Evolution of Venus Temperature & Climate

[Wangler]

If you take a look at Venus' atmosphere at a location (height) where the atmospheric pressure is similar to earth's atmospheric pressure, the Venusian temperature is higher, at least for those regions of each atmosphere where the temperature change is approximately linear with altitude change.

Isn't this higher temperature at points of similar pressure the true indication of differences in solar input and greenhouse gas effects for the two planets?

 

[Ziggurat]

Well, then one of us is reading his responses improperly, if it is I, I apologize for the improper charaterization, but I have a hard time reconciling the following statements with that understanding:

I'm not sure where the problem is. Go back to that paper you cited. It talks about how both the atmospheric composition and temperature of Venus have evolved over time, due to greenhouse gas changes. But look at the surface temperatures: they are ALL dramatically higher than Earth's temperature. Likewise, Earth has had drastic atmospheric composition changes over time too, including the substitution of oxygen for carbon dioxide. Major greenhouse gas changes. But Earth's surface temperature has never been close to Venus' (at least, not since initial formation). I'm not claiming greenhouse gasses don't matter, I'm not saying they can't or won't affect us. I'm saying we will never look like Venus because we don't have enough gas in our atmosphere to support such high temperatures, and Venus will never look like Earth, because it's got too much gas to permit such low temperatures.

 

[lomiller]

I'm not sure where the problem is. Go back to that paper you cited. It talks about how both the atmospheric composition and temperature of Venus have evolved over time, due to greenhouse gas changes. But look at the surface temperatures: they are ALL dramatically higher than Earth's temperature. Likewise, Earth has had drastic atmospheric composition changes over time too, including the substitution of oxygen for carbon dioxide. Major greenhouse gas changes. But Earth's surface temperature has never been close to Venus' (at least, not since initial formation). I'm not claiming greenhouse gasses don't matter, I'm not saying they can't or won't affect us. I'm saying we will never look like Venus because we don't have enough gas in our atmosphere to support such high temperatures, and Venus will never look like Earth, because it's got too much gas to permit such low temperatures.

Again this certainly seem to me like you are trying to claim Venus’s surface temperature has something to do with pressure and density of its atmosphere, which simply isn’t the case. Venus gets its surface temperature from its greenhouse effect, and the only major effect pressure plays is pressure spreading of the CO2 absorption bands. If it had an equally dense and reflective atmospehre of a non-greenhouse gas it's surface temperature would be similar to that of the Earth.

 

[Ziggurat]

Again this certainly seem to me like you are trying to claim Venus’s surface temperature has something to do with pressure and density of its atmosphere, which simply isn’t the case. Venus gets its surface temperature from its greenhouse effect, and the only major effect pressure plays is pressure spreading of the CO2 absorption bands.

Convection is a major factor in atmospheric and surface temperature, and the thickness of the atmosphere (which is intimately related to how much gas there is, for reasons I already explained) is the primary determinant of the temperature differential between the top and bottom of a convection cell. You are claiming it's irrelevant, but it isn't. It matters a hell of a lot, both on Venus and on Earth.

If it had an equally dense and reflective atmospehre of a non-greenhouse gas it's surface temperature would be similar to that of the Earth.

Evidence?

 

[BenBurch]

Who, pray tell, are you referring to?

The OP.

 

[CapelDodger]

If you take a look at Venus' atmosphere at a location (height) where the atmospheric pressure is similar to earth's atmospheric pressure, the Venusian temperature is higher, at least for those regions of each atmosphere where the temperature change is approximately linear with altitude change.

Isn't this higher temperature at points of similar pressure the true indication of differences in solar input and greenhouse gas effects for the two planets?

Good question. I hope you get an answer.

 

[CapelDodger]

The OP.

I think the OP lost relevance when wogoga described the greenhouse effect as an "ideology". The rest is detail .

 

[wogoga]

If you take a look at Venus' atmosphere at a location (height) where the atmospheric pressure is similar to earth's atmospheric pressure, the Venusian temperature is higher, at least for those regions of each atmosphere where the temperature change is approximately linear with altitude change.

Isn't this higher temperature at points of similar pressure the true indication of differences in solar input and greenhouse gas effects for the two planets?

According to WP, on Venus at 50 km height, atmospheric pressure is 1.066 bar and temperature is 75°C.

Thus, at a pressure of around 1 bar, we have a temperature of 288°K on Earth and 348°K on Venus. (By the way, to the average temperature on Earth probably corresponds an average height above sea level, with an atmospheric pressure lower than 1 bar. Does anybody know this average value of atmospheric pressure at ground level or a theoretical average temperature at sea level?).

Venus receives around 1.9 times more radiation per square meter than Earth. As the power of thermal radiation is proportional to the fourth power of temperature, a temperature 1.18 times higher (fourth root of 1.9) results in 1.9 higher infrared emissions, thus remaining in equilibrium with the 1.9 times higher incoming radiation. If we multiply the 288°K of Earth by 1.18, we get 340°K for Venus, not far away from the above referenced 348°K.

Greenhouse-effect supporters will argue: As Venus reflects much more of the incoming radiation, the radiation energy absorbed by Venus is similar to the energy absorbed by the Earth. Thus, the fact that the incoming radiation is 1.9 times more powerful on Venus is not relevant, and the higher temperature of Venus at 1 bar is evidence of a green house effect.

However such reasoning in favor of a greenhouse effect is exactly what I criticize as ideologic:

The fact that the clouds (at 60-70 km height) interact with incoming radiation is explained by normal physics. Yet an analogous interaction of outgoing radiation is explained by special (i.e. greenhouse-effect) physics. At least on Earth, clouds significantly slow down cooling at night.​

(I do not call into question the physical principles of the greenhouse effect. Like solids and liquids, also gasses have "colors", determining the interaction with radiation. A change in the composition of an atmosphere can make it "darker" in the infrared, whereas its transparency in the visible and ultraviolet is not (significantly) affected.)

Cheers, Wolfgang
www.pandualism.com

An ideology can be thought of as a way of looking at things, a set of ideas proposed by the dominant class of a society to all members of this society. The main purpose behind an ideology is to offer change in society, and adherence to a set of ideals, through a normative thought process.

One billion malnourished humans and all the focus on climate change! Perverted!

 

[Dancing David]

Considering , hmm why is Mercury's temperature lower than Venus's at night?
Considering you seem to post nonsense and not respond to posts, why do you post here?

 

[Wangler]

Wogoga,

I'm not sure your calculations are correct, but the basic gist of your last post is what I was getting at.

At similar atmospheric pressure, the difference in temperature is about 60K; if you account for albedo, cloud effects and other effects, you possibly will be left with effect due to greenhouse gases alone. That remaining effect is most likely not zero.

This get's back to Ziggurat's point: a primary reason Venus' atmospheric temperature at the planet surface is so high is because of the higher atmospheric pressure.

But it seems certain that a portion of Venus' higher temperatures is due to the greenhouse effect.

 

[CapelDodger]

However such reasoning in favor of a greenhouse effect is exactly what I criticize as ideologic:

The fact that the clouds (at 60-70 km height) interact with incoming radiation is explained by normal physics. Yet an analogous interaction of outgoing radiation is explained by special (i.e. greenhouse-effect) physics. At least on Earth, clouds significantly slow down cooling at night.
​

(I do not call into question the physical principles of the greenhouse effect. Like solids and liquids, also gasses have "colors", determining the interaction with radiation. A change in the composition of an atmosphere can make it "darker" in the infrared, whereas its transparency in the visible and ultraviolet is not (significantly) affected.)

Cheers, Wolfgang
www.pandualism.com

There is nothing special about the physics involved in the greenhouse effect. It arises from standard physics, and would do without ever having been observed. The fact is that it was observed, before it was explained, when Boyle's Law and thermodynamics were already established science. They do not explain the temperature at the Earth's surface, but you're trying to make them explain temperatures on Venus.

Describing reflection of radiation from Venus's atmosphere as an "interaction" but the greenhouse effect of that atmosphere (which is an interaction with radiation) as "special physics" is not going to cut any ice here.

 

[wogoga]

At similar atmospheric pressure, the difference in temperature is about 60K;

What I consider relevant is atmospheric mass, not weight or pressure.

Venus gravity is only 0.904 G. So we must choose for Venus a height where pressure is 0.904 times lower than on Earth, in order to get the same atmospheric mass per square meter as on Earth. If we take further into account that average ground level on Earth is around 250 m above sea level (see) with a pressure reduced by around 0.97 with respect to sea level, then the concerning height on Venus (table) is 53.6 km (instead of 55 km) and temperature is 62°C (instead of 75°C).

This would mean that at similar atmospheric mass per surface, the difference in temperature is only 47°K (288°K on Earth, 335°K on Venus, where 335°K < 1.18*288°K).

if you account for albedo, cloud effects and other effects, you possibly will be left with effect due to greenhouse gases alone. That remaining effect is most likely not zero.

The high albedo on Venus is due to its clouds. From the fact that Earth satellites cannot look through clouds in the infrared (e.g. temperature measurements of the oceans), we can conclude that clouds on Earth are not only a barrier for incoming but also for outgoing (thermal) radiation. Is there any evidence that the opaque sulfuric acid clouds on Venus affect outgoing thermal radiation significantly less than incoming radiation from the sun?

This get's back to Ziggurat's point: a primary reason Venus' atmospheric temperature at the planet surface is so high is because of the higher atmospheric pressure.

Ultimately, me too, I consider lapse rate rather an effect of surface temperature than a cause of it. Otherwise, (as far as I can see) I would have to retract this statement of post #1:

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

The next glacial seemed rapidly approaching, when paleoclimatologists met in 1972 to discuss this issue (a period of so-called global cooling). The previous interglacial periods seemed to have lasted about 10,000 years each. Assuming that the present interglacial period would be just as long, they concluded, "it is likely that the present-day warm epoch will terminate relatively soon if man does not intervene." (Quaternary glaciation)

 

[Ziggurat]

Ultimately, me too, I consider lapse rate rather an effect of surface temperature than a cause of it. Otherwise, (as far as I can see) I would have to retract this statement of post #1:

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

Then you better get ready to retract that statement, because it's NOT simply a function of surface temperature, as I detailed here.

The surface of Venus does receive some heating from the sun. But if the surface is frozen, then it won't lose much heat from radiation, and it will lose NO heat from convection (which it currently does, which is why the adiabatic lapse rate matters). So it won't need a lot of heating to unfreeze it, and it won't last close to a million years at that temperature.

 

[CapelDodger]

What I consider relevant is atmospheric mass, not weight or pressure.

Why, exactly?

Venus gravity is only 0.904 G. So we must choose for Venus a height where pressure is 0.904 times lower than on Earth, in order to get the same atmospheric mass per square meter as on Earth.

The question was about where the pressure is equal to surface pressure on Earth. So what you choose isn't relevant. Answer the question or shut up about it.

If we take further into account that average ground level on Earth is around 250 m above sea level (see) with a pressure reduced by around 0.97 with respect to sea level ...

0.97 what? Surely not 0.97 of an Earthly surface pressure.

then the concerning height on Venus (table) is 53.6 km (instead of 55 km) and temperature is 62°C (instead of 75°C).

This would mean that at similar atmospheric mass per surface, the difference in temperature is only 47°K (288°K on Earth, 335°K on Venus, where 335°K < 1.18*288°K).

Well there you are. Gibbering.

The high albedo on Venus is due to its clouds.

Yes, and irrelevant. Solar radiation that is reflected away from Venus does not influence its temperature. Think about it.

From the fact that Earth satellites cannot look through clouds in the infrared (e.g. temperature measurements of the oceans), we can conclude that clouds on Earth are not only a barrier for incoming but also for outgoing (thermal) radiation. [

So they are.

Is there any evidence that the opaque sulfuric acid clouds on Venus affect outgoing thermal radiation significantly less than incoming radiation from the sun?

Whatever incoming radiation is absorbed by Venusian clouds comes from the Sun, but whatever radiation is re-emitted will go in any direction - including sideways and down towards the surface. Have you fully thought that through?

Ultimately, me too, I consider lapse rate rather an effect of surface temperature than a cause of it.

You're in a very small club there.

Otherwise, (as far as I can see) ...

We should probably leave it at that.

 

[wogoga]

What I consider relevant is atmospheric mass, not weight or pressure.

Why, exactly?

Please, try to understand what I've written in my previous posts. I explain the high crust surface temperature of Venus by atmospheric insulation from a colder environment, and therefore the decisive parameter is a form of quantity (mass, thickness), and not pressure of the atmosphere.

The high albedo on Venus is due to its clouds.

Yes, and irrelevant. Solar radiation that is reflected away from Venus does not influence its temperature.

Albedo due to clouds may be irrelevant in your prejudiced, ideological thinking (see post #48).

An informative quote:

"The effect of clouds depends upon their type and the time of day. The more interesting and important type is the low thick clouds. At night the reflection effect is zero so the greenhouse effect and reflection of thermal radiation dominate and the low thick clouds have a warming effect. One can easily see that the reflection of thermal radiation is far more important than the greenhouse effect. The greenhouse effect could at most return 50 percent of the outgoing radiation back to the Earth. Reflection from the underside of clouds probably returns 90 percent of the radiation. The two effects are not in competition. Clouds could return 90 percent from reflection and half of the unreflected 10 percent. Thus it is easy to see why there is such a difference in temperature between a clear night and a cloudy night in the winter. Since the greenhouse effect from the atmospheric gases would be the same on a clear and a cloudy night one could say that the effect from greenhouse gases is negligible compared to the effect of low thick clouds."​

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.

Then you better get ready to retract that statement, because it's NOT simply a function of surface temperature, as I detailed here.

The surface of Venus does receive some heating from the sun. But if the surface is frozen, then it won't lose much heat from radiation, and it will lose NO heat from convection (which it currently does, which is why the adiabatic lapse rate matters). So it won't need a lot of heating to unfreeze it, and it won't last close to a million years at that temperature.

The blackbody temperature of Venus is around -40°C (source), resulting a thermal emission of 163 W/m^2. Venus obviously also absorbs (nearly) the same amount of sun radiation.
(Solar irradiance: 2614 W/m^2, mean irradiance over the whole sphere: 1/4 * 2614 W/m2 = 653.5 W/m2, not reflected: 25% * 653.5 W/m2 = 163 W/m2)

The -40°C can be seen as the temperature of an averaged thermal-emission-surface of Venus (around 70 km above crust surface). The thick atmosphere is able to insulate the more than 450°C hot crust surface from this -40°C cold radiation-surface.

And now you tell me, that such a -40°C radiation-surface could thermally not be as well insulated from a crust surface of 0°C, as from a crust surface of more than 450°C!

Cheers, Wolfgang

 

[ben m]

And now you tell me, that such a -40°C radiation-surface could thermally not be as well insulated from a crust surface of 0°C, as from a crust surface of more than 450°C!

OK, I'll tell you: A -40C surface can be in perfectly good convective-thermal contact with a 450C surface if they are at different pressures. In fact, the laws of thermodynamics tell you that convection between regions of different pressure will give them different temperatures.

Do you think that this law of thermodynamics is somehow turned off on Venus? Then why do you want to ignore it?

More generally, the presence of a temperature difference doesn't tell you a darn thing about heat conduction. Right now, it's much warmer inside my house than it is outside. Can you use this fact to tell me how well insulated my walls are? Can you use it to predict how fast my house would cool down if the furnace turned off? No you can't.

 

[Ziggurat]

Please, try to understand what I've written in my previous posts. I explain the high crust surface temperature of Venus by atmospheric insulation from a colder environment, and therefore the decisive parameter is a form of quantity (mass, thickness), and not pressure of the atmosphere.

The distinction is essentially irrelevant, since atmospheric mass, weight, and surface pressure are all uniquely related to each other on a planet.

The -40°C can be seen as the temperature of an averaged thermal-emission-surface of Venus (around 70 km above crust surface). The thick atmosphere is able to insulate the more than 450°C hot crust surface from this -40°C cold radiation-surface.

And now you tell me, that such a -40°C radiation-surface could thermally not be as well insulated from a crust surface of 0°C, as from a crust surface of more than 450°C!

You seem to be having some problems understanding the concept of energy flow. The surface gets some small amount of heating from solar radiation. Even with a small amount of heating, the surface must lose energy to stay at a constant temperature. And it must do so at the same rate that it gains energy from solar radiation. At 450°C surface temperature, the surface is able to lose heat to the upper atmosphere largely through convection.

But at 0°C surface temperature, convection would stop. The temperature gradient is too small (it needs to meet or exceed the adiabatic lapse rate - that's why the amount of atmosphere matters). Without convection, the surface would lose energy at a much slower rate, slower than it gained energy from solar radiation. So it would not stay at 0°C, it would heat up. And in much less time than a million years.

 

[CapelDodger]

Please, try to understand what I've written in my previous posts. I explain the high crust surface temperature of Venus by atmospheric insulation from a colder environment, and therefore the decisive parameter is a form of quantity (mass, thickness), and not pressure of the atmosphere.

I might understand what you write if it didn't include such gems as "a form of quantity (mass, thickness)", which is completely meaningless.

There would be no thermal insulation by the atmosphere if said atmosphere was transparent to the radiation - however thick it might be. (By "thick" do you mean "dense"? The terms are interchangeable in some contexts. This may be one of them.)

Albedo due to clouds may be irrelevant in your prejudiced, ideological thinking (see post #48).

Oh, I saw it. You are a gift which keeps on giving.

Reflection of incoming radiation due to clouds has nothing to do with the energy budget within the atmosphere, since it whips in and out at the speed of light.

An informative quote:

"The effect of clouds depends upon their type and the time of day. The more interesting and important type is the low thick clouds. At night the reflection effect is zero so the greenhouse effect and reflection of thermal radiation dominate and the low thick clouds have a warming effect. One can easily see that the reflection of thermal radiation is far more important than the greenhouse effect. The greenhouse effect could at most return 50 percent of the outgoing radiation back to the Earth. Reflection from the underside of clouds probably returns 90 percent of the radiation. The two effects are not in competition. Clouds could return 90 percent from reflection and half of the unreflected 10 percent. Thus it is easy to see why there is such a difference in temperature between a clear night and a cloudy night in the winter. Since the greenhouse effect from the atmospheric gases would be the same on a clear and a cloudy night one could say that the effect from greenhouse gases is negligible compared to the effect of low thick clouds."
​

This refers to "reflection of thermal radiation" by clouds, which is nonsense. Infra-red (long-wave, that is) radiation is not reflected by anything in Earth's atmosphere (nor Venus's, for that matter). What happens is that the liquid water in Earthly clouds absorb and re-emit infra-red, which is the same as the greenhouse effect. The difference is that liquids, unlike gases, absorb and re-emit over a continuous spectrum which is why the effect of clouds at night is so much more marked.

You quote from someone who lacks some very basic understanding. Thayer Watkins, Department of Economics, San Jose State University.

Department of Economics. Can't say I'm surprised, but does SJSU have no scientists to provide this kind of "information"?

 

[wogoga]

Infra-red (long-wave, that is) radiation is not reflected by anything in Earth's atmosphere (nor Venus's, for that matter).

Do you have evidence for the non-reflectivity of atmospheres based on more than wishful thinking?

From On observing the compositional variability of the surface of Venus using nightside near-infrared thermal radiation:

A simple radiative transfer model demonstrates that multiple reflection of thermal radiation between the atmosphere (including clouds) and the solid surface has a significant influence on the observed radiance under the condition of Venus, where reflectivity of overlying atmosphere and clouds is high.​

From Warming Early Mars with Carbon Dioxide Clouds That Scatter Infrared Radiation:

Model calculations show that the surface of early Mars could have been warmed through a scattering variant of the greenhouse effect, resulting from the ability of the carbon dioxide ice clouds to reflect the outgoing thermal radiation back to the surface.​

From Thermal radiation fluxes in the lower atmosphere of Venus:

It is found that with an H2O content of about 0.00001, the fluxes may agree if the clouds reflect more than 60% of the thermal radiation incident on them.​

You quote from someone who lacks some very basic understanding.

It doesn't matter whether somebody has a degree in a field. What matters is knowledge and scientific (logical, consistent, critical, skeptical) reasoning. I like Thayer Watkin's articles, because (unlike the results of untransparent computer simulations, in which one only can believe or not) he uses interesting, concrete, transparent lines of thought, which I can judge for myself.

A statement of Thayer Watkins which could turn out correct in the long term:

A small change in cloudiness over the rest of the Earth's surface can be far more important than major changes in the area of the ice caps. It is important to keep such things in perspective. Climate modelers have a distinct tendency to focus on a sensational minor topic while neglecting the major topics of climate. Clouds and cloudiness are the major factors in the Earth's climate. Clouds rule the Earth's climate. Everything else, including the atmospheric greenhouse gases, is marginal.​

Cheers,
Wolfgang

1. Define the problem as apocalyptic because apocalypse sells.
2. Present the apocalytic vision as mainstream view, and dissenters as crackpots or in the pay of evil giant corporations.
3. Build massive financial support.
4. Use that lobbying support to fight the dissenters and to expand the political, economical and scientific power of the new ideology.

(adapted from)

 

[macdoc]

Do you understand the difference between inside the box reflections which you discuss and albedo reflection in the long wave IR range?

http://docs.google.com/viewer?a=v&q...muqtaj&sig=AHIEtbRy0VnapKWTeo9nEGdjgbMXl2nf1w

and Thayer ought to be ashamed.
Read the second paragraph from the link above