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How do we know more CO2 is causing warming?

What the science says...

Select a level... Basic Intermediate Advanced

An enhanced greenhouse effect from CO2 has been confirmed by multiple lines of empirical evidence.

Climate Myth...

Increasing CO2 has little to no effect

"While major green house gas H2O substantially warms the Earth, minor green house gases such as CO2 have little effect.... The 6-fold increase in hydrocarbon use since 1940 has had no noticeable effect on atmospheric temperature ... " (Environmental Effects of Increased Atmospheric Carbon Dioxide)

Predicting the Future

Good scientific theories are said to have ‘predictive power’. In other words, armed only with a theory, we should be able to make predictions about a subject. If the theory’s any good, the predictions will come true.

Here’s an example: when the Table of Elements was proposed, many elements were yet to be discovered. Using the theory behind the Periodic Table, the Russian chemist Dmitri Mendeleev was able to predict the properties of germanium, gallium and scandium, despite the fact they hadn’t been discovered.

The effect of adding man-made CO2 is predicted in the theory of greenhouse gases. This theory was first proposed by Swedish scientist Svante Arrhenius in 1896, based on earlier work by Fourier and Tyndall. Many scientist have refined the theory in the last century. Nearly all have reached the same conclusion: if we increase the amount of greenhouse gases in the atmosphere, the Earth will warm up.

What they don’t agree on is by how much. This issue is called ‘climate sensitivity’, the amount the temperatures will increase if CO2 is doubled from pre-industrial levels. Climate models have predicted the least temperature rise would be on average 1.65°C (2.97°F) , but upper estimates vary a lot, averaging 5.2°C (9.36°F). Current best estimates are for a rise of around 3°C (5.4°F), with a likely maximum of 4.5°C (8.1°F).

What Goes Down…

The greenhouse effect works like this: Energy arrives from the sun in the form of visible light and ultraviolet radiation.  The Earth then emits some of this energy as infrared radiation. Greenhouse gases in the atmosphere 'capture' some of this heat, then re-emit it in all directions - including back to the Earth's surface.

Through this process, CO2 and other greenhouse gases keep the Earth’s surface 33°Celsius (59.4°F) warmer than it would be without them. We have added 42% more CO2, and temperatures have gone up. There should be some evidence that links CO2 to the temperature rise.

So far, the average global temperature has gone up by about 0.8 degrees C (1.4°F):

"According to an ongoing temperature analysis conducted by scientists at NASA’s Goddard Institute for Space Studies (GISS)…the average global temperature on Earth has increased by about 0.8°Celsius (1.4°Fahrenheit) since 1880. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade."

The temperatures are going up, just like the theory predicted. But where’s the connection with CO2, or other greenhouse gases like methane, ozone or nitrous oxide?

The connection can be found in the spectrum of greenhouse radiation. Using high-resolution FTIR spectroscopy, we can measure the exact wavelengths of long-wave (infrared) radiation reaching the ground.


Figure 1: Spectrum of the greenhouse radiation measured at the surface. Greenhouse effect from water vapour is filtered out, showing the contributions of other greenhouse gases (Evans 2006).

Sure enough, we can see that CO2 is adding considerable warming, along with ozone (O3) and methane (CH4). This is called surface radiative forcing, and the measurements are part of the empirical evidence that CO2 is causing the warming.

...Must Go Up

How long has CO2 been contributing to increased warming? According to NASA, “Two-thirds of the warming has occurred since 1975”. Is there a reliable way to identify CO2’s influence on temperatures over that period?

There is: we can measure the wavelengths of long-wave radiation leaving the Earth (upward radiation). Satellites have recorded the Earth's outbound radiation. We can examine the spectrum of upward long-wave radiation in 1970 and 1997 to see if there are changes.


Figure 2: Change in spectrum from 1970 to 1996 due to trace gases. 'Brightness temperature' indicates equivalent blackbody temperature (Harries 2001).

This time, we see that during the period when temperatures increased the most, emissions of upward radiation have decreased through radiative trapping at exactly the same wavenumbers as they increased for downward radiation. The same greenhouse gases are identified: CO2, methane, ozone etc.

The Empirical Evidence

As temperatures started to rise, scientists became more and more interested in the cause. Many theories were proposed. All save one have fallen by the wayside, discarded for lack of evidence. One theory alone has stood the test of time, strengthened by experiments. 

We know CO2 absorbs and re-emits longwave radiation (Tyndall). The theory of greenhouse gases predicts that if we increase the proportion of greenhouse gases, more warming will occur (Arrhenius).

Scientists have measured the influence of CO2 on both incoming solar energy and outgoing long-wave radiation. Less longwave radiation is escaping to space at the specific wavelengths of greenhouse gases. Increased longwave radiation is measured at the surface of the Earth at the same wavelengths.

These data provide empirical evidence for the predicted effect of CO2.

Basic rebuttal written by GPWayne

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 1 August 2015 by MichaelK. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.

Further reading

A good summation of the physics of radiative forcing can be found in V. Ramanathan's Trace-Gas Greenhouse Effect and Global Warming.


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Comments 151 to 200 out of 436:

  1. Ok thanks Scaddenp

    Just to clarify

    1. Yes that is what I meant, I used a line analogy rather than a photon traveling in a straight line.

    2. If I read you correct then, when a photon strikes a CO2 molecule it re-radiates exactly the same amount of energy without losing energy to heat, either by heating itself or surrounding molecules.

    3. Yes I understand that the only way heat leaves earth is by radiation, but is it not greatly diminished in the band that CO2 responds to.

    4. My question is, does air, primarily O2 and N2 give off Long wave radiation when it's heated.  What is radiating the heat at the top of storm clouds?

    5. Maybe a better way to ask the question, what percentage of the total heat budget is in the long wave radiation band that CO2 responds to.  If none of that band were allowed to escape, then the earth would have to heat to expel more at the frequency bands that gets through.

    I'm new at this but enjoy reading all the discussions, thanks


  2. Just_Curious - "...when a photon strikes a CO2 molecule it re-radiates exactly the same amount of energy without losing energy to heat, either by heating itself or surrounding molecules." No.

    Checking the numbers, that is not actually the case. Relaxation to emission of a radiation excited CO2  molecule takes about 10-6 seconds, whereas at sea level pressure a CO2 molecule will undergo a collision about every 10-9 seconds. There are therefore about 1000 collisions exchanging energy at sea level before that molecule can emit.

    What happens is that the air mass containing the absorbing CO2 (including O2, N2, etc.) molecule warms due to the absorbed energy, and (statistially) some other GHG molecules will radiate at some frequency in their spectra in a matching amount, due to the changed temperature of the air mass. Not the same molecule in 999/1000 cases. 

  3. Just-Curious @149 asks:

    "1. If an infinitely thin line were extended out perpendicular from the earth, how far would it extend before it reached a 99.9% probability (aprox.) of coming in contact with a CO2 molecule? At 280 ppm and 400 ppm."

    Answering this question literally, the answer is much, much greater than 150 kilometers.  That is, there is essentially zero chance that such a line will strike a CO2 molecule before exiting the Earth's atmosphere.

    This answer is very different from that by scaddenp @ 150, but that is because scaddenp made the "mistake" of answering the question he thought you intended rather than the question you asked.  As a result he gave an approximate answer to the question, how long would an IR photon travel before interacting with a CO2 molecule if the photon was at the right wavelength, and if the CO2 molecule was in the right excitation state.

    Lines do not have electrical fields.  Therefore to come into contact with a CO2 molecule, it would need to strike the nuclei of the one of the three atoms in the molecule.  As you have probably heard somewhere, atoms (and molecules even more so) are mostly empty space.  The nuclei are very small relative to the size of the electron shells.  So small that neutrons (which because they have no charge, interact only with the nuclei of atoms) have a mean free-path length of 1.91 cm when travelling through uranium oxide.  In contrast, of all the CO2 in the atmosphere were to be reduced to a solid (dry ice) layer evenly covering the surface of the Earth, it would only be 0.1 cm thick.  That is, you would have to increase the Earth's CO2 concentration by a factor of 19, or the thickness of the atmosphere by a similar amount, to have an approximately 50/50 chance that a neutron traveling vertically from the surface would strike a CO2 molecule.  And, of course, lines are much thinner than neutrons, and so have an even lower chance of striking a molecule.

    I note this not just from empty pedantry, or an inordinate love of trivia.  It is to emphasize that the interactions between light and CO2 molecules are mediated by the electromagnetic force.  Because of that, the IR radiation must have exactly the right wavelength if it is to interact.  If it does not, if its wavelength is 18 microns rather than 15 microns, for example, it will breeze past all the CO2 in the atmosphere with no effect.  Even if the wavelength is very close to 15 microns, the CO2 molecule has to be traveling in the right direction at the right speed (so that the doppler shift will result in the correct resonance), the and the molecule has to be at the correct excitation state, and so though a number of other factors.  If not, the IR radiation will not be absorbed, but simply continue on its way.  Consequently, for most IR photons, they will travel through the atmosphere without significant interaction with CO2.  But at the crucial wavelength, their mean free-path length is quite short (and at 15 microns, is very close to 3 meters).

  4. Just_Curious @151, KR @152 makes a very astute point.

    The result of the fact that most energy absorbed as IR radiation is redistributed to the adjacent atmosphere as some for of kinetic energy via collisions is that the IR radiation from any level of the atmosphere is set the temperature at that level of the atmosphere, plus the radiation not absorbed by that level of the atmosphere.  When the radiation leaving the top of that atmosphere is calculated on that principle, with a suitably high resolution, the result is a stunningly accurate prediction by the models of the observed radiation.  Any such calculation shows that the greatest impact on outgoing radiation in terms of percentatage of radiation blocked at a given wavelength, is the impact of CO2; and will also show that the active wavelengths of CO2 coincide with the peak IR radiation from the Earth:

    (In this graps, the strong spike around a wavenumber of 600 is CO2.  The smaller spike around 1100 is ozone.  Methane is responsible for the effect around 1300-1400, with H2O responsible for the rest of the reduction in OLR, which is shown by the red shaded region.)

    The result is that CO2 is by far the strongest of the IR active gases, with the exception of water vapour.  It also means that the greenhouse effect of CO2 is not blocked by that of water vapour.

    I recomend that you read my post discussing the basics of the greenhouse effect to help get clear in your mind the relevant facts.

  5. Just_Curious@151

    Your questions are quite clear and logical. One way to better understand these things, if you are not an expert yet, is to simplify the 'experiment' you are thinking about. For example:

    Let's say we have an atmosphere of nitrogen and some CO2 only. Looking at a layer near the surface (say a hundred meters) in isolation (as if there is nothing above it), how would we characterize (a) the absorption of radiation from the surface and (b) emission at the top? (With the same pressure and temperature, of course.)

    If you can explain that, you are already something of an expert, and the rest of it is much easier to follow.



    how does this square with what you have here?

  7. Old Engineer,

    One of the basic predictions of Climate Theory is that CO2 will warm the lower atmosphere and warm the stratosphere.  The measurement of this effect is one of the long term successes of Climate Science.  Your reference describes the absorption of a small amount of energy from a solar flare in the stratosphere that is then radiated back into space as was long ago predicted by Climate Theory.  

    Your source states at the end "Some diehard climate alarmists will still say that in the lower atmosphere the action of carbon dioxide is reversed", acknowledging that this is the accepted effect.  

    If you read the "start here" button at the top of the page it will explain this and many other basics to you.

  8. Typo: my previous post should say "warm the lower atmosphere and cool the stratosphere"

  9. Let's take a look at a small scale model. As everybody knows if you cover a greenhouse frame with clear plastic it quickly gets much hotter inside than outside the greenhouse on a sunny day. Yet if you cover the frame in shade cloth which is perforated, the temperature in the greenhouse goes down in full sunlight. The cloth helps retain some warmth during the night, thus helping to stabilize the extremes. This is a typical greenhouse effect model and is in fact the reason why greenhouses and shadehouses are so popular in backyards. It is also the reason why shade cloth is so popular in large car parks.

    Now, consider the following experiment. I have two greenhouses completely covered with clear plastic and both are in full sunlight, out in the open, and side by side, on the same day. I extract all of the air out of the first greenhouse and then pump it full of CO2. I do nothing to the air inside the second greenhouse. Question: Will greenhouse 1 get any hotter than greenhouse 2?

  10. Skinny_Pete...

    1) You should read all 3 levels of the article you're commenting on first.

    2) You should understand the difference between a greenhouse and the greenhouse effect.

    3) You should read the comments policy for SkS before you make another comment.

    Now, to answer your question. Yes. Greenhouse 1 will get hotter than greenhouse 2.

  11. Skinny_Pete...

    And here is your experiment performed (for all intents and purposes).

  12. Thanks for the brush off. I disagree with the You Tube video. I have tried this experiment numerous times in sunlight and the temperature has always stayed the same in both greenhouses. Clearly many other factors are needed to make the temperature go up, e.g. smoke, dust, pollen, pollutants, water vapour etc.


    [JH] Please keep it civil.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

  13. Skinny_Pete @159 & 162:

    1)  With regard to your experiment, nearly all incoming solar radiation is in the visible wavelengths.  CO2 does not trap energy in visible wavelengths, and moreover, the ground is a good absorber in the IR wavelengths at which CO2 is a good absorber.  Therefore increasing the CO2 in a small box will not increase the temperature of the box in sunlight appreciably due to traping more incoming.  Further, due to the small size of the box, the normal motion of atmospheric particles within the box will keep the entirety of the box at essentially the temperarature of the ground on which it is located (or the floor of the box).  Therefore any excess energy trapped by CO2 in the box from outgoing IR radiation will be replaced by an equal amount of outgoing IR energy radiated by the CO2.  Therefore, and contrary to Rob Honeycutt, the temperature will not be appreciably different in either case.  (I have seen several videos of this experiment done, with some showing a slightly higher temperature for the box containing CO2, and some showing the reverse.  Both differences are down to errors in the conducting of the experiment.)

    2)  I am dubious about the experiment shown in the video linked by Rob Honeycutt.  The two bottles with stoppers and thermometers installed are essentially air tight.  Therefore, plausibly, the CO2 released in the bottle will raise the pressure in the bottle, thereby increasing temperatures.  I do not see how this contaminating effect is controlled for, so I consider the results to be dubious at best.

    3)  Having said that, if the CO2 could be generated seperately and then poured into the bottle before sealing, and then the bottle left to sit till it was at room temperature before turning on the light, you would then have a far better experimental design than typically seen.  Specifically, because the light shines in from the side and all sides are transparent, visible light for the most part will shine straight through the bottle without warming, so that IR radiation absorbed by the CO2 would in fact be additional warming.  The amount of additional IR radiation absorbed is likely to be small, however, so I am not convinced that the additional warming would be appreciable relative to experimental error.

    4)  I have given considerable thought as to how to perform the experiment you are interested in correctly.  It would be difficult, however, and require maintaining a vacumn in parts of the experiment for the duration of the experiment, so I don't expect to see it done correctly on Youtube any time soon. 

    5)  Such experiments are, however, entirely beside the point.  Simple radiation models have shown the ability to predict upward and downward radiation in the Earth's atmosphere with stunning accuracy.  Here, for example, is a comparison between predicted and observed upward IR radiation at a site in Texas from 1970:

    And here is a comparison of measured and predicted total Outgoing Longwave Radiation for 134,862 observations over a wide range of atmospheric conditions (both as to temperature and latitude) reported in 2008:

    These are models of radiation only.  They involve no problems with chaos theory, and no problems with performance.  It is the output of models like these that predict the greenhouse effect, and that the greenhouse effect is not saturated.  The greenhouse effect has been observationally proved to exist, as much as such a term is ever appropriate in science.

  14. Isn't there a "But I built this box/bottle/aquarium experiment, and it proves that . . ." myth somewhere in the list?

  15. Skinny_Pete...  You seem to have failed on my other suggestions of reading the relevant material presented in the articles above, and the suggestion that you read the comments policy. I resubmit both of those suggestions to you.

    The fact is, the radiative properties of CO2 are extremely well established physics. I can accept Tom's sense that the bottle experiment is not a well controlled one, but you can see the same effects at work with a thermal camera set up. Here.

  16. Question. ... will outgoing LWIR  decrease as co2 increases? ???.... producing the greenhouse effect?

  17. Donny @166, increasing the CO2 content of the atmosphere initially decreases the outgoing LWIR.  Changes must then occur at the Earth's surface or in the atmosphere to either decrease incoming SW radiation, or increase outgoing LWIR radiation until the two again match, reestablishing equilbrium.  Until that occurs, the imbalance will result in additional energy being stored in the Earth's surface systems which will result in rising temperatures.  Further, raising surface temperatures is the simplest and most direct means restore the balance.  Further, for any other change than raising temperatures to occur, some physical change at the Earth's surface must occur to drive that change, and as that physical change is driven by the imbalance (otherwise the Earth would not reestablish equilibrium), the physical change that drives the other changes will be a change in temperature.  Ergo, increasing CO2 will raise temperatures.  Tracing the most obvious physical pathways show that it will rise by a significant amount (as do other direct observations, and the paleo record).

  18. In an ever increasing co2 environment shouldn't the OLWIR decrease as the co2 increases? 

  19. Especially if you do find rising global temperatures?

  20. Donny @168 and 169, increasing CO2 decreases outgoing IR radiation all else being equal.  Increasing surface temperatures increases outgoing IR radiation all else being equal.

  21. Moderator's Comment

    Please refrain from responding to Donny's future posts until a Modrator has had time to review their content. Given Donny's propensity to repeatedly violate the SkS Comments Policy, his future posts are likely to be deleted. If they are, your responses to them will be deleted as well. 

  22. Moderator's Comment


    Please note that posting comments here at SkS is a privilege, not a right. This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Moderating this site is a tiresome chore, particularly when commentators repeatedly submit offensive, off-topic posts or intentionally misleading comments and graphics or simply make things up. We really appreciate people's cooperation in abiding by the Comments Policy, which is largely responsible for the quality of this site.

    Finally, please understand that moderation policies are not open for discussion. If you find yourself incapable of abiding by these common set of rules that everyone else observes, then a change of venues is in the offing.

    Please take the time to review the policy and ensure future comments are in full compliance with it. Thanks for your understanding and compliance in this matter, as no further warnings shall be given.

  23. John.... I am not sure what I said that violated the policy????  Can you be more specific so I know? 

  24. I am trying to figure out why the OLWIR would not be acting like it should. ... if that is even the case.... is that wrong to do??  I am confused.   Why do you say I have repeatedly violated?

  25. Donny, the OLWIR radiation is acting as it should, ie, as a function of surface temperature and greenhouse gas concentrations.  You have provided no evidence to the contrary.  Indeed, the TOA energy imbalance that is demonstrated by the rising Ocean Heat Content shows the current OLWIR radiation to have increased significantly less than would be expected from the increased surface temperature alone.  Indeed, without a decrease of OLWIR due to CO2 (and other greenhouse gases), we would expect a negative imbalance (oceans loosing heat) due to the rise in surface temperatures alone.

  26. I read an article on another site that eludes that OLWIR should be decreasing over the last few years as co2 has risen. ... but instead had increased.   I am trying to understand this relationship.   It seems like if the LWIR was decreasing because more co2 was trapping it.... it would result in warming.  Is that correct? 

  27. Donny @176, it is a bit hard to rebut "another article" when you provide no link so that I can read it myself.  Nevertheless, the article probably refered to this graph from Harries et al 2001:

    The graph shows the difference in OLR between April-June, 1970 and April-June 1997 over the eastern central tropical pacific (10 S to 10 N; 130-180 W).  It shows that the OLR has increased slightly (top), but that the observed increase was matched by an predicted increase in the models (middle).  The graphs are offset to allow easy comparison.

    The question you should ask is why did the models predict an increased OLR even though the CO2 level had risen.  The answer is that the region observed is right in the center of the ENSO pattern of variation.  If you look at the pattern of ENSO variation, you will see that while there were slightly cool ENSO conditions in that zone in 1997, they were very much cooler in 1970:

    Remember, warmer temperatures increase OLR, and the 1997 temperatures were distinctly warmer, and warmer beyond the mere expectation from global warming due to the ENSO pattern.  That additional warmth above the AGW trend increased OLR beyond the additional reduction due to the slight increase in CO2 over that period.  Indeed, it was only because of the additional warmth due to ENSO that the OLR increased.  Had the increase in warmth been only that of the trend, the net OLR would have declined slightly.

    Harries et al did not leave it there.  They used a model to correct for the temperature difference, thereby showing the impact of greenhouse gases apart from the changes in temperature:

    As expected, the change in GHG concentration reduces OLR.

    I know that pseudoskeptics attempt to dismiss this data because a model was used to generate it.  It was not, however, climate model.  It was a radiation model (specifically Modtran3).  This is the sort of accuracy you can get with radiation models:

    Because the adjustment was done with radiation code, denying the validity of the adjustment is tantamount to denying radiative physics altogether.  It puts those who do it into flat earth society territory as regards to the level of their pseudo-science.


    [PS] Isaac Held has also blogged on this.

  28. I'm curious about something, and I'm not sure if this is the right page to ask about it, but here goes anyway. I understand that plants might not necessarily migrate north as temperatures increase and as their climatic boundaries change, but why is that the case? If you could point me towards a page or two that explains it, it would be appreciated.

  29. tkman0 - I have responded in a more appropriate place.

  30. tkman0 @178, I have responded here.

  31. Replying to comment from here.

    The very basics of science is comparing what your hypothesis predicts to observation.

    "What they say" - is the calculated spectrum of IR with increased CO2.

    The observation is what is actually measured of the CO2. See article above and graphs in comments for these comparison. I think it is simply that you person misunderstands the physics. See also "The CO2 effect is saturated" which might illuminate the basis of misunderstanding.

    But in short, the observations of IR spectra, whether DLR observed at the surface or OLR observed from space, fit what is expected from theory for increased CO2.

  32. Quick, following on from the previous thread

    Your commenter is full of it. It is not Raman Scattering. It is molecular absorption spectroscopy. And CO2 absorbs over an absorption range not just a single frequency. Across that range there are 10's of thousands of individual absorption lines.

    Point your 'expert' here

    SpectralCalc plots line strength data for any of the gases in the HiTran spectroscopic database. Have him select CO2, Microns rather than wavenumber and a range from say 5 to 20 microns then plot.

    He can then look at the detailed tabulated data for the plot extracted from HiTran at this link:

    If he still has an issue then he needs to take it up with the Cambridge Research Laboratory at Harvard and the US Defense Dept who have been behind the acumlation of data in Hitran for many years - currently data on 43 different gases, 120 isotopologues and over 7 million individual absorption lines

    And if he does question the lab they will politely hand him his ignorant head on a platter!

  33. Next his reference to Wien's Displacement Law???

    Wiens Law is used to calculate the location of the peak of a Planck curve. But CO2 (and any other gh gas) doesn't necessarily absorb at the peak. The each absorb at different parts of the Planck curve, and perhaps not at the peak. This just pseudo-scientific waffle to try and sound smart.

  34. Thanks Glenn and scaddenp! It would've taken me quite awhile to dig this up on my own. I called him out on it being pseudoscience and asked for no avail....shockng as that may be.

  35. Glenn, I posted #182 and 183 almost verbatim. Here was his response:

    When viewed under high resolution, EVERY gas has numerous small transitions along the entire EM spectrum. That has never been under dispute. I guess you can't distinguish between that and an absorption peak. And by the way, that also shows that EVERY gas is a "greenhouse gas."

    Additionally, I'm well aware of the various factors that will influence absorption. Factors such as natural, temperature (also called Doppler) and pressure broadening. These same factors will also affect emissions to varying degrees.

    But now you've shifted gears and are talking about ABSORPTION. As I recall, your beloved Greenhouse Gas Theory claims that CO2 absorbs and then "re-emits" a photon of IR. But that's not absorption since absorbed energy isn't least below 85km in altitude. Below that altitude, absorbed energy is passed on to other molecules as KE during a collision. So I guess it looks like you've disproven your own beloved theory. Nice going.

    As for my reference to Wien's displacement law, you have things backwards...which is normal for an AGW cultist. I reference it to show surface temperatures that will produce specific [peak] wavelengths that are emitted by a surface at that specific temperature, NOT to show what is being absorbed. Were you a breech baby as well?

    But since you've deflected to absorption instead of scattering, I notice you left out the absorption coefficients of the TWO and ONLY two absorption peaks that are within the atmospheric window. Just so you don't have to waste time scrambling to try and find out what they are, they're 9.4 microns and 10.4 microns. Maybe you should post the absorption coefficients for all to see. You think?

  36. Oh, and I have asked repeatedly for ANY any reference, but he deflects. My BS meter redlined when I first saw his original post, but I lack the bandwidth and advanced acumen to effectively debunk this. I also laid down the gauntlet for him to join here and engage. So far it's been met with more deflection.


    [JH] The use of "all caps" is akin to shouting and is prohibited by the SkS Comments Policy.

  37. Then same guy, (Jim in CA) added this:

    "And yes, GHG theory is wrong. Here's an equation that shows the temperature increase moving from 280ppm to 560ppm:

    ΔT = (0.443 W/m^2) ln[(560 ppmv/280 ppmv)] / 4 (5.6697x 10^-8 W/m^2*K^4) (300.15 K)^3 = 0.307 W/m^2 / 6.13 W/m^2*K = 0.05 K = 0.05 C = 0.09 F

    That's it, just 0.09 F. Wow and double wow!! We're all going to die from heat exposure. LMAO Additionally, that value is most likely high as it's based merely on atmospheric partial pressure of CO2 and emissivity. It isn't taking into account the likelihood of energy transfer to other molecules with higher specific heats that can absorb the energy without changing temperature....molecules like water vapor.

    And that brings me to another point. You morons are constantly saying that CO2 "traps" heat. Don't know about you, but to me if something is "trapped", then it's removed from the environment. "Trapping" heat would COOL things down, not warm them up. Additionally, the CO2 molecule at our atmospheric pressures and temps simply has TOO low of a specific heat to carry much thermal energy anyway. It doesn't have the thermal headroom. Sorry about your bad luck on that one.

    CO2 is quite simply an energy conduit. Nothing more. It quickly transfers energy from one source to another without storing it."

  38. Where is this conversation going on, Quick?

  39. Ah! Just figured out where "Jim in CA" is getting his information.

    Nasif Nahle Sabag.

    The equation is a direct cut and paste.

  40. Rob, conversation is here.

    Quick. He has the equation wrong (note not explaining it). The correct answer is around 1.1C. However this is temp change from radiative forcing alone. Feedbacks (water vapour, albedo primarily) lift this higher to something in range 2-4.5C.

    Jim needs to realise that just because he doesnt understand something doesnt make it wrong, especially on basis of a cock-eyed semantic argument. Secondly, if your understanding of something doesnt agree with actual measurements (eg the increase in DLR) and textbook calculations do, then guess who is wrong.

  41. Quick, for starters his fixation on 9.4 and 10.4 is way off. there are two minor peaks there but the main one is closer to 15 micron. He wants a graph, show him this:

    you can get a copy here: Notice that the vertical scale is logarithmic. So the peak at around 15 micron is nearly 10,000 times stronger than those peaks he is referring to. And this is the actual measured spectral intensity for CO2, from HiTran. Spectral Intensities 1000,s of times higher than his numbers means that is distance of kilometers becomes meters.

    Next he clearly doesn't get that absorption and emission are mirror image processes. Gases that absorb at certain wavelengths also emit at those wavelengths.

    He is right that when a single CO2 molecule absorbs a photon then virtually all the time this extra energy is passed off to other molecules in the air, typically within less than a microsecond of the absorption. But he is missing the fact that collision between molecules are continually raising molecules to higher energy states and dropping them back down again.

    At any instant half of all the molecules in the air will be in an energy state higher than the average. And a proportion of those will be CO2 molecules. So a small proportion of those CO2 molecules will be able to spontaneously emit, de-energising by emission rather than by collision. And since there are millions of CO2 molecules in just the first meter of travel for each photon, even a small number of spontaneous emissions is enough to emit as much as is absorbed.

    And most of the emitted photons are in turn absorbed by another greenhouse molecule and the energy redistributed via collisions, then another emission by another molecule ... and so on. When a gaseous medium is 'optically thick' - meaning most EM radiation passing through it is absorbed, then energy transport via radiation through the medium is extremely slow. This process is called Radiative Diffusion.

    A similar process occurs inside the Sun. In the inner part of the Sun there is no convection, so all energy flow is via radiation so it is extremely slow at transferring generated heat from the core outwards. It is only when one reaches the outer layers of the Sun and convection starts occurring that the rate of heat transport increases dramatically. The estimates are that it takes over 100,000 years for energy generated in the core to reach the surface and escape to space.

    And it is similar here on earth except that convection is able to transport heat upwards right from the surface. It is only when the air is thin enough that some of the emtted radiation is able to escape to space. For the very peak of the CO2 absorption band this is up at 30-40 km up. However for much of the wavelengths around that between roughly 13-17 microns, the altitude is much lower, even down to around 2-3000 meters. There is a smilar behaviour for the other GH gases, depending on the profile of their spectral intensity.

    Thus, athough the altitude at which the atmosphere becomes 'optically thin' varies significantly from wavelength to wave length, the average altitude at which it becomes optically thin, averaged for all GH gases, is around 5 km.

    Hope this helps, and is clear.

  42. scaddenp@190, Thanks again for the input, but my last physics class was early 80s, so bear with me please. What equations yield the 1.1C and 2.0-4.5C?

  43. Glenn, this is helpful. However, here is how he explained absorption and emission: "Speaking of science, did you people know that the AGW cult claims that when a molecule of carbon dioxide "absorbs" and "re-emits" a photon of IR (actually Stokes-Raman scattering) that it re-emits a photon of the "exact" same wavelength as the one "absorbed"?

    This is the claim to got me interested in researching their pseudo-science. Reason being, I already knew this was impossible. There is only one process that can absorb and re-emit a photon of the exact same wavelength and that process is called resonance fluorescence and it involves an electronic transition (electron jump). It's IMPOSSIBLE with a vibrational transition."

    Can you please clarify the last sentence here?


    [JH] For future reference, it would be extremely helpful to everyone if you were to put all quotes from you blogging adversary(ies) in italics. Thank you. 

  44. "[Impossible] with vibrational transition"?  I think not:

  45. Quick - The 1.1C from direct forcing from doubling CO2 comes most directly from Myhre et al 1998, computed using the HITRAN spectral database and numeric radiative codes to estimate reduction of IR to space with increasing CO2, not to mention other GHGs. This spectral change has been experimentally verified with satellite readings at GHG frequencies (Harries et al 2001 and later papers).

    The 2.0-4.5C warming from a doubling of CO2, with a mode of ~3.0C (including feedbacks) comes from a broad range of studies (discussion here), including paleoclimate, GCMs, recent observations, etc. While uncertainties are present, the changes of warming outside that range are very low, apply to both the high as well as low extrema, and even 2.0C warming per doubling is likely to give us significant impacts based on our current economic path. 

  46. To expand slightly on my previous comment:

    The forcing change from doubling CO2 is on the order of 3.7W/m2. To calculate how the the climate must warm in response, consider the effective emissivity of the Earth to space, and the Stephan-Boltzmann law.

    Power = Area * emissivity * SB constant * TK4

    The Earths surface receives an average of 240 W/m2 of energy from the sun, and with a surface temperature averaging 15C emits 240 W/m2 back in balance (solve for original emissivity). If that drops by 3.7 W/m2, reducing effective IR to space (solve for changed emissivity), the surface of the Earth has to warm by 1.1C to come back into balance and again emit 240 W/m2 (use new emissivity and solve for temperature)

  47. Quick

    "did you people know that the AGW cult claims that when a molecule of carbon dioxide "absorbs" and "re-emits" a photon of IR (actually Stokes-Raman scattering) that it re-emits a photon of the "exact" same wavelengthas the one "absorbed"

    Simple answer. No 'it' doesn't. No scientist knowledgeable about the processes involved in the GH efect says that. It is along the lines I described previously.

    Absorption of a photon by a CO2 molecule is decoupled from emission of photons by other CO2 molecules. They absorb across a wavelength ban and equally they emit across that band, with differing probabilities of occurring at each wavelength.

    Maybe your interlocutor read commentary on blogs from laymen that said this, but an Atmospheric Physicist for example wouldn't. He seems to be an example of someone who thinks that commentary in the media and public forums constitutes an accurate description of the science. It isn't, it's just commentary.

    And all the science behind AGW is based on accurate spectroscopy as for example the HiTran database.

    As for his last sentence, there are several ways in which atoms and molecules can absorb/emit photons. The two that matter here are:

    1. Atoms can absorb a photon and one of the electrons within the atom will be raised to a higher energy state. This mainly occurs around visible and ultra-violet wavelengths. This is purely an electrical process inside an atom.
    2. The atoms of a molecule are a bit like balls bouncing on strings - they 'jiggle around'. A molecule can absord energy from a photon that causes this vibration ('jiggling') to increase. This mainly occurs in the near Infrared which we are dealing with here. This is an electro-mechanical process encompassing the whole molecule - electro because the molecule is able to 'reveal' electric charges to the outside world because it has a 'charge separation' across the molecule, and mechnical because it involves the physical movement of the atoms within the molecule. One of the pre-requisites for a molecule to possibly be a GH gas is that it must be able to produce a charge separation. Symmetrical molecules such as Oxygen and Nitrogen can't do this, thus they can't act as GH gases. There is also a form of this absorption/emmission that occurs for some GH gases, water particularly, where the rotation of the molecule allows absorption, increasing the rotation.
  48. @Rob Honeycutt

    I know I'm 5 months after the fact, but Jim (in CA) commonly posts to climate stories in the Yahoo! News blogs.  He and another character who goes by JDAM, love to quote all sorts of Boltzman calculations as "proving" that CO2 can't possibly be a GH gas.  Problem is they would never be convinced that their black box calculation of 1°C per double CO2 misses about half the reality, feedbacks, associated with increasing GHG concentrations as some other later folk pointed out.

  49. Hi... This is my understanding of how CO2 in our atmosphere works. Was hoping y'all could tell me where I'm off.

    CO2 makes up about 0.04% of our atmosphere. It absorbs infrared in the 3, 4 and 15 micron ranges. 3 and 4 micron are centered around 451c and 693c respectively and the earth's black body curve doesn't hit that much. The 15 micron blackbody curve centers around -79c (from what I understand). 

    Earth's blackbody curve is around 10 microns ( Toward the tail is where CO2's absorption kicks in, overlapped by water vapor. 

    So, there's some absorption by CO2 for the amount of blackbody radiation molecules give off in that range (since bbr is a curve).

    But once a CO2 molecule absorbs a 15 micron photon, wouldn't it either re-emit at the bbr curve of it's temperature, far more likely to be centered around 10 micron, or shed the extra energy as heat transfered to another molecule? Eventually heat is emitted as radiation, but wouldnt' the odds be against that energy being re-emitted at 15 microns?

    Also, wouldn't each molecule (at 0.04%) essentially have to absorb 2,500c of energy and transmit that heat to other molecules in the atmosphere to increase the atmosphere's temperature 1c?

    Also, considering water vapor overlap, even at 10% humidity at 70f, there's a lot more water vapor than CO2 in the atmosphere. Wouldn't that skew the numbers for the 15 micron range?

    I don't have the math background to calculate this stuff, I'm really a noob, but I just don't understand how CO2 can contribute that much. 

  50. @Tom Curtis

    Very cool video... However, since CO2 absorption happens at 3, 4 and 15 microns (3 and 4 being centered around 451 and 693) doesn't it make sense that a very hot flame giving off heat around there would disappear in IR when CO2 is pumped in? Simply because it absorbs at temperatures much higher than our atmosphere normally is?

    If they did that experiment in a freezer, and held up a human hand, would we see the same thing?

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