We all know Venus is hot.
A few billion years ago, Venus had a collision with something that turned it on its side and slowed its rotation way down. One day on Venus is almost six Earth months long.
Because of Venus’ proximity to the Sun and its very long afternoons, it never developed oceans. Because it never developed oceans, it has a huge amount of CO2 in its atmosphere. (On Earth most of the CO2 is trapped in limestone, which forms in water.)
The very large amount of CO2 in Venus’ atmosphere has created very high surface pressures, which causes very high temperatures. PV = nRT
The difference between Earth and Venus is that we have oceans, which allowed limestone to form, and keeps our atmospheric pressure down to 1/100th of that on Venus. Thus Earth is much cooler.
Hansen got his PhD for writing a completely nonsensical theory about Venus heat. My dissertation took five minutes. Can I have my Columbia PhD now?
No. You didn’t follow the script, so not PhD.
However, the temperature on Venus has nothing to do with the presence or absence of water. The temperature of the atmosphere is due to gravitational compression. It is irrelevant that the atmosphere is 96% CO2.
Venus is not a greenhouse as sunlight does not reach the surface. The upper level cloud deck prevents this. The atmospheric wind speed is not effective in causing a global circulation but the sun-lit and shadow sides have very similar temperatures. It’s all about the permanent cloud deck and the gravitational heating that makes Venus what it is.
If there was water, the atmosphere would be much less dense and it would be much cooler.
The surface temperature of Venus was predicted by Carl Sagan before anyone knew what the composition of the planet’s atmosphere was. Sagan surmised that the atmosphere was composed of a mixture of Nitrogen and CO2 and then calculated the surface temperature for a range of gas compositions.
I won’t trouble you with the full set of papers but here is the correction that was published when Sagan realized that the specific heat of CO2 varies with pressure.
Just click on the above link and then click on the “Send PDF” button.
Sagan was not sure about the altitude of the cloud tops so he calculated for 44 and 65 km. We now know that 58 km is correct (See Magellan measurements published by Jenkins et al.)
Note that the calculated surface temperature changes by less than 10 Kelvin when the gas composition varies from 100% CO2 to 100% Nitrogen. Why? The Cp of these gases is nearly identical. Notice that Sagan got the right answer without any mention of the IR absorption properties of gases. All he needed was thermodynamics.
Why does anyone take Hansen seriously when he got it wrong and Sagan got it right? Take a look at Charles Mackay’s “Madness of Crowds”:
I’ve always been amazed by people saying compression causes permanent heat. It boggles my mind. Listen carefully…..when gas is being compressed, it gets hot, then after it’s compressed, it cools. Are your tires still hot?
Yes, I agree. But the temperatures of atmosphers on the planets seems to be tied to thier pressure. If you travel up in earth’s atmosphere to a pressure equal to Mar’s surface pressure, you have a temperatue at that location roughly equal to Mar’s surface temperature. A similar thing is true for many planets. If you go into Jupiter’s atmosphere to a depth that yeilds a pressure similar to earth’s surface pressure you will find a temperature roughly equal to earth’s surface tempreature. Of course all this can be dismissed by simply saying “That’s impossible!”
That’s just a coincidence. If you travel up in earth’s troposphere the pressure gets less and the temperature get less. The temperature gets less because of the lapse rate and the pressure gets less because there is less air above you. They have nothing to do with each other. If you travel up, the people look like ants too. Is that related to temperature?
What you said about Jupiter and other planets is a comment that comes from outer space because it’s just…..out there.
Heating a small volume of gas by compression where the container of the gas is in thermal contact with a much larger “environment” at ambient temperature is an entirely different thing to compressing a whole atmosphere. A lapse rate inverse to pressure establishes and the only mechanism for energy loss is radiation to a surrounding vacuum where the radiation flux is constantly of the order of 2613.9 W/sqm except for the small shadow on the night side of the planet.
Temperatures increase with pressure – ie increasing depth in the atmosphere.
I would have thought that was obvious.
Temperatures would rise if the atmosphere was in a state of gravitational collapse. in other words, converting potential energy into heat energy. But the atmosphere is collapsing and overall the molecules traveling up are balanced by molecules traveling downward (neglecting the miniscule portion that escape earth’s gravity). So the idea that planetary atmospheric temperatures are a function of “gravitational compression” is wrong. the planetary surface temperatures are a function of atmospheric mass though. The atmospheric mass sets the height of the tropopause where the major portion of radiation to space occurs. The the surface temperature is prescribed by the lapse rate extended down from the tropopause to the surface.
Sorry, I meant to say the atmosphere isn’t collapsing.
higley – “The temperature of the atmosphere is due to gravitational compression.” You don’t seem to understand gas laws, e.g. Gay-Lussac’s law.
If you adiabatically compress a gas the temperature will rise – that’s clear.
But after that the emission of energy to the outer space will be higher than before. So after a certain time – when the equilibrium state has been reached again – the temperature will be the same as before.
So explaining the higher temperature of the Venus with a higher atmosphere pressure is not correct.
Nonsense. The amount of energy leaving Venus atmosphere is equal to the amount being received from the sun. Everything is at steady state equilibrium. The pressure remains and so does the temperature. PV=nRT
If the pressure, volume and number of molecules is constant, then so is the temperature.
That’s right. But the equilibrium state has already been reached a long time ago.
So the high pressure cannot be the reason for the high temperature today.
Look at this experiment:
You have a gas within a closed containment of – let’s say – 300 K. Compress this gas to a pressure twice as before. Then you’ll get a temperature of 600 K. Do You really believe that this temperature will stay at this level when you leave this pressure at the higher value? Nope!
I forgot to mention that in this experiment the compression is gained by adding additional gas to the containment so the volume is constant.
So it’s not in equilibrium if you added additional gas.
When reaching equilibrium state again you will have the same temperature as before.
So, it doesn’t stay hot forever? Rats. I thought we invented a perpetual heat machine.
Let me try again, and explain this very slowly. The conversation has drifted off from mindless to idiotic.
The “perpetual heat machine” is the Sun which is constantly providing huge amounts of energy to Venus atmosphere. Without the sun, Venus would be frozen solid.
PV=nRT has no time component. P, n and R don’t change – they are constants. They only things that could change are volume and temperature. As long as the volume is held constant, the temperature will remain constant too. The height of the atmosphere is controlled by steady solar energy received at the top of the atmosphere, so the temperature is fixed.
Obviously Venus is not a closed system – it has a massive ball of fire heating it up. How dense can you be?
Sorry, but your explanation is simply wrong.
Okay, this is your house. But calling my explanations “nonsense”, “mindless”, and “idiotic” is very unfriendly. So you may discuss here by yourself. 😦
You don’t know what you are talking about. Energy is constantly being provided to Venus atmosphere from the Sun
Steven relax. Everybody is discussing the comment made by higley7, where he said the heat on Venus comes from gravitational compression. Nobody was talking about the sun.
4.6 billion years ago the solar system collapsed due to gravity and everything got hot from gravitational compression. But that heat is a one-off. Higley7 was talking like that’s a perpetual source of heat.
We all know about the sun.
Incorrect. The amount of energy leaving Venus, like several other planets in the Solar System, is MORE than that received from the Sun. It is an ugly fact that the Astronomers and others like NASA don’t like to talk about.
Really? And the stupid leaving this thread is greater than the smart.
Morgan, have any data to show that the energy going in and coming out is equal??
The intuitive way to understand how oceans eat carbon dioxide is to appreciate that though CO2 is at the bottom of a stairway metabolically, in a world of highly reactive O2 that drives animal life all that biological oxidation using plant created O2 actually renders carbon highly reactive in turn so that its two double bonds between C and O in CO2 make it quite receptive to forming a bonded partnership with lowly old water itself:
H-O-H + O=C=O -> O=C(OH)2 -> CO3– + 2H+
As this newly formed mild (“carbonic”) acid presents a carbonate anion (–) into the calcium cation (++) rich oceans and these two unhappily raw doubly charged ions happen to fit together very well into a simple crystal that is very stable and thus insoluble, it crashes out of solution to form dense rocks that sink.
You’re popping the poor little alarmist balloons!
We know that none of them understand chemistry or geology.
Nik, you might want to balance the charge on your equation.
Another way to get rid of CO2 is to invent plants. If the atmosphere had 20% CO2 and no O2, and now it has 20% O2, and almost no CO2, what happened to all the C?
Plants, and cyanobacteria too.
Our host said:
“If the pressure, volume and number of molecules is constant, then so is the temperature.”
No need to consider Radiative Transfer Equations and the ability of CO2 to absorb thermal IR radiation.
You forgot to mention the prerequisite: “in equilibrium state”.
When you compress a gas it will be heated. So it will emit more energy than before. If the incoming energy remains the same the gas will cool down until the equilibrium state is reached again – at the same temperature as before the compression.
I thought Mercury and Venus has lost their rotation because of tidal lock with the sun. Collided with something? Ouch.
It is my understanding that Mercury is tidally locked. Another mystery about Venus is its surface. It appears the entire surface was ‘replaced’ (surface went back to a molten state) yet Venus doesn’t have any subduction zones.
I think you might be off track there as far as Venus is concerned.
If P(Surface air pressure) is constant and V (atmospheric depth x surface area) is constant then T will be constant. The ideal Gas Law says so.
Steven wrote – “One day on Venus is almost six Earth months long.”
The system is already in equilibrium as can be seen by the diurnal temperature range.
Facts on Venus’ atmosphere, from NASA:
Surface Pressure: 92 bars
Surface Density: ~65. kg/m3
Scale height: 15.9 km
Average temperature: 737 K
Diurnal temperature range: ~0
Wind speeds: 0.3 to 1.0 m/s (surface)
Mean molecular weight: 43.45 g/mole
Atmospheric composition (near surface, by volume):
Major: 96.5% Carbon Dioxide (CO2), 3.5% Nitrogen (N2)
Minor (ppm): Sulfur Dioxide (SO2) – 150; Argon (Ar) – 70; Water (H2O) – 20; Carbon Monoxide (CO) – 17; Helium (He) – 12; Neon (Ne) – 7
Another inconvenient FACT.
The experts have no explanation for where the energy driving the winds come from and how it is transferred and why only the cloud level is moving at those speeds. The few measurements we have show little movement at the surface.
It is an interesting discussion, when folk can refrain from making it a hostile debate. To me, common sense dictates most of the lapse rate is atmospheric density driven. Near the top of the atmosphere, individual molecules can be very heated, agitated if you will, by high insolation. The individual molecules are hot, but very few would strike a thermometer, so it would record a low T.
Deeper in the atmosphere, that same, but reduced insolation, is absorbed by many more molecules, which also more readily establish a local thermodynamic equilibrium via conduction.
(It is always a mistake to consider radiation only) The lower atmosphere addition of more molecules and a longer residence time of energy due to conduction to non GHG molecules, and GHG molecules, means far more molecules, although at a less individual T compared to the upper atmospheric molecules, striking a thermometer causing it to register a higher T.
Who tells us that Venus is not cooling down ? But how long would it take in a dense high pressure atmosphere on a planet in motion to cool down the surface by 1ºC ? We know Venus has wind so there is no equilibrium .
On Earth we have partial cloud cover so it is at least plausible that variations in CO2 concentration will affect the emissivity of the planet in the thermal Infra Red region.
Hansen ignored the fact that Venus has 100% cloud cover so there is no way for CO2 or any other gas to affect the emissivity of Venus. The emissivity of that planet is determined by sulphuric acid cloud tops at a height of ~58 km. See Jenkins et al:
Does anyone still believe Hansen’s loony notion that the ability of CO2 to absorb in the thermal Infra Red region caused a “Runaway Greenhouse Effect” on Venus?