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
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Nullius (if you happen by):
I don’t want to get you blushing or anything, but that was a nicely put together explanation you posted on Science Of Doom website. Admirable clarity.
/dr.bill
Smokey:
Why is there daylight seen on the surface of Venus?
Well, because daylight is VISIBLE LIGHT, NOT INFRARED! CO2 does not absorb visible light.
When a blogger’s shaky knowledge conflicts with actual data, it’s the blogger that is wrong.
Hey, you started it!
Mike M:
Great. Anybody got some 50km long cylinders?
Well, actually, yes. You can model long cylinders of gas at constant temp and pressure on
http://www.SpectralCalc.com
For free if you just want the graph and not the text data file.
Please excuse me if I’m showing attitude, cuz I’ve enjoyed half a bottle of white tonite.
George Turner said
“I ran CO2 spectra at ~90 atm and there’s a transmission window from 3840^cm-1 to 4600^cm-1, so yes there is a narrow window.
I calculated that 799 W/m^2 could be emitted into that window (blackbody), ”
Yo, George, how are you doing this calculation to get the 799W/m2? Is there an online tool?
Not doubting you or nothin’. Just want to check it out and “Favorite” it.
BTW, I think Spectralcalc.com lets you specify a radiation source to use with your gas transmittance case??? Been a long time so not sure. But I think you must pay for that.
Gary W:
As you suggest, the “runaway” narrative is entirely speculative. It “could” have happened, but there is no historical proxy data to back it up, and maybe never will be anything more than theoretical models.
It assumes Venus started like Earth, with oceans.
Once the oceans reach 100 deg C, thanks to proximity to the sun, water vapor steadily enters the atmosphere, increasing the greenhouse effect all the more and boiling more water which leads to more greenhouse until the oceans are boiled away. That’s the “runaway”. Once it starts boiling, it can’t stop until the oceans are gone.
However this is entirely fantasy because there is no data to specify Venus’s original conditions. Well, except for the high deuterium/ hydrogen ratio in Venus’s atmosphere. But that doesn’t prove Venus was ever like Earth.
Barry Kearns:
In re your May 11 11:47 AM Q#3 to Steve:
Yes, transmittance/ absorbance is not a function of percent of a gas in the atmosphere, but rather a function of the mass or moles of gas that the radiation must pass through. Each molecule of gas has a tiny chance to hit a photon of IR, reducing the IR by a certain very small percentage. The more molecules of gas you have, the more chance of hitting photons. But it’s not a linear function.
If 1kg of gas absorbs 1%, 99% comes out the end.
The next kg of gas absorbs 1% of 99%, leaving 98.01%
3rd kg absorbs 1% of 98.01%, leaving 97.03%
10th kg leaves 90.4%, 100th kg leaves 36.6%, 200th kg leaves 13.4%, 500th leaves 0.66%
1000th leaves 0.0043%. And so on. It is easily calculated by spreadsheet if you know the absorbance/transmittance factor.
Correy Dukes:
Ran across an article in Science today (a March issue, a little behind on my reading) apropos to Earth’s primordial atmosphere:
Recent thinking is that after Earth accreted from asteroids, the sun was rotating much faster than today. Over time, its angular momentum or energy of rotation got transferred to its atmosphere, the corona, creating a solar wind much more powerful than today’s, strong enough to strip all the “terrestrial” (i.e., “non-giant”) planets of their atmospheres, especially the ones without magnetic fields, but even Earth’s WITH a mag field. Then the planets re-acquired atmospheres courtesy of being pelted by asteroids and especially soggy comets.
Venus being closer to the sun and therefore hotter to start out, there is just no way of knowing what kind of atmosphere it had after the comet-pelting. It may NEVER have been like Earth. Any rocks that would testify to its “initial conditions” have all been cooked. Therefore all we have to go on are computer models and any obscure clues from its current atmosphere, and even these have a healthy degree of speculation and assumptions.
Sadly, a Venus-like fate IS envisioned for the Earth, but only because the sun is eating its hydrogen and slowly becoming denser and therefore reacting hotter and faster over the eons as a result, but even this fate will take a billion years or so, and anthropogenic global warming CANNOT turn Earth into Venus.
So where is Earth? Evidence is convincing that humans are increasing CO2 in the atmosphere (this blog notwithstanding) and that this will result in a temperature increase of some degrees C by 2100 (this blog…). IF we want to try and stop CO2 from exceeding some value, it will take a BIG pile of money. The $3 trillion question is why would we do that?
A: To prevent FUTURE human suffering and
B: To prevent FUTURE mass extinctions.
Because the REAL temperature increases and ice melt and sea level rise won’t come until 2050 and later, and despite DOCTOR James Hansen’s wild extrapolations, the Greenland ice sheet probably will not melt for at least 500 – 1000 years.
BUT: There are billions of people suffering today AS WE TYPE. Their suffering can be reduced much more “easily” for much less money than it takes to stop climate change (if only anyone cared enough to actually DO anything about it, like Bill Gates is doing WRT fighting debilitating tropical diseases – YAY BILL!!… even though you double-charged us for 28 years for your bug-eaten software!).
AND: The economic benefits from “stopping” climate change won’t be seen for many decades, and the BIG benefits not even for centuries. If we invest a trillion dollars today, is it worth getting a 1% return on our investment (as the Stern report claims it is) compared to a typical business investment return of 15% to 30%, or gov’t spending return of 5% when we could continue to pour less money into energy research and get the technology costs down and then deploy the cheaper technologies at a later date, like 2020 (My “drop dead” date)?
It is a pickle. We much choose a path, and if we choose the wrong path we will either be screwed, as you say, or “shot in the foot”.
Barry Kearns, May 13, 2010 at 2:57 pm, quoting Correy Dukes:
“Why take the chance? Why not make major changes in our ways that make our planet a healthier place to live? What’s the harm? If I’m wrong (I’m not, trust me)…”
You first, Correy. Start hoofing it from your mud hut down to the river to wash your loincloth on the rocks. Enjoy those mud grubs for dinner.
Anyone who says ‘trust me, I’m not wrong,’ must be about 15 years old, at least emotionally. It’s an attempt to end the debate, and it won’t work here. This isn’t the censoring realclimate, climate progress or tamino. This is the “Best Science” site. All points of view are welcome, and are hotly debated. The ones that remain standing are accepted. That’s why the alarmist crowd hates WUWT: Their arguments generally fail due to lack of hard facts.
Also, Barry, I second your recommendation of Henry Hazlitt’s Economics In One Lesson, which I still have after forty years. The essence of the book, demonstrated through numerous examples, is that when the free market is abandoned, then every dollar that one person gets is a dollar forfeited from another. That is what we’re seeing today. And it is causing enormous harm.
Mass transference of wealth from those who earned it to those who did not cheats the honest, hard working citizens, and hands unearned wealth to the grifters and the government’s subsidized class. It leads to the rule of law becoming an insider’s joke, by taking more and more from those who earned it by actually producing goods and services, and rewarding fast talking scam artists who hide out from any honest debate, and who sell their ethics to whoever provides their constant, all expenses paid trips to Bali, Copenhagen, Mexico City, Hawaii, etc., in addition to the lucrative grants regularly handed out to them with little oversight, and with no rigorous, honestly peer reviewed science either required or performed. It’s simply a back-scratching clique pushing an agenda at the public’s expense.
People aren’t stupid when it comes to knowing what is honest, after tax compensation for their work. They see what is happening. When dishonesty is financially rewarded, it promotes widespread dishonesty — as we see in the Climategate emails, and throughout the stacked deck of the clearly gamed climate peer review process.
The same wealth transference from the productive members of society to the grifters is everywhere we look, from the totally corrupt UN, to universities and their pet grant rainmakers, down to city councils and their developer and union benefactors. Like ravenous hyenas, they all have their eyes on our wallets, intent on confiscating money they never earned, all
based on emotional hand-wringing guilt projection and bogus scare stories unsupported by any real scientific evidence.
Zimbabwe, here we come.
.
</rant>
Dr. Bill, May 13, 8:45 PM
Did a search on “Venus” on ScienceDirect yesterday.
Recall running across an abstract that said there was convection near the surface of Venus [presumably to move the surface energy from visible lite absorption around to the dark side of the planet] and again in the cloud layers (i.e., above 50 km.), but not in between.
Bob Armstrong, May 13, 10:49 (was that AM or PM?)
“still see no alternative to internal heating being the cause of Venus’s steady state surface ”
Literature suggests that Venus was resurfaced 500 million years ago, surely enough time to cool down since then.
Venus can’t have a huge amount more of uranium than Earth, but then again because plate tectonics has stopped since GKW (“God knows when”), energy has gotten bottled up. So WHO the hell knows!?
Hi Bob_FJ
Kicked bottle 3 blind moose. Opening Grand Marnier. Wife away for weekend!
[1] Measurements indicate that Venus’s upper atmosphere takes 5 days to circle the planet, much faster than the Earth, at one of the 3 cloud layers, all of which are above 49km altitude. Undoubtedly it carries energy from the day side to the night side. Below that altitude, the temperature profile around the planet is “constant” – no “diurnal” variation.
Temperature at that altitude around 60C. High conc CO2 means some IR from surface reflected back toward surfacefrom above 49 km.
Surface absorbs measly 100W/m2 visible light TOPS.
However, surface is 733K, radiating “12,000 W/m2” IR – or some high number.
Dense CO2 atmosphere is SO absorptive, 12,000 W/m2 goes up, 11,900 comes back down at surface. Based on some radiative energy-balance profile yet to be calculated by person in this blog (but probably already modeled by some scientist), temperature decreases with increasing altitude, IR energy radiated upward decreases with altitude, IR energy reflected back down decreases with altitude, until at 49km it reaches 333K, circa 600W/m2 radiation.
Have to allow some reflectance of IR at cloud bottoms at 49km too.
This detailed calc is beyond my ability, or at least beyond my time available. UNLESS you pay me!
[2] You referring to Steve’s photos? Shadows appear to be illuminated from directly above. Let me ask you… what kind of shadows would you see on Earth in a cloudy sky with hidden sun? Would not rocks on Earth still cast some shadows?
Nullius [cool name] and Mike M,
May 14, 1:32 Pm
At any altitude from zero to 49 km on Venus, more IR is directed upward than downward, and atmospheric temperature decreases with altitude. In theory, at 49 km altitude, 100w/m2 (or thereabouts) of visible lite goes downward, and a net excess of 100W/m2 (or thereabouts) of IR goes upward. Therefore the Laws of Thermodynamics are not violated.
However, the details of this phenomenon are beyond my available time to analyze.
It’s 11:35PM. Think I should leave some Grand Marnier for tomorrow night!
RE: High steady-state surface temperatures on Venus
Given the extremely dense atmosphere of Venus, I think that errors in the estimation of low-temperature thermal conductivity and heat flow are more believable causes of that planet’s ‘unexplained’ stygian surface temperatures than any mysterious internal heat source.
I have found a study that provides a series graphs similar to the ones provided by Steve Goddard in this article except that have been extended down to the surface.
These were provided as a first step in a study to determine if there are chemical, temperature, pressure environments in the Venusian atmosphere that are suitable for the replication of viruses.
http://www.datasync.com/~rsf1/vel/1918vpt.htm
George Turner, Reur May 11, 2010 at 4:14 pm
Sorry George to take so long to look at this, but I was delayed trying to find a Planck curve at 740K.
According to my reading of your ESA “Venus Express” VIRTIS citation, the open window that you refer to does not occur below about 35 Km altitude, (at ~570K), and thus will not be seen from the surface. VIRTIS uses different wavelengths to view different levels in the atmosphere. In order to view the surface, (or in other words, where up-welling surface EMR/ infrared can escape directly to space), VIRTIS utilizes a narrow window at 1 micron.
If you look at the Planck curve for 750K that I found here, you will see that the proportion of EMR energy that can escape through that 1 micron window is tiny, even if the surface were a black body.
Thus, the mechanism for most HEAT loss from the surface would appear to be conduction/ convection/ advection. (converting to EMR escape at progressively higher altitudes)
Spector: May 14, 2010 at 9:44 pm
Thanks for the links to the extended Magellan graphs, Spector. It’s not the same as actual data, but I can at least check my own ballpark extrapolations against someone else’s. Much appreciated. I tracked the source data back to a JPL site that hasn’t been updated very recently (still talking about selling physical slide-sets and videotapes). Given that the numbers don’t go lower than 34km, though, having tha raw data might not be much better than digitizing the gif’s, but I’ll dig some more.
Your original site you pointed to is a bit ‘different’. Oedipus, Akhnaton [sic], Velikovsky, The Virgin (ha’Almah), and Flu Viruses ?? Eclectic, to say the least!
/dr.bill
CO2 is mostly transparent at wavelengths shorter than 1.2 microns, and your 750K curve shows a not insignificant amount of radiation below 1.2 microns. If there’s only a narrow window at 1 micron, some other gas must be blocking the shorter wavelengths.
Jbar : May 14, 2010 at 6:32 pm
Just a quick note: Water does not boil at 100 degrees C at 90 atmospheres. It takes a higher temperature at that pressure to get bulk boiling of water. I’d have to dig out my steam table to even guess what the behavior of water would be. I’ve never had occasion to deal with a high temperature, high pressure CO2 gas atmosphere and water together. I’m not even sure my standard steam table is valid for that situation.
Jbar, Reur May 14, 2010 at 8:18 pm , in part:
[1] See my ongoing discussion with Dr. Bill. I don’t think S-B blackbody radiation alone applies when immersed in a highly opaque fluid like the Venus atmosphere. (and Dr. Bill has yet to dispute this)
[2] Regardless of how much radiation there may be from the surface, (hemispherically) when it is absorbed in any particular layer of the atmosphere, that layer radiates in all directions. (spherically). Crudely speaking, the same amount goes up as what goes down, and a great deal of it goes sideways, which does nothing in itself.
Yes, shadows can be seen on overcast days on Earth, but it is a matter of context here. The shadows evident in the photos from the various Soviet landers, (both enhanced and raw), do not support the hypothesis of immense scattering of sunlight around to the dark side, as a reason for uniform temperature. (not visible under the clouds)
For more surface imaging and processing, see:
http://exoplanet.as.arizona.edu/~lclose/teaching/a202/Venus_surface.jpg
http://nineplanets.org/thumb/lander.jpg
http://www.mentallandscape.com/C_CatalogVenus.htm
http://www.mentallandscape.com/V_DigitalImages.htm
And he won’t, Bob, because you’re right. ☺
Most of the radiation emitted by the Earth comes right from the surface and goes straight out into space. The S-B temperature associated with that would be the surface temperature of the Earth (if the Earth actually had a single surface temperature, which is another matter altogether).
The rest of the radiation is ‘impeded in progress’ (which is not the same as being ‘trapped’) by the gases through which it passes. Some of it, as you say, is re-radiated down to the surface, where it has some effect on the total striking the ground. That bumps up the surface emissions a little bit from what they would be if the atmosphere were completely transparent, and this process iterates itself until an equilibrium is attained (if all other things were magically kept fixed). On each iteration, however, the added effect of the bits coming back down decreases significantly, like a small fraction multiplied by itself over and over (one-tenth of one-tenth of … etc). To get the total, you’d have to do an infinite sum, but the first one or two bits would be the bulk of the effect.
Then, of course, there’s the matter of what temperature to associate with those extra bits that are going up and down. That’s actually rather tricky. One of the things that’s sometimes forgotten about blackbody stuff is that it’s a ‘whole molecule’ effect, not just a matter of electron transitions, whereas most of the absorption of radiation in the atmosphere simply involves the excitation of electrons in the molecules, and the re-emitted photons will thus have the same energy as the originals. That energy in turn will have been determined by the temperature of the Earth’s surface, which is where they came from in the first place. The ones sent back down will thus be readily re-absorbed by the surface since anything that emits a given frequency will also absorb that same frequency. (Again, of course, they might not end up in the same patch of land or sea that they came from, and that’s part of what makes all this stuff so damned difficult to process with actual numbers.)
There is, nonetheless, a small ‘atmospheric thermalization’ effect involved in these processes, so the molecules higher up that are absorbing and re-emitting the upwelling radiation will end up a little bit hotter than if they were left alone. I’m not sure that anyone knows how to quantify that. I certainly don’t, but most of the radiation they absorb won’t make them move faster. It just ‘messes with’ their electrons, which then re-emit in short order.
On a tangential note, there’s an interesting example of this ‘back and forth’ process that occurs in the construction of anti-glare coatings for camera lenses and eyeglasses. It’s based on thin-film interference among the multiple reflections and transmissions that take place in the thin layer of the coating, which is sandwiched between the air on the outside and the glass of the lens itself (which is considered ‘thick’ for such purposes). Again, you figure out the total effect by adding up the series of weakening rays of light. Then you apply the condition that all of the reflections add up to destructive interference, and that determines the required thickness and index of refraction needed for the coating. In this case too, there is no ‘energy buildup’ of any significance in the coating. It just takes a little bit of time (less than nanoseconds) for the first round of multiple reflections to work their way through, and then the steady state conditions set in. The coatings don’t keep getting hotter and hotter. Maybe we should get the optical people involved in atmospherics. 🙂
/dr.bill
The fact that the atmospheric pressure is the same in the Sahara desert in midsummer and the Antarctic in midwinter is the same shows that surface temperature is not proportional to pressure.
Jbar, Reur May 15, 2010 at 9:11 am
The Planck curve gives the distribution of energy flux at quantum level for a given black body temperature, and it is the area under the curve that gives total flux.
Per my eyeball, I would guess that the area to the left of 1.2 microns, is less than 5% of the total flux.
BTW, did you notice that the Y axis of the graph of three sample Planckies does not have any units? Have a play with the applet on this web page, and you can see that there is a scaling difficulty even between 190K and 360K, (the range of the applet), if units were shown
Don’t worry about the blue Wein curve; it is irrelevant to this discussion.
Hi dr.bill, you sill around? Watch out, it can be addictive. This has turned into a hearty discussion here.
Update: my realization that by ρ = MP/RT it’s the pressure to density ratio that rather dictates the temperature and that put a complexity in my simple example, but I’ll give it some more attention later when time allows.
If you should have the time I’ve got a quirky question.
Got into a heated discussion on albedo in space’s case. Take two identical planets similar to Mercury in identical perfectly circular orbits, rotating to equalize the radiation heat from the sun and with no atmosphere, cold to the core, stable irradiation from the sun. One is white and the other is black.
My argument was that after enough millions or billions of years both would equalize to have identical core temperatures because conduction to space could not occur in a vacuum to help remove heat as air would in a lab experiment, it would just take the white one much longer to reach radiation equilibrium. A good reflector being assumed an equally poor radiator. The white was accepting less radiation per unit of time but the incoming radiation intensity was a constant and would win the battle in the end in both cases. But that would only hold in a vacuum as space.
The other person swore that by physics the white one would always be much colder, it’s albedo was so much lower, end of discussion, as if albedo controls temperature, not just reflection.
Any thoughts? No problem if I’m missing something, just want a second opinion from someone who seems to understand physics.
So, if I understand correctly, many global warming alarmists seem to dismiss the relevance of the difference between the atmospheric pressures of Mars v. Venus to explain differences in their respective temperatures. Does that make these folks atmospheric pressure deniers? And, does that help explain why these deniers also think MBH98 (aka, the ‘hockey stick’ graph) is good science instead of 10% reality and 90% scientific fraud?