# Basic Physics For Climate Dummies

Temperature in the Venusian troposphere increases linearly with altitude. At an altitude of 50km in the Venusian atmosphere, the temperature is about the same as at Earth’s surface.

At an altitude of 50km in the Venusian atmosphere, the pressure is also about the same as the earth’s surface.

http://www.datasync.com/~rsf1/vel/1918vpt.htm

What this demonstrates is that planetary temperature correlates with atmospheric pressure, not atmospheric composition. Venus’ atmosphere has 95% CO2, Earth’s atmosphere has 0.04% CO2.  Incredible that an entire field of (junk) science could be based on such a fundamental misunderstanding of basic physics.

The surface of Venus receives very little sunlight, and receives no sunlight for months at a time. yet the temperature never drops. How could anyone be stupid enough to believe the high temperatures are due to the “greenhouse effect?”

This entry was posted in Uncategorized. Bookmark the permalink.

### 71 Responses to Basic Physics For Climate Dummies

1. “50km in the Venusian atmosphere, the temperature is about the same as at Earth’s surface.”

Allowing for the smaller distance from Venus to the Sun.

Important to remember that bit. The Sun’s energy inflates the atmospheric volume, and gravity acting on the atmospheric mass produces the pressure gradient. Together Insolation and pressure define the energy envelope within which all other climate parameters and feedbacks have to inter-operate to produce the surface temperature and lapse rate.

• Yes, you now have the thermal effect of downward convection shown as compression heating.
That supplies the necessary additional energy to the surface that is required to cause a greenhouse effect in place of the incorrect alarmist theory that downward radiation from greenhouse gases causes it.

Trenberth et al omitted the thermal effect of downward convection and to balance the budget then had to assume a warming effect from downward radiation but in reality downward radiation has no thermal effect at the surface because it is neutralised by adjustments in convective overturning so as to maintain hydrostatic equilibrium for the atmosphere as a whole.

• There is no “additional energy” brought to surface by downward convection. More heat is carried upwards by convection than is returned to surface by compression heating. Convection is a net cooler of the surface.

However, the compression heated air returning to surface creates IMPEDANCE. In other words, it reduces the RATE of conduction of heat from surface to air from what it would be if there were no compression heating of descending air.

That forces the surface temperature to rise to the point where it can be in equilibrium with the overlying atmosphere.

• R. Shearer says:

Nevertheless, he’s describing adiabatic heating from downward compression and effects thereof.

• Yes. I’m just being emphatic about mechanism because any theoretical description which adds an adjective such as “additional” or “enhanced” or “extra” to the word “energy” sets the climate dogs off barking about “violations of the first law”.

• Just a typo. I meant additional heat, not additional energy as is clear from my linked articles.
Convection does carry up more than is brought down but only if there is radiative leakage to space from within the vertical column. Note that any KE converted to PE adiabatically cannot leak and must all return to KE in the descent.
For a non GHG atmosphere ALL that is taken up is returned to the surface.

• As well as “radiative leakage to space from within the vertical column” there is release of the latent heat of condensation as expansive cooling reduces T to below dew point. that reduces the lapse rate to moist value around half of dry adiabatic lapse rate.

• Hi Rog
Condensation out of water vapour which then radiates some of the latent heat to space is included in ‘leakage’.
What you need to note is that such release of latent heat results in both additional adiabatic uplift AND radiation to space from the condensate.
The portion of latent heat used in extra adiabatic uplift cannot be lost to space because it has become PE rather than KE and PE does not radiate because it is not thermal energy.

That PE is then recovered as KE during the subsequent descent and it is that ADDITIONAL PE derived from EXTRA uplift that accounts for the difference between the dry and moist lapse rates.

• Hi Stephen, yes, I think that may be right. I was working along the same line of thought before I saw your comment. I need to do more reading and thinking. Good line of research!

• Thinking it through a bit more; while it’s true descending dry air will warm at DALR while ascending moist air cools at MALR, it’ll have less heat capacity back at surface. So I think that effect won’t add to surface > air impedance. There will be a general and important impedance effect from the adiabatic heating of descending air however.

• --B-- says:

Keep in mind that Venus reflects a large amount of the energy from the sun that reaches it.

• R. Shearer says:

And so does the earth.

• RAH says:

The albedo of Venus is huge compared to earth. On earth you can see the surface from space. When one looks at Venus all they see is a brilliant white bright sphere without a bit of the surface visible.

• R. Shearer says:

No argument there.

• --B-- says:

Ahh, the usenet style reply, where one knows what was meant but responds in literal manner anyway.

Venus reflects a much larger proportion of what it receives from the sun than the earth.

• Richard Wakefield says:

I really wish people would stop using the flat earth model for the energy flow from the sun. Energy from the sun is not 340. Its 1350W/m2. That 340 is an average, includes the many more hours of less sun and night time. That is not a proper view of what is physically happening. The earth’s rotation is very important in curtailing how much energy any given region gets solar energy. No region gets the full amount of accumulated energy from the sun because the planet rotates that region away from the sun before the maximum accumulation can happen.

If the earth rotated slower more energy would build up, with more time for the cooling at night. That would build up a much larger gradiant of energy differential between day and night, making the planet unlivable for life. If it rotates faster, it wouldnt have time to build up enough sun energy to support life.

Like what happens with your hand when moving over a candle flame at different rates.

• R. Shearer says:

Yes, and the atmosphere (air masses) to a large extent, and water masses to a lesser extent, move about.

• Karl Zeller says:

Rotation has no impact on the long term amount of energy an atmosphere holds, here’s the empirical evidence: https://t.co/SgWzeWz5WE. Think about it from the outside looking in (or down) perspective, any planetary atmosphere intercepts the Sun’s energy and come to an equilibrium including the surface below, that has nothing to do with the spin rate of the solid ball inside the atmosphere.

2. richard says:

In one fell swoop totally debunks the whole Co2 causes warming meme! Best I have ever seen.

• R. Shearer says:

Not necessarily totally but AGW is probably a second order effect. The system is very complex and really we are talking about temperature differences much less than experimental error and certainly much less than natural variability.

• richard says:

As the atmosphere of Venus is pretty much co2 I think we can put to bed any idea that is has any effect if the temps are pretty much the same as explained above.

• Tom says:

That is the rub. The AGW crowd routinely publishes sensational headlines that when you look at the actually data (if you can get to it) are well below the experimental A&P. When they look at long term temperature data sets they will also invariability apply the A&P of the modern instrumentation to the entire data set in the popular articles and will sometimes try to slip it into papers. Trying to explain accuracy and precision to a non technical person all you get is, “well it was hotter”. I’m a physical chemist by training and an analytical chemist by profession so understanding the A&P of experiments is integral to my work.

3. richard says:

It is such a great comparison.

“Despite the harsh conditions on the surface, the atmospheric pressure and temperature at about 50 km to 65 km above the surface of the planet is nearly the same as that of the Earth, making its upper atmosphere the most Earth-like area in the Solar System”

4. Credit where it’s due. There have been a number of important contributors along the way to this pivotal moment in understanding planetary atmospheres. Step forward;

Harry Dale Huffman 2010 blog post
http://theendofthemystery.blogspot.com/2010/11/venus-no-greenhouse-effect.html

Ned Nikolov and Karl Zeller 2011 conference poster, 2017 Elsevier/Omics paper
https://tallbloke.files.wordpress.com/2017/07/new-insights-on-the-physical-nature-of-the-atmospheric-greenhouse-effect-deduced-from-an-empirical-planetary-temperature-model.pdf

Apologies to anyone I left out.

• richard says:

It is the visual interpretation that makes this one sing. For the general public maybe an even more simple quick glance would be useful- I guess a version of the debunked hockey stick

• Tallbloke’s amended Trenberth diagram inserts my adiabatic loop as described here:

in place of downward radiation from GHGs which is something I also put forward a few years ago at WUWT and got roundly mocked for it.

I think my description of the mechanical conduction/convection process inducing surface heating is the only one out there that sets it out clearly enough for the lay reader and goes several steps further than all those who have simply pointed out the phenomenon.

• Douglas Hoyt says:

Another interesting discussion on this topic is by Holmes:
http://article.sciencepublishinggroup.com/pdf/10.11648.j.earth.20170606.18.pdf

• tonyheller says:

I have been blogging about this topic for as long as I have been blogging. This post is largely a re-post of one I did in 2011.

• richard says:

• Nice to see Chris Colose admitting extra CO2 acts as a coolant in that post. ;-)

• That post points out the same observation as others have done before and since but like them makes no attempt to explain it.
I have explained it.

• CheshireRed says:

Fair play Roger. Good to see you acknowledging the efforts of others. This racket was never going to be swung by a single person with a lightbulb flash of game-changing genius. (Too much vested interest elsewhere riding the AGW gravy train)
The Venus-Earth-Mars comparison nails it. Verifiable, reproducible and beyond any statistical chance of coincidence.

5. Tim A says:

“How could anyone be stupid enough to believe the high temperatures are due to the “greenhouse effect?””
A griffter would attempt to convince people that he believes it because there’s under-‘lying’ money to be made…..

6. Bob Hoye says:

It’s the best explanation for the lapse rate as one goes “up to the sky”.
The nonsense that I made notes on years ago was published in a newspaper at around 1971. Rasool pushed the theory that particulate carbon in the atmosphere was forcing cooling. “Everyone” was into cooling then. The article included James Hansen’s name (I recall). Then more recently, there was a note somewhere that Hansen provided Rasool with the theory and “model”.
Then about five years ago, Hansen was going on about such carbon forcing heating.
I hope he and I live long enough such that natural cooling forces him to explain it as caused by particulate carbon in the atmosphere. :)
Bob Hoye

7. arn says:

For people who wonder how people like Hansen can get to the top.
It is the education system:)

• Tom Bakert says:

Was that satire or a documentary?

• arn says:

After month of research i found out:
Neither.
It was a mitigated dokusoap(=no gender pronouns,no mandatory gay+islam worship,no forced AGW,noone is called nazi or hitler) simulating real life in modern universities :)

8. sunsettommy says:

Is this the Greenhouse Effect at work?

“Early in the 19th century, scientists began to speculate that the Earth, surrounded by the frigid vacuum of space, was habitable because its atmosphere contained special molecules like CO₂ and water vapor, molecules that can absorb heat rays emanating from the Earth and thereby trap its heat. That the Earth was warmer than one might expect was apparently confirmed when Kirchhoff’s blackbody concept was adopted. Today it is considered a matter of course that the Earth’s blackbody temperature is minus 18° Celsius, i.e., around 255 Kelvin, whereas its average temperature is 288 Kelvin. By the early 20th century, this temperature disparity started to be called The Greenhouse Effect.

NASA lists the predicted blackbody temperatures for the planets in our solar system at Planetary Fact Sheets. What’s intriguing, though, is that through the efforts of NASA and other such agencies, we now have some insight into the atmospheres of these other solar system bodies.

Here, for instance, is the atmospheric temperature profile for Jupiter.”

http://tech-know-group.com/essays/Greenhouse_Effect_at_work.pdf

9. Kent Clizbe says:

Tony,

Does this same analysis apply to Mars’ atmosphere?

Thanks.

• No, because Mars’ atmosphere has such a low mass it’s surface pressure is only about the same as at Earth’s tropopause, where the Temperature is around -56C.

• Kent Clizbe says:

So does that pressure/temperature ratio explain Mars’ temperature profile?

That is, is Mars’ temperature at the surface the same as Earth’s at the tropopause?

• Kent Clizbe says:

If Earth’s temperature/pressure ratio is the same as Venus’ and Mars’–that is on all three the temperature at a given pressure is the same–does not that invalidate the CO2 is an evil heat-generator hypothesis?

Thanks.

• tonyheller says:

The density of CO2 molecules in Mars’ atmosphere is about 10X higher than Earth, but due to the low atmospheric pressure and low solar radiation – temperatures on Mars are very cold.

• Kent Clizbe says:

Thanks, Tony.

So, does that statement of facts falsify the hypothesized CO2 “Greenhouse Effect?”

• tonyheller says:

The greenhouse effect is real, but not the primary driver of planetary temperature as Hansen claims.

• The radiative greenhouse effect is not real but the mass induced greenhouse effect is real.

10. Jimmy Haigh says:

Isn’t Hansen supposed to be an “expert” on the Venusian atmosphere?

• arn says:

When you are an expert in failed predictions(97%+) and noone calls you out
than you are an expert on everything.
(1st law of lysenkoism)

11. RobbCab says:

The folks that actually landed things on the surface of Venus seem agree with you Tony.

12. GCsquared says:

I want to thank Tony for his discussion, but ingrate dummy that I am, I have to disagree with his conclusion that “planetary temperature correlates with atmospheric pressure, not atmospheric composition.” After a great deal of pondering, I’ve come to this rough explanation:
1. The temperature drop from planetary surface to troposphere is well-explained by the LAPSE EFFECT associated with decreasing pressure. However, the rate of this temperature drop with altitude depends only on gas properties, which depend neither on specific gas pressure, nor on greenhouse/infrared activity. The number is roughly 10 C/km, depending directly on gravitation, somewhat on moisture, and only a little on gas type. Therefore, the DIFFERENCE between surface and tropospheric temperatures is largely determined by the height of the troposphere, i.e., the vertical distance over which the lapse effect operates.
2. To maintain steady-state temperatures, planets have to dump the unreflected optical energy they absorb from the Sun, by re-emitting an equal amount of infrared (IR) energy back to the universe. Because of albedo differences, and because infrared emission is determined by the 4th power of temperature, the emission temperatures (ET’s) of the planets are fairly close (232, 255, 209K for V,E,M), even though solar absorption amounts (662, 342, 145 W/m2) differ substantially.
3. In one hypothetical extreme case where atmospheric gas is IR-inert (e.g., N2), outgoing IR radiation escapes right from the surface. In this case, the planetary surface is at the ET, and the atmosphere is below this temperature, more so with increasing altitude according to (1). Mars is an approximation to this case, insofar as its small CO2 concentration provides only weak greenhouse absorption. (Despite its CO2 concentration being twice that of Earth, Mars has none of the water vapor that dominates IR absorption on Earth.)
4. At the other extreme where the atmosphere is a near-perfect IR absorber, radiation can escape into space only from the upper atmosphere, because outgoing radiation from lower gas layers is blocked by higher layers. In this case, the upper reaches of the troposphere will be at the ET. Descending toward the surface, the temperature will increase because of the lapse effect, and the surface will be correspondingly hotter than the ET. Venus is a good approximation to this case: the atmosphere is at the planetary ET at 50-60km, and the surface is so hot because, due to the lapse effect, the atmosphere warms 10C every kilometer downward, i.e., by hundreds of degrees C.
Conclusion: The pressure-generated lapse effect AND atmospheric greenhouse activity determine surface temperatures. But both factors play a role.

• GCS said:

“However, the rate of this temperature drop with altitude depends only on gas properties, which depend neither on specific gas pressure, nor on greenhouse/infrared activity.”

which is not quite right so the conclusion is wrong.

The critical factor is that the gas density affects the efficiency of conduction from the surface. Denser gases absorb more surface heat which is nothing to do with the gas laws. The gas laws only describe what happens after such conduction has occurred.
So, the greater the pressure (higher atmospheric mass) the more effective is conduction from surface to atmosphere, the greater is the energy required to support the greater weight of the higher atmospheric mass off the surface in hydrostatic equilibrium and the higher the surface temperature will (must) rise.
No part played by radiative gases in connection with the surface temperature at all though such gases will alter convective overturning patterns to a miniscule extent in order to neutralise radiative imbalances and keep the system stable.

• Physicist says:

It is NOT a case of hydrostatic equilibrium Stephen as I have explained many times. It is thermodynamic equilibrium, that is, maximum entropy. You have never explained how the Venus surface gets new thermal energy on the sunlit side and rises in temperature from 732K to 737K over the course of four months while it continues to radiate over 16,000W/m^2 and also to lose energy by conduction to the atmosphere on the dark side. How does the NEW energy get there? The answer is in my 2013 paper and nowhere else in world literature. It’s your choice whether or not you want to download it free and study it – https://ssrn.com/author=2627605 but you will never correctly refute it. Doug.

13. Brett Keane says:

GCs: Anything to avoid the truth that gases are not solid. Therefore they all act the same under gravity, as near-point-sources. With molecular volume differences so inconsequential as to make Ideality effectively the same as if they were all one specie. Energy changes cause volume changes at Km per second speeds hardly affected by molecular mass, so only gravity and solar input have discernable effect.

Mass is too little to act as batteries also. But as convective and latent heat transfer coolant, why, yesiree!

• GCsquared says:

Of course, gases aren’t solid. I hope you don’t think that I argue to the contrary.
I don’t quite grasp the overall intent of your reply. I think we’re in agreement that thermodynamic gas properties, e.g. pressure and temperature, are aggregate effects of essentially point molecules moving at km/sec velocities. But you lose me when you say that mass acts as “as convective and latent heat transfer coolant” (agree), but not “as batteries” (huh?).
Can you be more specific?

14. James McGinn says:

Vortices and jet streams (jet streams being collectives of vortices) have the most dramatic effect on the pressure in earth’s atmosphere, these being the “pressure relief mechanism” of earth’s atmosphere. Vortice activity is also what underlies storms and uplift.

Unfortunately the atmospheric sciences are saddled with a 19th century model that depends upon non-physical notions like moist air convections, dry layer capping, and “latent” heat of H2O. These pseudoscientific notions prevent progress in the scientific paradigms that maintain this silliness.

Without understanding the role of vortices and jet streams you can’t understand pressure and changes thereof.

Accounting for Lorenz’s missing lubrication in the atmosphere
https://www.thunderbolts.info/forum/phpBB3/viewtopic.php?f=10&t=16430
“We have always known from whence comes the energy that powers the winds: differential air pressure due to the differential heating/cooling from the sun/night, exacerbated by friction from surface features (mountains, valleys, etc.). But what has been perplexing is how and why the flow that ensues from this energy becomes concentrated, producing the high wind speeds we see in jet streams and storms. Generally things in nature don’t reverse entropy (going from less organized [scattered] to more organizes [directed]) unless there is a physical reason for them to do so. A river channels into a stream due to the hills and valleys of a landscape. Where are the hills and valley of the atmosphere and what is the substance, apparently invisible, of which these hills and valleys are comprised and why is evidence of it so fleeting?”

• James, I have read some of your stuff but regret to have to say that it was not helpful.
The jets are the consequence of differences in air mass characteristics such that the points of contact are then forced into narrow bands by rotation of the Earth.
There is nothing perplexing about it so you are chasing a chimaera.

15. James McGinn says:

SW:
The jets are the consequence of differences in air mass characteristics such that the points of contact are then forced into narrow bands by rotation of the Earth.

JMcG:.
Stephen, your description here as meaningless (and as absurd) as the concept of spontaneous generation in biology.

Additionally, your epistemological approach is too vague to be of much consequence to anything. IOW, all you got is vague rhetoric.

Jet streams are a consequence of collectivization of vortices. Vortices are a result of water based plasma, the structural nature of which is plainly observable in a tornado. The basis of this plasma involves the surface tension of H2O which is maximized on moist/dry wind shear boundaries. This is where vortices originate and this observation is correlated with the tropopause being the most significant moist/dry boundary in the atmosphere.

Vortices are extremely common in the atmosphere and usually run laterally. They are mostly unseen because they tend to be associated with clouds, which obscure them, and are otherwise invisible in that the plasma that spins up (literally) on wind shear boundaries shares many characteristics with gaseous H2O (steam) including invisibility.

Convection is based on nothing but an analogy to a pot on a stove. The correct analogy of atmospheric flow is a siphon.

Storms don’t cause tornadoes/vortices; tornadoes/vortices cause storms. As a matter of fact, vortices deliver the LOW PRESSURE energy of storms–something your model completely fails to explain. (Stephen, can you explain how your convection model predicts the cold, gusty winds of storms? I think not.)

Let me put you on the spot Stephen. You have seen pictures/video of tornadoes, right? How do you explain the structure that is plainly apparent therein? Magic?

I’ve noticed, Stephen, that you are very careful to maintain the vagueness of your theoretical thinking on this subject. That is a defensive strategy. Because you know that vagueness can never be disputed/refuted.

• James,

If you would trouble yourself to learn some basic meteorology you would find simple explanations that have no need to call on undefined phenomena such as your ‘plasma’.

I’m afraid you have built up just as illogical construct as has Doug Cotton with his vague and unnecessary concept of ‘heat creep’ in which he mixes up the discrete processes of conduction and convection.

• James McGinn says:

Stephen,

Predictably you have no dispute with anything I’m saying. Having been educated in meteorology I know your model very well. It was developed in the 1840s. Back in the days of the steam engine. Time has moved on. Science has moved on. Vagueness never dies.

Have you ever noticed that meteorologists do not (and will not) discuss the details of this ancient model? Why do you think that is? Because it is just marketing to them. It isn’t a real theory. It is just a way to placate the public.

One need only draw attention to he magic associated with its three major tenets to see that it’s just marketing and not really science: 1) ‘cold’ steam based convection; 2) dry layer capping; 3) ‘latent’ heat based explanation of gusty winds. This is all blatant pseudoscience that no meteorologist is willing to defend or even discuss. They just wallow in vagueness.

Nobody on this planet–including yourself–is actually willing to flesh out the details of this vague model so that it can be tested. It remains untested and untestable; unmeasured and immeasurable. (It is easier to believe vagueness because our minds fill in the details for us–subconsciously.)

However, the biggest shortcoming of your model is that it completely fails to explain vortices and jet stream. My model doesn’t carry this shortcoming. And my model goes on to explain all of the phenomena that your model pretends to explain, like uplift, storms, etc.

The physics of the water based plasma of my model are difficult to understand but revolutionary. And a large part of the difficulty has to do with the fact that our understanding of H2O has been dumbed down due to an error made by Linus Pauling about 70 years ago.

The public is gullible and tends to buy in to dumbed down models that conform to their anecdotal experiences. This is the reason the convection model of storm theory is so widely believed. And the fact that it is so widely believed is the reason meteorologists are so careful to maintain its vagueness. Nobody wants to kill the goose that laid the golden egg.

Are You Confused About Hydrogen Bonding in Water?
https://youtu.be/RfNuWJDJvRw

16. Physicist says:

No Tony. High pressure does NOT maintain high temperatures. No law in physics says it should. Pressure does not rise when the sun shines and so you cannot explain how the surface temperatures on Earth and Venus rise then.

Pressure does not supply new thermal energy, and even if it did during the day the reverse would happen at night leaving no new net energy into the surface. You can’t create energy out of nothing as you imply. The Venus surface is radiating over 16,000W/m^2 and also loosing thermal energy by conduction into the atmosphere at night. Where does that energy come from?

Your hypothesis is no more valid than that of Joseph Postma. If it were correct then you have proved Postma wrong and vice versa if his were correct.

But NEITHER the HELLER hypothesis NOR the POSTMA hypothesis IS CORRECT.

BOTH OF YOU ARE TOTALLY WRONG as the laws of physics tell us.

PSI HAS NO VALID EXPLANATION for VENUS TEMPERATURES or EARTH’S.

I HAVE and it is BASED ON THE LAWS OF PHYSICS and COPIOUS EVIDENCE.

You need to read about the major discovery of the “heat creep” process in my 2013 paper “Planetary Core and Surface Temperatures” at https://ssrn.com/author=2627605.

• tonyheller says:

• spike55 says:

Its Doug Cotton, with his whacky ideas again.

• spike55 says:

A DESPERATE PLEA for attention. :-)

17. Physicist says:

If you have no defense against my refutation of your physics, Tony, we’ll leave it for those who understand entropy and such things to judge who’s right. I have the laws of physics on my side. Approximate correlation between pressure and temperature does not tell us what the cause is. Gravity forms the temperature gradient and the density gradient, these being one and the same state of maximum entropy and thus stable. The pressure gradient is merely a corollary by the Ideal Gas Law which tells us that pressure is proportional to the product of temperature and density. It tells us nothing more and nothing less. It is NOT telling us temperature is proportional to pressure. Temperature only rises if there is a net input of thermal energy. I have explained how that happens. You are incorrect if you think you can explain it with pressure. DC

18. Physicist says:

Tony. The fact that gravity forms the temperature gradient at the molecular level by accelerating molecules was first explained by Josef Loschmidt in 1876 – the brilliant physicist who was first to make realistic estimates of the size of air molecules. Do you think you know better? That is why the force of gravity is in the expression for the tropospheric temperature gradient, that being the negative quotient of that force and the weighted mean specific heat of the gases. However, some modification to the gradient is brought about due to the temperature-leveling effect of inter-molecular radiation. That is why the temperature gradient for high levels of water vapor is less than that above deserts, and so the supporting temperature at the surface is cooled by water vapor and by carbon dioxide for the same reason. The carbon dioxide on Venus actually cools the surface significantly. Nowhere did I have to mention pressure.

19. KarenHaume says:

Vultech : Les MENSONGES sur les consommations des voitures – VILEBREQUIN