Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Settings


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Donate

Twitter Facebook YouTube Pinterest

RSS Posts RSS Comments Email Subscribe


Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...



Username
Password
Keep me logged in
New? Register here
Forgot your password?

Latest Posts

Archives

Climate Hustle

Stratospheric Cooling and Tropospheric Warming

Posted on 1 December 2010 by Bob Guercio

This post has been revised at Stratospheric Cooling and Tropospheric Warming - Revised

Increased levels of carbon dioxide (CO2) in the atmosphere have resulted in the warming of the troposphere and cooling of the stratosphere. This paper will explain the mechanism involved by considering a model of a fictitious planet with an atmosphere consisting of carbon dioxide and an inert gas such as nitrogen at pressures equivalent to those on earth. This atmosphere will have a troposphere and a stratosphere with the tropopause at 10 km. The initial concentration of carbon dioxide will be 100 parts per million (ppm) and will be increased instantaneously to 1000 ppm and the solar insolation will be 385.906 watts/meter2. Figure 1 is the IR spectrum from a planet with no atmosphere and Figures 2 and 3 represent the same planet with levels of CO2 at 100 ppm and 1000 ppm respectively. These graphs were generated from a model simulator at the website of Dr. David Archer, a professor in the Department of the Geophysical Sciences at the University of Chicago and edited to contain only the curves of interest to this discussion. The parameters were chosen in order to generate diagrams that enable the reader to more easily understand the mechanism discussed herein.

Prior to discussing the fictitious model, consider a planet with no atmosphere. In this situation light from the sun that is absorbed by the surface is reemitted from the surface. Figure 1 is the IR spectrum of this radiation which is known as Blackbody radiation.

Figure 1 

                  Figure 1. IR Spectrum - No Atmosphere

Consider now Figure 2 which shows the Infrared (IR) radiation spectrum looking down at the planet from an altitude of 10 km with a CO2 concentration of 100 ppm and Figure 3 which shows the IR spectrum with a CO2 concentration of 1000 ppm. Both figures represent the steady state and approximately follow the intensity curve for the blackbody of Figure 1 except for the missing band of energy centered at 667 cm-1. This band is called the absorption band and is so named because it represents the IR energy that is absorbed by CO2. IR radiation of all other wavenumbers do not react with CO2 and thus the IR intensity at these wavenumbers is the same as that of the ground. These wavenumbers represent the atmospheric window and is so named because the IR energy radiates through the atmosphere unaffected by the CO2. The absorption band and the atmospheric window is the key to stratospheric cooling.

Figure 2/3 

                    Figure 2. CO2 IR Spectrum - 100ppm                             Figure 3. CO2 IR Spectrum - 1000 ppm

The absorption band in Figure 3 is wider than that of Figure 2 because more energy has been absorbed from the IR radiation by the troposphere at a CO2 concentration of 1000 ppm than at a concentration of 100 ppm. The energy that remains in the absorption band after the IR radiation has traveled through the troposphere is the only energy that is available to interact with the CO2 of the stratosphere. At a CO2 level of 100 ppm there is more energy available for this purpose than at a level of 1000 ppm, thus the stratosphere is cooler for the higher level of CO2 in the troposphere. Additionally, the troposphere has warmed because it has absorbed the energy that is no longer available to the stratosphere.

One additional point should be noted. Notice that the IR radiation in the atmospheric window is slightly higher in Figure 3 than Figure 2. This is because the temperature of the troposphere has increased and in the steady state condition, the total amount of IR entering the stratosphere in both cases must be the same. That total amount of energy is the area under both of these curves. Thus, in Figure 2, there is more energy in the absorption band and less in the atmospheric window while in Figure 3, there is less energy in the absorption band and more in the atmospheric window.

In concluding, this paper has explained the mechanism which causes the troposphere to warm and the stratosphere to cool when the atmospheric levels of CO2 increase.

0 0

Bookmark and Share Printable Version  |  Link to this page

Comments

Prev  1  2  3  4  5  Next

Comments 51 to 100 out of 247:

  1. Sphaerica @47 et al.

    Have a look at commments #17 and #19 in the RealClimate link mentioned by Andy S (@35):
    Why does the stratosphere cool when the troposphere warms?"
    0 0
  2. fyi: the author of comment #17 in the RealClimate link noted above, is Andy Lacis, who is a colleague of Gavin's.
    0 0
  3. Managed to pull out those molecular visualizations of CO2 from the GIF's (from Timothy Chase's website):

    Ground State Mode



    *********************************************************************************

    Pure Symmetric Stretching Mode
    The pure symmetric stretching mode v1 of CO2. While this is a mode that may gain and lose energy collisionally it is not infrared (IR) active as there is no transient electric dipole.



    *********************************************************************************

    Bending Mode V2
    The bending mode v2 of CO2, responsible for the 15.00 μm (wavenumber 667 cm-1) band -- the mode dominating the enhanced greenhouse effect and that primarily used by AIRS. This is infrared (IR) active due to a transient dipole: bending results in charge being asymmetrically distributed with net positive near the carbon atom and negative near the two oxygen atoms.



    And



    *********************************************************************************

    And Asymmetic Stretching Mode V3
    The asymmetric stretching mode v3 of CO2 is responsible for the 4.26 μm (wavenumber of 2349 cm-1) band. The asymmetic stretch result in a net positive charge near the carbon atom and a net negative charge with the isolated oxygen atom, creating an electric dipole and making it infrared (IR) active. Given the range of atmospheric temperatures and concentrations of CO2 the bending mode v2 plays a greater role in climate change.



    *********************************************************************************

    Now the hard part: understanding it...(if I've mis-attributed any of these, let me know)

    The Yooper
    0 0
  4. Knutti & Hegerl (2008): The equilibrium sensitivity of the Earth's temperature to radiation chanages -- the most relevant of which is Figure 1. However, not much ink is expended in explaining the change in the stratospheric temperature profile. It's based on similar plots appearing in several of Hansen's papers.
    0 0
  5. For what it is worth, I ran the Modtran model at Archer's website with the following values:
    CH4 = 0; tropospheric ozone = 0; stratosperic ozone scale = 1; Ground T offset = 0; Hold water vapor = pressure; Water Vapor Scale = 0; Tropical Atmosphere; and No clouds or rain.

    I then set an altituded of 18 km (the tropopause) and compared Iout for both 100ppm and 1000 ppm CO2, both looking up and looking down. By looking down, we measure the effect of changes in outgoing radiation, and hence of IR radiation in the CO2 absorption band entering the stratosphere. The effect was to reduce the outgoing IR radiation by 18 watts/meter^2. By looking up, we measure the change in IR radiation emitted by the stratosphere. The amount emitted downwards changed by 4 watts/meter^2, so the total change (both radiation directed to the surface and to space) would have been 8 watts/meter^2.

    None of these figures represent an equilibrium responce, as surface temperature is held constant in the model. As the atmosphere approaches equilibrium, the decrease in outgoing radiation from the troposphere would reduce as the surface warmed; and the difference outgoing radiation sourced from the stratosphere would also reduce as the stratosphere cooled. Further, it is not possible to simply compare the two values and say that because one is larger than the other it has a dominant effect. The decrease in IR warming of the stratosphere would be a function of the wave length specific emissivity times the reduction in incoming IR radiation, and the emissivity would be less than 1.

    Testing that later point, I checked Iout for 70 km, looking down. There was around 14 watts/meter^2 difference in the two cases. That suggests very little of the outgoing IR radiation from the troposphere is absorbed in the stratosphere, which in turn suggests improved efficiency in cooling the stratosphere with increased CO2 is the dominant effect.

    To the extent that we can trust this model for this (which is to say, not very far), that would indicate that:
    Both effects are active, and relevant for cooling; and
    Improved efficiency of cooling is the more important of the two effects.

    Having said that, Gavin certainly appears to prefer the theory that stratospheric cooling is predominantly because of reduced IR radiation from the troposphere. I would certainly appreciate if he were to have another attempt at explaining the effect.
    0 0
  6. I've just recently bought the 3rd edition of John Houghton's textbook, "The Physics of Atmospheres". I've done some perusing (which is nowhere near enough) and found that my suggestion in the first paragraph of comment #33 regarding the possible state of LTE (or non-LTE) in the stratosphere wrt the 15 micron band transitions is incorrect. For these transitions LTE is still a good approximation up to an altitude of at least ~70 km.

    However, the second paragraph of the same comment (#33) appears to be on firm (if somewhat muddy) ground. In section 4.8 of Houghton's book, "Cooling by carbon dioxide emission from upper stratosphere and lower mesosphere", it mentions that for these atmospheric levels:

    1) the temperature distribution is mainly determined by a balance between radiative cooling in the IR from CO2 and heating by photo-absorption of O3 by incoming solar radiation.

    2) an approximation known as "the cooling to space" approximation may be employed, "in which the exchange of radiation between layers is neglected in comparison with the loss of radiation direct to space".

    To me, this latter comment seems to imply that the stratosphere is largely optically thin to CO2's main IR band centered near 15 microns.

    Adding to Tom Curtis' post (#55), the stratosphere is definitely in radiative equilibrium, so your findings from Archer's radiative equilibrium model ought to be reasonable.
    0 0
  7. Daniel Bailey

    Its really more a question of optical depth for a given wavelength, the probability of it absorbing vrs emitting. Which is basically due to the number of molecules in a given area. If a molecule absorbs more than it emits, it increase its energy. If it emits more than it absorbs, it decrease its energy.

    So the further apart the molecules are, the greater the probability a given photon will travel further before it is absorbed. Its decreasing the probability of absorption vrs distance... Now if the atmosphere is opaque to say UV, but transparent to 15 micron... the UV will heat the other gases(well O3, and the O3 will heat the other gases) through absorption, and collisional energy transfer, but the probability is that energy that is lost by a molecule(O3) through emitting is replaced by absorption of radiation from a neighboring molecule.

    However, the heating of the other gases by the excited O3 will also heat CO2, causing it to emit, but if the probability is greater for it to emit more than it absorbs, just due to the distance a photon can travel between emission and absorption, it will cause a net energy loss from a given area through radiation.

    So what some of us are contending, is that above the troposphere, CO2 is a net emitter, due to the pressure.
    0 0
  8. This is a topic which I've never been able to understand to my own satisfaction.

    Let me test if I've got this right.

    1) The stratosphere features very little convection, so radiative heat transfer dominates
    2) The stratosphere is heated by UV absorption by ozone and also somewhat by IR absorption by CO2.
    3) Due to higher CO2 levels, more IR is absorbed in the troposphere, so less in the stratosphere, resulting in cooling of the stratosphere as CO2 rises.

    Is this correct ?

    It begs one question, which I think needs a full heat transfer model to answer:

    Consider a thought experiment with CO2 at zero. There is no CO2 IR absorption either in the troposphere or stratosphere. Now allow CO2 to rise.

    Initially, despite increased (from zero) tropospheric CO2 IR absorption, there will also be increased stratsopheric absorption (by definition, as it was zero)

    So we initially expect a rise in stratospheric temperature, peaking at some level of CO2, then falling as increased tropospheric absorption blocks stratospheric IR absorption by CO2.

    Is this correct ? And if so what's the CO2 level at which stratospheric temperatures start to fall ?
    0 0
  9. What this model is trying to emulate is the atmosphere of Mars without pressure compensation.
    0 0
  10. Joe Blog:
    "So what some of us are contending, is that above the troposphere, CO2 is a net emitter, due to the pressure."

    I think it is obviously a combination of things.

    Reduced Pressure: photons have a lower probability of colliding with other molecules. Also fewer collisions between molecules.

    Closer to space and a thinner atmosphere: Assuming a photon missed hitting another molecule, it also has a better chance of escaping away completely into a 'vacuum'.

    It's all down to probabilities.
    0 0
  11. Re: Joe Blog (57)

    Cool. But I think it's a bit like in the field of medicine, where there exists a world of difference between clinical studies and clinical practice. For radiative physics, CO2 and the stratosphere, I like the way Spencer Weart said it in the RealClimate post Spaceman Spiff (51) linked to earlier:
    "As for the stratosphere above the level where the heat is radiated out, who cares? It’s a very thin gas that doesn’t contain much heat energy and is easily influenced by anything. The real heat energy that we need to worry about is in the lower atmosphere. (In fact, still more in the oceans, where most of the new heat energy is going over the decades. At present we’re not radiating out quite as much as we take in, so there’s heat energy building up in the system.)"
    But I do understand the need to know. :)

    The Yooper
    0 0
  12. Camburn - 61

    The Martian atmosphere has a thermosphere and an exosphere in addition to a troposphere and a stratosphere, as does the earth.

    My very unrealistic and fictitious model has only a troposphere and a stratosphere.

    Bob
    0 0
  13. VeryTallGuy,

    Initially, despite increased (from zero) tropospheric CO2 IR absorption, there will also be increased stratsopheric absorption (by definition, as it was zero)


    This isn't true, because CO2 in the stratosphere is a net emitter (i.e. has a cooling effect). It might not be if the troposphere let enough IR through to make it a net absorber, but it doesn't, so the combination of the tropospheric CO2 blocking the appropriate IR band with the stratospheric CO2 primarily emitting IR causes the stratosphere to cool.

    Hence, CO2 only cools the stratosphere (at least at the levels we are discussing -- I'm unsure what would happen if CO2 concentration approached very high levels, if CO2 would at some point become a net absorber rather than a net emitter). There is no point where CO2 causes the stratosphere to warm.

    At least, this is my understanding.
    0 0
  14. Sphaerica

    that was where I had got to before this post - that forgetting any incoming radiation the stratosphere will act as a blackbody and emit thermal radiation. However, in the absorption lines for GHGs ie CO2, there will be enhanced emission.

    If this is the mechanism for cooling though, why the need to consider tropospheric absorption at all as in the above post? Surely it doesn't matter what happens in the troposphere, additional CO2 always cools the stratosphere?

    I have a feeling I'm being obtuse somewhere, but reading Gavin Schmidt's error strewn RC post on the topic cheered me up - at least I'm in good company.
    0 0
  15. VeryTallGuy,

    I would be very, very hesitant to describe anything Gavin writes as even erroneous, let alone "error strewn." I would be more likely to assume that I don't completely understand his words, and so to hunker down and quietly research more.

    That said, we are all waiting for (hopefully) some input from him on the issues.

    However, my understanding is that, as to the need to consider tropospheric absorption, if enough IR makes it through from the surface (i.e. is unblocked by the troposphere), then CO2 in the stratosphere could change from a net emitter to a net absorber.

    It all comes down to probabilities: is a CO2 molecule more likely to gain energy (heat) through collision with other molecules, and lose it through emission of IR, or is it more likely to gain energy through absorption of IR, and lose it through collision with other molecules?

    These probabilities are affected by the concentration of CO2, the overall density of the stratosphere, and the levels of incoming radiation (UV from the top, IR from the bottom). Less IR = less chance of heat through absorption, while less dense = more chance of emission through radiation rather than loss through collision. The combination = cooling.
    0 0
  16. There's been a minor revision to my post.

    I changed the unites on the ordinate from "watts/square meter" to "watts/square meter wavenumber" or watts per square meter per wavenumber.

    Now the area under the curve represents watts/square meter which makes more sense.

    Bob
    0 0
  17. Sphaerica @65:

    To be fair to VeryTallGuy -- Gavin wrote and re-wrote that post on RealClimate several times, and in my opinion it still leaves things rather murky (as some of the comments there indicate). No one knows everything about anything, and the deeper one probes nature the more subtle she is. So while I'm not taking anything away from Gavin's post, I'm also not inclined to assume that it is error free (or isn't lacking in clarity).
    0 0
  18. Spaceman Spiff - 67

    This was the reason for my blog. Whereever you go on the web, it is just as murky. However, Gavin is explaining it as clearly as possible considering that he is trying to explain it without talking about the absorption spectrum of CO2 or other greenhouse gas.

    Bob
    0 0
  19. Sphaerica

    On Gavin, I hasten to add I was in absolutely no way trying to imply any superior understanding on my part - I wish ! Merely a reflection of his own sub-heading: "This post is obsolete and wrong in many respects."(!)

    From your post

    "if enough IR makes it through from the surface (i.e. is unblocked by the troposphere), then CO2 in the stratosphere could change from a net emitter to a net absorber. "

    If this is true, and Bob's post implies it is, then there would, I think, be a maximum in the stratospheric temperature vs CO2 relationship.
    0 0
  20. Spaceman Spiff 67

    Yes, those threads were an "interesting" read... well for myself, i will go for Veerabhadran Ramanathan published work in this area over Gavin's postings at RC. At least until someone can explain where he has erred in his troposphere/stratosphere radiative interaction studies. Or how im misinterpreting them.
    0 0
  21. VeryTallGuy,

    Just to clarify, I probably shouldn't have said that if enough IR makes it through from the surface, CO2 could become a net absorber. That may not be true. It's more nuanced than that. The stratosphere could be so rarefied that no matter how much IR you pound it with, most of it will just get through, and CO2 would anyway still emit what it absorbs before it has a chance to collide with anything else and pass it on. So it could/would still be a net emitter in the end, but just with a smaller differential, and with some IR redirected back to the surface.

    In fact, when I think about it, this would actually cause the upper troposphere to warm more (as some of the IR absorbed by the stratosphere would be re-emitted back down), although maybe only by a meager amount, without really changing the temperature of the stratosphere.
    0 0
  22. VeryTallGuy @ 69

    "if enough IR makes it through from the surface (i.e. is unblocked by the troposphere), then CO2 in the stratosphere could change from a net emitter to a net absorber. "

    Hmmm yes. I was considering responding to that myself. If the stratosphere was blasted with continuous 15micron radiation, it would warm... until the input stopped, then it would cool... Its not going to make it more opaque.

    We have a bad habit of thinking of radiation as lil balls pinging around(i do it). Its light, its emitted in an expanding sphere from the emitting molecule. And it absorbs, the parts of radiation that the molecule intersects of the expanding sphere's of other molecules radiation.

    So when the molecules are spaced further apart, they absorb smaller proportions of the emitted radiation from their neighbors. So it increases the net loses. So increasing the IR input will increase the energy absorbed. It will however, not change the fact, that the molecules will receive less energy from their neighbors, than what they themselves emit.

    And the troposphere dosnt "block" IR... it increases its path length, if there were no GHG's in the troposphere, but the same quantity in the stratosphere, all it would change is the T of the troposphere to the effective radiating T of the energy received (-18C) But the quantity of radiation leaving the troposphere, would be the same as at equilibrium today. It would just be receiving it from the surface, instead of the variable altitudes caused by the lower atmospheres opacity to different wavelengths.
    0 0
  23. "i will go for Veerabhadran Ramanathan " - yeah! However, these posts and others (I like Eli Rabbit's attempt) are all about trying to explain this without the mathematics. Ramanathan is where to go for the maths.

    My relativity lecturer used to insist that you havent understood something unless you can give a qualitative answer without doing the maths (but then do the maths to check!). Its always hard however to produce a good explanation without the maths for those who wont/cant do the maths first and I take my hat off to all those who are trying to do so. Clear explanation is a service to humanity.
    0 0
  24. Joe Blog:
    "We have a bad habit of thinking of radiation as lil balls pinging around(i do it). Its light, its emitted in an expanding sphere from the emitting molecule. And it absorbs, the parts of radiation that the molecule intersects of the expanding sphere's of other molecules radiation."


    There is nothing wrong with visualising electromagnetic radiation in quantised 'photon' form.
    Also a photon is emitted in a specific direction, the reason you see a point source is because billions of photons are emitted per second in a 'radiating sphere'. You 'receive' just a small number of them.
    The 'signal' gets weaker the further away you are, because the emitted photons become more dispersed (fewer photons per square metre).
    0 0
  25. "*It is recognized that a fictitious planet as described herein is a physical impossiblity. The simplicity of this planet serves to explain a concept that would not be easily explained using a more complex and realistic model."

    That in a nutshell seems to be the problem.
    0 0
  26. Humanity Rules 75

    Why?
    0 0
  27. where can i find a long term graph of the troposphere temperatures and data showing that its temperature increase is correlated with increased CO2 in the atmosphere? the following
    link
    doesn't show it so there must be some other data that is validating this thesis.

    and by the way, i enjoyed this post, well done.
    0 0
  28. Re: garythompson (77)

    Try this:



    (BTW, the zero-year baseline is 1950)

    Source here.

    Note that there exists much more than mere charts establishing a link between rising CO2 levels and rising temperatures.
    -----------------------------------------------------------------------------------------
    [ - Edit - :

    In the graph I supplied, temperature changes occur a few hundred years before CO2 changes. CO2 does contribute to the temperature increase but as a feedback rather than a forcing. CO2 can act as a forcing (and has, post-1970 or so), but it's effects as documented in the paleo-record have been as a feedback to temperatures.

    The biggest exception to this is the PETM, which (unfortunately) is beginning to look more and more like the best comp for the modern era. Time will tell.

    - End Edit - ]
    -----------------------------------------------------------------------------------------

    The Yooper
    0 0
  29. Sphaerica 71

    "it could/would still be a net emitter in the end, but just with a smaller differential, and with some IR redirected back to the surface."

    I wouldn't dispute this, but if it is true, why do we need to consider the troposphere at all, as in the original post? Surely if CO2 is always a net emitter, then adding it will always reduce the temperature, regardless of what spectrum of radiation comes up from the troposphere?

    Your explanation was also my original understanding of statospheric cooling - that CO2 made the stratosphere more efficient at radiating than a blackbody by converting thermal energy to radiation at the absorption bands. To maintain the same overall emission, the temperature drops. But Bob's post says it's a whole lot more complex than that.

    Actually, as I write the last paragraph, maybe that's it - the internal radiative emission from the stratosphere (as opposed to mere transmission of ground level or troposheric radiative heat) actually falls because of reduced tropospheric tranmission in the CO2 absorption band.

    So are there two effects:

    1) increased emission in the CO2 emissions bands increases thermal to radiative heat conversion and thereby reduces the temperature necessary to maintain overall heat balance

    AND

    2) decreased absorption in the same spectrum because CO2 in the troposphere has already taken it out reduces the total heat input to the stratosphere
    0 0
  30. Re #40/41 Bob Guercio you wrote:-

    "the fictitious planet that I am using is a physical impossibility"

    You don't need to imagine a fictitious planet to see that O2 is essential for a 'stratosphere effect'. Venus has no stratosphere, the image below is a temperature profile of the Venusian atmosphere from 30km to 100km. (the lower part contains various extrapolations to the surface, further, you can open the image in another application to get a better quality). The green/red horizontal lines 2/3 up on the left are at 50-60km altitude and a pressure detween 1000 and 2000mB - thus the profile is similar in pressure terms to Earth.
    0 0
  31. Humanity Rules:
    "That in a nutshell seems to be the problem."


    Then I hope you are not a teacher.
    You don't go in guns blazing and teach someone who knows nothing about science, the complexity of a subject that only an experienced scientist knows. You start with simplicity and add complexity as the student has learnt the simpler principles.

    That applies just as much to climate science, as it does to carpentry, stonemasonery or welding.
    0 0
  32. Daniel Bailey - 78
    garythompson - 77

    This graph does show a correlation between CO2 and temperature. However, it may not show the correlation that you want.

    In this graph, temperature changes occur a few hundred years before CO2 changes. CO2 does contribute to the temperature increase but as a feedback rather than a forcing.

    This is often used by contrarians to debunk the present day issue of CO2 causing the temperature to rise.

    Bob
    0 0
  33. After carefull consideration, I believe the explanation of stratospheric cooling given in the original post is simply wrong.

    To see this, consider a hypothetical planet whose atmosphere is completely transparent at all wavelengths of electromagnetic radiation. In this case, its surface temperature will be its temperature as measured from space, ie, its effective temperature. The temperature at any point in the atmosphere above the surface will be less than the effective temperature, and the temperature profile of the atmosphere will be defined by the adiabatic lapse rate up to the thermosphere. (Like Venus, see graphic in 80 above, it will have no stratosphere.)

    Now, as we introduce CO2 into the atmosphere, what happens is that the altitude of the effective temperature gradually increases in height. As the temperature profile is still defined by the lapse rate, the temperatures at every altitude up to the thermosphere will also increase.

    Even if we exclude convection as a means of transfering energy in the atmosphere, and hence exclude the adiabatic lapse rate as a temperature profile, radiative transfer in an optically absorbing atmosphere will generate a lapse rate, indeed, typically a shallower (greater change in temperature for a given change in altitude) lapse rate than the adiabatic lapse rate. Therefore this reasoning should still hold.

    Looked at differently, and using Earth as our model, we need to consider that the effective altitude of radiation, ie, the average altitude from which radiation reaches space, lies several kilometers below the tropopause. Therefore most outgoing radiation at the tropopause reaches space, and the Beer-Lambert law is an appropriate approximation of the effect of changing CO2 concentrations in the stratosphere. Given that, then if we double the CO2 concentration we also double the amount of IR radiation absorbed by CO2 in the stratosphere. The amount of IR radiation outgoing from the tropopause will not itself double, but infact will slightly fall because the atmosphere is optically thick below the tropopause. Consequently, although the net radiation entering the stratosphere will fall in this scenario, the amount absorbed in the stratosphere will increase.

    Of course, the amount of IR radiation emitted at a given temperature will also double with doubling of CO2 in the stratosphere. The result is that, if the temperature of the stratospheric CO2 is less than the brightness temperature radiation emitted by CO2 in the troposphere, it will warm. If it is greater it will cool.

    Of course, had the temperature in the stratosphere followed the adiabatic lapse rate, it would have been less than that of the troposphere; and increasing CO2 would warm the stratosphere, all else being equal. But all else is not equal - the stratosphere is much hotter than the upper levels of the tropospere because of the absorption of UV radiation by ozone. Therefore, I would have to conclude that stratospheric cooling with increased CO2 is primarilly due to increased efficiency at radiating away energy absorbed by ozone due to increased concentration of CO2. There would be a small additional boost due to reduced outgoing radiation of IR in the 15 micron (CO2) band; but that is ony a secondary cooling effect, and would have been a warming effect where it not for the presence of ozone in the stratosphere.

    Having said all that, I now hope some one will knock some holes in my reasoning.
    0 0
  34. damorbel -

    Venus does have an atmosphere.

    http://adsabs.harvard.edu/abs/1983KosIs..21..205A
    0 0
  35. Re #84 you wrote:-
    "Venus does have an atmosphere."

    What I wrote was:-
    "Venus has no stratosphere."
    0 0
  36. Bob, neither Venus nor Mars have a stratosphere:



    But, contra damorbel, the absorber of shortwave radiation does not have to be O3 (or O2), as shown by the examples of Titan and the gass giants:
    0 0
  37. Tom Curtis @83

    " Therefore, I would have to conclude that stratospheric cooling with increased CO2 is primarilly due to increased efficiency at radiating away energy absorbed by ozone due to increased concentration of CO2. There would be a small additional boost due to reduced outgoing radiation of IR in the 15 micron (CO2) band; but that is ony a secondary cooling effect, and would have been a warming effect where it not for the presence of ozone in the stratosphere"

    vs my #79

    "So are there two effects:

    1) increased emission in the CO2 emissions bands increases thermal to radiative heat conversion and thereby reduces the temperature necessary to maintain overall heat balance

    AND

    2) decreased absorption in the same spectrum because CO2 in the troposphere has already taken it out reduces the total heat input to the stratosphere "

    I think we are in agreement, so clearly we've both got something wrong ;-)
    0 0
  38. Tom Curtis:
    "To see this, consider a hypothetical planet whose atmosphere is completely transparent at all wavelengths of electromagnetic radiation. In this case, its surface temperature will be its temperature as measured from space, ie, its effective temperature. The temperature at any point in the atmosphere above the surface will be less than the effective temperature, and the temperature profile of the atmosphere will be defined by the adiabatic lapse rate up to the thermosphere. (Like Venus, see graphic in 80 above, it will have no stratosphere.)"


    Not quite correct. Although this is an interesting game.


    If the atmosphere were transparent to electromagnetic radiation, the only way of transporting energy would be by conduction and convection. The only lapse rate would be as a result of convection and you may very well have an 'inverse' lapse rate, eg. hotter at the top over time.
    In fact it would get hotter and hotter, because the atmosphere wouldn't be able to emit the accumulating energy to space.

    Transparency = no absorption or emission
    0 0
  39. Re: Bob Guercio

    You are very much correct, sir. While I am aware that pre-1970 (or so) CO2 was primarily a lag/feedback to temps, I was remiss in not taking the time to point that out in my comment above.

    I will add verbiage to that effect in my comment.

    Apologies for adding to your workload. :)

    The Yooper
    0 0
  40. @Tom Curtis post 83

    Looking at your post and some other explanations about stratospheric cooling I think your description is more accurate than the post.
    The dominating factor for the cooling is not less IR radiation reaching the stratosphere from below, but the increased emission by increasing CO2 concentration. The difference between fig. 2 and fig. 3 show the cooling effect from less IR coming from below can only be slight.
    Gavin's post at real climate does seems to suggest greater concentrations of greenhouse gases warm the atmosphere up to a certain altitude and above that they cool as the balance between absorption from the surface and emission into space changes, as convection dominates in the troposphere though you don't get to see this effect in the troposphere.

    My post is only my understanding and is probably wrong!
    0 0
  41. damorbel - 85

    An editorial error on my part. I meant to say "Venus does have a stratosphere".

    http://adsabs.harvard.edu/abs/1983KosIs..21..205A
    0 0
  42. Mighty Drunken - 90

    In the steady state, which is what my blog was all about, there is not less IR energy reaching the stratosphere from below. The same amount of IR reaches the stratophere.

    However, the nature of this radiation is different. There is less in the frequency range that CO2 absorbs and more in the range that sails past the CO2 totally unaffected by it.

    Bob
    0 0
  43. The Ville - 81

    In addition to what you say about teaching, it sems that virtually everything in Physics depends upon ridiculously simple models.

    Bob
    0 0
  44. The Ville @88, my understanding is that if the atmosphere were entirely transparent to radiation, all energy flows from or to it would take place at the surface. Therefore, it would warm until the energy flows from the surface to the lowermost layer of the atmosphere equalled the energy flows from that layer to the surface. That should be when the surface and the lower most layer have the same temperature.

    The rest of the atmosphere would derive its heat from the lowest layer, primarily by convection. That convection would establish the temperature profile at the adiabatic lapse rate. Hot air rising would still cool as it expands from reduced pressure, ensuring that the upper atmosphere (excluding the thermosphere) remained cooler than the lower atmosphere at all times. (The situation is a little more complex if we include heat transfer to the poles.)

    Even if a hot air parcel rose to the top of the atmosphere at a temperature above that defined by the lapse rate, it would prevent more heat transfers to the upper atmosphere by convection at its location, and gradually cool back to the adiabat by conduction and turbulent eddies. If such hot parcels of air were generated frequently enough, and cooled slowly enough, then the lapse rate could be less than the adiabat; except that even in this case it would be defined by the adiabat for periods of peak surface temperature.

    Again, please correct me where I am wrong.
    0 0
  45. Bob Guercio @93, I understood the stratosphere to be a region of the atmosphere characterised by an inverted lapse rate (it gets hotter with greater altitude) in which convection played almost no role in heat transfer, allowing strata of distinct temperatures to form. Based on the lapse rates observed on Venus, there is no such region on Venus.

    On the other hand, the article you link to, and several others I found by googling "Venus" "stratosphere" do in fact refer to Venus' stratosphere. So, are you and they using a different definition to mine, or am I missing something?
    0 0
  46. I don't know but I'll give it a swag based upon the definitions below which I ran across on the web. Note that there seems to be many definitions and I didn't explicity see the one that I am guessing at.

    Maybe it depends upon which layer you are talking about regardless of the chemistry or any other characteristic. Apparently atmospheres on all planets are layered and perhaps the first layer is the troposphere, second the stratosphere, third the mesosphere and fouth the thermosphere.

    By the way, a swag is a highly technical term. It means sophisticated wild ass guess.

    Bob

    Definitions

    .layer of the earth's atmosphere located above the troposphere and below the mesosphere.

    Definitions of mesosphere on the Web:

    •the atmospheric layer between the stratosphere and the thermosphere
    0 0
  47. Bob Guercio at 00:47

    At what what wave lengths is the increased emission from? As i and others have stated, CO2 & H2O are both net emitters in the stratosphere(2:1), where as O3 is a net absorber(9-10 micron). So to examine this we need a little more detail. (the resolution in your graphs in the main article, make it hard to make out)
    0 0
  48. Tom Curtis@94

    Actually thinking about it, if the atmosphere was 'transparent' to electromagnetic radiation but the surface wasn't, then the electromagnetic radiation reflected and emitted by the planets surface would go straight back out to space!

    Basically it would be similar to the Moon, but with a small amount of energy heating the atmosphere via conduction.

    So, yes my example was wrong, but so is your account.

    Goodness, I was really wondering where all the energy was going. But your fictitious model still obeys some basic laws.
    0 0
  49. Re my last comment.
    Actually your example @94 was roughly correct, but I was forgetting that most of the energy would be reflected/emitted back to space through the transparent atmosphere.

    A small amount of energy would warm up the atmosphere via conduction. Probably only close to the surface though.
    0 0
  50. Re #96 Bob Guercio you wrote:-
    ".layer of the earth's atmosphere located above the troposphere and below the mesosphere."

    That's a rather broad definition, don't you think?
    A bit like beauty, in the eye of the beholder!

    Surely the UV absorption, the temperature inversion and the lack of convection are all relevant matters when considering the thermal properties of the stratosphere?
    0 0

Prev  1  2  3  4  5  Next

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.



Get It Here or via iBooks.


The Consensus Project Website

TEXTBOOK

THE ESCALATOR

(free to republish)

THE DEBUNKING HANDBOOK

BOOK NOW AVAILABLE

The Scientific Guide to
Global Warming Skepticism

Smartphone Apps

iPhone
Android
Nokia

© Copyright 2017 John Cook
Home | Links | Translations | About Us | Contact Us