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Tags atmosphere , greenhouse effect , planet formation , temperature , venus

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Old 23rd June 2010, 11:15 AM   #41
Wangler
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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?
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Old 23rd June 2010, 11:17 AM   #42
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Originally Posted by TShaitanaku View Post
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.
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Old 23rd June 2010, 12:40 PM   #43
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Originally Posted by Ziggurat View Post
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 Venuss surface temperature has something to do with pressure and density of its atmosphere, which simply isnt 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.
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Old 23rd June 2010, 12:56 PM   #44
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Originally Posted by lomiller View Post
Again this certainly seem to me like you are trying to claim Venuss surface temperature has something to do with pressure and density of its atmosphere, which simply isnt 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.

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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?
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Old 23rd June 2010, 01:52 PM   #45
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Originally Posted by Ziggurat View Post
Who, pray tell, are you referring to?
The OP.
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Old 24th June 2010, 06:38 PM   #46
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Originally Posted by Wangler View Post
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.
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Old 24th June 2010, 06:41 PM   #47
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Originally Posted by BenBurch View Post
The OP.
I think the OP lost relevance when wogoga described the greenhouse effect as an "ideology". The rest is detail .
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Old 26th June 2010, 10:28 AM   #48
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Originally Posted by Wangler View Post
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 75C.

Thus, at a pressure of around 1 bar, we have a temperature of 288K on Earth and 348K 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 288K of Earth by 1.18, we get 340K for Venus, not far away from the above referenced 348K.

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
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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!
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Old 27th June 2010, 07:00 AM   #49
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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?
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Old 27th June 2010, 08:14 AM   #50
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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.
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Old 28th June 2010, 06:26 PM   #51
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Originally Posted by wogoga View Post
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
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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.
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Old 1st July 2010, 12:28 PM   #52
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Originally Posted by Wangler View Post
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 62C (instead of 75C).

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

Quote:
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?

Quote:
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)
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Old 1st July 2010, 12:48 PM   #53
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Originally Posted by wogoga View Post
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.
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Old 2nd July 2010, 06:44 PM   #54
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Originally Posted by wogoga View Post
What I consider relevant is atmospheric mass, not weight or pressure.
Why, exactly?

Quote:
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.

Quote:
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.

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

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

Quote:
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.

Quote:
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.

Quote:
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?

Quote:
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.

Quote:
Otherwise, (as far as I can see) ...
We should probably leave it at that.
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Old 3rd July 2010, 01:14 PM   #55
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Originally Posted by wogoga View Post
What I consider relevant is atmospheric mass, not weight or pressure.
Originally Posted by CapelDodger View Post
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.

Originally Posted by wogoga View Post
The high albedo on Venus is due to its clouds.
Originally Posted by CapelDodger View Post
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."
Originally Posted by wogoga View Post
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.
Originally Posted by Ziggurat View Post
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 -40C (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 -40C 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 450C hot crust surface from this -40C cold radiation-surface.

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

Cheers, Wolfgang
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Old 3rd July 2010, 11:02 PM   #56
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Originally Posted by wogoga View Post
And now you tell me, that such a -40C radiation-surface could thermally not be as well insulated from a crust surface of 0C, as from a crust surface of more than 450C!
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.
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Old 4th July 2010, 10:48 AM   #57
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Originally Posted by wogoga View Post
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.

Quote:
The -40C 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 450C hot crust surface from this -40C cold radiation-surface.

And now you tell me, that such a -40C radiation-surface could thermally not be as well insulated from a crust surface of 0C, as from a crust surface of more than 450C!
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 450C surface temperature, the surface is able to lose heat to the upper atmosphere largely through convection.

But at 0C 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 0C, it would heat up. And in much less time than a million years.
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Old 4th July 2010, 07:00 PM   #58
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Originally Posted by wogoga View Post
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.)

Quote:
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.

Quote:
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"?
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Old 8th July 2010, 02:09 PM   #59
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Originally Posted by CapelDodger View Post
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.
Originally Posted by CapelDodger View Post
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,
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  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)
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Old 8th July 2010, 02:16 PM   #60
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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=...EGdjgbMXl2nf1w

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

Last edited by macdoc; 8th July 2010 at 02:18 PM.
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Old 8th July 2010, 02:45 PM   #61
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Originally Posted by wogoga View Post
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?
Quote:
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.
Quote:
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?

Quote:
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.
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Old 8th July 2010, 02:51 PM   #62
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Originally Posted by macdoc View Post
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=...EGdjgbMXl2nf1w

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.
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Old 8th July 2010, 06:02 PM   #63
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Originally Posted by wogoga View Post
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.

Quote:
Irrelevant, since scattering is very different from reflection.


Quote:
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.

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

Quote:
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?
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Old 8th July 2010, 06:24 PM   #64
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Originally Posted by TShaitanaku View Post
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?

Quote:
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.
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Old 8th July 2010, 06:39 PM   #65
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Originally Posted by macdoc View Post
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.
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Old 9th July 2010, 12:12 AM   #66
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Originally Posted by CapelDodger View Post
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")
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Old 10th July 2010, 07:01 AM   #67
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Originally Posted by macdoc View Post
http://docs.google.com/viewer?a=v&q=...EGdjgbMXl2nf1w
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."
Originally Posted by macdoc View Post
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
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Old 10th July 2010, 11:30 AM   #68
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Originally Posted by wogoga View Post
Anyway, I should return to the essential, and avoid pointless sideshow quarrels.
Indeed. Please read post #57.
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Old 10th July 2010, 06:27 PM   #69
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Originally Posted by Ziggurat View Post
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 )
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Old 12th July 2010, 12:36 PM   #70
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Originally Posted by wogoga View Post
And now you tell me, that such a -40C radiation-surface could thermally not be as well insulated from a crust surface of 0C, as from a crust surface of more than 450C!
Originally Posted by ben m View Post
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 0C) 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 10C/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
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Old 12th July 2010, 01:10 PM   #71
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Originally Posted by wogoga View Post
To sum up: You consider both the current Venus lapse-rate of around 10C/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.
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Old 13th July 2010, 11:08 AM   #72
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Originally Posted by wogoga View Post
On Earth we obviously have strong "adiabatic vertical air currents", because our atmosphere is heated up from the ground
Same thing happens on Venus.

Quote:
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 10C/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.
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Old 14th July 2010, 12:43 PM   #73
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Originally Posted by Ziggurat View Post
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 -140C. The ground however is at +470C (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.


Originally Posted by wogoga View Post
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.
Originally Posted by Ziggurat View Post
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 6070 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
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Old 14th July 2010, 01:03 PM   #74
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Originally Posted by wogoga View Post
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 -140C. The ground however is at +470C (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.

Quote:
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?
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Old 15th July 2010, 10:33 AM   #75
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Originally Posted by wogoga View Post
"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?
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Old 17th July 2010, 03:45 AM   #76
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Originally Posted by Ziggurat View Post
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 30C below zero, yet ground temperature is 470C. 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 470C to -30C). 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.)
Quote:
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.
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Old 17th July 2010, 10:07 AM   #77
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Originally Posted by wogoga View Post
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 30C below zero, yet ground temperature is 470C. 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.

Quote:
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.

Quote:
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.
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Old 18th July 2010, 07:42 AM   #78
wogoga
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Originally Posted by Ziggurat View Post
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 470C, and that 2) a hypothetical ground temperature of 0C 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
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Old 18th July 2010, 10:01 AM   #79
Ziggurat
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Originally Posted by wogoga View Post
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 470C
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.

Quote:
, and that 2) a hypothetical ground temperature of 0C would make such a heating much faster.
Of course it would. A 0C 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.

Quote:
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.

Quote:
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.
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Old 20th July 2010, 09:35 AM   #80
Trakar
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Originally Posted by wogoga View Post

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.
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