Evolution of Venus Temperature & Climate

[Trakar]

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.​

I'm sure "cherry-picking" and misrepresentation weren't your intentions, but do you not understand the difference in meaning between the sentence you present and the full context of the abstract from which you extracted it?

There are several windows in the near-infrared wavelength range (∼1 μm), in which thermal radiation emitted from the planetary surface penetrates through the thick Venus atmosphere and clouds. In this study we develop an improved method to estimate the surface emissivity on the basis of near-infrared thermal emission from the nightside Venus, which is observed through these windows. 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. Thus it is necessary to take the effect of the reflection by the planetary surface into account in order to estimate accurately the variation in the surface emissivity on the basis of near-infrared observation of Venus. The net effect of multiple reflection of surface thermal radiation between the atmosphere and the surface is to significantly reduce the spatial contrast in thermal radiation due to surface compositional variation. The model calculation demonstrates that despite this effect, detection of granitic rocks on the Venus surface using near-infrared windows is feasible. Since granitic and basaltic rocks have dramatically different 1 μm emissivities, granitic rocks are distinguishable from basaltic rocks by ground-based telescopic observation. A Venus orbiter that measures both the near-infrared thermal radiation and the surface altitude with great accuracy will provide us with a reliable surface emissivity map of Venus, which is a very valuable tool to detect granitic (i.e., Earth-like continental) rocks on Venus.

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.​

Exactly what relationship (other than having common search terms like "CO2." "infrared" and "Reflection") do you perceive between "carbon dioxide ice clouds" and anything that has or is being discussed?

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.​

Again, from a 45 year old Russian paper, speculating about issues long since resolved, and discussing the H2O content of the atmosphere and how it may interact with CO2 to alter the IR windows, rather like Lowel's speculations upon how the Martian canals were maintained, and about as relevent to what is being discussed

context and content are much more important than the simplistic term searches you seem given over to.

 

[Trakar]

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

Now, now, don't try to confuse the fellow with science and facts, he has already stated his lack of respect for education and professional standing, seemingly preferring pseudoscience distortions which agree with or accomidate his tightly clasped preconceptions of such issues.

 

[CapelDodger]

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

I was taking a risk with Venus's atmosphere, and I was wrong. I find that can often be a learning experience on JREF.

You've grasped at this point, and ignored the fact that clouds in Earth's atmosphere do not reflect thermal radiation, as was assumed by your "informative source". Unless you have evidence to the contrary, in which case I'm wrong again.

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

Irrelevant, since scattering is very different from reflection.

It doesn't matter whether somebody has a degree in a field.

It doesn't, nor did I suggest it did. It matters whether someone is right or wrong, and it matters how good they are at judging whether they're right or wrong.

What matters is knowledge and scientific (logical, consistent, critical, skeptical) reasoning.

Absolutely

I like Thayer Watkin's articles ...

I don't doubt it, but have you really looked at them in a sceptical fashion?
The things you like aren't necessarily right.

Watkin may not have thought sceptically about clouds reflecting thermal radiation, nor have any more idea of the difference between reflection and scattering than you do. Makes you think, doesn't it?

 

[CapelDodger]

Again, from a 45 year old Russian paper, speculating about issues long since resolved, and discussing the H2O content of the atmosphere and how it may interact with CO2 to alter the IR windows, rather like Lowel's speculations upon how the Martian canals were maintained, and about as relevent to what is being discussed.

A 45-year old Russian paper? How did that get on the internet - an FoI request?

context and content are much more important than the simplistic term searches you seem given over to.

When someone brings up such an obscure source, having show no sign they'd naturally be intimate with it, the inquiring mind wonders where this is all coming from. It ain't just Google, I'll be bound.

This whole Venus subject is a repetition of "Global Warming on Mars" a few years ago, before "Global Cooling" became the rage during the recent El Nino. When this planet refuses to play ball, attention is shifted to another.

As a cynic of long standing I find this very revealing. And rather amusing.

 

[CapelDodger]

and Thayer ought to be ashamed.

That's a little harsh, I think. Thayer was probably told as a child that cloudy nights are warmer than clear nights because the clouds "refect the heat". By someone as ill-informed as himself.

What he did do is embarrass himself by pushing the idea in public without checking his facts. A clear case of Dunning-Kruger Syndrome. Whether that condition is shameful is a matter of opinion.

 

[Ziggurat]

Watkin may not have thought sceptically about clouds reflecting thermal radiation, nor have any more idea of the difference between reflection and scattering than you do. Makes you think, doesn't it?

In fairness, scattering will lead to what's sometimes called "diffuse reflection" (with mirror-like reflection being referred to as "specular reflection")

 

[wogoga]

http://docs.google.com/viewer?a=v&q...muqtaj&sig=AHIEtbRy0VnapKWTeo9nEGdjgbMXl2nf1w
Read the second paragraph from the link above

You should tutor those who actually need further education of the basics.

From your reference:

"Figure 1: The shortwave rays from the sun are scattered in a cloud. Many of the rays return to space. The resulting cloud albedo forcing, taken by itself, tends to cause a cooling of the Earth."​

To my remark

"The high albedo on Venus is due to its clouds"​

CapelDodger responded:

"Yes, and irrelevant. Solar radiation that is reflected away from Venus does not influence its temperature." (#54)​

To Warming Early Mars with Carbon Dioxide Clouds That Scatter Infrared Radiation he objected:

"Irrelevant, since scattering is very different from reflection." (#63)​

By the way, clouds do reflect (or scatter back) thermal radiation. A quote from Longwave Multiple Scattering in Clouds: Climatic Implications:

"In most global climate models, the multiple scattering of longwave radiation by particles like clouds has been neglected. As the single scattering albedoes of both ice and water clouds are between 0.4 to 0.7, the mutipple scattering of longwave radiation by cloud droplets increases the effective absorption path length."​

Or from Longwave multiple scattering by clouds:

"… and the albedo R increases monotonically with optical depth. Of note in the thermal part of the spectrum is the rather large reflectivity exhibited in the 10 – 20 μm region by the smaller size (5μm) particles which shifts toward longer wavelengths for larger (25μm) particles. Accordingly, a substantial amount of longwave radiation is reflected by clouds reducing the cirrus emissivity at these wavelengths by a (1 – R) factor."​

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

Can your question be interpreted as more than a coward insinuation?

Let us assume a planet with fully transparent atmosphere and a universal cloud deck. Then a thermal-radiation cloud-albedo of 100% would mean that the cloud deck reflects (i.e. scatters back) the whole thermal surface radiation, resulting in no heat loss of the surface by thermal radiation.

And a cloud-albedo of 70% would mean, that at every moment, 70% of the amount of emitted thermal radiation comes in from the cloud deck. This obviously entails that the heat loss of the surface by thermal radiation is reduced by 70%.

Anyway, I should return to the essential, and avoid pointless sideshow quarrels.

Cheers,
Wolfgang

Sometimes the wrong is more instructive than the right

 

[Ziggurat]

Anyway, I should return to the essential, and avoid pointless sideshow quarrels.

Indeed. Please read post #57.

 

[CapelDodger]

In fairness, scattering will lead to what's sometimes called "diffuse reflection" (with mirror-like reflection being referred to as "specular reflection")

That "scattering" is not the same as the scattering of a photon, and the latter was what I was referring to. "Diffuse reflection" is just the sum of many reflections.

That said, I don't think there's anything in Earthly clouds which would reflect IR radiation in the first place. The wavelength seems to me too long, but I could easily be wrong.

(Thanks for the link, The Physics Classroom is now on my Reference list )

 

[wogoga]

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.

I have thought a lot about this comment, but it doesn't seem relevant to the question whether a much smaller lapse rate (starting with a ground temperature of 0°C) could remain stable on Venus over millions of years.

I fully agree with what you wrote in post #36 (emphasis mine):

"Regarding the adiabatic lapse rate: there *are* thermodynamic assumptions that go into that calculation. One of them is that there are adiabatic vertical air currents; the calculation that gives you the lapse rate is basically the calculation of how much a parcel of (high-altitude, low-pressure) air will heat up when descending and being compressed, or vice-versa. If air is moving vertically, then you *will* have this heating effect from standard textbook thermodynamics. …"

"But note that this is not the only way for an atmosphere to behave. An isothermal atmosphere is also a perfectly good solution to the thermodynamics. The stratosphere is another perfectly good solution."​

On Earth we obviously have strong "adiabatic vertical air currents", because our atmosphere is heated up from the ground, and ground temperatures vary widely depending on several parameters such as day-night-cycle, latitude, change of seasons, reflectivity of the ground, or weather.

The near-ground atmosphere of Venus however consists of isothermal layers, where temperature essentially only depends on the distance from the isothermal ground. And in such a horizontally isothermal atmosphere, there is nothing which could give rise to adiabatic vertical air currents of significant amount.

To sum up: You consider both the current Venus lapse-rate of around 10°C/km and an isothermal atmosphere (with a lapse rate of zero) as possible. So why do you oppose my claim, that also a lapse rate in between would be similarly stable?

Cheers,
Wolfgang

 

[ben m]

To sum up: You consider both the current Venus lapse-rate of around 10°C/km and an isothermal atmosphere (with a lapse rate of zero) as possible. So why do you oppose my claim, that also a lapse rate in between would be similarly stable?

If the vertical motion is nonzero but SO SLOW that adiabaticity is partly broken, then yes, you would get a highly-wind-dependent result somewhere between the adiabatic limit and the zero limit.

So what? Who cares if a hypothetical windless planet could be isothermal? Venus is not a hypothetical windless planet. It's a windy planet. We know many things about it, including its windiness, because we've sent probes there. It has Hadley cells, where equatorial air wells up (and cools---the equatorial cooling is visible from satellites), flows north, and sinks back to the surface near the poles.

 

[Ziggurat]

On Earth we obviously have strong "adiabatic vertical air currents", because our atmosphere is heated up from the ground

Same thing happens on Venus.

The near-ground atmosphere of Venus however consists of isothermal layers, where temperature essentially only depends on the distance from the isothermal ground. And in such a horizontally isothermal atmosphere, there is nothing which could give rise to adiabatic vertical air currents of significant amount.

To sum up: You consider both the current Venus lapse-rate of around 10°C/km and an isothermal atmosphere (with a lapse rate of zero) as possible. So why do you oppose my claim, that also a lapse rate in between would be similarly stable?

It's thermodynamically possible for a hypothetical atmosphere to be vertically isothermal. But it doesn't describe Venus. The atmosphere of Venus does receive heating from the ground. Venus does have convection.

 

[wogoga]

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.

The average solar flux reaching the ground is around 17 W/m2 (ref. of post #10). The black-body temperature of 17 W/m is only -140°C. The ground however is at +470°C (corresponding to 17,000 W/m2).

If we assume an emissivity factor (over the corresponding spectra) of 60% for both ingoing solar and outgoing thermal radiation, then absorption of 10 W/m2 is confronted with emission of 10,000 W/m2.

Thus, the assumption of a net radiation energy flow to the ground seems completely absurd to me, or do I overlook something?

Think also about the poles where the solar flux is virtually zero all the time. Ground temperature there is essentially the same as on the equator.

On Earth we obviously have strong "adiabatic vertical air currents", because our atmosphere is heated up from the ground, and ground temperatures vary widely depending on several parameters such as day-night-cycle, latitude, change of seasons, reflectivity of the ground, or weather.

Same thing happens on Venus.

If you think you are right, then you should be able to detail.

"Only about 11% of the solar radiation absorbed by the planet reaches the surface, and most of it is taken up in the clouds at altitudes of 60–70 km." (source)

"The movement of super-rotation starts around 10 km of altitude, develops regularly up to 65 km, where it reaches a speed at the equator of about 540 km/h, to decrease and cancel themselves around 95 km." (source)

Cheers,
Wolfgang

 

[Ziggurat]

The average solar flux reaching the ground is around 17 W/m2 (ref. of post #10). The black-body temperature of 17 W/m is only -140°C. The ground however is at +470°C (corresponding to 17,000 W/m2).

If we assume an emissivity factor (over the corresponding spectra) of 60% for both ingoing solar and outgoing thermal radiation, then absorption of 10 W/m2 is confronted with emission of 10,000 W/m2.

Thus, the assumption of a net radiation energy flow to the ground seems completely absurd to me, or do I overlook something?

You overlooked the fact that the cloud layer also emits/reflects radiation downward. That 17 W/m is not the total amount of power that gets absorbed by the ground, and it's not the total power that gets emitted from the ground, it's the difference in the power the ground emits (through radiation and conduction/convection) and the power the ground absorbs from the atmosphere. So assigning it an effective temperature of -140 C is absolutely nonsensical.

So, how does the ground lose that net 17 W/m power? In large part through convection.

Think also about the poles where the solar flux is virtually zero all the time. Ground temperature there is essentially the same as on the equator.

It's close to equatorial temperatures, because of convection. You can't get that kind of temperature homogeneity across the entire planet without it. Why on earth did you think that this piece of evidence undermined rather than supported what I've been saying?

 

[ben m]

"The movement of super-rotation starts around 10 km of altitude, develops regularly up to 65 km, where it reaches a speed at the equator of about 540 km/h, to decrease and cancel themselves around 95 km." (source)

Superrotation describes extremely strong *horizontal* (zonal, east-west) winds. We're talking about vertical air motion here. Every source I can find says that near-surface vertical air motion is somewhere in the 1mm/s or 1cm/s ballpark.

In any case, Wogoga, you're arguing in the wrong direction. Your hypothesis does not predict an isothermal atmosphere, nor a non-circulating atmosphere. Your hypothesis, "Venus's surface is heated from below", predicts that the lower atmosphere is circulating like crazy due to convection. That's what happens when you heat something from below. It's practically the textbook description of how convection works.

When I said "an isothermal atmosphere is thermodynamically possible", I forgot to point out that it's possible only under certain boundary conditions. It is possible only if the top and bottom of the atmosphere are at the same temperature to begin with, and kept that way. If the ground is further cooled somehow, you can get a stable layered atmosphere. If the ground is further heated somehow (as in your model), you get convection.

What was your argument again? Start from the beginning. Do you have any evidence that standard models of Venus don't work?

 

[wogoga]

You overlooked the fact that the cloud layer also emits/reflects radiation downward.

As to your "cloud layer emits":

The temperature of the cloud layer (at a height of 60 to 70 km) is in the order of 30°C below zero, yet ground temperature is 470°C. A heat transfer from the colder to the hotter is thermodynamically impossible, also in the case of thermal radiation.

By the way, if the atmosphere under the cloud deck were transparent for thermal radiation, as you suggest, then the ground would lose substantial heat to the clouds (i.e. there would be a strong thermal radiation flow from 470°C to -30°C). This would entail a significant increase in the thermal-emission-surface temperature (see #55) of Venus. As higher thermal-emission-surface temperature (corresponding to higher blackbody temperature) leads to higher thermal emissions of the planet, significant cooling of the crust surface would be an inevitable outcome.​

As to your "cloud layer refects":

If only 1% of the 17,000 W/m2 blackbody radiation (i.e. 170 W/m2) were emitted by the ground to the clouds, and as much as 90% of this emitted thermal radiation came back to the surface, then the resulting heat loss of 17 W/m^2 would already be as high as solar radiation reaching the ground on average.

We conclude: In the same way as a sea bed below tens or hundreds of meters of water does not significantly interact via thermal radiation with the atmosphere, the crust surface of Venus does not significantly interact via thermal radiation with its higher atmosphere.
(The pressure found on Venus's surface is high enough that the carbon dioxide is technically no longer a gas, but a supercritical fluid. The density of the air at the surface is 67 kg/m3, which is 6.5% that of liquid water on Earth.)​

That 17 W/m is not the total amount of power that gets absorbed by the ground, and it's not the total power that gets emitted from the ground, it's the difference in the power the ground emits (through radiation and conduction/convection) and the power the ground absorbs from the atmosphere.

If the dogma of a runaway greenhouse effect on Venus had something to do with reality and science, then something similar to what you write here were actually a correct scientific conclusion.

Cheers, Wolfgang

If greenhouse-effect science concerning Earth is as catastrophically biased, unscientific, and illogical as the one concerning Venus, then we should remain very skeptical.

 

[Ziggurat]

As to your "cloud layer emits":

The temperature of the cloud layer (at a height of 60 to 70 km) is in the order of 30°C below zero, yet ground temperature is 470°C. A heat transfer from the colder to the hotter is thermodynamically impossible, also in the case of thermal radiation.​

A net heat transfer is impossible. But you weren't talking about net transfer when you cited the total thermal radiative output of the ground. But the reflected bit is probably more important anyways.

By the way, if the atmosphere under the cloud deck were transparent for thermal radiation

It doesn't have to be. That's actually rather irrelevant to my point. In fact, if the atmosphere is opaque to thermal radiation, that's fine too: whether the emission/reflection is coming from the clouds or from the atmosphere right above the ground doesn't matter, the point is that you ignored this when trying to figure out your radiative balance.

Look, it's quite simple: the ground receives heating from the sun, and it loses heat through various mechanisms. Those mechanisms (be it radiation or convection) would radically slow/stop if you magically dropped the temperature of the surface, so the surface would heat up. And it would take far less than a million years to do so. Nothing you've said even addresses this rather basic point.

If greenhouse-effect science concerning Earth is as catastrophically biased, unscientific, and illogical as the one concerning Venus, then we should remain very skeptical.

If you would pull your head out of your rear end, you would notice that I'm not arguing for greenhouse gas effects. Regardless of greeenhouse gas effects, you're still wrong about a number of things you've claimed. Spectacularly wrong.

 

[wogoga]

I'm not arguing for greenhouse gas effects.

What I'm disputing, is the claim that 1) radiation from the sun has been heating up the crust surface of Venus from a significantly lower temperature to its current 470°C, and that 2) a hypothetical ground temperature of 0°C would make such a heating much faster. I must admit that I didn't pay enough attention to whether I was arguing against 1) or against 2).

It seems that the myth of a runaway greenhouse effect on Venus can be traced back to the authority of Carl Sagan. In the meantime the myth has become a dogma.

And if I'm not completely mistaken in my thermodynamic evaluation, then everybody supporting the idea of such a temperature increase on Venus is (intentionally or unintentionally) working for the greenhouse-effect ideology, even if the assumed temperature increase is (honestly or insidiously) attributed to another mechanism. The reason is simple: Alternative explanations of non-existing 'facts' give further credibility to such 'facts'.

From the premises

• The lowest mean crust temperature on is at crust surface
• The highest mean atmosphere temperature is at crust surface

I conclude:

• There is a tiny heat flow from the crust to the atmosphere

Cheers, Wolfgang

Whereas a scientific hypothesis is refuted by facts and logical reasoning, a dogma refutes facts and logical reasoning

 

[Ziggurat]

What I'm disputing, is the claim that 1) radiation from the sun has been heating up the crust surface of Venus from a significantly lower temperature to its current 470°C

It doesn't matter if it heated the surface from a lower temperature or just keeps it from cooling down further: the sun still provides the surface with heat. If the sun stopped shining, the surface would cool, and if the surface was magically made cooler, it would heat up.

, and that 2) a hypothetical ground temperature of 0°C would make such a heating much faster.

Of course it would. A 0°C surface temperature would drastically reduce both radiative and convective heat loss, but it would still receive the same amount of incoming heat. So there would no longer be any balance between heat in and heat out, and net heat flow in = rising temperature. Your million-year lifespan for a frozen surface is an absurdity.

It seems that the myth of a runaway greenhouse effect on Venus can be traced back to the authority of Carl Sagan. In the meantime the myth has become a dogma.

And if I'm not completely mistaken in my thermodynamic evaluation

You are completely mistaken in your thermodynamic evaluation. And what you haven't figured out is that the reasons you're wrong have nothing to do with Sagan being right, or with runaway greenhouse effects. You have made claims which don't withstand basic scrutiny.

From the premises

• The lowest mean crust temperature on is at crust surface
• The highest mean atmosphere temperature is at crust surface

I conclude:

• There is a tiny heat flow from the crust to the atmosphere

Cheers, Wolfgang

That's correct. But that tiny heat flow comes from the fact that the surface receives some heating from solar radiation. Thermal conduction from below the surface is pretty much irrelevant. The crust itself is a FAR better insulator than the atmosphere ever could be.

 

[Trakar]

By the way, clouds do reflect (or scatter back) thermal radiation. A quote from Longwave Multiple Scattering in Clouds: Climatic Implications:

"In most global climate models, the multiple scattering of longwave radiation by particles like clouds has been neglected. As the single scattering albedoes of both ice and water clouds are between 0.4 to 0.7, the mutipple scattering of longwave radiation by cloud droplets increases the effective absorption path length."​

Exactly what is this paper, and why is the only source available for it some obscure and mostly disfunctional personal website? It isn't referenced or locatable through any of the normal published science websites, nor apparently referenced by any other scientific publication. Perhaps it is just the issue that this isn't the name of the paper, rather hard to take any proffered reference too seriously when those offering it as support for their position can't be bothered to get something as simple as the name of the referenced paper correctly.