By Steve Goddard
ESA’s Venus Express mission has been studying the planet and a basic atmospheric model is emerging.
Venus has long been the CO2 bogeyman of climate science. 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. I’m not going to review that discussion, but instead will pose a few ideas which should make the concepts clear to almost everybody.
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.
Because we have a sun providing energy to the periphery of the atmospheric system, the atmosphere circulates vertically and horizontally to maintain equilibrium. Falling air moves to regions of higher pressure, compresses and warms. The greater the pressure, the greater the warming. Rising air moves to regions of lower pressure, expands, and cools. The amount of warming (or cooling) per unit distance is described as the “lapse rate.” On Earth the dry lapse rate is 9.760 K/km. On Venus, the dry lapse rate is similar at 10.468 K/km. This means that with each km of elevation you gain on either Earth or Venus, the temperature drops by about 10C.
It is very important to note that despite radically different compositions, both atmospheres have approximately the same dry lapse rate. This tells us that the primary factor affecting the temperature is the thickness of the atmosphere, not the composition. Because Venus has a much thicker atmosphere than Earth, the temperature is much higher.
dT = -10 * dh where T is temperature and h is height.
With a constant lapse rate, an atmosphere twice as thick would be twice as warm. Three times as thick would be three times as warm. etc. Now let’s do some experiments using this information.
Experiment # 1 – Atmospheric pressure on Venus’ surface is 92 times larger than earth, because the atmosphere is much thicker and thus weighs more. Now suppose that we could instantly change the molecular composition of Venus atmosphere to match that of Earth. Because the lapse rate of Earth’s atmosphere is very similar to that of Venus, we would see little change in Venus temperature.
Experiment #2 – Now, lets keep the atmospheric composition of Venus constant, but instead remove almost 91/92 of it – to make the mass and thickness of Venus atmosphere similar to earth. Because lapse rates are similar between the two planets, temperatures would become similar to those on earth.
Experiment #3 – Let’s take Earth’s atmosphere and replace the composition with that of Venus. Because the lapse rates are similar, the temperature on Earth would not change very much.
Experiment #4 – Let’s keep the composition of Earth’s atmosphere fixed, but increase the amount of gas in the atmosphere by 92X. Because the lapse rates are similar, the temperature on Earth would become very hot, like Venus.
Now let’s look at measured data :
http://www.astro.wisc.edu/~townsend/resource/teaching/diploma/venus-t.gif
http://www.astro.wisc.edu/~townsend/resource/teaching/diploma/venus-p.gif
Note that at one Earth atmospheric pressure on Venus (altitude 50km) temperatures are only about 50 degrees warmer than earth temperatures. This is another indication that atmospheric composition is less important than thickness.
Conclusions : It isn’t the large amount of CO2 which makes Venus hot, rather it is the thick atmosphere being continuously heated by external sources. It isn’t the lack of CO2 on Earth which keeps Earth relatively cool, rather it is the thin atmosphere. Mars is even colder than earth despite having a 95% CO2 atmosphere, because it’s atmosphere is very thin. If greenhouse gases were responsible for the high temperatures on Venus (rather than atmospheric thickness) we would mathematically have to see a much higher lapse rate than on Earth – but we don’t.
WUWT commentor Julian Braggins provided a very useful link which adds a lot of important information.
“The much ballyhooed greenhouse effect of Venus’s carbon dioxide atmosphere can account for only part of the heating and evidence for other heating mechanisms is now in a turmoil,” confirmed Richard Kerr in Science magazine in 1980.
The greenhouse theory does not explain the even surface temperatures from the equator to the poles: “atmospheric temperature and pressure in most of the atmosphere (99 percent of it) are almost identical everywhere on Venus – at the equator, at high latitudes, and in both the planet’s day and night hemispheres. This, in turn, means the Venus weather machine is very efficient in distributing heat evenly,” suggested NASA News in April 1979. Firsoff pointed out the fallacy of the last statement: “To say that the vigorous circulation (of the atmosphere) smooths out the temperature differences will not do, for, firstly, if these differences were smoothed out the flow would stop and, secondly, an effect cannot be its own cause. We are thus left with an unresolved contradiction.”
======================================================
An update for those interested in what Venus looks like at the surface.
On March 1, 1982, the Soviet Venera 13 lander survived for 127 minutes (the planned design life was 32 minutes) in an environment with a temperature of 457 °C (855 °F) and a pressure of 89 Earth atmospheres (9.0 MPa). The photo composite above shows the soil and rocks near the lander.
Here’s another Venera image that shows a hint of yellow atmosphere. – Anthony
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.
I have often thought that Venus, being much closer to the sun than the Earth, must intercept a larger flux of gases from the solar wind and the extreme outer layers of the solar atmosphere. Perhaps the atmosphere of Venus is as dense as it is because that planet has had a better opportunity to scoop up gases from the sun. [My speculation.] For some gases, there may be equilibrium condition where the rate at which each gas is acquired is balanced by the rate it escapes back into outer space.
If the Earth had the same surface pressures as Venus, I am sure that the ground temperatures would be much higher here also. I do not think CO2, per se, is the real problem.
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.
So let me get this straight, you have written two “Venus” blogs that have displayed your misunderstanding and misapplication of the ideal gas laws, and yet you wish everyone to believe that your insight on that planet trumps all the scientists at NASA and JPL?
REPLY: Still snotty and condescending but better than the last one that was snipped
>>>With a constant lapse rate, an atmosphere twice as thick would
>>be twice as warm. Three times as thick would be three times as warm.
>>>etc. Now let’s do some experiments using this information.
Without wishing to stir up too much controversy (remember last time !) , this is the same argument as Willis Eschenbach’s Steel Greenhouse posting (below). Willis doubled the number of steel spheres, to do exactly the same thing – double the temperature on the surface.
http://wattsupwiththat.com/2009/11/17/the-steel-greenhouse/
Pretty obvious, really.
.
GeoFlynx
If you have a specific objection, please post it. There is no constructive way to respond to ad hom attacks.
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.
jcrabb
Some greenhouse you are describing. It doesn’t lose even one degree of temperature over 1400 hours of pitch black. You should patent it. You will make a killing.
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.
DaveMcK says:
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 would be a wonderful world if it did radiate heat like that – but almost always the heat is conducted by cold surfaces (having already radiated the heat away) or transformed into kinetic energy warming supercooled gases, which have also already radiated the heat away.
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.
Dave McK
May 9, 2010 at 1:37 am
OH NO! Its worse then we thought. The green house affect is melting the planet!
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.
OkieSkeptic says:
May 9, 2010 at 8:37 am
“……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.”
————————————————————————————
It’s always puzzled me that peculiarity….. Just why is it that Earth has 70% nitrogen in it’s atmosphere, whilst Mars and Venus barely have any?
G’dam mystery if you ask me:-)
>>stevengoddard says: May 9, 2010 at 8:43 am
>>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.
Two sides of the same coin, is it not….
.
stevengoddard says:
May 8, 2010 at 2:57 pm
QUOTE
You can infer how thick the atmosphere of Venus is from this diagram:
http://www.astro.wisc.edu/~townsend/resource/teaching/diploma/venus-t.gif
UNQUOTE
That graph appears to support your hypothesis. It will be interesting to see what rebuttal James Hansen can come up with.
It looks as if there might be a “Goldilocks Zone” on Venus at an altitude of over 50 km!
With all these comments, some expanding, some disagreeing, some clarifying, I no longer know how much of the original Note stands. Would it be possible, once the Comments are closed, to modify as appropriate, with footnotes if necessary? This is, I suppose, the benefit of peer-review before publication: what remains is cleaned up and ready for distribution.
Just one final post on the subject and I will leave it at that. When we meteorologists speak of “atmospheric pressure” here is what we are referring to:
This from the AMS Glossary of Meteorology http://amsglossary.allenpress.com/glossary
“atmospheric pressure—(Also called barometric pressure.) The pressure exerted by the atmosphere as a consequence of gravitational attraction exerted upon the “column” of air lying directly above the point in question.”
If others have a different definition of atmospheric pressure, then that should be stated at the beginning of their thesis so that we are talking about the same things.
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
The Greenhouse Effect (GHE) and the thermodynamic lapse rate.
The phrase GHE muddles together the effect and the suggested cause. It suggests that the warming effect of the atmosphere is caused by the chemical structure of some of the gases in air, molecules that are made of more than one type of atom, especially CO2.
There is warming in addition to that caused by the sun, calculated using the concept of energy balance and the Stefan/ Boltzmann Law. What causes the extra warming?
Steve Goddard’s recent posts say the extra warming is explained by the pressure of the atmosphere. There is no need to consider the chemical composition. All gases create pressure, on Earth mainly N2 and O2, on Venus mainly CO2. All gases contribute to the extra warming. All of the extra warming is explained by physics. There is no need to consider the structure of these gases.
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.
dr.bill
How is Venus “warmed from the bottom” during it’s thousands of hours long nights?
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.
Here’s a paper by Carl Sagan that discusses the Venusian ‘greenhouse’.
http://adsabs.harvard.edu/full/1967ApJ…149..731S
You might be surprised by the mechanism he proposes for it.
Doesn’t it look familiar?
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..