OK, I used to do this stuff for a living, so I'm going to correct some of the physics that is a bit off.  psychoak is so far off that I'm not even going to bother, but a few people were 99% right but just a bit mistaken on a few things:

Your physics is generally correct, but this was a bit off.

Its not just the photons that make you warm - its absorbing the photons that make you warm.  The molecules in your body (especially the water IIRC) are really good at absorbing IR, so infrared is actually pretty good at heating up your body.  This is why so many people mistakenly refer to infrared radiation as "heat", even though its not.

On the other hand, visible light, even though its higher in energy, isn't absorbed as efficiently, so it won't make you as warm.  I mean, X-rays are obviously very high energy, but taking a dental x-ray doesn't heat you up much at all because your body is very bad at absorbing X-rays (which is why they are used).  I suppose intensity could be an issue here too (I don't happen to know the intensity of a dental X-ray off the top of my head).

Also, keep in mind that LEDs and sunlight are fundamentally different.  Sunlight is a blackbody spectrum (basically), while LEDs are generally an emission spectrum.  Comparing the heating properties of the two is really an apples and oranges deal.  Unless the LEDs happen to be emitting right in a band that your body absorbs really well, they aren't going to heat you up at all, while the continuous blackbody spectrum will always emit some power at an energy that will heat you up.

Anyway, I'm pretty sure that at ground level, most of the "warmth" we feel is infrared (see below).

There's also a messy issue of what your nerve cells happen to report as "warmth", but I don't know that much about biology, so I'm not going to get into that.

The Planck distribution is not really that close to a Gaussian, so you have to be real careful with the difference between "peaks in the visual" and "emits mostly in the visual".  See the "Composition and power" section of the following:

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

So while the Sun does obviously peak in the visual, most of the power from the Sun is actually in the infrared (at both the top of the atmosphere and the Earth's surface).  And the IR dwarfs the UV.  Basically, the distribution has a very long tail in the IR, while it falls of real quickly in the UV (there is a picture of this in the above article).

What this means is that what you "feel" here on Earth is largely IR, which is why you have the strong IR<->heat connection in people's minds, despite the fact that they are different things.

Yes sure... but all the short-wavelength-radiation that gets absorbed will be emitted as long-wavelength-radiation. And since only about half is reflected, the remaining half will become long-infrared.

As far as the ice cores and the ice ages are concerned... I've been thinking about it and the CO2 record is a bit strange.

You see... there's a quick rise of CO2, followed by a slow decay of CO2.

This suggests that the carbon cycle is not balanced. The input of CO2 by background volcanism or coalbed fires is lower then what's captured by plants and animals and then buried.

In principle the carbon capture could go on indefinitely until all CO2 is locked up. But occasionally there are these big events that replenish the CO2.

The weird thing is, that the CO2 returns to more or less the same levels. If it were caused by volcanism, such a pattern wouldn't be so neat, because volcanism is unpredictable in its strength.

So maybe it has to do with the lowering of sea level. A lowering would expose existing swamps/ peat deposits to weathering processes and since those deposits aren't buried deeply yet, they could be exposed and then recycled into the atmosphere.

But that would require that most carbon capture is land-based and not ocean-based.

This might make sense, since shells are made of calcium carbonate and this calcium carbonate comes from weathered rocks, it doesn't come from CO2. What does come from CO2 are the organic molecules of these organisms, but when the plankton dies, most of the organics is decomposed.

But... well I dunno, I haven't compared the CO2 records with oceanic levels.

Or, another scenario could be that in a normal situation the biosphere + weathering is capturing slightly more CO2 than volcanism can add to the atmosphere.

This leads to a gradual decline of CO2 over the millenia.

When an ice age sets in, much of the biosphere is destroyed, especially the swamps that act as carbon sinks. The northern forests are all buried under ice. Near the equator where the most active swamps are, the ocean has retreated and the swamps are simply not there anymore. The new coast lines need some time to form new swamp areas (by sedimentation) and during that time, the capacity to bury carbon under ground is greatly reduced.

During this time, the CO2 added by volcanism is (far) greater than the amount that can be absorbed. And CO2 levels will rise again.

I'm also assuming here, that weathering remains more or less constant during this time and that the main disturbances occur in the biosphere.

The only drawback of this is, that it doesn't really explain why there is an upper limit of 300 ppm at which the biosphere would recover and be in control again...

Or, another scenario could be a sudden surge in volcanism. Now and then a supervolcano erupts for example. Although I doubt just 1 volcano can replenish 100 ppm of CO2. And why would it stop there?

I stumbled on this interesting article, about a stalemate between intense volcanism (CO2 production) and intense weathering (CO2 consumption) about 450 million years ago.

http://www.astrobio.net/pressrelease/3293/volcanoes-set-the-stage-for-an-ice-age

This gives a bleak picture of the Toba eruption about 71,000 years ago.

http://www.bradshawfoundation.com/stanley_ambrose.php

Weirdly enough, such an event does the opposite of what I want to say... I want to say that volcanoes emit CO2 and make the earth a warmer and cozier place to live, but this event did the opposite.

Maybe it's because there was already little CO2 to begin with, 71,000 years ago...

http://climate.nasa.gov/key_indicators#co2

And it was an isolated, explosive event. Ancient extinctions had a longer duration of millions of years of extensive volcanism.

Not it's not, but it is closer than any other functional form that I know by name...I guess I could have said it was the product of a logistic function and cube function, but I'm thinking that wouldn't have helped...most people are familiar with bell curves, most are not familiar with blackbody emission spectrums...given how narrow the visible part is of the whole spectrum, I think my statement could have been just as faulty even if it was a perfect Gaussian...

You are correct and I probably should have looked more into the specifics of our sun's emissions...nevertheless, what I really wanted to point out was that our atmosphere both traps infrared and blocks infrared...it just so happens that the infrared it blocks is mostly negligible...

It's been awhile but if I recall correctly, your body registers IR as warmth better than higher frequency radiation....I haven't actually researched it but I asked a friend in medicine once and I think that was the "short version" of their answer...of course that same friend told me the red rash on my ear was earlobe cancer so take it as you will....

Quoting petrossa, reply 890It's the weight of the atmosphere that creates the heat by pressure. Simple calculation.

This is complete and utter bullshit.

The act of pressurizing a gas will indeed heat up a gas. That's because you have to make an effort to pressurize it.

Once the gas is pressurized and left on its own, it will cool down.

 [/quote]

Ever heard of gravity? The gas isn't normally compressed. So it wants to decompress all the time.  The gas is continuously compressed. So continuously heated up. The energy put into the system via gravitational pull must go somewhere. In the end you get a balance between cooling off/heating up and you reach a stable end temperature

I wrote this as simplistic as possible. A child can understand it.

I suppose I was a bit blunt in my previous post... this time I've taken more time to write an answer.

The gas is in equilibrium ... gravity wants to compress it, but the pressure of the gas acts as a counter.

This equilibrium exists at a certain value of temperature, pressure and density.

All of this doesn't prevent the gas to lose energy to its surroundings. It will cool down and grow denser. And it will still be in equilibrium at the earth's surface.

Of course you are right that gravity matters, because that influences the pressure at which the gas must achieve an equilibrium.

Gravity itself does not create energy, because the gravity does not actually move the gas. It tries to, but it doesnt. Doing "work" means that you've to move something. But nothing is being moved and there is no energy put into the atmosphere. That's because all forces are in equilibrium - the gravity and the pressure counteract each other, meaning there is no net energy change in the gas.

You are confusing this with the act of rapidly compressing a gas. If you do that, you are exerting a great force and you are adding lots of energy into the gas.

But once you stop movement, the gas will cool down to room temperature and find a new equilibrium at that temperature/pressure/density.

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

For an ideal gas: Pressure = constant * Density * Temperature.

Let's see a very simple example at the earth's surface:

force1 = Pressure * Area.

force2 = gravity = 9.8 * (Mass of a column of air with area A).

In equilibrium, the two forces cancel each other: force1 = force2. At the earth's surface, the pressure must be high enough to support the weight of all the air above it in a column of gas with area A.

Pressure * Area = 9.8 * Mass = constant * Density * Temperature * Area

If we keep the area constant, then you can consider the Mass a constant because we won't add or remove gas from the atmosphere. This means that Density * Temperature = some constant for the atmosphere.

So as temperature drops, density will increase. The gas will still be in an equilibrium state.

(I hope I didn't make some silly mistake here...)

Perhaps I should also mention the law of physics that says, "energy = work done"

And work means: applied force over some distance.

In short: Force * Distance = Energy.

It's easy to make the mistake that time is also a factor, but it isn't really. Forces may change over time, then it'll be part of the equation but only because the force changes, for example velocity * time = distance travelled. What matters is the distance.

I'm writing this, because you're under the impression that the longer gravity is present, the more energy it will create... well it doesn't. Gravity will only add energy to an object, if it's allowed to move. For example a stone that drops will gain energy. But a stone that's kept in the air by an opposing force, will not gain any energy.

How does this compare to the atmosphere... well... the atmosphere itself has energy (or temperature) and the atmosphere itselfs exerts this force to keep a balance. If the atmosphere could keep its temperature forever, then gravity can pull all it wants, it will never ever change anything... because the two forces would oppose each other into infinity.

In practice, the atmosphere continuously radiates energy out into space. Without the constant addition of energy from the sun, the atmosphere would slowly cool down. There's nothing that would prevent this from happening. Gravity doesn't stop radiation...

So in short:

Gravity controls the pressure / density.

The sun controls the temperature / energy.

And if you would like to be nitpicky, then you could argue for this: when the atmosphere cools down, it will shrink under the influence of gravity and it should heat up. But I'm not sure if even that is the case ... after all the shrinking is the result of loss of heat by radiation and occurs at a constant pressure ... gravity has nothing to do with that.

Another thing about "work" that should be mentioned is, that if the path over which a force is applied is "closed, then no net work is done: no energy is gained or lost. As an example, take one air molecule and let it bounce around in a cage. First it will go up, it will lose kinetic energy because it goes in the opposite direction of gravity. Next it will bounce down, and will gain kinetic energy because it goes in the direction of gravity. Net result? No change.

Now imagine a whole atmosphere of molecules bouncing around in the earth's gravity field. The field doesn't change and the molecules don't go anywhere, they're aimlessly bounding around, some gaining energy, some losing energy, but there is no net change in energy.

So basically you got the gravity force which doesn't change, and you got the air molecules that will bounce around forever, because they're really really good at bouncing. There is nothing gained...

There's only some loss because of heat-radtiation by the molecules.

If you would extrapolate temperatures of our atmosphere down to -100km below sea level, yeah this would be the case.

This conclusion of his is wrong, he forgets that the temperature of the earth's atmosphere is determined by the sun's radiation. Thus, at -100 km this would also be a result of the sun's heating.

Look I even did my best to show you the equations and to explain the physical reasoning behind it, even in more ways than just one.

What he shows are just a few graphics which he threw together. He doesn't understand any of the basics... and the way he combines those graphics ignores some important facts. By ignoring the important fact of "heating" he "proves" his point.

Basically he has a circular reasoning:

1. He says that the earth's atmosphere is hot because of pressure.

2. He extrapolate to -100 km and says that it's as hot as Venus there.

3. He then says that because of this, Venus is hot only because of pressure.

4. Then he applies this to earth. Back to 1.

It's circular reasoning, because in step 1 he made the assumption for earth and in step 4 he applies his "proof" on earth. But his proof and assumption are really the same.

But he doesn't really explain why you can ignore the influence of the sun. Even without CO2, the sun warms the atmosphere...

Read it a bit better. That's not what he says. But if you don't want to know, well..... That's religion for you.

This paper offers more interesting criticism of warming effects of (small) additions of CO2.

http://devinplombier44.free.fr/CoolingOfAtmosphere.pdf

It also mentions Venus, but in a more interesting way than the other link.

This paper argues that higher temperatures increase vertical convection, and thus lead to more effective cooling of the earth.

Therefore, there is no significant increase in temperature of the atmosphere ... at least not on the ground I suppose.

I think it's an interesting viewpoint and maybe they're right about it... who knows. They also say that it applies for increases of CO2 up to a few hundred ppm. Above those levels, convection won't be able to compensate.

But ... I don't understand from this paper how they take into account a buildup of CO2 above the 10km level. If that increases the temperature at the 10 km level, how would that influence the temperature of the bottom 10 km?

See figure 6 in this article, it shows buildup of CO2 above 10 km.

http://www.atmos-chem-phys-discuss.net/10/26473/2010/acpd-10-26473-2010-print.pdf

You're talking about an ACT of compressing - you overcome the natural air pressure by brute force and force the air into a smaller volume. That's something different, that's "net force" * distance = energy.

Gravity and pressure that are in equilibirum? Nothing happens, the sum of their forces = 0. There is no energy change.

If you think that gravity creates heat, then please give me the law of physics that describes that amazing process. It would be a perpetuum mobile!

I suppose you refer to wind and such things... but those variations are tiny and not a result of gravity. They are the result of the suns warmth and the rotation differential of the earth.

If you would put air in an isolated box, then it will not get warmer even though gravity acts on it all the time. That's because of the equilibrium. If gravity would create heat, the air in the box would get warmer and you could run a power plant on it ... but that doesn't happen, it's just not possible.

Huh? Wind is the result of differences in Air Pressure! This is pretty basic stuff here.

Zombie, those pressure differentials are due to temperature differences across the surface of the earth, differences that primarily exist because of sunlight and how it interacts with the earth's topography and surface composition...

In any case, an interesting thing to consider...

Jupiter is theorized to have a very high internal temperature (in the thousands of degrees)...why?  Is it because of the extremely high pressures in the interior?  Is it because of greenhouse gases?  Is it because there is a giant burning mass of coal in the center?

Funny how Venus is apparently hot because of greenhouse gases...but Jupiter is hot because, uhm...hmm...

Anyone care to explain why Jupiter has a very hot interior temperature without using high pressure as a reason?  I'll back out of the room slowly now...

While I know that Seleuceia is quite capable of defending himself, I THINK he was being sarcastic in this instance.