The same is true for an ideal gas, but I prefer to write it this way: Pressure = constant * Density * Temperature

I just don't get this part... it's a pressure change (= net force) that makes air rise. Gravity doesn't cause this pressure change. Gravity only causes the average equilibtium pressure of the atmosphere, and heat can make perturbations in that. It's the NET FORCE that does the work and you cannot single out just gravity from that and state that gravity causes heating ...

And I don't get this part either... in order to heat up, the atmosphere first needs to capture this energy.

But I suppose you're right that the Venusian atmosphere can hold more heat. And it will take much longer for heat the radiate out as well (unless there's a lot of convection going on of course, I don't know if that's the case).

Also, the presence of CO2 would mean that more energy will be captured closer to the surface, making the lower parts of the atmosphere hotter and the upper parts colder, than would be the case without CO2.

CO2 doesn't need sunlight to do this... the surface of Venus is hot and radiates a lot of infrared radiation which can be captured by the atmosphere.

Therefore the temperature near the ground will be higher than without CO2 ... although ... convection could mitigate this effect and redistribute heat in a larger part of the atmosphere. (To some extent at least.)

http://en.wikipedia.org/wiki/Atmosphere_of_Venus

This article says that on Venus, CO2 + water vapor + sulfur dioxide cause a greenhouse effect.

http://commons.wikimedia.org/wiki/File:Synthetic_Venus_atmosphere_absorption_spectrum.gif

From this graph it looks to me like the combination of gases leave very little transparency where energy can escape.

(The earth's atmosphere is far more transparent).

Solar radiation is a force.  What the energy is converted into, be it work that then produces friction or an increase in temperature, would still be a product of the Sun.  What is not a product of the sun is the opposing force.  You're correct that it's a net force that does the work.  It's the net force of gravity against the varied air density that causes currents in the air.  Gravity pulls everything inward, the Sun makes some of it lighter than the whole.  Gravity is responsible for much of the heating resulting from friction.

On Earth, the only time this really shows is on objects moving at high speeds.  When you ride a bike, you can get a wind burn from drying out, not actual heat.  Reentry on the other hand burns rock and metal.  On Venus, there's over 90 times as much atmosphere, the friction is immense.  Doing 90 on a highway on Venus would actually burn you, ignoring the reality that you'd implode long before you reached the surface.  Friction increases with pressure.

As I said though, it should be a minor factor, the main problem is that it takes forever for heat to escape because of sheer density.

The claim isn't that there is no greenhouse effect, or even that it doesn't account for the temperature on Venus.  It's that the counter claim, that the temperature on Venus is a result of a runaway greenhouse effect, is patently false.

CO2 does block some infrared.  On Earth, water would absorb most of the infrared blocked by CO2, and absorbs massively more that it doesn't.  On Venus, it hasn't got anything else to stop it.  CO2 is the only gas trapping anything near the surface because it's the only gas of any consequence.  Despite this, and an extremely high albedo, the planet is hot as hell.  Why?  Because no matter how little the absorption is from CO2, there's preposterously absurd amount of it.  The atmosphere on Venus is a blanket 90 times as thick as the one we've got, but they try to pretend that it means something for our situation.

It's quite silly to ignore the density and claim that it's because the atmosphere is CO2 that it's so hot.  The atmosphere is a product of it's condition, not the cause.  A slow retrograde spin and a weak magnetic field combined with a massive level of world wide volcanism that created a blanket of CO2 so thick that it keeps the surface hot enough to maintain it.

There is a greenhouse effect, CO2 does contribute to it.  The question is to what degree, and what kind of upper limits are we talking about.  Venus is a catastrophe, not a conclusion.  It bears no evidence, a completely irrelevant and unrelated setting.  Earth has a very light atmosphere with the water cycle dominating the equation.  Venus has no water cycle at all.  There is no rain, the clouds are sulfuric acid and precipitates never leave the cloud layer.  To use it as evidence for AGW just shows the complete lack of proof.

How we get from Earth to Venus is completely unrelated to how much CO2 is in our atmosphere, it's a product of other factors.  A slow retrograde orbit and no dynamo.

Edit:  Seleuceia, I think you need to just give up.  A sense of humor is beyond some people.

Well... all you're saying is that friction gives a contribution and that contribution is ignored by climatologists right?

I can't really argue with that, except that I have no clue how large a contribution it really is.

So let's just forget about gravity and keep it at that.

I don't think people ignore the density... due to the high albedo, it should be really cold on Venus if heat weren't trapped. The entire atmosphere of Venus would receive less energy than the entire atmosphere of earth. At lower temperatures, the Venus atmosphere would just be even denser than it is currently... well I think at least, I think it's not possible for an atmosphere that has no way to trap its heat to grow really hot because a hot atmosphere would lose its energy very quickly to space, but I'll think about it some more later on.

And there are also more extensive thoughts about it like this:

http://www.universetoday.com/22577/venus-greenhouse-effect/

That Venus might've started one day with a "normal" atmosphere and mild temperatures... but when it became too hot, carbon from rocks escaped into the atmosphere and inflated the atmosphere... interesting. Would such a thing be possible on Earth?

I sorta agree with that, you cannot compare them 1:1.

What you can do however, is test radiation models and assumptions to see if they hold up in such conditions.

If they are consistent, then it gives a little extra confidence that they can also be used on Earth - it's just another independent set of data.

After all, on earth we don't have an atmosphere with high levels of CO2, so we cannot test models and assumptions against observations on Earth. We don't have much sulfuric dioxide. And Venus doesn't have CFC's. But does it matter... you just measure the concentrations of gases, put them into a model and see if the temperature matches the observations.

For Venus to have ever been anything like Earth, it needed a decent magnetic field and a spin sufficient to avoid burning one side of the planet while the other froze.  It should have had the spin and the magnetic field, far enough back in time.  The loss of those is not a product of the greenhouse effect though.

Earth has a functional orbit, and a magnetic field strong enough to keep the water cycle in play.

We can't model Venus.

Essentially, the greenhouse effect deals in time.  You can't look at the current state of something and determine that it's fixed.  We have next to no information on the long term climate of Venus.  We don't really know much about it's current climate.  Much of it is guesswork.  The planet has these odd S shaped vortexes at the polar regions that they're still trying to figure out.  Don't expect a model that functions as a product of time to be accurate when they can't even figure out the present circumstances.

For the record, any friction experienced is independent of pressure...it is in fact due to density, and while this is still relevant to Venus there is an important distinction...

Well played...I suppose I could have inserted an "in the above examples", but I thought it was implied...

Unless you would like me to go into how fluid friction is different from kinetic friction...but we don't need to go there, do we?  I sure hope not...I've hit my quota for how much pseudo physics I can spew and I certainly have no interest in talking about real physics...

Okay, I can't help myself...

Is no one more serious than me going to address this?

CO2 has a logarithmic effect, it's fairly obvious.  If you double the concentration, you halve the distance the infrared travels between stops.  This then doubles the amount of time that energy spends planet side.

The IPCC claims 3C per doubling.  A hilariously high value.  They also claim CO2 is responsible for 26% of the current effect.  I find this hilarious too, considering water acts on a far broader spectrum, as well as overlapping the narrow spectrums CO2 covers.  Pretending this isn't all bullshit though, the total greenhouse effect is only 33C, putting CO2 under .  If going from 400 to 800 would change temperature by 3C, then from 200 to 400 was also 3C, and so was 100 to 200.  You're already up to 6 of the 8 and you haven't even gotten close to the point where CO2 stops direct radiation in the bands it effectively blocks.

The mean free path of infrared absorbed by CO2 is only like 25 meters.  Just the troposphere is 12km.  How low would CO2 have to be before direct radiation took place and the additional 3C from each past doubling stopped taking place?

We get all the way to 1.5ppm to reach the point where the mean travel is about half the way through the troposphere. 24C in a cumulative greenhouse effect.  So absurdly high that CO2 is no where near 26%.

The forcing effect of CO2 is made up to fit the increase in temperature since industrialization.  The temperature itself being a made up trend that didn't exist in the records until just the last decade.  When someone says it's saturated already, it's because 3C is sheer myth.

I think, while a bit pedantic, his objection is also accurate; radiation/pressure, is not a force.

You also have to deal with the top of the troposphere. There's a temperature inversion there, which blocks convection. The atmosphere cools down there mainly by radiation from CO2 and H2O (clouds radiating heat).

The surface of the troposphere is 2D (with a density of 400 ppm CO2 per area). However, The atmosphere is 3D (a density of 400 ppm CO2 per volume). The atmosphere is absorbing a certain amount of energy per volume. The top is radiating out all that energy through a surface. Doesn't that require a higher temperature gradient near the top?

I've not read about this, but I imagine it could be a factor.

It's not just a claim, it's been modeled.

I think that's pretty amazing, as it makes the difference between a snowball and a nice climate. And energy goes like T*T*T*T. So it's a lot of energy that's captured.

I don't know... at small concentrations of CO2 the effect of black-body radiation of the Earth's surface might be relatively less important. After all, rays are bounced back less often to the Earth when densities are lower. Then, the trapping effect of CO2 might be relatively strong.

Also, before you ridicule the contribution of CO2, have you even read this?

http://www.skepticalscience.com/news.php?p=3&t=118&&n=491

shows how you can reach a significant rise just by CO2 alone, by "simple" models (I haven't tried to understand them because it'll take me months to read up on that stuff but it looks fairly straightforward to me). I think that's more impressive than your guesswork when you say that CO2 has a negligible effect. It shows that in 100 years, because of about 300 ppm increase in CO2 (to about 700 ppm), the temperature can rise by about 1 degree celcius by CO2 alone, and this is just because of trapping heat and it ignores everything else.

You mean the forcing of H2O because of CO2.

Maybe you're partially right about that, after all it's an observation and how you interpret that is up to the beholder

However... if a 1 degree rise means that more water vapor resides in the atmosphere, then that can also be taken into account by models. And since most of the earth is covered by oceans that rise slowly in temperature,  this is pretty straightforward I would think. Deserts can also be taken into account because they have no humidity. Polar regions are so cold, there's hardly water vapor in the atmosphere there. All in all, I think it's fairly straightforward to take water vapor into account in models for 75% of the earth's surface. Only the remaining 25% may be a little tricky. But that means that you can only be off by 25% if you make a mistake, not by 100% like you claim.

Like... take Australia. It had very heavy rains a few years ago that flooded half the continent (well... 10% maybe) and that had a significant effect on the regional climate. It's hard to take such a thing into account I think. But is it significant on a global scale? I doubt it hardly makes a dent in the global picture of warming.

Let's see.. the paleo-records showed that a hundred million years ago, CO2 levels could be as high as 2000 ppm and it is guessed that temperatures at the time were very high. Let's see what a few steps of doubling will accomplish.

300 + 300 ppm = +3 degrees

1200 ppm = + 6 degree

2400 ppm = + 9 degrees

It seems about right ... it would be a lot higher than that in the Netherlands. So if temperatures here were +15degrees, it would indeed be subtropical here. In the winter, average temperature here is near freezing - if it were 15 degrees higher, it would be like being on holiday each day! But I suppose it won't be such a great effect, the temperature here is controlled by the North Sea. So it may actually be less than that... unless the water also warms up to 15 degrees of course, instead of cooling down to 5 degrees or so 

Extinction occured at higher CO2 levels.

4800 ppm = +12 degrees.

At such a temperature, the equatorial oceans would become about 40 degrees (I imagine they would have trouble getting rid of all the heat because where can it go? Only to the relatively small northern seas and oceans to cool down). Such a temperature is too hot for normal life. Extinction. That seems about right too.

They didn't pull it out of their ass. They observed anoxic oceans (which happens near 40 degrees celcius). They observed plantlife that migrated to the north. They observed no ice anywhere on the planet. They observed forests near the poles. Types of carbonates changed (temperature dependent). All of that indicates high temperatures.

Also, it is not a circular reasoning. The temperature rise is given by our understanding of physics, based on models that are pretty robust. Based on lab-measurements for the absorption spectra of CO2, H2O. Based on measurement of current radiation from the earth's surface. This is independent of the paleo-record.

But of course... the exact temperatures and CO2 concentrations at the time are an unknown. We can only guess at them, but those values don't look unreasonable to me. Those values of CO2 can be attained by extensive volcanic activity during a long, long period of time.

The thing that's scary to me is, that it ONLY takes a little over 10 degrees celcius of warming to get close to extinction levels. Fortunately for us, that takes a LOT of CO2 so it won't happen overnight, it'll take hundreds of years to reach that point.

Well, it's pretty obvious if you think about it. H2O molecules ("water vapor") in the air capture heat. When the air becomes warmer, it can contain more H2O. For example the poles are arid, because the air is so cold there is hardly any water in the air. If the poles become warmer, the air there can contain more H2O. The upper parts of the troposphere are also pretty cold, if they warm a little, the upper part can contain more H2O.

http://www.engineeringtoolbox.com/maximum-moisture-content-air-d_1403.html

Convection distributes a temperature rise more efficiently over the atmosphere. It cannot prevent the capture of energy of the atmosphere. It cannot prevent warming of the atmosphere. Also, convection stops at 10 km height (or something, I don't remember the exact height of the temperature inversion) - at that point energy is lost by radiation from clouds and CO2. Convection cannot carry heat all the way into space...

Of course you are right that if there are more clouds, then heating could be mitigated. But there already many clouds on Earth, and they are usually concentrated in depressions while the rest of the skies are clear. Maybe clouds become bigger and contain more rain, but will the total cloud cover of the earth be significantly larger than it is now? Maybe if depressions grow larger, maybe they can cover a larger area with clouds, but it's a very small percentage of the total area of the earth.

Rain does not transport heat out of the troposphere... only radiation loss from H2O in the clouds and CO2, not the raindrops.

And it's not just the water cycles, it's also the H2O concentration in the air that's important. More H2O in the air means that heat can be trapped longer.

I'm not going into that again... as far as I'm concerned you cannot make such a bold conclusion from those data.

On top of that, ice ages are quite different events, they're controled by a tipping point after which a runaway cooling occurs. We're now in a situation were there is far less ice, ice does not control our climate anymore. We've to search for other explanations for warming and fortunately our understanding of how greenshouse gases work helps us a lot.

Because clouds and H2O are not present. A lot of heat can escape at night. CO2 in itself is not enough of course.

Maybe, if all local factors (like the geography) are taken into account as well, then who knows ... but I don't know much about that place, never been there. Maybe I'll read some more about it.

I'll read your link later on.

Best refutation of AGW hysteria (e.g., Super Storm Sandy - which was anything but 'super' BTW) I've read in this thread so far.  Well done.

http://www.newsroom.ucla.edu/portal/ucla/last-time-carbon-dioxide-levels-111074.aspx

This one is pretty interesting. Measurements with an uncertainty of just 14 ppm

That's a lot better then the plant stomata.

And it gives support for the ice core data.

And it's by a nice female researcher too.

Although there are no graphs, that's a shame. But a free sciencemag account alleviates that problem (the statements in the text are the same as what you can conclude from the graphics).