Can anyone explain the precise mechanism/role of CO2 and Greenhouse Effect in an open Climate System?

BMR,

I will try to address your question.

1. I never really like the analogy to a blanket, but after thinking about your question 2, I don't think it is that bad of an analogy. Yes CO2 has a very small concentration. I think the point is that the radiative balance of the earth. I have not done the calculations myself. How much does the radiative balance have to be thrown off for a temperature change to be measured? Is the earth in equilibrium now or was it in equilibrium when CO2 was 280 ppm? I really do not know the answer to these questions, but I am sure this is something a professional climatologist has to deal with. I have seen websites where people try to do this calculate the radiative balance by using a column of air. In my opinion this is a flawed calculation since it assumes the earth is flat. I would imagine a paper and pencil calculation to determine the earth's radiative balance would have to be done using polar spherical coordinates along with the proper gradients of N2, O2, CO2, and H2O. The question comes down to does having 380 ppm throw off the radiative balance and it seems that all climatologists agree that it does. People like Spencer do not seem to argue against this but argue that the earth has other self correcting mechanisms.

2. If the upper troposphere is heating, there is no need for any thermodynamic laws to be broken to heat the lower atmosphere. I think you are correct that it is about heat transfer rates. The rate of heat flow is proportional to the temperature difference

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

Thus the lower atmosphere cannot transfer the heat to the upper atmosphere as fast causing an apparent heating effect.

The reason why I like the blanket analogy is that when you put a blanket over you to keep warm, you are in effect slowing the heat transfer of your body temperature to the ambient air.

3. I never bought the whole reflection argument. IR is not heat, it is electromagnetic radiation. It just so happens that at terrestrial temperatures things radiation in the IR region as black body radiation. This brings up the whole question, what is temperature and what is heat. Temperature is the measure of the average energy of a body. For a gas it can be split up into electronic temperature, vibrational temperature, rotational temperature, and translational temperature. In a physical chemistry sense heat is just a mechanism to transfer the energy to cause a temperature difference between two systems.

When CO2 absorbs an IR photon it goes into an excited vibrational state (not an excited electronic state as Dawei incorrectly stated). After a certain time it will revert back to the ground state and reemit a photon. As long as there are no collisions or other interactions with the environment, this will happen regardless of the temperature of the surrounding gas. So basically the CO2 molecule is back to the original state and there is no increase in temperature.

A photon will bounce around until it escapes the earth's influence. What if the photon hits the earth? The earth can be thought of as a black body (remember a gas is not a black body which a few websites incorrectly assume). The earth will absorb the photon and reemit it just like the CO2 molecule. This is a zero net sum process.

So how does the greenhouse effect work? Collision with another molecule is absolutely necessary. Let's say the excited CO2 collides with a nitrogen molecule before it can relax to the ground state. It may transfer some of the energy to a vibrational state of the nitrogen or to translational energy of the nitrogen. I honestly do not know the coupling between the vibrational states in CO2 and the vibrational states of N2, but I am just using that as an example. Excited vibrational states of N2, do not radiate, it is called a forbidden transition. Thus that energy is trapped. Translational energies do not radiate either, thus trapping the energy. In other words the IR energy through this process is transferred to another form of energy that cannot be readily reemitted at IR energy.

Just a note on equibrium. You have to be careful when discussing thermal equilibrium and molecules at the same time. Equilibrium is a macroscopic concept. If you have one molecule and look at it for a long time, its average energy state will depend on the temperature. If you have an collection of molecules you can look at the average energy of the molecules at any instant in time and that will depend on the temperature. But if you look at a single molecule for a very short time, the concept of equilibrium has no meaning. It will have a certain energy state and the probability of finding it in that energy state is dependent on the temperature, but you cannot state whether that molecule is in equilibrium with the environment.

Edit: Dawei, no because IR radiation does not have enough energy to do that. Generally you need visible and UV light to cause an electronic transition that is described in your link. The general trend is this but of course there are exceptions:

Microwave- rotational transitions

IR- Vibrational transitions

Vis and UV- electronic transitions

Ok, you're asking a lot, but I'll try to answer some of this. It is not like a blanket. Blankets work because their insulation suppresses conduction and convection of heat away from the body. The blanket analogy is a bad one.

Similarly, the greenhouse analogy is also bad (despite the prevalence of the terminology). You mentioned the rock salt greenhouses. Despite the supposed effect of absorption of long wave IR by ordinary glass, the rock salt greenhouses got just as warm. Again, greenhouses suppress convection. They do this in a somewhat different fashion than blankets, though.

It's not about reflection, it's about absorption, thermalization and emission.

CO2 does absorb some long wave IR travelling upwards that would otherwise leave the Earth system and go into space. It warms the CO2 molecules, which also radiate and collide with other air molecules. Therefore the temperature of air at that level will be slightly warmer than it would be otherwise. As a blackbody (or gray body) it radiates thermally.

I'm not sure why you're bothered by the surface of the Earth being warmer than it would be with less CO2 (or other greenhouse gases). Clearly this effect is real--the Earth is substantially warmer than it would be without an atmosphere containing greenhouse gases. If you're thinking that it violates the second law of thermodynamics because there is downward radiation from the atmosphere, that is too simplistic, there is also upward radiation. It's not like the surface of the Earth is warming solely at the expense of the atmosphere, there is more of the sun's energy being retained in the Earth-Atmosphere system, shifting the radiative equilibrium of the system to a higher temperature.

CO2 is slightly heavier than nitrogen and oxygen, but not enough for it to settle out. It is usually well-mixed in the lower atmosphere, except in those unusual cases with little vertical mixing and a large source of CO2, like the tragedy that killed 1700 people at Lake Nyos in Cameroon in 1986.

I'm probably not the best one to answer this, but I'll take a crack while you're waiting for better answers.

First, you're right that the greenhouse effect behaves in no way like a blanket or a greenhouse. This is an oversimplification to help the average person understand what is going on. (And for the record, a real greenhouse does not work by changing the balance of radiation. It simply traps hot air from rising, causing the structure to be warmer than it would be if the air were free to escape.)

Here's my understanding of how it works:

You wonder which method it is, 'absorption' or 'reflection', and the real answer is both. There are two distinct mechanisms by which a greenhouse gas works. The first is that it can directly absorb the photon from IR radiation, causing the photon's energy to be converted into the vibrational energy of the molecule (a.k.a. the definition of "heat"). This is a direct warming effect.

The other, more significant source could sort of be called "reflection" of IR, but even this is not very good terminology. What happens is the photon gets absorbed by the molecule, and the electrons within it get excited to a higher energy state. This does not last long, and the electron quickly falls back to its original energy level--releasing a photon of IR in the process.

The photon is emitted in a random direction. It may be straight up, in which case it would appear as if the photon never stopped. Or it could be vertically down, and interact with other greenhouse gasses or be absorbed into the surface.

The atmosphere is, as you note, an open system. But it is what you would call an open system in steady-state equilibrium, with energy in equaling energy out. The internal energy of the system should, therefore, be constant. The only way to change internal energy is to alter the rate of energy in or energy out. By changing (slowing) the rate of energy out, we are causing the earth's internal energy to rise.

As the temperature rises, more IR is released. This will occur until equilibrium (energy in = energy out) can be re-established. It is a bit like a bathtub, with a drain and a faucet both adding and removing water at the same rate. Partially clog the drain (without changing the rate of the faucet), and the water level rises. It rises until the pressure is great enough that more water is forced out, and equilibrium is again reestablished.

This is of course an oversimplification--a more detailed diagram is here. Note that energy in (total solar minus cloud and land albedo, or 235) equals energy out.

http://www.windows.ucar.edu/earth/Atmosphere/image...

As you can also see from the diagram, the 'back radiation' from greenhouse gasses is responsible for quite a bit more energy on Earth than direct heating of visible light. This is why they say it would be so much colder here without a greenhouse effect.

This is a very interesting read. As I understand it this paper raises two major issues with ‘the standard model’. 1. The standard model might be fine for representing astronomically distant objects, but it assumes that the object is a flat disk, and that the derived surface temperature is constant across the surface of the disc. This is not a valid model for the earth. 2. The standard model does not consider the dark side of the earth where the radiative conditions (and therefore the corresponding surface temperatures) are quite different. I’m not aware of how the radiative balance is ACTUALLY represented in the GCM’s, so don’t know if, or to what extent these two factors are considered. But I would be very interested in reading any responses on the substance of this document. Has anyone see a response to the substance of this paper from anyone in the climate science community?... anything from Trenberth on this?

Just to add one thing to Dawei's explanation by addressing your point #1, the atmosphere isn't flat as a blanket essentially is. Sure CO2 is 'only' 380 ppm, but there are a lot of 'layers' to the atmosphere. If you calculate the probability that a photon moving upward from the Earth's surface will be absorbed by a CO2 (or other greenhouse gas) molecule, as I recall, the probability is almost 1. Then the only question is why direction it's re-radiated in. The more CO2 you add to the atmosphere, the more layers there are such that a photon radiated upwards by a greenhouse gas molecule may be re-absorbed by another and then re-radiated once again.

You seem to have a pretty good understanding of what is happening. The CO2 absorbs the IR in narrow bands that amounts to 8 percent of the heat being reflected. It immediately translates the absorption of the IR into kinetic or heat energy that it transfers to nearby molecules when it impacts them. That heat energy is distributed by convection or random impacts of other molecules. The warm air radiates heat and some of that impacts the Earth and that is the insulation effect. Obviously most of it is lost to space and never absorbed since it only absorbs 8 percent. The rest is lost when the warm air radiates to space. Some of that will warm the air further but the IR in the bands that CO2 absorbs is absorbed to extinction in the first few thousand feet. The only way you can get additional warming is from rising air masses. That should cause you to concentrate warming about 10,000 feet relative to the ground and that hasn't happened.

All you get is the relatively small warming at the surface with convection and Beers law counteracting the lowering of the level at which all the IR that can be absorbed is absorbed. Convection simply diffuses the concentration of heat and Beer's law means that the efficiency of IR absorption is dramatically less efficient as the concentration of CO2 increases.

There are obviously negative feedbacks like less cirrus clouds are observed following times of temperature spikes in the tropics. The reduced cloud formation cools the planet. It is rational to assume that CO2 won't change that feedback system so the thermostat is already set and you get virtually no actual warming from increased CO2.

I seriously doubt you will get a rational answer to your question from the alarmists. The fact that the models don't work obviously makes no difference to them. They would be justifying something to you that obviously isn't demonstrated by real world data. There is no relative warming of the mid troposphere so the climate shows no increased greenhouse warming. It would be hard to explain no increased greenhouse warming as increased greenhouse warming and that is what you are asking them to do.

First, don't confuse radiative, convective, and conductive transfer. The planetary greenhouse effect, in it's most easily visualized model, is a pure radiative process. Here is a simple discussion that assumes we are dealing with planetary atmosphere that is bone dry so no clouds (or latent heat fluxes to consider), and perfectly transparent to shortwave radiation but absorbs infrared radiation.

1. Incoming shortwave radiation passes through a shortwave-transparent atmosphere and is absorbed at the surface of a planet that is a perfect blackbody.

2. The planet's surface heat up from the shortwave energy flux.

3. The planet, which has now increased its temperature, being a blackbody, begins to emit radiation whose total energy follows the Stefan-Boltzman law with a frequency distribution given by Planck's law. For realistic shortwave fluxes and planetary conditions, this means the planet radiates in the infrared (IR) region of the spectrum. Furthermore, the net energy flux in the IR will be equal to the incoming shortwave flux.

4. Assume that the atmosphere is *not* transparent in the infrared. That means that the upwelling IR radiation from the surface of the planet gets absorbed before it can escape to space.

5. Each molecule of gas that absorbs an upwelling IR photon can re-radiate it through 4*pi steradians, meaning it can go up, sideways, or back down. Alternatively, the excited molecule can dump off the energy of the photon into the mean kinetic energy of the gas molecules (i.e., a molecule that absorbs an IR photon generally is then in an excited vibrational state that can re-emit IR, or transfer the energy to mean translational motion). If the molecule re-radiates upward, then there is no net effect of the process. But that only happens on average 50% of the time, the other half of the time the photon goes back down, towards the surface.

6. As you have correctly observed, the atmosphere has to also obey the ideal gas law, so the adiabatic lapse rate dictates it has to cool as you go higher in altitude. (That means that photons traveling downwards go "against the conductive flow of heat" which isn't a big deal for gases since advection is more important.) But the cooling is secondary to the effect that pressure, and total number of molecules per unit volume decreases as you go up. This means that there are fewer absorbing molecules (and fewer emitting molecules since the absorbers are the emitters) and that the net IR re-radiated over the 4*pi steradians decreases as you go up through the atmosphere. Therefore, if you think of the atmosphere as a bunch of layers, vertically stacked, each layer provides just a little more energy to the layer above it than it receives from that layer, meaning there is a net upward flux of energy through the atmosphere (this is how the atmosphere can radiate to space at all).

7. Because the atmosphere is radiating IR energy downwards, the surface of the planet is now not only receiving the shortwave energy from the solar flux, but also the downwelling part of the longwave IR from the atmosphere. This causes the temperature of the surface to increase, and it has to radiate more IR upwards because it is still obeying Stefan-Boltzman.

Eventually a new equilibrium is reached, where the outgoing total IR flux from the surface matches the incoming shortwave solar flux *and* the downwelling IR longwave flux. But in its simplest form, there is no conduction, no convection, no latent heat flux. In my opinion, you must understand the physics above before you can consider the more complicated case of a wet planet. Most skeptics do not understand the above physics, making most of their objections laughably ignorant.

Adding water drastically complicates things because you now have latent heat fluxes to consider and things in the atmosphere that are reflective (clouds), radiative (clouds). Most of the uncertainties in climate models are related to parameterizing the effects of water on the basic radiative transfer processes.

A great book on radiative transfer through planetary atmospheres is "A First Course in Atmospheric Radiation" by Grant W. Petty (Dept. of Atmos. Science, Univ. of Wisconsin-Madison). Petty publishes the book himself so it's very reasonably priced (I am not Petty, I just really like the book and his business model) and anyone who wants to seriously discuss the physics behind climate science should read this book.

Over the last 6 months I have run several experiments on this with the help of some friends. We have never been able to achieve the advertised heat blanket effect unless the test samples contained greater than 50% relative humidity as measured by a hygrometer. In all the documented experiments including the original ones in the 1800s there is no mention of any humidity testing as part of the experiment and the procedures used in the experiments both for producing the co2 and checking for its presence assure that the humidity levels of their samples were well over 50% humidity, probably over 90% as our first experiment using the documented procedures was.

In our final experiments using one sample of ambient air and one sample of almost pure co2 with both samples having less than 10% relative humidity, when the IR heat lamps were removed both samples reached room air temperature almost equally within a second or so of each other. It seemed the pure co2 sample cooled slightly faster than the air sample did, but the variation was so small it was hard to detect. This matches the specifications for co2 used as a refrigerant in air conditioners because the ability of co2 to phase change easily between gas and liquid forms is what makes it a great low cost refrigerant and a lousy green house gas.

http://www.appliancemagazine.com/editorial.php?art...

In 1909 physicist R.W. Wood disproved that greenhouses stayed warm by trapping IR.

And to make the proponents of global warming happy. This was peer reviewed. He was published in the Philosophical magazine , 1909, vol 17, p319-320

I totally agree with you, also since CO2 is a gas it has to follow the gas laws. Since both Nitrogen and Oxygen, the main ingredients in our air are gases these should act similar to CO2. Then again, from my understanding of the science behind CO2 cause is high humidity, I am thinking that water vapor plays a bigger role then any one wants to admit.