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The weirdest millennium

Filed under: — stefan @ 29 May 2007

Much research effort over the past years has gone into reconstructing the temperature history of the last millennium and beyond. The new IPCC report compiles a dozen reconstructions for the temperature of the Northern Hemisphere (including of course the original “hockey stick” reconstruction, despite opposite claims by the Wall Street Journal). Lack of data does not permit robust reconstructions for the Southern Hemisphere. Without exception, the reconstructions show that Northern Hemisphere temperatures are now higher than at any time during the past 1,000 years (Figure 1), confirming and strengthening the conclusions drawn in the previous IPCC report of 2001.

Fig. 1: Figure 6.10 (panel b) from the paleoclimate chapter of the current IPCC report (see there for details).

“Climate sceptics” do not like this and keep coming up with their own temperature histories. One of the weirdest has been circulated for years by German high-school teacher E.G. Beck (notorious for his equally weird CO2 curve). This history shows a medieval warm phase that is warmer than current climate by more than 1 ºC (see Figure 2). So how did Beck get this curve?


Fig. 2, modified from E.G. Beck (we added the green parts).

The curve is a fake in several respects. It originally is taken from the first IPCC report of 1990: a scan of the original is shown in Figure 3. At that time, no large-scale temperature reconstructions were available yet. To give an indication of past climate variability, the report showed Lamb’s Central England estimate. (Unfortunately this was not stated in the report – an oversight which shows that IPCC review procedures in the early days were not what they are now. We will post in more detail on the history of this curve another time.)


Fig. 3. The past millennium as shown in the first IPCC report of 1990, before quantitative large-scale reconstructions were available. This curve was based on Lamb’s estimated climate history for central England.

But Beck did not stop at simply using this outdated curve, he modified it as highlighted in green in Figure 2. First, he added a wrong temperature scale – the tick marks in the old IPCC report represent 1 ºC, so Beck’s claimed range of 5 ºC exaggerates the past temperature variations by more than a factor of three. Second, the original curve only goes up to the 1970’s. Since then, Northern Hemisphere temperatures have increased by about 0.6 ºC and those in central England even more – so whatever you take this curve for, if it were continued to present, the current temperature would be above the Medieval level, as in the proper reconstructions available today. As this would destroy his message, Beck applied another fakery: he extended the curve flat up to the year 2000, thereby denying the measured warming since the 1970s. With this trick, his curve looks as if it was warmer in Medieval times than now.

When approached directly about these issues, Beck published a modified curve on a website. He changed the temperature range from 5 ºC to 4.5 ºC – but he shortened the arrow as well, so this was just cosmetics. He also added instrumental temperatures for the 20th Century at the end – but with his wrong temperature scale, they are completely out of proportion. (In fact his version suggests temperatures have warmed by 2 ºC since 1900, more than twice of what is actually observed!)

Beck goes even further: in a recent article (in German), he has the audacity to claim that his manipulated curve is right and the more recent scientific results shown by IPCC are wrong. And for years, he has offered his curve on an internet site (biokurs.de) that distributes teaching materials for schools, with support from German school authorities. It is quite likely that his fake curve has been shown (and will continue to be shown) to many school children.


507 Responses to “The weirdest millennium”

  1. 401

    Re #194 & #394

    Deja,

    You were correct. Itis just that the later data sets are more accurate.

    The thermometer was not invented until the 1600s, so any temperature reconstructions before that time have to use “proxy” data such as tree rings or isotope ratios in ice cores. Even the short (300 years) thermometer record is unreliable, because thermometers were not available globally as they are now.

    The proxy records are published where they overlap the thermometer record, as that gives an indication of how reliable they are. The proxy record also gets less reliable as you go back in time, since there is less earlier data.

    The lines on the graph are just the results of different sets of scientists investigating their speciality. If you download the PDF linked in Figure 1 above( http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Pub_Ch06.pdf ) you will find that the each of the lines is referenced in Table 6.1 there. The PDF is from the latest scientific report by the IPCC, and as such is an up to date review of the current knowledge on Paleoclimatology.

    Does this answer your question?

    Cheers, Alastair.

  2. 402

    [[But if the atmosphere is in equilibrium there should be no net loss of radiative energy to warming the neighboring air molecues. And if the greenhosue gas molecule re-radiates quickly there will not be much time for kinetic energy transfer. So, it appears there will be no significant warming of the atmosphere by this method]]

    The excited molecule is likely to strike another, non-excited molecule, transferring some of the energy to kinetic energy in the collidee. With the molecules moving faster, the atmosphere does heat up.

  3. 403

    [[Thus the change in water vapor pressure acts as a positive feedback system, water vapor is converted to snow and so the vapor pressure above the ice is always less than over the sea. There is a net transfer of water from the liquid sea to the soild ice.]]

    Amazing, then, that the whole ocean hasn’t frozen over. Once again, DM, your argument rests on ignoring part of the process, in this case the mechanisms of ice loss (you know, glaciers, calving, icebergs, sublimation, melting at top due to impurities and sunlight, melting at the bottom due to changing pressure effects, etc.).

  4. 404

    [[ It did this before humans evolved and will do it after we are extinct. As pre-industrial CO2 stayed at about 280 ppm for a long time, we must look for a mineralization pathway that gets rid of 0.5 GT per year. If it is a cation/carbonate process, it might be nice to know something about the order of the reaction. ]]

    It’s part of the silicate-carbonate cycle, to be specific, weathering. The basic paper on the subject is here:

    http://www.geosc.psu.edu/Courses/Geosc320/walker.pdf

  5. 405
    DocMartyn says:

    The picture in that collection shows the seasonal rates of CO2 change are >10 time the slow increase in CO2

    http://www.globalwarmingart.com/images/8/88/Mauna_Loa_Carbon_Dioxide.png

    This means that the influx rate-efflux rate April to Oct is greater than 10X the yearly (overall) influx-efflux rate; so it is reasonable to describe the system as being at steady state. From this you can calculate the influx, efflux and size of the two sinks (if we approximate to as two sink system atmosphere (Troposphere) and not atmosphere(Troposphere)).

    Now we know the amount of CO2 WE are adding and we know what the steady state CO2 level is after we have added CO2, so we can workout what the influx rate was before we strated burining all the fossil fuel. Thake the information from these plots:-

    http://www.globalwarmingart.com/images/5/52/Carbon_History_and_Flux_Rev.png

    Plot the level of [CO2] ppm vs Human CO2 emissions.

    http://i179.photobucket.com/albums/w318/DocMartyn/Atmosvsinput.jpg

    When x=0 we have an intercept of what the [CO2] level would be without human CO2 in the atmosphere; it comes out at about 280 ppm. So far so good.
    The slope of the graph is 1/atmospheric efflux and gives about 9.2 years. This is also a “good” number as it is just about perfect for the disappearence of 14CO2 from the testing of atomic weapons in the 50’s and 60’s.
    It puts the “natural” (non-human) annual atmospheric sink as 21 GT p.a. and the “natural” CO2 input into the troposphere, also at 21 GT.
    Using this data you can estimate the effects of further CO2 emissions on the atmospheric [CO2]ppm.

    http://i179.photobucket.com/albums/w318/DocMartyn/Effectsoffuturerelease.jpg

    ———————————————————————-
    #398 “Getting rid of the accumulated excess by natural mineralization will require geological time scales. Tens of thousands to millions of years. Using chemical or physical methods for mineralization requires significant energy, which we would get by?”

    That is not quite true, lets take a simple mineralization reaction:-
    3H2O + 2[CO2] + CaSiO3 —> Ca2+ + 2HCO3(1) + 4H+ + SiO4(4-)

    now in the reaction the rate constant is going to be third order [CO2]^2[CaSiO3] = k.
    Increasing the level of CO2 by a factor of 2, increase the rate by a factor of 4. So double the amount of CO2 and the rate at which is disapears increases by a factor of four. Many of the mineralization reactions have the same rate order. You will also find that plants and photosynthetic microorganisms have a non-liner response to CO2 levels. Plants do a lot of work to fix CO2, relitively small changes in CO2 make it much easier for them to fix CO2, and so they grow much more quickly at 360 ppm, than they do at 280 ppm. The biotic sink rate may be increased in the same time frame as the burning of fossil fuels.
    It has been known for a long time that C4 photosynthetic plants do much better at low CO2 levels than do C3 plants. The 13C changes in the atmosphere may indicate some biase in the selection of C3 plants over C4 plants either by human selection (draining land, growing crops and planting trees) and CO2 changes (fertalizing C3 plants).

  6. 406
    Ray Ladbury says:

    Alastair, I think it was you who claimed that the vibrational modes of CO2 were frozen out at room temperature. While that is true if you have a gas in eqb., in the atmosphere, the gas must also equilibrate with the IR radiation field. Thus, while the vibrational mode will not be excited by collisions, it maybe relaxed thereby, thus imparting kinetic energy. So, I do believe atmospheric heating is possible.

    Ike, thanks. I think the analogy is to a well insulated house, which will look dark in IR and a poorly insulated house, which will light up like a Christmas tree. Venus atmosphere has a great R value.

  7. 407
    Ray Ladbury says:

    DocMartyn
    1) The CO2 may leave the atmosphere (temporarily) after 9 years, but where does it go? Into plants, which die and decay, yielding their carbon back to the atmosphere (much initially as CH4 which is a more effective ghg). Into the ocean, where it stays until it goes back to the atmosphere, since most of it does not overturn into the deep oceans. Ther is no process other than geology that gets rid of the CO2 long term. And we have a measure of how quickly geology works from the paleoclimate record, and the answer is centuries to millennia. And as to your discussion of plants, do we really want to live in a world with a lot more poison ivy?

  8. 408
    Hank Roberts says:

    Is that image on your website one you put together from other info? Where are the sources?
    I searched CDIAC’s image file and did not find it.
    (It’s “anthropogenic” not “anthropomorphic” carbon discussed here; the latter word describes a golem, I think.)

    This may help:

    http://www.treatiseongeochemistry.com/contents/sample8.pdf

    The Contemporary Carbon Cycle
    R. A. Houghton
    Woods Hole Research Center, MA, USA

    —– excerpt ====

    “This chapter addresses, first, the reservoirs and natural flows of carbon on the earth. It then
    addresses the sources of carbon to the atmosphere from human uses of land and energy and the sinks
    of carbon on land and in the oceans that have kept the atmospheric accumulation of CO2 lower than
    it would otherwise have been. The chapter describes changes in the distribution of carbon
    among the atmosphere, oceans, and terrestrial ecosystems over the past 150 years as a result
    of human-induced emissions of carbon. The processes responsible for sinks of carbon on land
    and in the sea are reviewed from the perspective of feedbacks, and the chapter concludes with some
    prospects for the future.

    The basic aspects of the global carbon cycle have been understood for decades, but other aspects,
    such as the partitioning of the carbon sink between land and ocean, are being re-evaluated continuously
    with new data and analyses. The rate at which new publications revise estimates of these
    carbon sinks and re-evaluate the mechanisms that control the magnitude of the sinks suggests that
    portions of this review will be out of date by the time of publication.”

    —– end excerpt =====

    He’s right about the latter one. Both the info on ocean pH changes and the reports on the shutdown of the carbon sink in the Southern Ocean have come in since that publication, for example. But he makes clear the basics of this area of science.
    The whole chapter is available to download and read. I recommend it as a starting point.

  9. 409
    Don Fontaine says:

    RE: 283
    Gavin, thanks for setting me straight on my misinterpretation of the Lu article. I got the complete article but it is a bit beyond me, PhD Physical Chemistry (far infrared and raman spectroscopy of molecular crystals) Mich State 1983.

    So if I understand it the Lu article provides evidence for the LACK of contribution of cosmic rays to climate effects, because the lack of a longer term (1950 to present) trend in solar geomagnetic activity (Figure 1b in Lu et al J Geophysical Res vol 112 D11109 doi:10.1029/2006JD007864, 2007

    Therefore no trend in stratospheric temperature would be seen if cosmic ray mechanisms were the primary driver and this is contradicted by the observation of a longer term trend showing a cooling stratosphere (as reported in AR4). This cooling is consistent with CO2 forcing as reported in AR4.

  10. 410
    Hank Roberts says:

    Today’s news on ocean pH changes here:

    http://coralnotesfromthefield.blogspot.com/

    “NSF today announced that the first buoy to monitor ocean acidification has been launched in the Gulf of Alaska. If you’ve forgotten why the threat of ocean acidification keeps coral reef conservationists awake at night, refresh your memory here.

    “Anchored in water nearly 5,000 meters deep, the buoy (pictured …) began to transmit data via satellite once it hit the water. … The instrument package attached to the buoy will, however, measure the air-sea exchange of carbon dioxide, oxygen and nitrogen gas in addition to the pH of the surface waters. Information from this buoy will lead to a better understanding of ocean acidification–a growing threat to the world’s oceans–by helping scientists determine exactly how physical and biological processes affect carbon dioxide in the north Pacific Ocean, said Fred Lipschultz, program director in NSF’s division of ocean sciences.”

  11. 411
    Timothy Chase says:

    Ray Ladbury (#381) wrote:

    The excited molecules can relax in different ways. They can collide with other molecules, and impart thermal energy to them–that keeps the energy in the lower atmosphere. They can re-radiate back toward Earth. That also keeps the energy in the lower atmosphere.

    Blair Dowden (#400) responded:

    You are describing two separate warming processes. Again, I would like to know the relative significance of the transfer of thermal energy directly to the atmosphere. The greenhouse gas models I have read about (including Gavin’s Learning from a Simple Model) do not mention it, they only talk about IR radiation warming the ground. You then say…

    There is a great deal which the “simple model” leaves out. For example, Gavin treated the atmosphere as if it consisted of a single, thin shell. He omitted any mention of what wavelengths CO2 absorbs and re-emits infrared as a greenhouse gas. He didn’t deal with the evaporation of water and how this amplifies the effects of carbon dioxide. Nor should he – because it is a simple model intended to give people a handle on the central principles behind the greenhouse effect – principally that the surface (both land and water, presumably – although he does distinguish between these) radiates thermal radiation, some of which is absorbed and re-emitted by the atmosphere, which then increases the amount of radiation that the ground is receiving. Ultimately, the entire system will reach equilibrium, with the amounts of incoming thermal energy entering the system, the surface and the atmosphere equaling the amount of energy which is outgoing, but only by raising temperature of each.

    Ray Ladbury (#381) wrote:

    …because the atmosphere is cold here [upper atmosphere], the density of IR photons is lower than it is in the lower atmosphere.

    Blair Dowden (#400) responded:

    I thought the density of photons was lower because they had been absorbed lower in the atmosphere and converted to thermal energy, whether on the ground or in the air. If the temperature has anything to do with how a greenhouse gas emits IR radiation, I would like to know what it is.

    Thermal energy absorbed at the surface has to reach equilibrium where the amount of upwelling radiation equals the amount of downwelling radiation, otherwise the temperature would continue to increase indefinitely. The question is: what temperature has to be achieved before the amount of thermal radiation that in upwelling will equal the downwelling radiation.

    Blair Dowden (#400) wrote:

    Re #378: Ike, thanks for the information of the broadening of the rotational water vapor bands under atmospheric pressure. I would thus assume that the graph of overlapping water vapor / carboin dioxide aborption bands on this NASA page is misleading. They do not say where this was measured – at the surface or is it an average of the entire atmosphere.

    It isn’t misleading – that information is simply omitted. Otherwise you could make the same claim regarding the weather that day – including air pressure and temperature. And the list for such things as the intensities at different parts of the spectra could be quite long – as this would involve cloud cover, humidity, pressure and temperature of the atmosphere – both in the given location and at various distances in various directions – much of which they won’t have anyway. But people with a knowledge of physics will be aware of all this anyway – and that to a fair extent, the information which is given omits these other factors.

    Blair Dowden (#400) wrote:

    Re #388: Timothy, you state that the effect “of carbon dioxide and water vapor (in terms of radiative forcing) is actually greater than the sum of their individual effects, but I do not agree with your explanation of this statement. I do not think what happens after the photon is aborbed is relevant to the question. The effect is logarithmic, not additive – it does not matter if you add another unit of water vapor or carbon dioxide.

    What happens to the photon (although it is not the same photon – but I suppose that it simplifies the narrative if one treates it as such) is relevant since the photon (or alternatively, thermal energy may be re-emitted back toward the ground – which is essential to the greenhouse effect. Likewise, if the photon is absorbed and re-emitted towards space, this is relevant – since it is only by means of such re-emission that some of the thermal radiation will ever leave the system. Similarly, if it is absorbed and re-emitted by different parts of the atmosphere, this is relevant.

    However, this is already built into the “logarithmic effects.” But at the same time, it does matter whether the unit of gas is water vapor or carbon dioxide – if for no other reason than carbon dioxide has a much longer residence time.

    Blair Dowden (#400) continued:

    I do share with you the desire to come up with a qualitative “story” of how the greenhouse effect works based on the physical processes involved. This is different than Gavin’s simple model which emphasises the mathematics. I am learning a lot of pieces to the puzzle, but a coherent picture remains elusive.

    This might explain why you are having difficulty grasping much of the coherent “picture.”

    In any case, a “story” can either be a true story or a fictional one. By “story,” I simply mean a “narrative.” Being a narrative, it will procede linearly, and there are some aspects which will be told and other aspects which will be left out – depending upon what the narrator wishes to communicate, what the teller thinks is important, given the context. You for example have a narrative of how you came to be where you are at this moment, the events which are worth remembering, and a rough sequence in which they happened. Likewise, you have a narrative of how the world came to be what it is now.

    Narratives are, in one form or another, necessary, and qualitative narratives which divide the world into actors, places and times are necessary before one can begin any kind of quantitative analysis, and longer narratives of one kind or another are necessary if one is to grasp what the mathematics means and are often instrumental in picking up much of the mathematics, at least early on. Likewise, even a mathematical proof or the process of solving an equation is a narrative of a sort.

  12. 412
    DocMartyn says:

    #411 Timothy.
    So it appears we have a two phase atmosphere, a hot and wet one and a cold dry one; with CO2 in both.

    In the bottom one the molecules all bump into to each other transfering heat and they also transfer IR photon packets to each other. Some of these IR energy packets can go up and get into the second phase. However, water will be the main player in the loer atmosphere as there is more of it than CO2 and it has a wider and stronger IR absorption spectra than CO2.

    In the upper one, there is less gas, hence less collisions and CO2 is the only major IR absorbtion/emission source (I will ignore Ozone).

    Now in the lower level, water will radiate like crazy, and its emission dont over lap dry CO2 too much, most of the IR it radiates will go up and past the CO2 in the upper phase. The low level CO2 will radiate a bit, and some fraction of the CO2 emission will go up and then go down. However, most of the IR that comes from the surface will come from water and it will sail past the CO2 picket fence.

    Doubling CO2 will increase the reradiation from CO2 up and back down by 0.5 x the square root of 0.16 what it was before, but have very little effect on the trapping of IR issued by water.
    Did I get that right?

  13. 413
    Ike Solem says:

    RE#400, #411
    No, the NASA chart isn’t misleading. The IR absorption of water and CO2 do overlap. Let’s take another look at http://www.atmos.washington.edu/1998Q4/211/absorption.gif

    Let’s walk through it. The middle line shows the wavelength, and at the bottom of the ground level spectrum are the assignment of the water and CO2 vibrational modes in the IR absorbtion spectrum. Right around 2.7 microns, you can see an overlapping water / CO2 absorption band, especially at ground level.

    One of the main differences between the ground level absorption spectrum and the 11 km absorption spectrum is that the upper troposphere is much drier than the lower troposphere, while the %CO2 is essentially constant (though you can see CO2 plumes from industrialized Western countries using satellites, and there are regional scale CO2 variations)

    Now, if you look around, oh, 4.4 microns you can see an isolated CO2 band that is broader at the ground then at the 11km level. That’s the band-broadening effect, but it’s clear that the main effect at 11km is the large reduction in all of the H2O bands.

    This is why water vapor feedback plays such a large role in the total increase in radiative forcing, and why so much attention is paid to the increasing water vapor in the upper atmosphere.

    For more, see The Radiative Signature of Upper Tropospheric Moistening, Soden et al Sci 2005

    Alastair, you haven’t answered my question – has the issue of radiative transfer been cleared up? Willing to admit a little error? I’ve made a few errors on realclimate posts myself, but I try and keep in mind that one learns quickest by making mistakes, and by friendly discussion with others.

  14. 414
    Timothy Chase says:

    Ike Solem (#413) wrote:

    I’ve made a few errors on realclimate posts myself, but I try and keep in mind that one learns quickest by making mistakes, and by friendly discussion with others.

    This would appear to be the key to a great deal, not the least of which is learning.

  15. 415
    Timothy Chase says:

    Ike Solem (#413) wrote:

    RE#400, #411
    No, the NASA chart isn’t misleading. The IR absorption of water and CO2 do overlap. Let’s take another look at http://www.atmos.washington.edu/1998Q4/211/absorption.gif

    Thanks for seeing that.

    I hadn’t noticed that he claimed the absorbtion regions didn’t overlap. Trying to respond to too much all at once, I guess, or else not with enough attention.

    A little distracted today. Other things.

  16. 416
    Eli Rabett says:

    No, Doc.

    a. CO2 emission and absorption is significant atmospherically at lower altitudes.

    b. Collisional transfer of energy is dominant at all relevant altitudes up through the stratosphere, essentially anywhere where you can find a local thermodynamic equilibrium (e.g. a distribution of molecular velocities and quantum states that follow Maxwell-Boltzmann statistics)

    c. CO2 is more important at higher altitudes because the saturated vapor pressure of water decreases with temperature, water condenses out the higher you go and very little gets through the tropopause, if there. There are interesting implications to this.

    d. The lines that the water radiates on are limited by the temperature of the atmosphere where the H2O is excited by collisional transfer. This means that water only radiates on rotational lines in the IR, below 1000 cm-1 where there is a good overlap with CO2. The water bends and stretches are essentially never collisionally excited under atmospheric conditions and thus never radiate. They are significant for absorption, but lose energy by collision before they radiate. Moreover rotational transitions are weaker than vibrational ones so even at low altitudes the H2O/CO2 emission ratio is less than the ratio of concentrations.

  17. 417
    Eli Rabett says:

    Oh yeah:

    “That is not quite true, lets take a simple mineralization reaction:-
    3H2O + 2[CO2] + CaSiO3 —> Ca2+ + 2HCO3(1) + 4H+ + SiO4(4-)

    now in the reaction the rate constant is going to be third order [CO2]^2[CaSiO3] = k”

    Has got to be a joke. First, this obviously does not occur in a single step as written, so you really cannot assume the reaction rate is third order or as written. The rate law depends on the detailed mechanism. The weak attempt at kinetics is both incompetent and irrelevant.

    Second, all you get is hydrogen carbonate ion in water (you appear to be assuming that the water will be in excess) so then the HCO3(-1) [the (-1) means singly ionized] will participate in an equilibrium with CO2, H2CO3, HCO3(-1) and CO3(-2). Since water exposed to the atmosphere already is saturated in CO2/H2CO3/HCO3(-1)/CO3(-2) the system will spit the CO2 back out at you in the equilibrium

    CO2 + H2O < --> H2CO3
    H2CO3 < --> HCO3(-1) + H(+1)
    HCO3(-1) < --> CO3(-2) + H(+1)

    If you want to degas the water, that costs you a lot of energy. Not worth it. The bio stuff as noted is worth about as much.

  18. 418
    Blair Dowden says:

    The only CO2 band of interest for the greenhouse effect is the 15 micron band, because the other bands are mostly outside the Earth’s emission spectrum (as can be seen on Ike’s chart). There is some overlap, which looks to be around 50% according to the NASA chart, with water vapor in the lower atmosphere. So significant radiation should make it up to the upper atmosphere no matter what happens in the lower layer.

    Kirchhoff’s Law says objects that absorb radiation strongly at a given wavelength will emit strongly at the same wavelength. Does this apply to rotational absorption by water vapor, which is a very broad band? DocMartyn implies that the 15 micron radiation will be absorbed by water vapor and re-radiated at a different frequency, which will bypass CO2. Maybe, but an absorbed longer wavelength may also re-radiate at 15 microns. I see no reason there should be a net loss at that bandwidth.

  19. 419
    Blair Dowden says:

    The idea that the atmosphere warms by the transfer of vibrational energy from a greenhouse gas to kinetic energy makes logical sense. My problem with it is that no other description of the greenhouse effect mentions it. All of the ones I have read, such as Gavin’s simple model, Raypierre’s Busy Week for Water Vapor, and others only talk about downwelling or outgoing longwave radiation. Until shown otherwise, my interpretation is that it is a minor effect at most.

    In Raypierre’s water vapor discussion, he states, in this response:

    The essence of the argument is simply that, in a part of the spectrum where water vapor is a good absorber (hence, by Kirchoff, a good emitter) when one puts some water vapor at a high,cold level one blocks the infrared coming from below, and replaces it with infrared emitted at a lower temperature by the high-cold layer. Putting more water vapor near the ground, where the air temperature is nearly the same as the ground temperature, does not do this because you are replacing one radiating surface with another with nearly the same temperature. In fact, if the air is warmer than the underlying surface, as often happens, putting more water vapor in the boundary layer will actually increase the OLR, until adjustment occurs to bring the system into balance.

    Here he is claiming that the greenhouse response of water vapor can have a cooling effect. Not much room for molecular heating here. My reading is the only important factor is the temperature at which a greenhouse gas radiates.

  20. 420
    David Warkentin says:

    DocMartyn – in (405) and earlier, you suggest that if we “Plot the level of [CO2] ppm vs Human CO2 emissions” we’d get this figure:
    http://i179.photobucket.com/albums/w318/DocMartyn/Atmosvsinput.jpg
    The R^2 values of 0.9997 and 0.9998 for your linear fits seem remarkably high. I’ve been trying to reproduce your plot what I think are the sources you give, but my results aren’t nearly so straight. For CO2 concentration, I’ve been using the April entries in column E (CO2, ppm) of
    http://scrippsco2.ucsd.edu/data/in_situ_co2/monthly_mlo.csv
    (it’s the “Mauna Loa Record” link under the heading “In Situ CO2″ on this Scripps page: http://scrippsco2.ucsd.edu/data/data.html )
    and for CO2 release I’ve been using column B (Total CO2, millions of metric tons) of
    http://cdiac.ornl.gov/ftp/ndp030/CSV-FILES/global.1751_2004.csv
    (third link on this Oak Ridge Carbon Dioxide Information Analysis Center page:
    http://cdiac.ornl.gov/trends/emis/tre_glob.htm ) This is total fossil fuel emissions

    Am I looking at different data? Are there links to documents with the underlying numbers you used to make your plot?

  21. 421
    Eli Rabett says:

    Blair, what Gavin described is exactly what you expect from collisional energy transfer in a 200-300 K bath. Unexcited water absorbs across its vibrational/rotational spectrum. Water vapor’s vibrational modes are very high frequency (for vibrations). When excited the molecule loses energy to the bath by collision, however, since it is so dilute and the temperature is low compared to the energy needed to excite vibrations (thermal energy at 300 K corresponds to an average collisional energy of about 200 cm-1 ) So compared to the roughly 1000-4000 cm-1 needed to excite a vibration, it is very unlikely that a collision will be effective. OTOH, a collision can easily excite a rotational state in water or a bending mode in CO2 (~600 cm-1).

    Mid IR photons will be absorbed by water vapor, the energy converted to motion, e.g. heat. The heat excites vibrational modes in CO2 and rotational ones in water vapor which can either radiate or be cooled by collisions. Because the rate of collisional excitation is low compared to the rate of de-excitation, the population of molecules in vibrationally/rotationally excited states is governed by a steady state approximation, e.g. roughly constant in time. At room temp, it is about 6% for CO2.

  22. 422
    Timothy Chase says:

    Re Eli Rabett (#421):

    The material I found was stating specifically that in the case of water, the spreading of the bands around room temperature is due to rotation and vibration is too high. I had thought that such kinetic motion was responsible – particularly since the bands are much more narrow at lower temperatures, but it was nice to see it in print.

  23. 423
    Timothy Chase says:

    PS

    (#422) That the ir for bending bands is spread out by collisions doesn’t surprise me, but I don’t remember it being mentioned.

  24. 424
    Ike Solem says:

    Blair, I think you’re misreading that graph. The top curves are for theoretical blackbody emitters – at 255 K, or -18C, which is what things look like from space. The surface temperature of the Earth is 15C, or 288K.

    For more, and for an image of the actual emission spectrum of the Earth, under tropical clear sky conditions see http://climate.gsfc.nasa.gov/~cahalan/Radiation/ (click on the Earth Spectrum box embedded in the page)

    Compared to the 255 K blackbody, the most obvious feature of the observed Earth spectrum is the much higher emission in the region of 800 – 1250 cm-1 (12.5 to 8 microns), where the blackbody temperature is closer to 290 degrees Kelvin. This spectral band is the “water vapor window” in which the cloud-free atmosphere is very transparent, so that the emission to space comes from regions very near the warm ocean surface. It is this window which allows the Earth to keep as cool as it does. The window is cut off on the lower wavenumber side by the strong CO2 absorption band centered around 650 cm-1, or about 15 microns, where the emission corresponds to temperatures well below 255. There is also significant absorption by ozone (O3) at around 1100 cm-1, or 9 microns. The many absorption bands on either end and throughout the measured spectrum are from water vapor, which is the primary absorber in the atmosphere. The primary reason that the surface temperature remains near 290, (or +15 C) rather than the 255 (-18 C) it would be if there were no atmosphere, is the absorption in the thermal infrared by atmospheric water vapor, as seen throughout this figure.

    Also, I think you misunderstand the comment you quote. The correct phrase would seem to be that increases in upper troposphere water vapor have a cooling effect..on the stratosphere..since that blocks part of the outgoing longwave radiation. The main gist of the comment seems to be that where the water vapor goes matters… but we know that the upper troposphere is getting moister.

    Claims about ‘water vapor being responsible for 95% of the greenhouse effect’ are unsupported – see “How to talk to a climate skeptic for more.

    P.S. That’s not “Ike’s Chart”, that’s from Prof. Mike Wallace’s Climate and Climate Change Course web page at the University of Washington – which will give you an excellent overview of this topic.

  25. 425
    Blair Dowden says:

    The graph I was talking about “shows the percentage of energy absorbed in a clear tropical sky by water vapor and carbon dioxide” around the 15 micron band. It looks like half of the outbound radiation gets absorbed by water vapor. But what would the graph look like in a dryer region? And what level of carbon dioxide is assumed? I understand that at higher concentrations the CO2 absorption spectrum broadens.

    And what exactly does 100% absorption mean? The emission spectrum graph shows outbound longwave radiation at all wavelengths.

    The University of Washington web page attributes greenhouse warming to downwelling longwave radiation warming the surface. I realize it is only a model, but there is no mention of direct atmospheric warming. If direct absorption was the main cause of greenhouse warming there would be little downwelling radiation, which contradicts what we can measure.

  26. 426

    Re #390 where Ike wrote:

    RE Alastair’s comments: Nowhere did I state that the Earth is a perfect blackbody. The issue of concern is the wavelength dependence, i.e. the emissivity. Again, see the figure http://www.atmos.washington.edu/1998Q4/211/absorption.gif The top line shows what blackbody curves look like; the bottom is the atmospheric absorption.

    Ike,

    Prof. Wallace’s chart does not convince me that I am wrong. There are three figure, not two as you suggest, and the first is misleading. I suspect that you are unaware that the top one shows the two black-body curves using different scales for solar and terrestrial radiation. An idea of the true relative intensities can be obtained from the figure shown on the Wednesday page. The true situation is that although the amount of solar infra-red radiation which overlaps with the terrestrial radiation is small compared to the total solar radiation, it is significant when compared with the total terrestrial radiation. This belies Ray’s claim that no solar radiation is absorbed. Absorption of solar radiation plays its part in heating the air in te troposphere adding yet another complication to the radiation problem.

    The second figure and third figures show that there is less absorption at height that at the surface, yet the current models argue that the greenhouse effect is due to absorption high in the troposphere. I do not understand ow you think that these two figures do not support my idea that the greenhouse effect is mainly at the surface.

    On the Thursday page, Wallace shows the same model as Gavin, and on Friday he adds another layer, but the model still does not fit reality, because the Earth, instead of emitting twice the incoming solar radiation (ISR) as on Thursaday , then has to emit three times the ISR on Friday. Add more levels and the amount of outgoing long-wave radiation (OLR) from the surface gets even more ridiculous!

    If the atmosphere was pure CO2, and no absorbed vibrational energy was converted to translation energy by radiationless transitions then that scheme might apply. However, in the real world the absorbed radiation is converted to heat, which warms the air molecules which cannot re-radiate their energy back to the surface.

    You seem to think that because I am arguing that the models are wrong then I believe that “global warming is a big hoax… “. That is as illogical as to believe that the models are right because global warming is happening. Global warming is not caused by models!

    In #413 you also wrote:

    Alastair, you haven’t answered my question – has the issue of radiative transfer been cleared up? Willing to admit a little error? I’ve made a few errors on realclimate posts myself, but I try and keep in mind that one learns quickest by making mistakes, and by friendly discussion with others.

    Since you are willing to admit your errors, perhaps in the spirit of friendship you might like to admit you were wrong again on this point. It was not you fault. You were misled by some of the best brains in the buisness. I forgive you :-)

    Cheers, Alastair.

  27. 427

    Re #419 Blair,

    The equipartition theorem is used to justify the claim that greenhouse gases radiate with a strength that is related to their temperature. However, with the advances in understanding that happened with the development of quantum mechanics, the physicists now know that the relaxation of vibrational excitation is not subject to that theorem.

    Unfortunately the climate modellers are still using a method that originated around 1910 to explain the limb dimming of the Sun. This model first appeared just after the discovery of the quantum theory, but before the development of quantum mechanics. So it is based on classical thermodynamics and Kirchhoff’s Law. Of course the Sun does radiate like a black-body, and its interior is probably in thermodynamic equilibrium locally. Thus it is quite likely the correct model for the Sun. However, where the Sun’s spectrum deviates from that of a black-body is where the gases in its outer atmosphere produce dark lines! In other words, gases are anti-blackbody radiators.

    This stellar model, called the Schuster-Schwarzschild method by the great astrophysicist Chandrasekhar in 1960, was introduced into planetary science by Schwarzschild’s brother-in-law Robert Emden in 1917. If this models is tuned with the today’s conditions, such as a lapse rate of 6.5 K km^-1, it not only matches what you see today, but also gives a reasonable picture of yesterday, so long as you don’t wind it back too far. The rapid climate change at the start of the Holocene only ten thousand years ago is just such a step too far.

    It is possible that the scientists would have discovered their error by now, but they have been too preoccupied defending their model from the global warming sceptics. As you know, the sceptics claim the models are wrong and warming will not happen or will not be as severe as is being predicted. With the model being wrong, the sceptics, such as Barrett and Christie & Spencer, have succeeded in delaying the needed action. Moreover, the sceptics claim that the wrong model is overestimating the problem. In fact the current models predict a logarithmic climate sensitivity, but the real model would give a climate sensitivity proportional to greenhouse gas concentration, far worse. Wayne confirmed that the current models are underestimating the warming in post #310.

    But, although using the wrong source function (Planck’s blackbody function) for greenhouse gases has severe consequences, that is not the only error.

    In #406 Ray wrote:

    Alastair, I think it was you who claimed that the vibrational modes of CO2 were frozen out at room temperature. While that is true if you have a gas in eqb., in the atmosphere, the gas must also equilibrate with the IR radiation field. Thus, while the vibrational mode will not be excited by collisions, it maybe relaxed thereby, thus imparting kinetic energy. So, I do believe atmospheric heating is possible.

    That is correct. and when it was thought that gases radiated according to the Planck function, it is easy to see how this equilibrium would be reached , and that state was called LTE (local thermodynamic equilibrium.)

    So Ray, I quite agree! In most of the atmosphere, where there is only slight convection because it is in layers, the IR radiation field will be in a state of equilibrium, in which the exciting collisions plus the absorbed radiation will equal the relaxing collisions plus the emitted radiation.

    Near the top of the atmosphere, some of the emitted radiation escapes to space, thus it is not able to excite the surrounding molecules and the equilibrium no longer exists. At higher altitudes the molecules collide very infrequently so the molecules are not excited and cannot emit. This state is called non-LTE.

    David Donovan challenged me to find the flaw in Goody and Yung’s (G&Y) arguments. They base their arguments on a paper by E.A. Milne “Thermodynamics of the Stars” Handbuch der Astrophysik, Vol. 3 Part 1, Chapter 2, 1930 pp. 65-255. In that paper, Milne defines local thermodynamic equilibrium (LTE) as the state where the kinetic temperature equals the blackbody temperature. But Milne wrote “This permits us to see in a general way why the state of local thermodynamic equilibrium in the interior of a star breaks down as we approach the surface.” p. 81. A star has only one surface, but a planetary atmosphere has two.

    At the base of a planetary atmosphere, a different type of non-LTE will be true. There, the absorption will exceed the emitted radiation, whereas at the top of the atmosphere the emissions exceed the absorption. However, on Earth it is even more complicated.

    In the lines at which CO2 absorbs, during the day the blackbody radiation from the surface is more intense than that emitted by the “frozen out” CO2, and so the absorbed radiation warms the air through relaxing collisions. At night, when the surface is cooler than the air, the air will cool by the emission of radiation from the greenhouse gas molecules, but at a lower intensity than the surface. Hence the occurrence of ground frosts when the air is still above freezing.

    I started this reply several days ago, and could probably spend several more days refining it. I will stop here, hoping it makes sense. Now, I really must start writing that paper.

    Cheers, Alastair.

  28. 428
    Ike Solem says:

    Alastair, I think your fundamental misconception is that you are mixing up 20th century and 19th century physical concepts in a bizarre manner. This is most evident by your statement:

    “However, in the real world the absorbed radiation is converted to heat, which warms the air molecules which cannot re-radiate their energy back to the surface.”

    This seems to be a fundamental misconception of some basic physics – namely, that there are three basic methods of heat transfer: radiation, conduction and convection. These concepts are part of 19th century physical theory, which is not ‘incorrect’, just incomplete. Why can’t a molecule radiate energy? It’s just nonsense, strung together in various ways.

    You also state that ‘you have been misled by some of the best minds in the business’. This seems to be the central point – that there is a great conspiracy, that the science isn’t understood, and that you know why this is, but that there is ‘not enough space in the margin for me to right down the proof’.

    Your physical explanations are a mish-mash of concepts which, while they sound ‘scientific’ are apparently only intended to create a false sense of controversy and doubt. If you really are interested in understanding the science behind global warming, you have a lot to un-learn. However, after reading your posts for quite some time now, it seems that your only goal is to inject doubt into the debate.

    When tobacco companies were trying to prevent the public from becoming aware of the role that smoking played in lung cancer and other diseases, their main strategy was to attempt to create doubt in the public mind about the validity of the science – a well-documented effort that stretched out over decades. It’s clear that similar tactics are now being used by the fossil fuel lobby in an attempt to create doubt in the public’s mind regarding the science behind global warming.

    Would you agree that this is the central PR tactic being used by the fossil fuel lobby?

  29. 429
    Hank Roberts says:

    Alastair, I’ve been trying to look up phrases from your postings to see if I can find agreement with them in other sources.
    No luck so far. You’re dominating the explanations here. I can’t tell whether the contributors agree with you or not.

  30. 430
    Ray Ladbury says:

    Alastair,
    You know, as a physicist, I tend to understand only things that are pretty simple, so one thing I tend to do is ask whether a description violates any fundamental laws of physics. Everything we are talking about here is electromagnetic or mechanical in nature, so time-reversal invariance ought to apply–that is, if a process goes from A–>B, it ought to also go from B–>A. If a molecule can de-excite via collision, then some finite number of molecules will have to exist that can excite the same molecule via collision. Now, it is true that if you impart a high momentum to a molecule, that momentum will relax after repeated collisions, but there has to be a finite probability of exciting another molecule early, just as there may be a finite probability of collisional de-excitation. Given the short lifetime or the excited vibrational state, I’d imagine radiative processes dominate. I think you need to look at fundamental physics.

  31. 431

    Ike,

    If a greenhouse gas molecule absorbs a photon of infra-red radiation, and then collides with a nitrogen molecule before it has had time to re-radiate that energy, then it will not be re-emitted. The nitrogen molecule will be warmer, but cannot does not emit. All this relies on is classical thermodynamics and the law of conservation of energy.

    From what I can gather, the tobacco industry recruited the oil industry in a joint campaign to discredit the scientists. However, when the greenhouse effect is such an established phenomenon, why have the sceptics been so successful? Why, if the science is so correct, do scientists such as Spencer and Christie, who are not in the pay of the oil industry, argue against the global warming? Other established scientists such as Lindzen have doubted the models, and it is only after being demonised that they have accepted finance from the fossil fuel industry.

    I do know more than I have already written. For instance, when Fourier first explained the greenhouse effect he was drawing on the work of de Saussure who invented the hotbox. The hotbox works in the same way as a car left in the sun with all its windows closed. The infra red radiation from the interior heats the air. The glass in the windows has little effect. Open them by an inch, allowing the hot air to escape, and the interior of the car will remain cool enough for a dog or baby trapped inside to survive.

    This was shown by R.W. Wood in 1909. http://www.wmconnolley.org.uk/sci/wood_rw.1909.html and Weart reports that the idea that CO2 could cause climate change was abandoned. However, the astrophysicists, led by Einstein and ending with Chandrasekhar, had so much prestige that their model for radiation within stars was inappropriately adopted by the climate modelers for planetary atmospheres.

    You only have to read Bill Bryson “A Short History of Nearly Everything” or Spencer Weart http://www.aip.org/history/climate/index.html to see how often scientists make mistakes. Science is always correct because that is what is left over when the scientists mistakes are removed. But the theories of scientists are not impeccable. Worse, it seems that this mistake with modeling greenhouse gases is going to be disastrous for the human race.

  32. 432
    Blair Dowden says:

    Re #428: Ike, while it is fine to criticize Alastair’s science, I think you are out of line to attack his motives. He clearly states that he thinks global warming is being underestimated by the current models. Did the tobacco industry ever claim cigarettes were more harmful than scientists claimed they were, just to confuse people? Please, lets deal with the arguments made here on their merits, not imagined motives.

  33. 433
    Ike Solem says:

    Alastair, again that’s a misrepresentation of basic physics. There are a number of ways that an excited molecule can lose energy – by direct emission, by flouresence, by collision – and that’s all quantum theory. There is always a distribution of processes, depending on both the molecule and the local environment. Classical thermodynamics is incapable of handling the situation.

    What’s odd are your statements such as “However, the astrophysicists, led by Einstein and ending with Chandrasekhar, had so much prestige that their model for radiation within stars was inappropriately adopted by the climate modelers for planetary atmospheres.”

    What you seem to be saying is that the past hundred years of physics are all wrong – which is the kind of nonsense one hears from creationist scientists. However, you have managed to steer the discussion on this thread away from the original post, which was about the ridiculous data manipulation carried out by some crackpot climate skeptic and which was presented in the press as fact.

    Multiple comments on this thread have pointed out the basic errors in your posts, and yet you refuse to respond to them. The only conclusion that makes sense is that you are simply trying to inject doubt into the discussion.

    Isn’t that the primary PR technique being used by the fossil fuel lobby?

  34. 434

    Ray,

    Here we are talking about thermodynamics and quantum mechanics. I am quite happy not to talk about quantum mechanics, which I find not only extremely complicated but also non-intuitive. In thermodynamics there are two tyes of process, reversible and non-reversible. Non reversible processes lead to an increase in entropy, and one way of expressing the Second Law of Thermodynamics is that entropy always increases. It is postulated that the climate system operates to maximise entropy. Thus I don’t find your argument about reversibility at all convincing :-(

    I have investigate the fundamental physics and discovered that the physical chemisst and the spectrometrists find the problem of the vibrational relaxation of polyatomic molecules not only difficult but also uninteresting since it tells them nothing about the chemistry of the molecules. However, that is taking me into quantum mechanics!

    I will say that at STP typically a vibrationally excited molecule will receive 1000 collisions before it re-emits its photon, and since CO2 is less than 1 part in 2000 of the astmosphere, not many of these collisons will be CO2 to CO2!

  35. 435
    Ray Ladbury says:

    Alastair, Now you are not only wrong on the physics, but also on the history and the positions of the climate science skeptics as well. First, neither Christy nor Spencer doubt the fundamental mechanisms of the greenhouse mechanism. Christy has even stated before that he believes that humans are affecting climate–he just disputes the degree. Lindzen, too, when you get him on a day when he isn’t feeling too contrary will conceed that humans are causing climate to change–he just believes we’ll be saved miraculously by his iris effect. Second, you contend that reputations of Einstein et al. forced the scientific community into agreement despite the evidence. Well, Einstein’s reputation certainly didn’t help him wrt quantum mechanics, now, did it? Please, please, please, take a look at the accompanying index, as I fear you may be in some danger of going well off into the weeds:
    http://math.ucr.edu/home/baez/crackpot.html

  36. 436

    Re #429

    Hank, I realised soon after I started the “campaign” in this thread that even if I did convince anyone I was right, it would have little/no effect in the wider world :-(

    However, I have learnt something from it. First, about the Theorem of Equipartition (thanks Ray) and that it does not apply to vibrational excitation, (which I had already guessed :-) Second, if I am going to convince the big wide world I am correct I will have to break Goody and Yung’s argument. That is easier said than done because I don’t think it makes sense. But I do have copies of the two papers they cite.

    Anyway, I will soon leave you all in peace and try to get a paper published. The posts from all of you have been useful, so thanks for replying.

    Cheers, Alastair.

  37. 437
    Rod B says:

    re 388; But only one of the major CO2 absorption bands overlaps H2O, two bands overlap slightly, and one band doesn’t overlap at all. Does it still turn out that most CO2 absorption is in the stratosphere? Why would some of the IR bypass the troposphere CO2?

  38. 438
    Timothy Chase says:

    re 388; But only one of the major CO2 absorption bands overlaps H2O, two bands overlap slightly, and one band doesn’t overlap at all. Does it still turn out that most CO2 absorption is in the stratosphere? Why would some of the IR bypass the troposphere CO2?

    Judging from the diagram I saw, there was a fair amount of overlap – but I would want to check again. Doesn’t have to be a great deal in any case.

    The important thing is that infrared (either from the surface or from H20) does make it to the CO2 in the stratosphere, some of which is absorbed, some of which is re-emitted towards the surface – resulting in the evaporation of water and more water vapor. This is what results in the initial amplification of CO2s effect – and the added water vapor results in positive feedback since it raises the temperature which results in additional water vapor.

    As for infrared bypassing the troposphere, some of it will be in the wrong part of the spectrum for absorbtion by H20. But much of it won’t bypass the troposphere. Instead will take a kind of random ladder climb through the atmosphere, skipping some rungs, sometimes stepping back down, sometimes stepping farther up. At some point the energy which it contains will leave the atmosphere, but the added time it spends in the earth system due to absorbtion and re-emission (and of photons like it) will keep the energy within that system at a higher level than it would be without the greenhouse effect.

  39. 439
    Hank Roberts says:

    Rod, a greenhouse gas doesn’t grab a photon and hold on to that energy forever.

    Once infrared photons are moving in the stratosphere, they are most likely to hit CO2.

    You know why —- there’s very little water vapor at that altitude. On the way, that energy has been transformed repeatedly. Do you understand it’s sometimes a photon, sometimes another form of energy in a bond or moving molecule, bouncing around?

    > Why would some of the IR bypass the troposphere CO2?

    It can’t. It moves as infrared photons or other forms through the atmosphere — that energy has been transformed repeatedly. Do you understand it’s sometimes a photon, sometimes another form of energy in a bond or moving molecule, bouncing around?

    Eventually it goes ‘off the table entirely’ — into space.

  40. 440

    [[If a greenhouse gas molecule absorbs a photon of infra-red radiation, and then collides with a nitrogen molecule before it has had time to re-radiate that energy, then it will not be re-emitted. The nitrogen molecule will be warmer, but cannot does not emit. All this relies on is classical thermodynamics and the law of conservation of energy.]]

    Right, but we’re not dealing with two molecules in isolation. The nitrogen heating up will eventually heat up the CO2, and the CO2 will radiate more than it did before. Energy has to be conserved. If CO2 absorbed infrared energy and endlessly transferred it to nitrogen which didn’t radiate, then the atmosphere would heat up indefinitely. And it doesn’t. Therefore, there must exist a method by which the air loses energy. And that method appears to be radiative. The amount absorbed by the Earth system in the atmosphere and at the ground is reradiated out to space, except for tiny differences when the system is out of equilibrium. And it’s no good saying the earth system is never in equilibrium because it heats up during the day and cools down at night. It is in long-term equilibrium (a day or more) with regard to radiative balance.

  41. 441

    Alastair,

    It just occurred to me that my computer models might have misled you. I take the layers of atmosphere to be radiating like graybodies because that’s an approximation which allows me to get close enough results. The GCMs don’t use that approximation, they do radiation from the gases just like they do absorption from the gases — in bands.

    Remember that the lines greenhouse gases absorb/radiate at aren’t sharp in a thick atmosphere. And there are so many secondary lines that large parts of the spectrum can be treated as if they had continuum radiation in bands. Water vapor absorbs almost everything from 12 microns to 125 microns, plus its few earlier bands. CO2 has earlier bands, again affected by pressure broadening, and in most of the windows you find ozone, methane, nitrous oxide, or some other greenhouse gas. (Hell, even normal oxygen absorbs solar ultraviolet significantly from 0.15 to 0.25 microns.) And don’t forget clouds, which absorb all radiation from 4 microns up (and consequently emit that way). The models I was using use gross approximations, but they are close enough to reality that the errors cancel out.

    -BPL

  42. 442
    Blair Dowden says:

    Barton, you said in #440 that “If CO2 absorbed infrared energy and endlessly transferred it to nitrogen which didn’t radiate, then the atmosphere would heat up indefinitely.” But the atmosphere has other ways to lose energy. Added atmospheric energy will reach the surface, which will warm and radiate at a higher rate.

    I have a different problem with the idea that a significant amount of energy from longwave radiation is transferred as heat to the atmosphere. This, by definition, means that no longwave radiation will be re-emitted. However, downwelling radiation reaching the surface can be measured, and sources such as this one tell me it amounts to something like 340 watts per square meter. That does not leave much room for losses by transfer to kinetic energy.

    I conclude that, as you said, any energy lost in that way is returned to the greenhouse gas molecule in a subsequent collision, and little net energy is transferred in this way.

  43. 443
    Eli Rabett says:

    Ray, #430. Vibrational radiative lifetimes are very long, seconds. Collisional lifetimes at atmospheric pressure are of the order of 1-10 microseconds. However, the amount of energy necessare to excite a CO2 bend (~600 cm-1) is about 3x the average energy of a collision at 300 K (~200 cm-1) so about 5% of all CO2 molecules at 300 K are excited, just not the same ones at any instant. This is a steady state problem.

  44. 444

    [[I have a different problem with the idea that a significant amount of energy from longwave radiation is transferred as heat to the atmosphere. This, by definition, means that no longwave radiation will be re-emitted.]]

    What? What in the world does that mean? It absorbs longwave radiation, therefore it can’t emit longwave radiation? Where did you get that idea?

  45. 445
    ray ladbury says:

    Eli, Thanks, that is very helpful. Still, I wouldn’t call 5% “frozen out”, but maybe thats my experience with depleted semiconductors. Out of curiosity, how does that compare to the proportion that are excited on average by the outgoing IR?

  46. 446
    Blair Dowden says:

    According to the Greenhouse Effect page in Wikipedia, “Most of the infrared absorption in the atmosphere can be thought of as occurring while two molecules are colliding. The absorption due to a photon interacting with a lone molecule is relatively small.” So there is not even a single specific molecule that receives the longwave radiation.

    I would infer from what Eli said in #443 (also in the Wikipedia article) that as the temperature goes up, the percentage of CO2 molecules that reach the energy level required to emit a photon goes up, so more photons get re-emitted.

    I want to ask again how much energy gets absorbed, and how much re-emitted. But any warm atmosphere with greenhouse gas in it will radiate, no matter how it got warm. More greenhouse gas means relatively more photons get ejected at a given temperature.

    So what difference does it make when the atmosphere is thinner and colder at high altitude? I see smaller absorption bands because of less pressure broadening, and less probability of the collisions required for photon absorption to take place. Back in #291, Eli said “the absorption per molecule at line center is HIGHER for colder molecules.” Does this mean a higher probability of absorption, or more energy absorbed? The air gets relatively warmer, but when a collision of sufficient force to cause a photon to be ejected occurs, the photon as the same intensity as always. Is this where the idea of the upper atmosphere radiating at a lower temperature comes from?

  47. 447

    Re #443

    Eli, Do you know of a web page where I can see the calculations? I would like to build a simple spreadsheet model of the steady state situation, but I am missing some of the parameters and details of the mechanisms.

  48. 448
    Blair Dowden says:

    Re #444: Barton, I had the idea that the atmosphere warmed by absorbing a photon, and when it was re-emitted the warming was gone. I have already discarded that idea, and now think greenhouse gases will emit radiation no matter where the thermal energy comes from.

    The warmer the gas, the higher the probability that a collision will have sufficient energy to cause a photon to be emitted. So how is the greenhouse effect supposed to be more important in the upper atmosphere? I am still not understanding the end game here.

  49. 449
    Hank Roberts says:

    Blair, you are asking for words and the answer is in the numbers. Best words can do for radiation math is an approximation, not an explanation. That’s why Weart’s entire chapter on radiation physics is admittedly so difficult and why he invites questions there from people who haven’t understood his explanation.

  50. 450
    Rod B says:

    re 444, which says: “[[I have a different problem with the idea that a significant amount of energy from longwave radiation is transferred as heat to the atmosphere. This, by definition, means that no longwave radiation will be re-emitted.]] — What? What in the world does that mean? It absorbs longwave radiation, therefore it can’t emit longwave radiation? Where did you get that idea?”

    I have a basic question/clarification (which may have already been discussed here, in which case I apologize). LW radiative energy is absorbed by GH gas molecules in bond translational or rotational energy, which does not raise that molecule’s temperature. Is this correct? Then the molecule will re-emit that radiation, losing its bond energy (in part); or it might collide with some other molecule. In this case does the molecular bond energy get transferred to the collidee’s bond energy (which can’t happen with N2 or O2… can it??) or as kinetic energy thereby increasing the temperature of the collidee molecule (and the atmosphere). Given either can happen, it sticks in my mind that the collision transfer is much less than the radiation emission…. or is it vice versa???


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