Evolution of Venus Temperature & Climate

[Ziggurat]

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

"adiabatic" - occurring without loss or gain of heat

Highly unlikely with respect to Venus and the issue of its atmospheric and surface heat content. There are some adiabatic processes playing important roles in the atmospheric physics of Venus, but by definition, adiabatic processes are energy neutral

They are heat neutral. They are NOT energy neutral. There's a major difference.

and don't seem particularly relevent to issues of Venus' surface/atmosphere heat

It's damned relevant. Hell, it's very relevant to earth's surface temperature too. That's why Death Valley is so damned hot: it's below sea level.

nor any proposed nullification of the CO2 greenhouse effect.

This isn't about a nullification of greenhouse effects. It's about the relative sizes of effects. And atmospheric thickness effects will dominate over greenhouse effects when you want to discuss the difference in surface temperature between, say, Earth and Venus.

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

Composition will be VERY important to the upper atmosphere temperature. But lower down, it becomes much less important. Look at figure 2 of your paper. Below about 40 km, notice how the temp vs. altitude graph becomes pretty much a flat line, fairly close to that 10 C/km adiabatic lapse rate I cited earlier. That's not radiative heat transfer. Yes, adiabatic compression and expansion aren't the ONLY factors at play, but they are the dominant component at lower altitudes. So whatever you want to do to the upper atmosphere, you'll still have that slope at lower altitudes, and you'll still end up with a surface temperature MUCH hotter than Earth's, regardless of what you do to the composition. That paper doesn't actually claim otherwise. In fact, let's see what they say about adiabatic processes:

"Convection was treated by taking the radiative equilibrium temperature profile and adjusting the lapse rate to be adiabatic wherever the radiative
equilibrium lapse rate exceeded the adiabat (McKay et al. 1989)."

Hmm.... seems they thought it was important after all.

 

[Xephyr]

Thanks for the explanation Ziggurat.

It makes perfect sense... heat gets trapped in the atmosphere due to the composition of high CO2 and the atmospheric pressure forces that heat to escalate until it hits its maximum based on physical laws. At that point the temperature is maintained.

Sounds like Venus is sitting on an equilibrium to me...

But here's my next question :

What causes Venus' atmospheric pressure to be so much higher than ours ? Rotation ? Axis tilt ? Direction of revolution ? Atmospheric composition ?

Could that answer the question of what our maximum temps could possibly reach in a worst case scenario if CO2 jacks up to 95% here on earth...? Of course the differences of our hydrological cycle, etc would all have to be factored in as well in order to calculate max temp possibilities.

Or am I completely off my crock thinking of it this way ?

 

[Ziggurat]

Thanks for the explanation Ziggurat.

It makes perfect sense... heat gets trapped in the atmosphere due to the composition of high CO2 and the atmospheric pressure forces that heat to escalate until it hits its maximum based on physical laws. At that point the temperature is maintained.

Sounds like Venus is sitting on an equilibrium to me...

But here's my next question :

What causes Venus' atmospheric pressure to be so much higher than ours ? Rotation ? Axis tilt ? Direction of revolution ? Atmospheric composition ?

The amount of gas there is. Venus has much more gas than Earth.

Could that answer the question of what our maximum temps could possibly reach in a worst case scenario if CO2 jacks up to 95% here on earth...? Of course the differences of our hydrological cycle, etc would all have to be factored in as well in order to calculate max temp possibilities.

Or am I completely off my crock thinking of it this way ?

You might be able to ballpark it. The problem is the uncertainty. A 20 degree C uncertainty (for example - real uncertainty may be different) is plenty good enough to distinguish Earth climate from Venus climate (which is more than 400 deg. C hotter at the surface), but it's not enough to gauge impact on humans, since 20 degrees makes a huge bloody difference to our lives. So gas volume considerations are enough to tell us we'll never look like Venus. They aren't enough to tell us what we really want to know.

 

[Xephyr]

I agree.

As I see it, the only way we could become Venus-like is if all of our oceans suddenly vapourized within minutes (or at least most of it to permanently alter the hydrological cycle). Maybe a catastrophic event happened on Venus that vapourized all the water, or perhaps it never formed water in the first place.

So long as there is evaporation (hydrological cycle), we have a pretty steady range of barometric pressure limitations going on. Water has less mass than gas in the air. More moisture, pressure drops, less moisture, pressure rises. That plays a huge role on earth's surface (at sea level) temp min/max possibilities.

... but as for Venus, I've often wondered if rotation speed/direction plays a role in any of that as to how and why it evolved to what it is today. Or maybe it just simply boils down to the very beginning of how a planet's formation starts off that determines the path of evolution it'll see.

Or maybe I just think too damn much.



Edit to the edit.

 

[lomiller]

Greenhouse gasses controls surface temperature while atmospheric composition controls how much temperature decreases as you go up and how high you go before that relationship breaks down. If Venus’s atmosphere were equally thick but opaque to neither IR nor visible light it’s surface temperature would be approximately equal to it’s blackbody temperature and if the there were any lapse rate at all temperatures would decrease from these.

IOW you can’t do this the way Ziggurat is attempting, and it does indeed seem to be based on a blog posting by Goddard that has been thoroughly debunked. Lapse rate is ultimately a function of surface temperature not a cause of it.

BTW he does seem to be echoing a blog posting from last month, and one that has received considerable debunking. Here is a good example

http://moyhu.blogspot.com/2010/05/greenhouse-effect-and-adiabatic-lapse.html#comments

 

[BenBurch]

Which political anti-science woo site was the OP copied from?

 

[BenBurch]

An educational resource; http://www.aip.org/history/climate/co2.html

 

[Ziggurat]

Greenhouse gasses controls surface temperature while atmospheric composition controls how much temperature decreases as you go up and how high you go before that relationship breaks down. If Venus’s atmosphere were equally thick but opaque to neither IR nor visible light it’s surface temperature would be approximately equal to it’s blackbody temperature and if the there were any lapse rate at all temperatures would decrease from these.

In other words, if you radiatively decouple the atmosphere completely from its surroundings, so that it can only absorb and release heat through conduction, then blackbody temperature of the surface is your only constraint. Well, yeah. But that's an irrelevant scenario, with or without greenhouse gasses, because that doesn't describe the atmosphere of any planet.

IOW you can’t do this the way Ziggurat is attempting, and it does indeed seem to be based on a blog posting by Goddard that has been thoroughly debunked. Lapse rate is ultimately a function of surface temperature not a cause of it.

No. Adiabatic lapse rate is a function of gravity and constant-pressure heat capacity. Surface temperature is part of the boundary condition for the problem (as already pointed out, this lapse rate won't hold over the entire atmosphere), but you're confusing boundary conditions with the solution to the problem.

BTW he does seem to be echoing a blog posting from last month, and one that has received considerable debunking.

And yet, your attempts to describe what's wrong with what I said are incorrect.

 

[bobdroege7]

Where did Venus get all the CO2 gas in the first place?

Or, the earth has about the same amount of carbon as Venus, how come ours is mostly dissoved in water and in rocks?

Venus is not big enough to catch and hold that much gas during its formation early in the history of the solar system.

 

[lomiller]

No. Adiabatic lapse rate is a function of gravity and constant-pressure heat capacity.

As I said, the hypothesis you are pushing has been debunked extensively since it appeared in a blog posting a month ago but by all means go ahead and try your derivation of lapse rate from gravity and heat capacity if you want.

Surface temperature is part of the boundary condition for the problem (as already pointed out, this lapse rate won't hold over the entire atmosphere), but you're confusing boundary conditions with the solution to the problem.

So you were not attempting to explain surface temperature in your posts above?

 

[CapelDodger]

Where did Venus get all the CO2 gas in the first place?

Or, the earth has about the same amount of carbon as Venus, how come ours is mostly dissoved in water and in rocks?

Venus is not big enough to catch and hold that much gas during its formation early in the history of the solar system.

Life might have something to do with it. And I've heard that the Moon may have had an effect as well - it was a lot closer when our atmosphere was forming, so tidal forces may have liberated a significant portion of the gases present back then.

 

[lomiller]

Where did Venus get all the CO2 gas in the first place?

Or, the earth has about the same amount of carbon as Venus, how come ours is mostly dissoved in water and in rocks?

Venus is not big enough to catch and hold that much gas during its formation early in the history of the solar system.

Liquid water plays a big role in the formation of Carbonate rock. If Venus had oceans it lost them very early

 

[Ziggurat]

As I said, the hypothesis you are pushing has been debunked extensively since it appeared in a blog posting a month ago but by all means go ahead and try your derivation of lapse rate from gravity and heat capacity if you want.

It isn't my derivation (though I have also done it myself). It's standard textbook thermodynamics. And the derivation was included in that NASA page I linked to before (I can cite thermo textbooks too if you care), but here it is again. I notice that, once again, you can only state that what I'm saying has been debunked, you can't actually offer up an argument yourself for why anything I said is wrong. In fact, given your responses, it appears that you don't even understand what I said.

 

[wogoga]

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

Nope. First of all, gases are excellent insulators against *conduction* and only conduction. Given convection and advection, over large distances they're actually worse insulators than solids.

Do you know evidence of significant vertical convection on Venus?

In heights where atmospheric temperatures are (significantly) influenced by the sun, there is strong horizontal convection (zonal circulation, transporting heat between the day and night sides of the planet). At lower than 50° latitudes, such east-west winds decrease from around 100 m/s at 60-70 km height to less the 1 m/s near surface.

Heat is also transported from the equator to the poles. However, near surface, such heat exchanges are not needed, as the temperature there does not depend on sun radiation, but on the iso-thermic heat from within the crust. (see)

And they're no insulation at all against radiation, except in the normal atmospheric-greenhouse-effect effect sense.

Also liquids and solid are "no insulation at all against radiation, except in the normal" not-being-transparent "sense".

To characterize a well-known normal physical principle by a trendy ideological concept such as greenhouse-effect seems rather problematic to me.

That Venus may seem hotter than expected, results primarily from the fact that planets with atmospheres have no clearly defined surfaces.

A black body with Venus' surface temperature (~740° Kelvin) radiates around 17,000 W/m2, whereas a black body with a temperature of Venus' upper cloud deck (~240° Kelvin) less than 200 W/m2.

If we defined the boundary between Jupiter's atmosphere and Jupiter's fluid interior as Jupiter's surface, then we also could explain its high temperature by a super greenhouse effect.

Cheers, Wolfgang

Ideology driven science is rather rule than exception

 

[lomiller]

It isn't my derivation (though I have also done it myself). It's standard textbook thermodynamics. And the derivation was included in that NASA page I linked to before (I can cite thermo textbooks too if you care), but here it is again. I notice that, once again, you can only state that what I'm saying has been debunked, you can't actually offer up an argument yourself for why anything I said is wrong. In fact, given your responses, it appears that you don't even understand what I said.

As I said we’ve seen this all before. Atmospheric height is not a constant, it’s a function of surface temperature and lapse rate.. The equation you cite is perfectly acceptable to us in that context. You cannot use the way you are attempting and try to pick a fixed atmospheric height and us lapse rate to derive surface temperature.

 

[ben m]

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. It gives you a relationship between the derivatives of pressure and temperature---it doesn't give you the temperature itself. You apply this relationship to (a) hydrostatic equilibrium and (b) surface temperature and *all together* these constraints fix the lapse rate and the scale height. They're not independent.

But Zig is not, as far as I can tell, claiming anything different. He's not claiming that basic thermo "magically" tells you the surface temperature or the scale height. He's claiming that there's a basic thermo lapse rate which, combined with the hydrostatic equilibrium equation (which includes the total mass of the atmosphere, which differs from planet to planet) and some temperature setpoint (which depends on radiation and whatnot, and differs from planet to planet) tells you that a massive atmosphere has higher lapse rate than a low-mass one. Sounds good to me.

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.

 

[BenBurch]

What we are seeing here, AGAIN, is what happens when people with essentially no physics education and transparent political motives try to refute a scientific consensus that took many years to reach.

 

[Ziggurat]

As I said we’ve seen this all before. Atmospheric height is not a constant, it’s a function of surface temperature and lapse rate.. The equation you cite is perfectly acceptable to us in that context. You cannot use the way you are attempting and try to pick a fixed atmospheric height and us lapse rate to derive surface temperature.

I'm not picking a fixed atmospheric height. Rather, you are assuming that the surface temperature is the only relevant boundary condition. And it isn't. The convective zone where the adiabatic lapse rate dominates does not extend to the edge of space. Where the adiabatic lapse regions meets the upper atmosphere, the temperatures AND the pressures must be equal. This region will end when the atmosphere gets thick enough, and its temperature will be determined largely by radiative balance between the sun and space. That sets our pressure and temperature for the top of the adiabatic lapse region.

If you try to fix a set surface temperature and use the adiabatic lapse rate, you can calculate an altitude where it will match our upper atmosphere, and it will indeed vary depending on the surface temperature you picked. But since the pressure will also need to match, doing this also constrains the amount of gas that the atmosphere has. But of course, that's wrong: temperature can vary quite a bit, but atmospheric content is essentially a conserved quantity, at least over the time scales needed to reach thermal equilibrium. Pick the wrong surface temperature, and you'll have the wrong amount of gas. Going the other direction, starting from the upper atmosphere at a fixed temperature and pressure, we can use the adiabatic lapse rate PLUS the total atmospheric content to calculate an altitude, which will give us a final surface temperature. And more atmosphere means more altitude, and higher surface temperature. That's a simplification, of course, but it's a far more accurate simplification than what you suggest.

But it's more than a little ironic that you basically ignored radiative transfer in the upper atmosphere in order to defend your understanding of the green house effect.

 

[Ziggurat]

What we are seeing here, AGAIN, is what happens when people with essentially no physics education and transparent political motives try to refute a scientific consensus that took many years to reach.

Who, pray tell, are you referring to?

 

[Trakar]

...But Zig is not, as far as I can tell, claiming anything different...

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:

"...So the fact that Venus's atmosphere is so much thicker than Earth's atmosphere is the primary cause of its dramatically higher surface temperature. Conversely, Mars has a much thinner atmosphere, and is much colder, despite being primarily CO2..."

"...That's why Death Valley is so damned hot: it's below sea level..."

"...This isn't about a nullification of greenhouse effects. It's about the relative sizes of effects. And atmospheric thickness effects will dominate over greenhouse effects when you want to discuss the difference in surface temperature between, say, Earth and Venus..."