a distance above the planet and thus minutely farther from the center of attraction of the mass of the planet.”
———————————————————————————
At absolute zero…. No molecule is in a gasseous state…. It is solid and inert…. even with no pressure…. This is a theoretical limit of course…. for Absolute zero has never been observed….. So a planet with a 100 percent nitrogen atmosphere would have a surface of solid nitrogen at 0K. There would be no sublimation… Because no molecule has any energy left.
That’s my understanding anyway.

Dave McK
You can stop hyperventilating now. The average measured lapse rate on Earth is a little lower than the dry lapse rate. About 6.5. On Venus the average measured lapse rate is also a little lower than the dry lapse rate at 8.5. Not much difference.
Your argument doesn’t provide much useful information about why Earth is 20C and Venus is is 485C.

Gary W,
If the atmosphere on Venus stopped circulating, then I agree that the compression effects would dissipate. But the atmosphere there is constantly rotating in two giant Hadley cells. The air rises near the equator, moves to the poles, descends, and moves to the equator again, so it is always undergoing cycles of compression and expansion. This means it is also undergoing cycles of adiabatic heating and cooling.

George Turner says:
May 8, 2010 at 7:54 pm
George, I think you are on the right track, all you need is a downward sensor facing the crust in the shadow of the craft and an upward sensor sensing radiative energy from above and compare the two.
Willis, in the earlier thread, suggested that the surface pressure was such that a super critical fluid would occur, the images above would suggest otherwise.

Ugh, stop quoting Wiki as a source guys.

Phil.
You must have forgotten your high school chemistry.
A mole is most definitely a non-dimensional number. It is 6.023 * 10^23 molecules.
One of the interesting properties of gases (Avogadro’s law) is that they all occupy about the same volume at the same pressure and temperature, regardless of molecular weight. That is why the ideal gas law does not have a term for mass.
http://en.wikipedia.org/wiki/Avogadro's_Law
Avogadro’s law (sometimes referred to as Avogadro’s hypothesis or Avogadro’s principle) is a gas law named after Amedeo Avogadro who, in 1811,[1] hypothesized that “Equal volumes of ideal or perfect gases, at the same temperature and pressure, contain the same number of molecules.” Thus, the number of molecules in a specific volume of gas is independent of the size or mass of the gas molecules.

Steve Goddard “If there were no Sun (or other external energy source) atmospheric temperature would approach absolute zero.”
But planets the size (or more) of the Earth and Venus have a significant internal heat source from radioactivity, which surely would heat the atmosphere.
Lord Kelvin, without knowing about radioactivity, calculated the age of the Earth as 40 million years.
In 1904 Rutherford, allowing for radioactive elements in the Earth’s core, calculated the age of the Earth in billions of years.

Expanding on the points that Leonard Weinstein and Nick Stokes make. What is being discussed is the dry adiabatic lapse rate, which starts from the assumption that everywhere in the atmosphere the radiative energy absorbed is balanced by the energy emitted. If not, you get convective energy transport to re-balance the situation. That leaves gravitational compression, but it is not saying that radiative energy flow is negligible, just that it is balanced. As Nick and Leonard say, the lapse rate does not set the surface temperature, which is determined by the solar radiation absorbed at the surface and the IR re-emitted by greenhouse gases in the atmosphere.
What does the lapse rate determine? Looking at extremes is useful. Nick points out that if the surface is at absolute zero the thickness of the atmosphere (at least for an ideal gas) would be zero. What if the surface were at infinite temperature. Then the height of the atmosphere would be infinite also. From this, we conclude that the height of the atmosphere is determined by the lapse rate and the surface temperature
There are, of course, a few other things to consider. First, the dry adiabatic lapse rate is not 10 K/km for every atmosphere. For example it is 4.5 K/km on Mars and 2.0 K/km on Jupiter. Better put it is the ratio of the local gravitational constant divided by the specific heat (in J/(kg-K) or g/Cp. For the case of Venus, where the surface and the atmosphere are very hot, we have to account for the contribution of molecular vibrations to the specific heat, which will change with temperature and thus with altitude.

On the subject of ocean depth, liquids are certainly compressible, just not as compressible as gasses. At 6 km depth for example, water would be at 600 atmospheres, density increases 3.7% and temperature would be 10 deg C above what water at 1 atmosphere AND the same heat content would be. Yet the temperature is only 3 deg C in the ocean deep. The only thing keeping water from freezing at ocean depth would seem to be waters compressibility, since little or no heat from the surface is reached at the bottom except via some convection, in fact it’s main heat source is the heat from the ocean floor and hydrothermal vents .
Air at 30,000 ft is at quite a low temperature, due to it’s low density and pressure, yet it’s heat content on a per molecule or mass basis is close to that at the surface. If it were adiabatically compressed to 1 atmosphere (ie, w/o losing heat), it’s temperature would be close to air at the surface. This points to the difference between heat and temperature.
In the upper atmosphere well above the stratosphere, temperatures reach 1000 deg C, yet air density is so low, you would feel little heat, as the mass and thus heat density is low. If you were able to survive the lack of oxygen, lethal radiation and needed no oxygen, you would quickly lose all your body heat despite the high temperatures. A real world example would be that of heating a thin needle to several hundred degrees C. It will not burn your finger since it’s heat content is so low (little mass) it dissipates quickly before it can do any damage.
Temperature of air at 2-3 meters (or 14,000 ft via satellite) or on the surface of the oceans is a very poor way to determine if our planet is heating. Temperatures can increase or decrease locally, or even in aggregate over short time periods (decades) but tell you little about if the heat content of the planet is increasing or decreasing.
The oceans are tremendous heat sinks with a heat capacity 50 times greater than the atmosphere. Heat gained by the atmosphere is quickly be absorbed by the oceans and temperature increases would be minimal as a result of evaporation and downward transport of heat due to increased salinity. In fact, the ocean surface area actually warms the atmosphere in the higher latitudes since it is at a higher temperature than the air. If not for the oceans ability to transport heat to the higher latitudes, we would be in a permanent ice age. Most of the Northern Hemisphere releases more energy to space than is received from the sun. It is only at the tropics that the energy balance is positive, and weather and the oceans then transfer this energy to the higher latitudes.
Attempts are made to determine the heat capacity of the ocean, but these are uncertain estimates and changes exceed the uncertainty of the estimates.

Phil. said on May 8, 2010 at 8:50 pm:

Steve Goddard says:
May 8, 2010 at 7:27 pm
Mole is a non-dimensional number. A mole of H2 weighs much less than a mole of UF6
The mole is the SI unit of the amount of substance, it is not non-dimensional, a mole of a substance has a mass equal to the substance’s molecular weight.

A mole is just a number, a commonly used divisor when talking about a count of something.
You have a quantity of identical objects, be they atoms or ping-pong balls. You can describe the count in terms of thousands, millions, quadrillions, even moles. No one would argue a term like a quadrillion has a dimensional quality, in use you just take the count, divided it by a quadrillion, report that number. Exact same thing with a mole, you take the count, divide by a mole (6.02214 x 10^23), report that number.
3.28 * 10^24 = 5.45 moles. Left side is a count, an ordinary number. It has no dimensional quality. How can you argue the right side is not non-dimensional?

stevengoddard says:
May 8, 2010 at 9:02 pm
Dave McK
You can stop hyperventilating now. The average measured lapse rate on Earth is a little lower than the dry lapse rate. About 6.5.
————————————————
The adiabatic lapse rate of dry air is -9.8K/km
You are calling 2/3 ‘little’ and avoiding to name the real number.
Sir- 66% of something is significantly less than 100%.
The effect is due to water and the hadley pump that moves the working fluid from the heated surface to the infinite heat sink of space.
Don’t try to belittle me- you act like a damn climatologist.

The surface of Venus is dominated by volcanism. It has a crappy heat pump to lose the heat.
About 80% of the planet consists of a mosaic of volcanic lava plains, dotted with more than a hundred large isolated shield volcanoes, and many hundreds of smaller volcanoes.
Volcanoes less than 20 kilometres (12 mi) in diameter are very abundant on Venus and they may number hundreds of thousands or even millions.
Forget about greenhouse, dude. You aren’t helping.

http://www.engineeringtoolbox.com/spesific-heat-capacity-gases-d_159.html
Gas or Vapor kJ/kg
Air 0.287
Carbon dioxide 0.189
Water Vapor 0.462
Steam 1 psia.
120 – 600 oF
That’s what it takes to change the temperature 1 degree K.
When CO2 changes from 1 to -1 C, a change of 2 degrees C, it radiates 2(0.189 kJ/kg) = 0.378 .
http://en.wikipedia.org/wiki/Enthalpy_of_vaporization
When water vapor changes from 1 to -1 (and condenses) it radiates 2257 kj/kg + 2(0.462 kJ/kg) = 2257.853776 kJ/kg.
It does this every single time you see a cloud.
But CO2 has no phase change so it carries no heat – the numbers:
All gases at the same temperature have the same number of molecules per unit volume. (Avogadro)
Water, being light, masses 18g/mole and CO2 masses 44 g/mole
Using 1 mole of air, just to make math easy:
We lowball the water in the atmosphere at 1% of the molecules
So, in a mole of atmosphere, we have 0.01 moles of water = 0.18g
now we highball the CO2 at 500ppm which is 0.0005, or 1/2000 of a mole of CO2.
1/2000 * 44g/mole = 0.000484 moles of CO2 = 0.021296g
So in our mole of air with but 1% H2O and a generous 500ppm CO2-
the water condensing radiates 0.18g * 2257.853776 kJ/kg = 406.41367968 J
while the CO2 radiates 0.021296g * 0.378 kJ/kg = 0.008049888 J
the ratio of 0.008049888/406.41367968 = .00001980712855516645290496438242332
or as much to say that water vapor in the example carries 50486.873814890343815963650674393 times more heat than the CO2 does.
And that’s just rain. If it turns to snow- multiply by 5-6.
Meanwhile, Venus is a ball of active volcanoes with a dry heat pump to radiate it poorly.
That is why Earth’s climate doesn’t resemble that of Venus.
Forget about CO2.

Dave McK says:
May 8, 2010 at 8:42 pm
Dave, what was the point of that “rant”?
Did you appeal to authority? Or that “they” have more money?

Dave McK
There are more than 50 active volcanoes on Earth’s land surface, not to mention hundreds under the oceans. Their tiny contribution to the energy budget is much less than the measurement error.
http://www.geo.mtu.edu/volcanoes/world.html

Anthony,
I think this could be a really big nail in the coffin of climate change because it demonstrates more clearly than anything else that the normal critical processes that operate in science haven’t worked in “climate science” for some time! Can you get this published in a journal somewhere?

Gareth
I was thinking the same thing. Small differences in atmospheric pressure could explain the early faint sun paradox and possibly ice ages as well. Certainly something worth looking into.

Nick Stokes,
The 700K surface of Venus doesn’t emit 12,000 W/m2. That would be (close to) the emittance of a black body radiating at near 700K, but Venus’s surface is NOT a black body.
Venus’s surface must be 733K to remain in radiative balance with sunlight because almost the entire infrared spectrum is blocked by the CO2 atmosphere and water vapor at high altitude. When you block parts of the infrared spectrum, the Stefan Boltzmann law no longer applies. Instead of having a simple formula based on T^4, now you have to integrate over the whole emission spectrum wavelength by wavelength, excluding the wavelengths that are blocked.
When you start blocking parts of the emissions spectrum, it takes a much larger increase in temperature than given by the T^4 law to emit the same amount of energy.

Jbar
Your arguments don’t work.
Night on Venus is thousands of hours long, and the temperature is the same as the day side – which doesn’t receive much SW either.
Almost all of the IR is absorbed by Earth’s atmosphere, but we seem to be able to keep temperatures below 733K.

Gareth,
“Convection currents on Earth cause warm air to rise, expand and cool whilst pushing cool air down, compressing and warming it. If Venus has convection currents it is not behaving any differently.”
As I understand it, convection comes from air that is being heated (and hence expands and then rise as it is lighter that the surrounding air) either by the sunlight on the surface or by the sunlight itself or both. If we turn off the energy source the convection stops, which also happens on earth during the night. What this tells us, is that without an external energy source as the sun, the temp on the surface on the earth will drop rapidly due to energy being lost to space.

Spector:
Let’s do a thought experiment. If a “supernova flash-boils the ocean” as you suggest, then you have an extremely high water vapor concentration in the atmosphere causing a surface pressure of 265 atmospheres (including N2 and O2). At that concentration, water vapor’s capacity to block infrared would turn Earth into a Venus, at least temporarily, and the oceans might never condense again. At that pressure, surface temperature would have to fall below 390C for water to condense.
On the other hand, the whole atmosphere would be enshrouded in water vapor clouds. Some clouds reflect light but others trap infrared, so whether or not this brave new world would stay stuck in “runaway greenhouse” mode or reflect more light back into space and cool back down (allowing the oceans to reform) depends on what type of clouds dominate. Even if the globe cooled enough to form oceans, there might still be enough water vapor left in the atmosphere to keep the surface at some higher pressure and temperature than today (greater than 100C), depending on the balance of cloud types and global albedo.
Either way, the intense blast of radiation from any supernova close enough to boil the oceans would directly kill every living organism on the planet instantly. Game over. Reboot.

pft
The ocean does not freeze at the bottom because water is most dense a few degrees above freezing. It cools at the surface of the ocean and then sinks down before it freezes. It cannot freeze then because there is no mechanism to cool it to a lower temperature down there.
We’re very lucky that water works this way or ice would continue to pile up on the ocean floor until all the oceans and lakes would be entirely frozen over and our planet would be an ice ball.

If the seas of Venus boiled in a runaway greenhouse meltdown, where is the water?

Without greenhouse gases in Venus’s atmosphere, Venus would be hundreds of degrees cooler. That means Venus is that hot because of the greenhouse effect.
Talk about pressures and lapse rates is just dancing around the above fact.

Based on this text and others, it seems Venus is hot because of its thick atmosphere. The cause of this runaway-building-of-a-thick-atmosphere might be its proximity with the sun. Now it is in equilibrium because of the high albedo of its atmosphere(negative feedback).
The way I understand the adiabatic lapse, I might be wrong, is like this.
If you have a differential of pressure through a column of gas, you have more molecules on one side. I the gas is well mixed, all molecules will have the same distribution of chaotic-kinetic-energy(heat). So the side of the column with more molecules will have more heat.
Now if there was no movement, after some time I guess the warmest molecules would get on top and the coldest at the bottom.
So basically, the system has to be somewhere between those two tendencies.
I also took a look at what a supercritical fluid is. Based on wikipedia, “In addition, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties of a supercritical fluid to be “fine-tuned” “. So it seems a supercritical fluid CO2 has the compression properties of a gas, not of a liquid.
Finally, there is also a place on Earth where temps are high, under the crust. It is also possible that Venus atmosphere could be a good insulator just like Earth’s crust, so the geothermal heat could build there. Just like I believe the geothermal heat could build under a thick layer of ice on Earth, but this is another subject.

On the motion to the motion to the motion..
Everyone in favor of NASA being given the mission of diverting a comet into Venus in the next two decades (and thereby gaining the wherewithall to save us from a similar impact) and beginning the transformation of Venus into a habitable planet say YES!
Those opposed?
The motion is carried and will be open for discussion for the next session, following the Memorial Day and 4th of July Break! One hour, equally divided will be allotted to the discussion by the Committee of the House.

Jack Morrow
It is nice today, but supposed to be 45 degrees for a high on Wednesday. That is close to normal for January 1.

Dry lapse rate looks suspiciously like ‘thermal gradient’ and this gradient shouldn’t occur without a thermal difference between the upper atmosphere (at space) and the surface. From this viewpoint, if the top of a dry atmosphere were at the same temperature as the surface, there would be a pressure difference from gravity but no thermal gradient. That gradient in the Venus example should be mostly from solar heat trapping at the bottom of the atmosphere.
One major difference between Earth and Venus is Nitrogen content and Venus would have probably have been entirely different if it had as much as the Earth’s atmosphere. The million dollar question is how Venus and Mars managed to be without it as it was abundant in the early solar system.

Ralph
Actually the argument is different from what Willis posted. I’m not discussing the radiative budget – rather just the basic physics of gas warming as it moves to areas of lower pressure lower in the atmosphere. The higher the pressure, the higher the temperature.

Tom in Florida
May 9, 2010 at 5:41 am
I have pointed out here and in another post that one really big difference between the Earth and Venus is our monstrously oversized moon which played a major role in the creation of our atmosphere and plays a major role in weather today, but no one seems to remember what was once understood science.

Steve (Goddard),
Your insistence on relating pressure to molecular motion, and heating due to pressure, is ruining what should have been a good discussion. I believe that it also impedes your understanding of your own proposal. As many others have put forth, and I will re-iterate, the atmosphere is warmed from the bottom, and only then will things start moving up. It is not the other way around. Where the surface gets its heating from is another matter. It might be simple percolation of Solar energy down to the surface, whether directly or in the form of a bit of back-radiation from the atmosphere, or it might be vulcanism, or it might be something that the Borg are doing with slipstream drives, but it is the bottom that does the heating of the atmosphere, not the other way around.
Regarding pressure, it can be caused by molecules in motion. It can also be caused by the simple weight of whatever is sitting on something else. It can furthermore be caused by the application of any force of any kind from any source to whatever is feeling the pressure. We figure out the pressure at depth in the oceans, for example, by calculating the weight of the water above that depth, and then we add the atmospheric pressure that exists at sea level, which in turn is due to the weight, not the motion, of the air molecules stacked up above that. This is basic Physics. It doesn’t matter if the atmosphere is in the form of a gas, as solid, or a slurpy. It’s just its weight that determines the pressure at ground level, or the bottom of the ocean, nothing more.
I say this as a physicist who has taught many subjects, including Thermodynamics, over many decades, but you do not need to simply take my word for it. There are 10’s of thousands of textbooks that will tell you the same thing.
Regarding your original proposal, the data you presented shows that there is no need to invoke a “runaway greenhouse” effect on Venus, any more than there is on Earth. The graph of Temperature vs Altitude that you include looks very much like that of the Earth in the bottom two regions. There is a linear “lapse rate region” up to 60km, followed by an isothermal region for about 10km, much like the bottom part of our own stratosphere.
If one can extrapolate back down to the surface using the lapse rate that can be found from the graph, it would have a temperature of about 500°C or so, purely on the basis of ordinary atmospheric dynamics, with no need for massive effects of any other kind. Note again, that by extrapolating back down to the surface, I am not saying that the atmosphere of Venus heats up because you are going down. I am purely using the apparent straight line to estimate the value at its bottom end, given what the graph shows for its top end.
The higher regions of Venus depart from Earth’s pattern, but the lowest 60km looks very much like a “regular troposphere”, albeit much thicker than our own, which only shows that it is being heated more strongly, from below, than is the case on Earth. That “thickness effect” may also be seen on our own planet. As you likely know, the tropopause in our Polar regions is only at a height of about 8km, while in the Tropics, it is generally at a height of 16km, or even a bit more above very hot places. That is not a coincidence. It is simple cause and effect, and they need to be put in the right order, which you are not doing. Umbrellas don’t cause rain.
I do not like “getting personal or confrontational”, and I generally like the things you post on WUWT, but I think it’s time you stopped being so dogged about “being right”, and accepted the valid and well-intended interventions of many other posters who have carefully explained their points of view, only to be summarily dismissed by a one-liner from you. This isn’t very respectful, there is no need for it, and it simply impedes understanding.
/dr.bill

Nice post. I like the Venera images. Since it’s VE parade day in Moscow, let’s toast a Russian aptitude for Polar scientific expeditions, space exploration, and the encirclement of Axis armies.

Venus has no oceans, so it has no limestone. No limestone means a thick atmosphere of CO2. A thick atmosphere means high temperatures.
It took decades for science to accept the obvious fact of continental drift. Scientists can be just as bone headed as anybody else.

Since neither Mars nor Venus has any planetary magnetic field, I would expect that the solar wind carries away any lighter gases, such as H2O vapor, leaving behind the more dense gaseous molecules. With it being far to hot on Venus for carbon based life, there is no conversion of CO2 to oxygen and carbon.
Venus is vastly different from Earth in most respects. To attempt to equate the workings of the atmospheres on Venus and Earth is an exercise in futility. Too, we know very little about the charastics and composition of Venus itself.
Back when I was a lad, from what I personally read (and I had a greal of interest in things scientific), it was speculated that the temperature of Venus was about 125 degrees F, and that Venus was a “wet” world, since the dense clouds were thought to be of water. Very warm and balmy, was the scientific speculation circa 1950 or so.
“A little knowledge is a dangerous thing.” ~ Alexander Pope
To attempt to “extrapolate” only a little knowledge into a “grand theory” is one of the most dangerous of all things that can be done..

I am finding this thread as baffling as the previous one about Venus. Why are the following points not obvious?
(1) The surface must support the weight of the atmosphere, regardless of its temperature. Gases have weight! Thus, the surface pressure is determined by the mass of the atmosphere and the gravity of the planet, independent of temperature.
(1′) There is a very small effect of temperature, since it does affect the depth of the atmosphere, and gravity diminishes slightly with height. This is a small effect.
(2) An atmosphere should approximately follow an adiabat — that is, pressure and temperature varying at the adiabatic lapse rate — provided the conditions are suitable for convection. This is true in the lower atmosphere of both Earth and Venus. But convection will only occur if the fluid is heated from beneath. In other words, the net heat flow in the fluid in the convective zone must be upward.
(3) If the atmosphere of Venus were heated from the top — which I gather is Steve’s theory — then there should be no upward heat flow in the lower atmosphere. Ergo, no convection. The temperature profile would be much flatter than the adiabatic lapse rate. Indeed, in the long run it should be quite flat, an isothermal atmosphere.
(4) This is not what is happening. Thus, the surface is heating the atmosphere at the bottom. Internal energy sources, volcanism and such, are orders of magnitude too small. The surface must be heated by the short-wave radiation that reaches it. That is, it must be heated by sunlight (however attenuated). This net heat input to the surface accounts for the net upward heat flow in the atmosphere.
(5) The surface is really hot, and so it radiates strongly. (Most natural surfaces are pretty good blackbodies at IR wavelengths.) In fact, the surface radiates dozens of times more IR radiation than actually emerges into space at the top of the atmosphere. So almost all of this must be absorbed by the atmosphere, and reradiated (both up and down, of course, in each layer).
So we have an atmosphere heated from below, by a surface that is getting its energy input from short-wave radiation. The thermal radiation from the surface is strongly absorbed by the atmosphere. If we turned off this absorption and made the atmosphere transparent to IR, then the planet would quickly cool off to a much lower temperature, until radiative equilibrium would be re-established. Doesn’t that pretty much define the greenhouse effect?
I keep expecting this thread to be about WHY Venus has developed such a strong greenhouse effect, and whether the term “runaway greenhouse” appropriately describes this process. Fascinating question, and present theories involve a good deal of speculation. I would probably count as a moderate AGW skeptic — a “luke-warmer” in common parlance — but the discussion here does not inspire me with confidence that this community has a firm grasp on the basic physics. Sorry to be so blunt, but the thing is pretty distressing to someone who reads WUWT regularly and with pleasure.
I’d like to see Steve respond to the points about hydrostatic equilibrium and the upward heat flow associated with the adiabatic lapse rate.

Here’s another clear explanation of the role of the adiabatic lapse rate in ‘greenhouse’ warming.

Steven
Over at “The Reference Frame” Lubos Motl has a detailed dicussion of your WUWT posts on Venus temperature.
You will be interested to find that in his conclusion he is largely in agreement with you. i.e. that the greenhouse effect on Venus amounts to a few dozens of degrees C and that the very high temp at the surface relates primarily to the environmental lapse rate.

It’s been confusing on both articles how people are talking about pressure.
Pressure is force exerted on a surface, can be expressed as pounds per square inch or even newtons per square meter. Atmospheric pressure is being discussed, which basically is the average of the forces involved from gas molecules hitting a surface.
So if the temperature drops to where all the gas molecules precipitate out, what atmospheric pressure is acting on a vertical surface? None. What if I set up a pressure gauge with a horizontal surface pointing upwards, a meter above the ground, what would it read? Nothing, as all the formerly gaseous molecules are already in a layer on the ground below the gauge. Same thing if the horizontal surface is pointing downwards, rotated to vertical, or in any position.
Yes, you can talk of pressure from a substance laying on a surface that’s not completely vertical. But that would be pressure based on gravitational force, while here atmospheric pressure (all-surrounding) is being discussed. So why all the nit-picking?

Didn’t mean to be condecending, but using the closed volume ideal gas laws to describe atmospheric pressure, equating temperature with atmospheric pressure, and implying that gravity disappears at the lowest temperatures are your ascertions. When lucid comments are made to correct these misconceptions there is no acknowlegement nor attempt at retraction. It would therefore appear that your intent is somewhat other than achieving an understanding of the question at hand.

If you changed the composition of Venus atmosphere to 100% nitrogen, the planet would be much colder due to the lack of absorption of IR. The atmosphere would also necessarily be much thinner (lower volume.) P = nRT/V
However, if you changed the composition of Venus atmosphere to 95% nitrogen and 5% CO2, the temperature and height of the atmosphere would not be hugely different than it is at present. Why? Because the greenhouse effect is logarithmic. After the first few percent, additional CO2 makes much less difference to the temperature.
Consider earth, where a doubling of CO2 only increases temperatures by <1 (Lindzen) to 3 (IPCC) degrees C.

Steve:
“However, if you changed the composition of Venus atmosphere to 95% nitrogen and 5% CO2, the temperature and height of the atmosphere would not be hugely different than it is at present. Why? Because the greenhouse effect is logarithmic. After the first few percent, additional CO2 makes much less difference to the temperature.”
I have difficulty seeing this. I can understand the reason for the thick CO2 blanket since there are no water/carbonates to remove the volcanically generated CO2. However, this wouldn’t apply to nitrogen and there should still be less of it relative to Venusian gravity using earth as an example. Couldn’t the major source of heat trapping on Venus simply be because of the thick atmosphere and lack of water vapor, making vertical convective transfer to space difficult (unlike Earth)? It has already been mentioned that the ground level density of the CO2 may be in the supercritical or near liquid state, which would make vertical thermal transfer very difficult relative to that of a gas.
As covered in other comments regarding CO2 depth pressure and temperature, if one could enclose a vertical section of Venusian atmosphere in a sealed insulated tube (closed system), after a period of time the temperature would completely equalize throughout the volume through convective transfer even though the gravity pressure at the tube bottom would still be 93 atmospheres. If this insulated tube of CO2 where originally in space and dropped into Venus’ gravity field, there would be immediate heating at the ‘bottom’ from the pressure increase but this would be cause by mass and potential/kinetic energy transfer to that section. Again when this closed system is left alone in the constant gravity field, the temperature would eventually equalize through convective transfer throughout the gas (at a higher temperature because of the gravity potential energy added) even though the pressure would be higher at the ‘bottom’ of the tube.
If this were not the case, all one would have to do for free energy is to install a heat engine between the top and bottom of the tube since there would be a constant temperature difference even in the closed system.

RealClimate [yeah, yeah, I know] provides some insight into why Venus’s surface temperature is so uniform even though there is very little surface wind to redistribute energy, and minimal light on the dark side.
The Venutian atmosphere is incredibly massive, roughly 40% of the weight of Earth’s oceans. Consequently it would take an incredibly long time for the entire atmosphere to heat up or cool down. (In contrast, much of Earth’s thin atmosphere easily heats and cools in a day.) So expecting the surface temperature of Venus to vary would be like expecting the temperature at the bottom of Earth’s ocean to vary. This massiveness means that the lower atmosphere of Venus is able to equilibrate in temperature all the way around the planet with very little convection (i.e. very low wind). A simple solution when you think about it.
Venus Express finds no significant “daily” variation in Venus’s atmospheric temperature below an altitude of 45km. That altitude is equivalent to a depth (or rather, pressure) of two Earth atmospheres. All the action takes place in the upper atmosphere. The high speed winds in the upper atmosphere transfer energy from the day side to the night side and by the time you get down to 45km altitude, the temperature there remains constant. (This is a few km below the lowest cloud layer.)

stevengoddard says:
May 9, 2010 at 12:36 pm
Venus has no oceans, so it has no limestone. No limestone means a thick atmosphere of CO2. A thick atmosphere means high temperatures.
Bless the clams for saving us from venereal discomfort, for while Venus was being repaved with lava, they were constructing the white cliffs of Dover and starting to crawl from the sea.
Did I get the physics of this right, finally, Steve? It’s all about the fizz in the beer?
I think Dr. Pangloss was right and it’s time to get back to the farm where they don’t believe the rooster actually makes the sun come up.

First let’s clear up some very basics physics.
The ideal gas law is appropriate when talking about gases in confined volumes. When talking about atmospheric pressure, you use the barometric formula.
http://en.wikipedia.org/wiki/Barometric_formula
There are several constants used that are specific to the atmosphere you are trying to use it on.
Atmospheric pressure is dependent on mass and gravity, among other things, and is derived from the ideal gas law.
To wit, as you approach zero kelvin your atmospheric pressure approaches infinity, not zero. (NOTE: Of course, under that scenario you can’t use basic formulas anyway.)
But back to the main discussion. Mr. Goddard is proposing that pressure is somehow driving the temperature on Venus. However, this makes no sense. Titan is a solid counter-example. It has a dense N2 based atmosphere and yet it is still bone chilling cold. There is simply nothing there that can hold onto the meager amounts of heat it receives from the sun (or Saturn).
Venus is another matter entirely. You don’t need a complex experiment to verify that the atmosphere is preventing almost all heat from escaping. We have a good idea of the surface temperature. We also can figure out how much combined IR radiation is escaping the planet (both reflected and emitted through day and night side IR measurements). If what is radiating from the planet is much less than what it should be given the other constraints, then SOMETHING between the surface and the TOA is preventing heat from escaping.
If it were merely density of the gas and NOT composition, then we can verify this quite simply. Take a few different gases (GHG and non-GHG) and place them in IR transparent containers at various pressure levels. Fire an IR laser through each sample at each level and measure. If pressure is indeed the key player, then we should see similar results across all the gas samples. However, if composition is the key player, then we should see disparate results across the gas samples. GHG gasses at higher pressures would absorb more IR while non-GHG gasses would show little to no differences regardless of pressure level.
Fortunately, these have already been done many times over in establishing thermal properties for various gases. It should come as no surprise that atmospheric composition is what matters. Density matters as well. After all, if you don’t have much of an atmosphere you’re not going to be absorbing much of anything no matter the composition. But you can have an N2 atmosphere at 1000 atmospheres and it still won’t create a greenhouse effect. Saying otherwise is the equivalent of saying you can can make salt taste like sugar by adding more salt.
Can what happened to Venus happen to Earth? Not very likely. We’d have to try really hard to do so, and it would take a long time of trying hard (centuries). I’d like to think that we would be smart enough to notice palm trees growing in Antarctica and know that something might be amiss.
At any rate, composition AND density determine the IR profile of an atmosphere. Basic high school/college level physics that has been validated many thousands of times in labs across the planet.
~X~

To Nick Stokes:
OK, let’s say the surface emits 12,000 W/m2. Yet Venus only radiates 300-400 W/m2 from the top of the atmosphere, and the net radiation from the surface must be on the order of 70 W/m2. (That is 16% of the radiation received by Earth’s surface, which is what my source says reaches the surface of Venus.)
Doesn’t this prove how dramatically large the greenhouse effect is on Venus??!! The surface radiates 12,000 W/m2, but 11,930 W/m2 gets reflected back down to it by the atmosphere!!! That is a SUPER-GREENHOUSE.

Marc77:
Another thing about supercritical fluids – the supercritical point is the point at which the transition between liquid and gas disappears. There is no longer liquid and gas – there is only this supercritical fluid thing.
Something weird must go on at the altitude in Venus’s atmosphere where the pressure makes the CO2 supercritical.

Bjorn & others: You haven’t heard the story of the “runaway greenhouse”?
Supposedly a long time ago Venus may have been like Earth, but being so close to the sun the oceans got hotter until the ocean started to boil. Water is a good greenhouse gas, so once the water started to boil, it made the greenhouse effect stronger, boiling more water, which made the GH effect stronger still, etc. and the greenhouse “ran away” as the oceans completely boiled away.
After that, there might have been 100 atm of water vapor in the atmosphere for some time. With water vapor reaching all the way to the top of the atmosphere, solar radiation could knock the hydrogens loose from water. Venus’s gravity is strong enough to hold onto oxygen but not hydrogen, so the hydrogen gets kicked out into space. Eventually almost all the hydrogen from the water got stripped away from Venus.
Meanwhile all the free oxygen (created by the stripping away of hydrogen from water) reacted with anything it could near the hot surface, especially carbon. Eventually this turned all the carbon on Venus into CO2. 90 atmospheres of CO2 makes a strong enough greenhouse to heat the surface to 470deg C.
Some evidence – what little water vapor there is left in the upper atmosphere is rich in deuterium. Deuterium is twice as heavy as hydrogen and so it’s harder for solar radiation to knock into space, so it gets more concentrated as the hydrogen goes away faster.

Okie Skeptic May 9 2010 5:17.
Again when this closed system is left alone in the constant gravity field, the temperature would eventually equalize through convective transfer throughout the gas (at a higher temperature because of the gravity potential energy added) even though the pressure would be higher at the ‘bottom’ of the tube.
If this were not the case, all one would have to do for free energy is to install a heat engine between the top and bottom of the tube since there would be a constant temperature difference even in the closed system.

More like radiative transfer as you are assuming(I think) no convection in your column.
You are right on the last point, a point I feel is the Achilles Heel of Steves conjecture. If Steve is correct, then he has invented the Venusian equivalent of perpetual motion.

Xyrus
You wrote ” as you approach zero kelvin your atmospheric pressure approaches infinity, not zero. “
PV = nRT
Pressure is proportional to temperature, not inversely proportional as you claim. Now start over.

Nick Stokes
Your heat transfer analogy doesn’t work, because the amount of required work also increases by 90X.
The key issue is wind velocity, because that limits how far the differentially heated air can move in a given amount of time.

Bob_FJ and Steve, if pressure could create heat it would mean gravity is not a conservative force. Energy could be extracted from gravity and converted to heat via the “Goddard PV = nRT” relation.
If Steve was right you would have to take an oxygen tank with you to the Arctic because low temp would mean low pressure. Low pressure systems would have lower temperature than high ones. Etc.
If it’s not greenhouse I think the answer lies more along the lines of: 1) There’s a lot more internal planet heat than given credit for. 2) There’s heat generated somehow from the solar wind and Venus gets twice as much of that as Earth.