Evolution of Venus Temperature & Climate

[wogoga]

It is often claimed that Venus surface temperature as high as 450 - 500 degrees Celsius suggests a carbon dioxide greenhouse effect (around 96.5% of its atmosphere consists of CO2). However, if one deals with the question in an unprejudiced, honest way, then the hypothesis of such a greenhouse effect being the culprit of the high surface temperature becomes completely untenable.

What is called greenhouse effect on Venus would be quite different from both the original greenhouse effect and the global-warning greenhouse effect.

The original greenhouse effect:

The sun heats the ground of a greenhouse, the ground heats the air, and the glasses prevent the hot air from flowing outside the greenhouse​

The global warming greenhouse-effect:

Radiation from the sun heats the earth, and a corresponding amount of energy is lost as thermal radiation to outer space. An increase in CO2 significantly reduces such thermal losses (outgoing radiation), whereas it does not reduce significantly the absorption of incoming radiation.​

A Venus greenhouse-effect would work in this way:

Although only a small proportion of radiation from the sun reaches the ground of Venus, carbon dioxide is assumed to somehow heat up the ground.​

The true reason of the high temperature on Venus is much simpler:

The very dense atmosphere of Venus has prevented the planet's surface from cooling down after its formation to a temperature similar to thermodynamic radiation-equilibrium.​

So what is called greenhouse effect in the case of Venus is nothing more than atmospheric heat insulation over hundreds of millions of years. Gases are excellent insulators.

And if it were possible to cool down the whole planet Venus to zero degree Celsius, its temperature would remain near water freezing point over millions of years.

Cheers,
Wolfgang

Atmospheric carbon dioxide per square centimeter: on Venus 100 kg - on Earth 0.6 gram

 

[AndyD]

I understood that (theoretically at least) Venus used to be pretty much like Earth - with oceans and stuff.

How does your "always hot" theory square with that?

 

[MichaelN]

Don't forget that Venus receives around DOUBLE the intensity of solar radiation that Earth does, since it is much closer to the sun. Comparisons with Earth are quite ridiculous for that reason alone.

 

[MG1962]

Although only a small proportion of radiation from the sun reaches the ground of Venus, carbon dioxide is assumed to somehow heat up the ground.

Are you going to back this statement up
​

 

[MG1962]

Don't forget that Venus receives around DOUBLE the intensity of solar radiation that Earth does, since it is much closer to the sun. Comparisons with Earth are quite ridiculous for that reason alone.

The comparrison being drawn is clearly ridiculous. However I am not aware of any planetary scientist who are making the comparrison. There is great interest in why Venus ended up the way it did and why Earth is as it is

Venus however does give us a giant chemistry kit to play with. To understand conditions in worse case senario etc.

One example of this that stands out was the destruction of the global cooling theory of the 1970's. Venus shows us what carbon can do in an atmosphere, not what it will do

 

[Lukraak_Sisser]

I doubt anyone these days makes a direct comparison between Venus and Earth. Apart from all the other mentioned differences, its rotation is so slow we have no idea what sort of extra effects that might have had on the evolution of its atmosphere, as well as its slightly lower density and the fact that the solar wind hits its atmosphere harder and the fact that it (at least currently) does not have a magnetic field to protect the atmosphere from the sun.
The comparison is sort of saying that because footballs and apples are both round, apples will never rot, because obviously that doesn't happen to footballs.

 

[ben m]

So what is called greenhouse effect in the case of Venus is nothing more than atmospheric heat insulation over hundreds of millions of years. Gases are excellent insulators.

Nope. First of all, gases are excellent insulators against *conduction* and only conduction. Given convection and advection, over large distances they're actually worse insulators than solids. And they're no insulation at all against radiation, except in the normal atmospheric-greenhouse-effect effect sense.

 

[dasmiller]

Although only a small proportion of radiation from the sun reaches the ground of Venus, carbon dioxide is assumed to somehow heat up the ground.

If the sunlight isn't reaching the ground because it's being absorbed by the atmosphere, then the atmosphere is being directly warmed by the sun. I don't understand the "somehow" remark - are conduction and convection not well-understood?

The true reason of the high temperature on Venus is much simpler:

The very dense atmosphere of Venus has prevented the planet's surface from cooling down after its formation to a temperature similar to thermodynamic radiation-equilibrium.​

So what is called greenhouse effect in the case of Venus is nothing more than atmospheric heat insulation over hundreds of millions of years. Gases are excellent insulators.

Do you have any supporting math?

 

[Trakar]

http://dipastro.pd.astro.it/planets/barbieri/schneider/astronomia/CosmicPerspective_Ch10.pdf

http://www.skyandtelescope.com/news/3304501.html?page=1&c=y

http://www.is.wayne.edu/mnissani/a&s/GREENHOU.htm

http://www.lpi.usra.edu/vexag/nov_2007/presentations/crisp.pdf

Not that these, in themselves, are topic ending pieces, but if you are going to attack longstanding (close to two centuries old) mainstream scientific understandings, you would think that somewhere along the way, the actual science (preferrrable with a solid reference to the science, rather than a caricatured and distorted strawman version to beat up on) itself should be presented, if for no other reason than to clearly demonstrate how and where you think it to be incomplete or wrong.

 

[wogoga]

Although only a small proportion of radiation from the sun reaches the ground of Venus, carbon dioxide is assumed to somehow heat up the ground.

If the sunlight isn't reaching the ground because it's being absorbed by the atmosphere, then the atmosphere is being directly warmed by the sun. I don't understand the "somehow" remark - are conduction and convection not well-understood?

The question is, whether Venus surface got heated up from the sun (as suggested by the greenhouse effect ideology), or simply remained hot because of a heat flow from inside (as suggested e.g. by common sense).

It is obvious that core, mantle, and crust are hotter than the surface. The atmosphere however is colder, continuously decreasing from the surface temperature of more than 450 °C next to the surface, to around -30 °C at the upper cloud deck in 60-70 km altitude (source).

Do you actually suggest that the atmosphere (warmed by the sun) can by conduction and convection increase surface temperate beyond its own temperature?

In Greenhouse Effect and Radiative Balance on Earth and Venus, page 4, we read:

Only ~2.6% of the solar flux incident at the top of the atmosphere reaches the surface

– Solar flux at the surface is ~17 W/m2 (global avg.)

Surface temperature of ~730 K maintained by an efficient atmospheric greenhouse mechanism

– Net downward thermal flux at surface ~15,000 W/m2​

It seems rather astonishing to me that as much 2.6% of solar radiation should reach the surface, despite the mass of Venus' atmosphere corresponding to a mass of more than 1 km depth of water (more than 1000 metric tons per square meter). For comparison, at 100 m underwater the light present from the sun is about 0.5% of that at the surface. (source)

In any case, how "an efficient atmospheric greenhouse mechanism" should somehow transform a "solar flux at the surface" of around 17 W/m2 into a "net downward thermal flux at surface" of around 15,000 W/m2, will probably always remain a complete mystery.

Cheers, Wolfgang

Ideology driven science is rather rule than exception

 

[Dancing David]

Don't forget that Venus receives around DOUBLE the intensity of solar radiation that Earth does, since it is much closer to the sun. Comparisons with Earth are quite ridiculous for that reason alone.

Um, the ratio of intensity if probably 1/r², since we are have about 90 to 67 pretty close

67 million mile vs. 93 million miles so we have that the ratio of the in intensities is the ration between the distances squared
http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/safe_use/distance.htm

I₁/ I₂=(D₂)²/(D₁)²
So we set I two and D two as earth and we get
(X)/(1)= (93)² ( 67)²X=8649/4489

X=1.926

But again it doesn’t matter you can still have insulation play a much larger role that ambient radiation, you will note that the energy of Venus is NOT twice that of the earth in stored energy per unit of the atmosphere.

Somehow I doubt that 14 C (Earth) and 464 C (Venus) is twice the energy storage,.
So what is the average surface temperature for Mercury compared to Venus, I mean it is that much closer than Venus , right?

I mean we have 40 million miles vs. 67 million mile so the ration is (67)²/(40)² or 4489/1600=2.8 or almost three times the radiation,

But what is the mean day time temperature for Mercury?
350C and 170C for night time!
And venus has a mean surface tempertature of 464C.

So Why is that? I mean really it gets three times the radiation that Venus does!

That means Mercury should be three times hotter than Venus, right?

 

[Xephyr]

I thought it had something to do with atmospheric pressure ?

 

[soylent]

Um, the ratio of intensity if probably 1/r², since we are have about 90 to 67 pretty close

67 million mile vs. 93 million miles so we have that the ratio of the in intensities is the ration between the distances squared
http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/safe_use/distance.htm

I₁/ I₂=(D₂)²/(D₁)²
So we set I two and D two as earth and we get
(X)/(1)= (93)² ( 67)²X=8649/4489

X=1.926

Keep in mind also that the power emitted by a black body is proportional to the fourth power of the temperature. If you double the irradiance on a barren rock with no atmosphere you expect the new equilibrium temperature to be ~1.2 times higher(fourth root of 2).

If Earth and Venus were identical barren rocks, with Venus 2.5 times hotter, you'd need 2.5⁴ = ~40 times the solar irradiance on Venus.

 

[Trakar]

The question is, whether Venus surface got heated up from the sun (as suggested by the greenhouse effect ideology), or simply remained hot because of a heat flow from inside (as suggested e.g. by common sense).

To most educated and intelligent individuals, "common sense" says that the well researched, studied and evidenced understandings created by generations of very smart people who devote their lives to investigating natural phenomena probably have much more accurate and meritorious understandings of these phenomena than individuals who lack that training, experience and foundation of knowledge.

 

[lomiller]

Don't forget that Venus receives around DOUBLE the intensity of solar radiation that Earth does, since it is much closer to the sun. Comparisons with Earth are quite ridiculous for that reason alone.

Venus reflects about twice as much incoming radiation as the earth does so Venus actually gets slightly less solar energy entering it’s atmosphere then the Earth does.

To the OP, nope sorry there is no way for Venus to hold onto it’s heat over billions of years without incoming solar energy. While relatively little sunlight actually reaches the surface of Venus the energy that does get there has no way to escape because the solar energy absorbed on the way in heats the atmosphere and heat can’t escape the surface unless it’s warmer then the atmosphere above.

Another error in the OP is that at equilibrium the (non reflected) solar energy entering the atmosphere is going to be in balance with the IR leaving the atmosphere. What the greenhouse gasses are doing is increasing the temperature gradient required in order to have that much outgoing IR.

 

[lomiller]

I doubt anyone these days makes a direct comparison between Venus and Earth. Apart from all the other mentioned differences, its rotation is so slow we have no idea what sort of extra effects that might have had on the evolution of its atmosphere, as well as its slightly lower density and the fact that the solar wind hits its atmosphere harder and the fact that it (at least currently) does not have a magnetic field to protect the atmosphere from the sun.

Dispite it's slow rotation there is almost no difference between nighttime and daytime temperatures on Venus. This is a classic characteristic of heating caused by greehouse gasses.

 

[dasmiller]

Another error in the OP is that at equilibrium the (non reflected) solar energy entering the atmosphere is going to be in balance with the IR leaving the atmosphere. What the greenhouse gasses are doing is increasing the temperature gradient required in order to have that much outgoing IR.

I'm still sorting it out, but the OP seems to be saying that Venus is far (>450 deg C) from equilibrium. I'm a little boggled at the idea that it could be substantially out of equilibrium for billions of years, and the OP seems to have a poor understanding of the greenhouse effect. But I'll have to wade through the posts a little more (I've been busy).

 

[lomiller]

I'm still sorting it out, but the OP seems to be saying that Venus is far (>450 deg C) from equilibrium. I'm a little boggled at the idea that it could be substantially out of equilibrium for billions of years, and the OP seems to have a poor understanding of the greenhouse effect. But I'll have to wade through the posts a little more (I've been busy).

Equilibrium in this case means non-reflected solar energy in the top of the atmosphere vs IR out the top of the atmosphere. The OP seems to be trying to argue IR is very slightly larger then solar energy in because its initial heat has been retained by it’s atmosphere for 4 billion years.

How its atmosphere is selectively letting energy from incoming sunlight escape but preventing geologic heat from escaping is a mystery to me…

 

[Ziggurat]

I thought it had something to do with atmospheric pressure ?

It's got a hell of a lot to do with atmospheric pressure (and thickness). Atmospheres circulate. When air rises, it expands and cools, and conversely, when air drops, it compresses and heats. Air at lower altitudes is hotter than air at higher altitudes in large part because of adiabatic expansion and compression. This works out to roughly 10 deg. C per km, both on Earth and on Venus. So the fact that Venus's atmosphere is so much thicker than Earth's atmosphere is the primary cause of its dramatically higher surface temperature. Conversely, Mars has a much thinner atmosphere, and is much colder, despite being primarily CO₂.

 

[Trakar]

It's got a hell of a lot to do with atmospheric pressure (and thickness). Atmospheres circulate. When air rises, it expands and cools, and conversely, when air drops, it compresses and heats. Air at lower altitudes is hotter than air at higher altitudes in large part because of adiabatic expansion and compression. This works out to roughly 10 deg. C per km, both on Earth and on Venus. So the fact that Venus's atmosphere is so much thicker than Earth's atmosphere is the primary cause of its dramatically higher surface temperature. Conversely, Mars has a much thinner atmosphere, and is much colder, despite being primarily CO₂.

Surely, you aren't echoing Mr Goddard and trying to bring WUWT woo pseudoscience into a legitimate discussion of Venus,...are you?

"adiabatic" - occurring without loss or gain of heat

Highly unlikely with respect to Venus and the issue of its atmospheric and surface heat content. There are some adiabatic processes playing important roles in the atmospheric physics of Venus, but by definition, adiabatic processes are energy neutral, and don't seem particularly relevent to issues of Venus' surface/atmosphere heat, nor any proposed nullification of the CO2 greenhouse effect.

I'd recommend "The Recent Evolution of Climate on Venus" Bullock & Grinspoon as a good reference on Venus's heat.