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.”
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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
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.
jaymam
The amount of energy coming out of the earth is 44.2 × 10^12 W
http://www.agu.org/pubs/crossref/1993/93RG01249.shtml
The amount of energy reaching earth from the sun is 1.366 kilowatts per square meter * 510,072,000 km2 * 1,000,000 m^2/km = 69 x 10^16 W
http://en.wikipedia.org/wiki/Sunlight
The sun contributes more than 10,000 times as much energy to the atmosphere than does the internal heat of the earth.
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.
As day and night temperatures are so similar on Venus something must be maintaining the night time temperatures, especially considering the Venusian night is around 120 Earth days long, surely without the direct input of heat from the Sun over this period a significant amount of heat would be lost, unless there was a significant Greenhouse effect at work.
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.
P is given by the gravity (no gravity, the atmosphere escapes in space)
T is given by the heat equilibriums which are depending from many process including density, thus pressure… radiation and initial heating by the sun of course.
Only V could be the consequences of the others because there is no solid shell around the earth.
So you can’t prove anything from a general PV=nRT; you must go the the differential equations in each dV portion of the atmosphere (what are doing the models, but I do not say that the models are doing this well!).
Imagine that T is close to zero, with an atmosphere, PV/n is close, to zero , V/n is close to zero , so the change would be a very high density of the atmosphere. (mostly going to liquid under some temperatures; that’s happening for water, after all , with our current temperatures)
I am not sure that it is usefull to compare earth and venus as the conditions are so different, especially the content of the atmospheres and the very different temperatures.
Phil. said on May 8, 2010 at 8:50 pm:
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?
Dr A Burns,
“The atmosphere is not static and conductive heat transfer to surroundings is small.”
Movement requires energy, and hence the energy must come from somewhere. After the initial compression of the gas, which releases energy in the form of heat, there has to be a heat/energy source to keep the gas warmer than the surrounding space.
I have no idea of how well insulated a planet is. Thinking about earth on a starry night, it is hardly perfect.
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.
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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.
George Turner Reur May 8, 2010 at 9:23 pm
[1] Yep. Any “initial point-in-time compression” of the atmosphere will result in increased T as a consequence of work done. (= mechanical energy). However, that “initial consequent heat” will be lost to the colder atmosphere above, (per thermo law 2), and for sustenance of it, equal replacement work energy in renewed air compression is necessary.
[2] At first sight that might partly explain an equatorial to poles redistribution of heat, but does not explain the reported daylight-time to night-time redistribution in terms of the ESA mapping of surface T‘s . However, how does your assertion fit in with the well reported large polar vortices, and how does it redistribute heat to mid latitudes?
Please elaborate on your assertion that Hadley cells arise at the equator and descend at the poles, (without any loss of T!!!), and provide a reference to show that these have been observed, including at what altitudes.
If you can answer that, I’ll elaborate more on the above.
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.
I’d say there’s not too much reason to be concerned, unless global warming was too big or too small. Other than that forget about it.
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.
Two fascinating posts along a similar lines to this one elsewhere.
They raise an interesting idea in my head. Are our notion of ice ages wrong? An increase in glaciation (for whatever reason) reduces sea levels. As sea levels sink the temperate zone where mammals and plants can most easily thrive moves with it onto what was formerly sea floor. What happens to temperatures? If the place where you are getting your proxy data from doesn’t move it would record a dropping temperature due to the atmosphere there getting thinner but there would still be plenty of surface with a thick and warm atmosphere.
Conversely, increases in sea levels (for reasons of less glaciation or volcanic and tectonic activity displacing water) would increase the apparent temperature for any given location that stays above water. The atmosphere appears to get thicker because it is being pushed upwards.
Are sea level changes factored in to temperature reconstructions?
Troels Halken said: 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?
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.
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?
stevengoddard says: “The ideal gas law works just fine, and gravity has nothing, nada, zippo to do with the accuracy of the equation.”
Yes, the equation itself works fine because it has nothing to do with gravity. But in this case pressure is a function of gravity. You are ultimately implying, (as I understand you), that the mass of a given control volume of air in a gravitational field decreases with temperature; that one half the temperature will give us one half the pressure at the surface. That sir is impossible. The amount of air remains the same so its weight remains the same and so the pressure at the surface remains the same.
I have two volley balls, (the reason air exists! ;), pumped them up to the same pressure at the same temperature – they weigh the same. If I cool one off to half (K) temperature of the other, it shrinks to half the volume of the other – but they still weigh the same. Instead of volley balls, we have two columns of air as control volumes in earth’s gravitational field with rigid walls and open at the top to vacuum space. They are each 1 inch square with the same amount air at the same temperature in each. The weight of the air in each of them exerts 14.7 pounds of force at the bottom and the very top-most molecule in each of them is at the same altitude. If we cool one column to say half the temperature of the other, the altitude of its top-most molecule will decrease to roughly one half the altitude of the other, (I’m not certain of the exact height but it will be a lot less than the other one).
I submit that the pressure in each column AT THE SURFACE will remain the same. As we go up in altitude however, that’s where we see a difference in pressure bewtween the two columns. The warmer column has a higher pressure than the cooler one at any altitude above the surface. The difference is zero at the bottom and increases the higher we go until it becomes infinite beyond the top of the cooler column.
But of course there are no walls up there, the air from the warmer column, having a greater pressure at altitude than the cooler one – flows into the cooler column increasing its weight and the measured barometric pressure at the surface.
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
The lapse rate on Venus is constant to 60 km. On Earth it is constant to about 14 km. Surface pressure on Venus is 92 times larger than Earth.
60/14 = 4.28
ln (92) = 4.52
Those numbers seem to be pretty close together, and hint that pressure differences explain the height of the tropopause, rather than greenhouse gas concentrations.
Earth’s atmosphere is mainly opaque to IR due to water vapour. Venus atmosphere is mainly opaque to IR due to spectral broadening of CO2 under high pressure. The addition of more greenhouse gas should be a minimal effect compared to the pressure differences.
Gareth,
Thanks for that interesting link:
http://www.countingcats.com/?p=4745
” Dave McK says: Troposphere, shmoposphere – clouds, rain, snow.”
I concur, 99% of the difference between the atmospheric temperatures of Earth and Venus is because of that amazing stuff called water. Without water I’d guess that we’d be almost as hot as Venus no matter how much CO2 there was. To me, the difference in temperature illustrates the immense power of water’s negative feedback.
People understandably have a lot of trouble wrapping their minds around the idea that something can cool off or warm up without losing or gaining heat and I therefore surmise that to be the reason so many choose to ignore the latent heat of water in vapor form being carried up adiabatically to higher altitudes.
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?
Mike M
Without water the earth would be much hotter, but not for the reasons you mention.
If there were no oceans, no limestone would have formed, and the atmosphere would be much more dense.
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.
My prior comment, the phrase “infinite difference”, I meant ratio-metrically. (We need an edit feature!)
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.