Fact: Short wavelength solar radiation heats the earth.
Fact: The hot earth re-emits longer wavelength radiation.
Fact: CO2 absorbs some of this longer wavelength radiation
Fact: By absorbing this radiation CO2 causes a thermo dynamical imbalance in the energy in-out equation for the earth as a whole and causes the earth to warm. Aka the greenhouse effect.
All fine and dandy and nobody is questioning that CO2 is a greenhouse gas.
Fact: The extinction distance for CO2 in the earth’s atmosphere is about 300 feet. That is to say that any thermal radiation emitted by the ground and in the wavelength that CO2 absorbs strongly at will all be absorbed within the first 300 ish feet. That would be no matter how intense the radiation was. Engineers discovered this back in the 60s when they were trying to develop laser communication through the atmosphere. CO2 an H2O completely absorbed the laser light in those wavelengths that they strongly absorb at. 300 feet is based on the 1960 CO2 concentrations BTW.
Fact: Increasing the concentration of CO2 only shortens the extinction distance it does not trap more heat. ALL the heat that CO2 can trap is already being absorbed in the extinction distance.
Conclusion: increasing the concentration of CO2 does not cause any more heat to be trapped and therefore cannot be the cause of global warming.
And to the point, Man is not causing global warming because CO2 can’t be the method by which it is happening.
Response:
I want to say that this submission, like the previous submission on the AMO, is a real treat. This submission is based on science, is logical, well thought out and the submitter did some homework. Well done.
So, let's look at it in detail.
The first four facts he states are all good. No problems there.
But then, some issues begin to arise.
Let's discuss extinction distance. This is the distance in which something is totally absorbed in a second something and adding more of the second something will not affect how much of the first something gets through.
As an example, the ocean has an extinction distance for sunlight. Within a kilometer of the surface 100% of sunlight will be absorbed by the ocean. That is the extinction distance for sunlight in the ocean (sorry, I don't know the exact value). Anything below that will be in darkness and adding more depth will not change that any. If you are deeper than the extinction distance there will be no light. That is equally true for 1.1 kilometers as it is for 5 kilometers.
So, the extinction distance for CO2 in the atmosphere is 300 feet (I don't know that myself, but I'll take your word for it. I know the extinction distances for the gases is dramatically less than the thickness of the atmosphere). What this means is that when the heat is radiated from the surface of the planet as infrared (IR) radiation it will be 100% absorbed (at the levels of CO2 present in 1960). So far, so good. We're in agreement.
Now, though, is when we get into trouble and this is where the extinction distance of light in the ocean is different than the extinction distance of IR in the atmosphere. When light is absorbed in the oceans it is turned into a different kind of energy - heat - and is not reemitted as visible light. When IR radiation is absorbed by CO2 molecules, it is reemitted as IR light.
In the ocean, light is absorbed and turned into heat, which then transmits it in pretty much random directions (let's keep it a simple environment without currents and convection and gradients and such). That means the heat could go up, down or sideways.
When IR is absorbed by CO2, it is reemitted as IR and it can go up, down or sideways. This means each molecule of CO2 in the atmosphere becomes a new source of IR radiation and there is an extinction distance associated with that source of IR radiation (300 feet). So, if we increase the amount of CO2, we increase the number of points where the IR can be absorbed and then be reemitted.
Suppose we had a layer of CO2 that was 300 feet thick. All of the IR will be absorbed before it gets to the top (using 1960 CO2 levels). But, each molecule will then reemit the IR light. If a molecule is at the top of the CO2 layer, there is a high probability the IR will be emitted in a direction away from the layer and that photon of light will be free to go off into space.
Now, add another layer of CO2 on top of the first one (let's make it less than 300 feet thick). That photon of energy that was free to go off into space will now have a chance of being absorbed in the second layer. As the second layer gets thicker and thicker, that probability goes up. By the time it reaches 300 feet thick there is a 100% probability that photon of IR light will be absorbed and then reemitted in a random direction.
So, you see, adding CO2 to the atmosphere really does increase the amount of IR that is absorbed.
And, there is conclusive proof of this. If it worked the way you posited, 100% of the heat would be retained in the atmosphere and we would incinerate in only a short time. The very fact that we have not burst into flames proves that the heat is able to escape the atmosphere after being absorbed by the CO2 molecules.
By the way, here is a really good article detailing the history of the discovery of the CO2 greenhouse effect. It is from the American Institute of Physics.
So, this was a great submission and a lot of fun. But, it certainly does not show man made global warming is not real.
William and Christopher,
ReplyDeleteThank you both very much for the highly informative exchange! I learned a lot about the physics of the greenhouse effect in short and enjoyable space of time. Moreover, your exchange demonstrates the great value of debate well done -- to surface a lot of information quickly. Some of the earlier challenges and responses haven't lived up to that standard, and have more demonstrated some of the worst aspects of debate (but not as well as Monty Pythons Argument Clinic sketch (http://youtu.be/kQFKtI6gn9Y)!
I'll ask: isn't the addition of CO2 a density issue not just "another stack", and wouldn't the addition of water vapor to this equation change the dynamic as well? Last I remember, the addition of water vapor effects the absorption on a logarithmic scale. I could be wrong, I have been before.
ReplyDeleteYou are not wrong. At no time am I trying to make it sound that this is all simple. The truth is there are many factors involved including density, water vapor, solar input, wind currents, volcanic eruptions (chemicals and ash), etc. But, this challenge was discussing one particular aspect and I kept it simple to discuss that one aspect. There was no intent to mislead about the over all complexity. I like to keep reminding people of just how complex this all is.
DeleteMr Keating
ReplyDeleteWhen CO2 absrobs IR it re-emitts it as a black body (lots of different IR frequencies for the bulk of CO2) based solely on the temp of the molecule. It does not do the "electron orbital" thing as it is a molecule. Another way of saying that is that your are not exciting the electrons (and then letting them emit when it de-excites) you are causing the molecule to vibrate faster. Black body radiation shifts the wavelength randomly to other (can be the same but that is based on the same randomness) wavelengths where the atmosphere is transparent or H2O traps it ...... repeat ad-nausium......... till it escapes the atmosphere.
Second point. Once the ground re-emits the long wave IR and CO2 intercepts it that heat is "in the atmosphere" A CO2 molecule must cool to cause another one (or something else) to heat up. IE no net heat is being added it is just being moved around.
You are saying that as heat leaves the ground and bounces around in the atmosphere that heat bouncing around makes things hoter. That is not how it works. Every time a air molecule has to cool to emit radiation which heats something else. This is not adding heat it is just moving it around. The ONLY thing that matters is the net into or out of heat. That is what causes temp change.
So where is the heat coming from?
Your said it yourself, heat is just being moved around. That is what the greenhouse effect is all about. Given unfettered movement, the photon would be emitted by the ground and shoot out into space. The greenhouse gases in the atmosphere 'move it around' and that slows its escape into space. There are several ways it can be moved around, including colliding with other molecules, but I am trying to avoid turning these discussions into graduate classes. Leaving out some details of molecular vibration shouldn't change the point. CO2 absorbs the photons, but the energy has to leave the molecule or we would all incinerate. When it does leave, it has to traverse any other molecules that can absorb it. Just because it is absorbed by one molecule and then released doesn't mean it has a free pass through the rest of the atmosphere.
DeleteHere is a very nice site that explains how CO2 absorbs and reemits IR radiation.
Deletehttp://scied.ucar.edu/carbon-dioxide-absorbs-and-re-emits-infrared-radiation
OK, you did not answer the question where is the heat coming from.
ReplyDeleteAll the heat that CO2 can intercept is getting intercepted NOW. Adding more CO2 does not cause more heat to be created it just makes it move around more. Without more heat the temp cannot go up.
So what you described is what is happening today and in the future. All is All, intercepting it in a shorter distance will not cause heat to be created. Something has to cool to heat the next thing and ...... you end up with heat flow out of the system to space. All that matters is net heat flow.
Another way of looking at this is to look at the energy flow diagrams. Where does the "new" heat labeled "back radiation" come from?
The heat comes from the Sun. There is some heat emitted from the planet's interior but that is very steady state. "Back radiation" is the label for energy that is reemitted by the atmosphere that goes back in the direction of the surface. No big mystery or hidden agenda.
Deletehttp://encyclopedia2.thefreedictionary.com/Atmospheric+Back+Radiation
I get the impression that you are using CO2 as a solid insulator which slows the IR moving through it and requiring a higher net effective temp (below the insulator in this earth example) to make the heat flow through the insulator. If you draw a surface at two different levels in the atmosphere and measure the net flow of all energy through each you must have a net gain or loss of energy between the two total energy flows through the two surfaces to get the temp of the VOLUME in between to change. Can we agree on this?
ReplyDeleteNo, I am not using CO2 as a solid block. A solid block typically does not have a density gradient and currents.
DeleteWhat you are saying is essentially true and has led to cooling of the stratosphere. As the heat is retained in the troposphere, it is being kept from the stratosphere. Given enough time, equilibrium would be achieved and the amount of heat radiating into the stratosphere would go back up. Equilibrium is not achieved because we keep increasing the amount of heat absorbing CO2.
So, I think the answer to your question is, yes, if we are keeping energy in one part of the atmosphere that means we are taking it away from another.
The amount of heat coming from the sun is not changing so how would the earth warm up using that theory? If the input is the same then I'd have to believe that the re-radiating into space is also the same so no net change in things by adding CO2 and not temperature increase.
ReplyDeleteI'm also ignoring that the sun does actually change and geothermal....... all the other noise stuff so we can focus on how CO2 effects the heat flow.
It is retaining more heat. This is just like putting on a coat in the winter. You are still radiating the same amount of heat. The coat is simply slowing down how fast it radiates out away from you. A thicker coat slows it down more than a thin one (all other things being equal).
DeleteIt cannot be "retaining" more heat thermo will not allow that to happen. Perhaps you mean "detaining for a short while" My coat does not slow down how fast I radiate. I still radiate at the same watts/sec as with my coat off. The difference is that I'm a heat source in the coat example and the earth is not. I don't have any extra heat to deal with beyond the amount coming from the sun.
ReplyDeleteHow (what is the method) is the CO2 causing more heat ot be retained in the lower atmosphere? CO2 absorbs these frequencies very well. It also re-emits them very rapidly. I could see an argument if the extinction distance was 100s of miles and a large portion of the energy escaped into space without being absorbed at CO2 frequencies. Then shortening it to 10 miles would cause an increase in the amount of heat bouncing around in the atmosphere. But if all the energy CO2 can absorb is being absorbed (and immediately re-radiated) ....... there is no increase in the amount of heat being intercepted and re-radiated when the extinction distance is 300 feet.
Earth is a source of IR radiation. It absorbs sunlight and reemits IR. Just like a coat, the atmosphere slows the movement of that IR radiation away from the source. You are having a difficult time understanding the extinction distance. It does not mean all IR radiation is absorbed within 300 feet of the surface. It means it absorb within 300 feet of where it was radiated. Earth's surface is not the only source of IR photons. Every CO2 molecule becomes a source of IR photons after it absorbs one and reemits it. The photon will then be absorbed within 300 feet of that molecule, which could be much more than 300 feet of the surface of the Earth, depending on which direction the photon travels when reemitted. If the photon is reemitted downward, it has zero chance of reaching space and it will hit something and warm it up.
Deletelast comment and then I'm going on vacation till the 8th
ReplyDeleteit is all about heat flow. It is my contention that all the heat is being intercepted and passed on rapidly and that CO2 is not a great insulator to radiation. Your coat example tells the tale. conduction and convection are the primary means by which I radiate with my coat off. The coat greatly reduces the convection and conduction so I have to start radiating at a higher temp (coat gets warm inside) to keep the energy balance going. But we are talking only about radiation transfer not conduction and convection in this discussion so coats are not a great example.
be back on the 8th
CO2 is a very good absorber of IR radiation. There many things that are more efficient, but CO2 is the principle driver of the greenhouse effect. A coat works by absorbing the heat and reemitting it in random direction, just the same way CO2 in the atmosphere does. Some of the reemitted radiation will go away from your body, but some will be reemitted towards your body. The transference of energy from your body to the air around you is slowed down and it keeps you warmer.
Delete