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Is CO2 a pollutant?

Posted on 11 February 2010 by John Cook

We commonly think of pollutants as contaminants that make the environment dirty or impure. A vivid example is sulphur dioxide, a by-product of industrial activity. High levels of sulphur dioxide cause breathing problems. Too much causes acid rain. Sulphur dioxide has a direct effect on health and the environment. Carbon dioxide, on the other hand, is a naturally occuring gas that existed in the atmosphere long before humans. Plants need it to survive. The CO2 greenhouse effect keeps our climate from freezing over. How can CO2 be considered a pollutant?

A broader definition of pollutant is a substance that causes instability or discomfort to an ecosystem. Over the past 10,000 years, the level of atmospheric carbon dioxide in the atmosphere has remained at relatively stable levels. However, human CO2 emissions over the past few centuries have upset this balance. The increase in CO2 has some direct effects on the environment. For example, as the oceans absorb CO2 from the atmosphere, it leads to acidification that affects many marine ecosystems. However, the chief impact from rising CO2 is warmer temperatures.


Figure 1: CO2 levels (parts per million) over the past 10,000 years. Blue line from Taylor Dome ice cores (NOAA). Green line from Law Dome ice core (CDIAC). Red line from direct measurements at Mauna Loa, Hawaii (NOAA).

Rising CO2 levels causes an enhanced greenhouse effect. This leads to warmer temperatures which has many consequences. Some effects are beneficial such as improved agriculture at high latitudes and increased vegetation growth in some circumstances. However, the negatives far outweigh the positives. Coast-bound communities are threatened by rising sea levels. Melting glaciers threaten the water supplies of hundreds of millions. Species are becoming extinct at the fastest rate in history.

How we choose to define the word 'pollutant' is a play in semantics. To focus on a few positive effects of carbon dioxide is to ignore the broader picture of its full impacts. The net result from increasing CO2 are severe negative impacts on our environment and the living conditions of future humanity.

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Comments 151 to 200 out of 234:

  1. The site Sceptical science should offer a way out of the mud slinging that gets nowhere and is unfortunately all to common with this topic. So what have I picked up from the discussion! CBDunkerso ...........As to your convection hypothesis... it fails because, amongst other things, greenhouse gases do not retain heat within themselves. They absorb and then immediately re-emit the infrared radiation..... However this is contradicted by Carrot Eater ....By the way, CO2 doesn't always instantly radiate a photon as soon as it absorbs one. It can collide with neighboring molecules and thus warm up that pocket of air...... I would tend to side with carrot eater- but now the energy in the form of vibrational KE can be picked up by nearby molecules(most likely to be N2) Carrot Eater goes on to say But that's still fine; the CO2 will still emit at some rate set by the local temperature..... It can only radiate in one of two possible IR bands and it has just lost one ! Carrot Eater has reassured me by saying of the use of Stephan Boltzmann equation is not used in realistic calculations. .....Those are extremely simplified cartoon illustrations, to help show people the basic concepts of the energy balance without having to write thousands of equations. However thanks must go to Philippe Chantreau 151 who has given a link to Eli Rabbits final draft of his attempt to refute the G&T paper. However Eli uses in his refutation ....guess what....Stepthan Boltzman equation for atmosphere re-radiating back to Earths surface. Eli has been keeping quiet about this recent effort and I think I can guess why. I am disappointed with Ricardo when he tries to defend what must be a silly mistake. ...A molecule moving vertically up in a gravitational field for say 10Km in the absence of any other interactions would keep the same speed...-this is nonsense Not only does it contradict the conservation of energy it contradicts the force of gravity. From the Kinetic Theory of Gases The KE of a molecule is directly proportional to its absolute temperature In my post 101 ... I gave a typical question from any high school physics book in the planet I have also given answers-try it for yourselves-if you cannot cope then I think you will find it very difficult to understand this topic
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  2. suibhne, i'm sorry, i thought we were talking at a more advanced level. If we can just stick to newtonian physics extrapolated at the single molecule level and even ignoring statistical thermodynamics it's hard to come up with something useful. There's no way i'm aware of to explain the difference between thermal emission and absorption bands without using quantum mechanics or the relation between particle velocity and temperature not using statistical thermodynamics.
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  3. Riccardo, try this... if G&T AREN'T morons then their postulate that EM radiation can't move from a colder area to a warmer one would prevent solar radiation from space (which is very cold) from entering the Earth's atmosphere (which is warmer). Not only have they disproved global warming... they've disproved sunlight.
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  4. Riccardo I really do think that you are following A P Smith and getting yourself into the most amazing muddle. To you apparently Gravity and the conservation of energy are passe. I am starting to think that if I gave you a very simple problem to do you might fail to answer it-will I?
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  5. CBDunkerson Do you still stand by your posting ...........As to your convection hypothesis... it fails because, amongst other things, greenhouse gases do not retain heat within themselves. They absorb and then immediately re-emit the infrared radiation..... Then imagine that a CO2 immediately re-radiated an IR photon and this photon underwent 100 similar interactions with "Greenhouse Gases" before escaping to space. How long would the process take at the speed of light? I would guess less than a microsecond. I prefer Carrot Eaters explanation of the IR energy being thermalized into the form of vibrational KE.
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  6. CBDunkerson, when G&T paper has been published on arxiv back in 2007, the very first thing i noticed was the 40 or so pages devoted to clarify that the atmospheric greenhouse gas effect does not work like a glass greenhouse! I have seen this explained in a high school textbook, the right place for it. But then came the good old 19th century physics and i got stuck. How can you force a colder object not to emit it's thermal radiation toward a warmer object? Does it have knowledge of the thermal distribution of the universe? In the end the net flux is still in the right direction and i couldn't see violation of any known (at least by me) law. Maybe i was missing something and G&T are reputable physicists after all. But how come we can routinely measure IR and even radio frequencies with detectors at room temperature? I might not be a reputable physicist like G&T but i'm quite sure that the IR radiation reaches my f**king warmer detector :D Here they lost me.
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  7. suibhne "It can only radiate in one of two possible IR bands and it has just lost one !" The 15 micron band is what's relevant here. CO2 is quite happy to radiate there. I don't see what the issue is. "However Eli uses in his refutation ....guess what....Stepthan Boltzman equation for atmosphere re-radiating back to Earths surface." I have already told you the context for such illustrations; they are merely illustrations for some educational purpose. In this example, he's merely showing that there is no violation of the Second Law when a cool body radiates in the direction of a warmer body, so long as the warmer body radiates more in return. This shows one of the fundamental errors of G&T (their claim that the Second Law is violated), and I wish you would address it. Please do not misrepresent things. Eli well knows about the details of the quantum mechanics and the need to keep track of wavelength-specific bands; just look at Fig 7 or read in the introduction, "In the first case quantum theory provides the theoretical background (for example, see spectroscopy textbooks such as Hollas and Bernath) and spectroscopic data base such as HITRAN provide line positions and cross sections."
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  8. CBDunkerson Riccardo Lets follow both your points with a thought experiment 1,000,000 IR PHOTONS leave the surface of the Earth and lets follow CBs postulate that 500,000 return back to the surface in less than 1microsecond. These 500,000 now join the upward stream and 1microsecond 250,000 return to the surface and join the upward stream etc,etc The flow of heat is always from hot to cold as G&T say but the delay caused by the co2 is negligible and in no way explains the insulating effect of the atmosphere. I think that Carrot Eater gave the more physically realistic explanation The IR energy is stored within the co2 molecule as vibrational KE. That is it is thermalized. the CO2 is much more likely to interact with N2(80%) then O2(19%) so the thermal energy will be shared between all the atmospheric molecules and so will delay the cooling of the Earth much longer. Of course sometimes a CO2 molecule will re-radiate but the IR photon will quickly be absorbed and thermalized or it may escape completely.
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  9. Suibhne, you seem to be forgetting the existence of all matter OTHER than GHGs. As in... some of that IR radiation which is absorbed and re-emitted by GHGs then goes back down to the lands and oceans of the planet. Making them warmer. Ditto non greenhouse gases. Poof... away goes the 'speed of light' objection. We are literally talking about the difference between 'up' and 'down' here. Solar radiation passes through the atmosphere and heats the planet. The planet gives off infrared radiation... which travels UP and escapes into space... UNLESS it is absorbed by GHGs and emitted back DOWN towards the planet. Carrot eater correctly noted that this infrared energy can also interact with non greenhouse gases in the atmosphere... but that's true regardless of which direction the radiation is traveling. The central point is that some of the energy which was going up and away into space gets re-directed back down and remains here on Earth. The more energy that happens to the warmer the planet gets.
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  10. suibhne Your thought experiment is ill-posed, and I can't discern any meaning from it. It isn't a matter of a tracing around a single photon and studying its "time delay", suibhne. It's a question of energy flows. Take this diagram as a simple illustration. windows.ucar.edu/.../earth_rad_budget_kiehl_trenberth_1997_big.gif Without greenhouse gases in the atmosphere, that back-radiation term would not be there. If you increase the concentration of greenhouse gases, the outgoing longwave radiation term would decrease, and the system would have to warm up over time until the two terms going out to space again balanced the incoming term (here, 342 W/m^2).
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  11. CBDunkerson ..... you seem to be forgetting the existence of all matter OTHER than GHGs. As in... some of that IR radiation which is absorbed and re-emitted by GHGs then goes back down to the lands and oceans of the planet. Making them warmer. Ditto non greenhouse gases...... If you read my post I have allowed for that the surface of the Earth(oceans etc) is a much better IR transmitter/absorber than CO2 and it is warmer. So the up flow from Earth of IR radiation is much greater than any that's returning. Whats more the non greenhouse gases seem to be better at retaining their heat than CO2 The speed of light is important and gives a boundary in which the duration of any effect can be quantified. carrot eater "It can only radiate in one of two possible IR bands and it has just lost one !" The 15 micron band is what's relevant here. CO2 is quite happy to radiate there. I don't see what the issue is....... Perhaps I am mistaken but I thought that the IR bands of CO2 corresponded to an intermolecular thermal excitation between its atoms, rather than one of the electrons moving to a higher orbit. If I am correct then in an interaction with a neighbouring molecule this energy may be transferred to that molecule as KE. The fact that Eli mentions a book on quantum mechanics in his introduction does not excuse him for ignoring it in the relevant parts, if as you say he fully realises that his diagrams are comic book then he should say so.
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  12. suibhne: Let's stay with http://www.windows.ucar.edu/earth/Atmosphere/images/earth_rad_budget_kiehl_trenberth_1997_big.gif A central claim of G&T is that such a diagram violates the Second Law. Do you agree with G&T on this matter? This is the critical question, so please address it directly. And as for the use of Stefan-Boltzmann, again from Eli's manuscript, "A more realistic model would split the atmosphere into a much larger number of layers for integration and take into account the detailed spectral dependence of absorption and emission, as is done with line-by-line radiation codes (HITRAN)." So please discontinue saying that Eli or anybody else is not aware of the details of spectral dependence.
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  13. carrot eater I looked at your diagram I take it that the diagram splits out horizontally for the purposes of illustration and it shows the energy balance transfers for a representative one square metre. All units in w/m2 Well what I see is a solar input of 342 and an available energy moving near the surface of the Earth of 168+324+390 = 882 If this square meter had a double sided solar panel it could turn this into useful work. However I don't think it is possible because it clearly violates the conservation of energy. So yes G&T are absolutely correct. I think this diagram is an even bigger clanger than the disappearing 2035 Himalayan glacier
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  14. suibhne: So you are one-upping G&T, and claiming a violation of the First Law, and not just the Second? Wow. Please look at the diagram again. Terms coming into the surface: 168+ 324 = 492 Terms leaving the surface: 24 + 78 + 390 = 492 You appear to have missed the outgoing arrow on the 390 term, suibhne. "I think this diagram is an even bigger clanger..." If you are going to make such strong statements, do check the arithmetic first.
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  15. carrot eater But this is all incoherent em radiation . It does not cancel out. Two equal spotlights facing one another from each side of a room do not produce darkness. Look at my example of a double sided solar panel say one metre above the surface and explain why it cant use all the radiation falling on it!
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  16. "Venus, too, like Mars, has an atmosphere of nearly pure carbon monoxide. Yet it, unlike Mars, is hellishly hot. RSVP, do you suppose, that, just maybe, distance from the sun has some slight influence here?" "And yes, I am aware that Mars only gets about half the sunshine as the Earth, however, shouldnt all that CO2 be keeping the plantet a little warmer?" I just wanted to add that not only does Mars get less sunshine, it is about half the size of Earth, and has sparser cloud cover. Venus is almost the exact analogy of Earth, being only a few hundred km smaller in diameter. The cloud cover on Venus is much greater than Earth, but that is a consequence of the vast amounts of sulpher dioxide and water vapour. The current state of Venus is much closer to the outcome of our own planet, should we fail to regulate CO2, among other things. Between the CO2 levels, thick cloud cover and strong winds in the higher atmosphere, Venus has a nearly consistent global temperature of 450C. The Earth already has relatively thick cloud cover, if the CO2 starts trapping the heat and evaporating water, that cloud cover will become thicker, leading to a runaway negative feedback loop. The conditions on Mars are not similar enough to our own to draw any conclusions. Venus is the planet we want to study if we wish to avoid the same fate.
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  17. suibhne: You are making stranger and stranger statements, to the point it really isn't worth continuing. The First Law requires that the total energy and heat flows into the surface, and out from the surface, are equal and opposite for the surface to remain at the same temperature. The diagram does exactly that, even though you tried to say it didn't.
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  18. carrot eater Given that you think the diagram is accurate. You still have not answered why a solar(or IR) panel Infra Red Down ---------- Double sided solar panel ---------- Infra Red Up I don't see why given the diagram that this wouldn't work But then if the diagram is wrong........
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  19. suibhne: Now it seems like you're questioning the fact that the Earth is emitting radiation, period. Is that what you're doing? Are you saying you want to absorb the IR radiation being emitted by the earth, and do useful work with it? Good luck with that. Your device would have to be much colder than the Earth's surface in order for the net heat transfer between the device and the Earth to be inwards to the device in the first place. In any case, please return to the Second Law. G&T say that this diagram is wrong by the Second Law. They say it is impossible for the atmosphere to emit radiation down towards the Earth. Do you agree with them? That is all we need here.
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  20. carrot eater The em radiation falling on top and on the bottom according to your diagram comes to 882 joules per second. But the Sun only supplies 342Joules per second. What I am and have stated is the diagram is utterly stupid. On the 2nd law and Greenhouse effect I thought that I had covered that with my flow of IR radiation at the speed of light. Net heat is always from hot to cold. G&T are aware that radiated IR from CO2 can fall on the Earth; its the massive quantities that are postulated that is in disputed. The 2nd law is a statistical law and can be formulated with entropy as the point of interest. An ice cube placed in warm water will dissolve most likely but for the ice cube to reform is most unlikely. Further the main emphasis of G&T on heat transfer concerns conduction and convection wind and frictional effects such as tides and so on. There was a small residual radiative effect in the Woods experiment but it was so small that it could not possibly account for the insulating effect of the atmosphere.
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  21. suibhne "The em radiation falling on top and on the bottom according to your diagram comes to 882 joules per second." I'm not sure what all you're adding up to get that, but it doesn't really matter, since I can't figure out what point you're trying to make. "On the 2nd law and Greenhouse effect I thought that I had covered that with my flow of IR radiation at the speed of light." Hardly. Your microsecond thought experiment didn't make any sense. At once point, you said the First Law was violated. Nowhere is that true. There is a balance at the earth surface, around the atmosphere, and at the top of the atmosphere. You say the Second Law is violated. Where in this diagram is net heat flowing from a cold body to a warmer body? This is exactly where G&T got hung up. I think you are incorrect: for them it was not a matter of degree; it's a matter of concept. Look at their Figure 32/Figure 3 in the manuscript. They think heat is being transferred uphill from atmosphere to surface, and this is a violation of the second law. They think that somewhere in my (Trenberth's) diagram, heat is flowing uphill. Please show where heat is flowing in the wrong direction in my diagram. If you cannot, then you have yourself refuted a central point to G&T.
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  22. carrot eater Of the other contributors an this topic I feel that you have shown most flexibility and discus the topic without being too polemical. I started looking at this area with an open mind. I read the G&T article and the attempts to counter their arguments. I looked up both Arthur P Smiths site and Eli Rabbet among others. I got my old text books out to best follow the points they were making. On the Smiths and Rabbit sites I found that Fred Staples took the discussion back to Smith and Eli and seemed to cut the ground from under them. Look up these sites and follow the discussion on the 2nd law. Don't dismiss the G&T paper out of hand. You may come to a different conclusion to me but your Physics will probably be all the stronger for it.
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  23. Here's an interesting report w/regard to C02 as a human artifact, where it goes and what it does: "Today, Ridgwell and Daniela Schmidt, also of the University of Bristol, are publishing a study in the journal Natural Geoscience, comparing what happened in the oceans 55 million years ago to what the oceans are experiencing today. Their research supports what other researchers have long suspected: The acidification of the ocean today is bigger and faster than anything geologists can find in the fossil record over the past 65 million years. Indeed, its speed and strength — Ridgwell estimate that current ocean acidification is taking place at ten times the rate that preceded the mass extinction 55 million years ago — may spell doom for many marine species, particularly ones that live in the deep ocean. “This is an almost unprecedented geological event,” says Ridgwell." Beyond the finding of concern, this article includes an excellent primer on the role of C02 in the oceans and is very helpful for putting this matter into context. An Ominous Warning on the Effects of Ocean Acidification
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  24. suibhne I've seen all that. The basic point remains. In the end, G&T have a problem with radiative exchange between bodies of different temperature. They think this violates the Second Law. This is just wrong, on the face of it. Nowhere in the diagram is heat flowing in the wrong direction. This is an example of Dunning-Kruger actually making it into a journal. G&T thought they could tear down an entire field with a single statement of undergraduate level physics. Unfortunately, they can't, but more unfortunately, some obscure journal published their rant. One wonders if the reviewers actually read it.
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  25. Oh, and as for not being polemical: Thank you for the compliment, but I must admit that the strict moderation at this site forces one to be on their best behavior. So long as you are making an honest attempt to learn and assess, that is good.
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  26. carrot eater ...........I've seen all that. The basic point remains. In the end, G&T have a problem with radiative exchange between bodies of different temperature...... I cant believe that you think that the G&T position is that no re radiation whatsoever from the atmosphere arrives back on Earth. In Physics it is quite common to disregard trivial quantities. An electric kettle contains 1kg of water say. Before (and after) the kettle is switched on the water and the kettles element radiate to one another. When the kettle is switched on heat energy from the element is transferred to the water. The electrical energy input is precisely known as is the internal energy gained by the water by independently derived equations. If the kettle is well insulated the input energy and the internal energy gained by the water are almost exactly equal. I have never heard of anyone including the back radiation from the water to the element in such a calculation
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  27. Suibhne, if you put a solar panel between the surface and the sun, that part of the surface below the panel does not receive the solar 342 joules/s any more. I'm not sure I see how that idea of a 2 sided panel applies to anything.
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  28. As I recall, it is exactly G&T's position that not only no radiation flows from the atmosphere to the surface but that this is altogether impossible. I believe they state it quite clearly.
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  29. Philippe Chantreau The top panel gets 168 +324 The bottom panel gets 390 All units w/m2 That is if you really believe the diagram in the first place. ....... it is exactly G&T's position that not only no radiation flows from the atmosphere to the surface but that this is altogether impossible. Could you give a page number for your quote?
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  30. Suibhne, see section 3.9.3. Specifically, the comment on figure 32; "A machine which transfers heat from a low temperature reservoir (e.g. stratosphere) to a high temperature reservoir (e.g. atmosphere) without external work applied, cannot exist - even if it is radiatively coupled to an environment, to which it is radiatively balanced. A modern climate model is supposed to be such a variant of a perpetuum mobile of the second kind." Also, later in the same section; "Since this system is assumed to be in radiative balance with its environment, and any other forms of energy and mass exchange with its environment are strictly prohibited, it de fines a system in the sense of thermodynamics for which the second law holds strictly." Ergo, the argument is NOT, as you say, that the amount of energy is trivial (which is also untrue), but that it is absolutely impossible for ANY energy to flow from cold to hot. Which, amongst other things, would make SUNLIGHT impossible.
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  31. It's odd that their figure and caption are mismatched stratosphere/atmosphere (?) and atmosphere/surface. But either way, yes, it is an argument of principle, not degree. suibhne: Why don't you like the magnitudes of the flows, anyway? You can scale them down if you really like (while keeping balances everywhere), and you'll still get an Earth surface which is warmer than it would be otherwise without an atmosphere, and so G&T would still imagine a Second Law violation.
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  32. The bottom panel can not get anything if the top panel intercepts the energy flux going downward. The surface is heated by energy coming from above, once heated it radiates up in the IR spectrum (btw, that gives you the task of devising a solar panel using IR). If it's not heated from above it's not going to radiate anything. Why would you expect otherwise? I did not look at the diagram but I doubt that it could be interpreted such as making a shaded surface radiate heat up as a sunny one would. As for G&T, the quote above contains the essence of the problem. The atmosphere and its entire environement are a system. Not just the atmosphere and the surface, or the atmosphere and stratosphere. G&T consider only a subsystem then say it can't exist.
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  33. I still cannot grasp what point suibhne is trying to make with the double-solar panel. But he'd have to recalculate all the energy flows around the system, if he added something to the system.
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  34. carrot eater Philippe Chantreau If we space two lamps one irradiating from the top(492w) and one from the bottom (390w)of a double sided solar device then this light energy can be utilised in some way. Now instead of lamps look at your diagram to see the absurd situation. The energy all must ultimately come from the Sun which is only supplying 342w/m2 CBDunkerson The atmosphere does not transfer heat to the surface of the Earth. Look up the definition of heat in a thermodynamics book. Heat is sometimes mixed up with energy when people talk loosely and for a lot of situations the confusion wont matter much. A bit like some people use interchangeably the mass and weight of an object. However there are situations where such woolly thinking will lead you astray.
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  35. Suibhne, so... what? The entire G&T argument is some kind of semantic game? 'Greenhouse gas absorption and re-emission doesn't transfer HEAT to the surface of the Earth... just energy... which generates heat.'
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  36. CBDunkerson Some of the back radiation from the Earth must reach the SUN eventually. Would it make any sense at all to say the Earth heats the Sun?
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  37. suibhne at 04:19 AM on 20 February, 2010 Imagine a lightbulb illuminated in an evacuated void, radiating. Now wish a silvered sphere into being, with the lightbulb concentric to the sphere. What happens to the temperature of the lightbulb? Is the sphere heating the lightbulb? Perhaps more to the ultimate point of the discussion here, would it matter to you whether the sphere was heating the lightbulb, if you were a strange being living on the surface of the lightbulb and you liked the temperature the way it was without the sphere?
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  38. Suibhne, the way you interpret Trenberth diagram does not seem to make any sense at all. The energy leaving the surface as IR radiation is the same energy that was previously received as mostly SW radiation (sunlight). The surface "converts" the SW energy into IR. The surface is not an energy source, neither is the atmosphere. If you are attentive to laws of thermodynamics, the energy coming from the Sun has to go somewhere, less the surface increase indefinitely in temperature until it reaches equilibrium with the Sun itself. Why are you shocked to see energy leaving the system? Where do you think it should be going? Thye panel example is inappropriate since these are average, global flows but let's look at it anyway. If you interpose a solar panel between the down going radiation and the surface, the diagram will obviously be radically altered. Your panel will get only 198 watts from above and, after a relatively short time for the surface to reach equilibrium, nothing from the bottom. The energy that was heating the surface is now received by the panel, the surface is not going to radiate IR as it was. If you think it could be otherwise, explain how. As for G&T, it is all about semantics indeed. Understood in the frame of thermodynamics, there is no heat transfer between the atmosphere and the surface, insofar as this would refer to a net heat transfer. G&T base the confusion on equating the simplification "the atmosphere makes the surface warmer" with "there is heat transfer between the atmosphere and the surface", implying it is a neat heat transfer. That's not what happens at all. The atmosphere just makes the equilibrium temperature of the surface higher than it would otherwise be without it. A radiant barrier makes the inside of a spacecraft warmer but there is no net heat transfer between the barrier and the craft. G&T is nothing but a multi page erudite obfuscation.
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  39. doug_bostrom ........... if you were a strange being living on the surface of the lightbulb...... Which surface,inner or outer? Philippe Chantreau .... the way you interpret Trenberth diagram does not seem to make any sense at all. Even on one side it does not add up 342 solar from Sun On Earth surface 168 solar + 324 back radiation Your right it does not make any sense at all.
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  40. Suibhne, I suspected it was a mistake to extend my model by including lightbulb dwellers. Just to be sure you understand the model, would the lightbulb be warmer if it was concentric to the reflective sphere? If you think not, how would that be so?
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  41. When it is claimed that the increased CO2 has upset the balance, what exactly is the critical balance between CO2 and water vapour, because that is the balance that is most relevant if CO2 is a forcing agent. The graph shows how the CO2 has increased over the last 10,000 years, but given the planet has warmed over that period, the amount of water vapour would have increased faster than the CO2 has thereby gradually decreasing the amount of CO2 per unit of water vapour for much of that time span.
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  42. suibhne: The Kiehl-Trenberth graphic is an excellent summary of a balanced energy system. Using their numbers for illustration, the input energy from the sun (342-107, or 235 watt/m^2) is balanced by the output (165+30+40 = 235 watt/m^2). Without atmosphere, the surface would directly radiate 235 w/m2 in balance, but the atmosphere insulates by radiating energy (324) back to the surface, allowing a considerably higher surface temperature that radiates ~390 plus thermals + evaporation heat. Increasing back reflection (above 324) with higher CO2 levels decreases the energy emitted to space - energy accumulates (heating the surface and atmosphere) until radiated energy increases from 390/surface and 165/atmospheric to some higher level that pushes a total of 235 out past the insulation, and the system reaches balance again. Note that this does not include potential positive/negative feedback mechanisms - those are outside the current discussion. As to the back-reflection and what I understand of the GT arguments: More CO2 means more scattering and absorption/reemission events from CO2/IR interactions, more IR diverted from direct surface emission to off angles, which means more heads back to earth (total scatter angle -> down). This is a mass effect; single photon tracing CAN be used to show the same thing IF you sum up the probabilities of CO2 interception and radiation scattering angles - choosing a single case where a photon escapes doesn't say anything about mass effects.
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  43. You guys have more patience than I do. suibhne "Even on one side it does not add up 342 solar from Sun On Earth surface 168 solar + 324 back radiation" What does this even mean? On the diagram, I can count three places to draw an envelope for checking the First Law. One is the earth's surface, and it checks. Second is the atmosphere, and it checks. Last is the top of the atmosphere, and it checks. Nowhere is there net heat transfer from a colder to a warmer body. Nowhere. And 'heat' is perfectly acceptable for referring to transfers of thermal energy, by either radiation, convection or conduction. Everything checks out thermodynamically, suibhne. Perhaps you should invest in a radiometer. One that covers longwave IR, mind.
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  44. On the CO2 absorption/insulation: More scatter events in the atmosphere due to higher CO2 concentrations, in addition to back-reflection to the ground, also increase atmospheric path length. This increases chances of IR absorption by other gases -> heating, as well as CO2 energy increase due to non-radiative heating of the CO2, which I believe (I work with fluorescent dye systems) occurs as a low probability event on IR absorption.
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  45. The diagram makes sense, you don't understand it. Net outgoing IR is 390-324= 66. Thermals and evaporation 78+24=102 Total net outflow from surface: 102+66=168. Now can you clarify what you were trying to say with your double sided solar panel idea?
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  46. KR .....As to the back-reflection and what I understand of the GT arguments: More CO2 means more scattering and absorption/reemission events from CO2/IR interactions, more IR diverted from direct surface emission to off angles.... Have you thought about the absorbedIR in CO2 being thermalised ie present as intermolecular KE which can be tranferred by collision with say N2. I think that that is what happens to the bulk of the Earths radiation in the IR bands.
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  47. Philippe Chantreau carrot eater Lets see if we can agree on something carrot eater suggests a radiometer I think a thermopile would be more appropriate. Lets say the measuring instrument is accurately calibrated against a known and trusted source. What would it read if placed; A above the Stratosphere 342w/m2-agreed? B Just above the Earths surface 390w/m2 up + (168+324)w/m2down = 882w/m2-agreed? If you agree, do you not think this is rather odd? If you don't agree, explain your reasoning.
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  48. doug_bostrom Presumably its a tungsten filament lamp from which heat cannot escape by any means other than conduction back along the electric wiring. The filament would continue increasing in temperature until evaporation of the tungsten compromised the reflectivity of the surface or until the filament melted. You probably think that the reflected IR would return to the metal. I think that that situation would be like someone trying to enter a football stadium as the crowds were exiting
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  49. suibhne, reflected IR would indeed return to the metal. Light as "particles" is very, very different from the particleness of people exiting a football stadium. Light also is waves that pass through each other and proceed to their respective destinations, despite "interfering" with each other on the way. This topic has been covered in the comments on the "CO2 Is Not the Only Driver of Climate" thread, including links to animations. Start with Riccardo's comment 05:28 AM on 6 November. Then click on the links in my three successive comments from 10:11 AM, 10:30, and 11:16.
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  50. suibhne at 00:02 AM on 21 February, 2010 That's good, we (appear) to agree the reflector will allow the lightbulb to become warmer, even though the temperature of the reflector is cooler than the lightbulb. Extending the model, assuming the reflector is not perfectly reflective and has thermal conductivity the system would of course eventually reach equilibrium as the reflector radiated into the surrounding void, with the lightbulb remaining at a higher temperature than it would if the reflector were not present.
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