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In the paper "Experimental Verification of the Greenhouse Effect", the authors (Hermann Harde, Michael Schnell (2022)) describe an experimental setup that they say demonstrates the atmospheric greenhouse effect.

(NOTE: Some commenters point out that downvotes may be due to flaws in the experiment that they say leads to a misleadingly lower measured magnitude of the effect. However that’s neither being affirmed nor questioned here. It seems to demonstrate some effect and my question is, whatever flaws the experiment may have, how did it not result in a higher air temperature corresponding to the higher heat source plate temperature?)

The experimental setup is as follows (from the paper):

enter image description here

For our studies we use an experimental set-up, which consists of two plates in a closed housing, one plate heated to 30°C, the other cooled to -11.4°C (Fig. 1). The plates have a distance of 1.11m to each other, and the tank can be filled with different gases to study the radiation transfer between the plates in the presence of the GH-gases.

They found that when keeping the energy input to the Earth plate constant, and adding IR-active gases such as CO$_2$, the temperature of the Earth plate increases due to the back-radiation effect:

enter image description here

(Note: the "Reduced Heating" section at the end is when they decrease the energy input to the Earth-plate until it gets back to 30°C; the difference in energy input is used to calculate the magnitude of the back-radiation effect.)

My question is: why did the addition of the IR-interacting gas not result in any increase in air temperature (denoted by T1, T2, T3, and T4)?


My understanding is that the IR-active gas (say, CO$_2$) interacts with the infrared light emitted by the Earth plate, by absorbing it, which causes the CO$_2$ molecules to vibrate. This is described as it heating up, for example (emphasis in the original):

When photons bump into other atoms, some of their energy can get the electrons in those atoms resonating or moving faster than they were before - that’s what we call heat. The properties of these molecules and their bonds determine if a gas in the atmosphere will absorb infrared radiation or not. [source]

Then the CO$_2$ spontaneously re-emits infrared light of the same wavelength, but this time in a random spherical direction. Some of it is emitted back to the Earth plate which is what results in its higher temperature.

However, between the period of absorption and emission, the CO$_2$ is vibrating more -- shouldn't this mean it has more kinetic energy? And as 10% of the air (in this trial) now has more kinetic energy for a constant amount of the time -- shouldn't that directly translate in a higher air temperature?


For another example with a different explanation (emphasis in the original):

Once the atmosphere is absorbing radiation something has to happen. [...] energy absorbed has to go somewhere and and in this case the energy goes into increased heat of that section of the atmosphere, as we saw in Part Two of this series.

In general, and especially true in the troposphere (the lower part of the atmosphere up to around 10km), the increased energy of a molecule of CO2 (or water vapor, CH4, etc) heats up the molecules around it – and that section of the atmosphere then radiates out energy, both up and down. [source]

In this case it's described as heating the air directly, which air then radiates energy out. But we observe no higher heating in the experiment.


What's the explanation for the air not getting hotter?

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    $\begingroup$ Why the downvote? $\endgroup$
    – Cloudyman
    Apr 14, 2023 at 21:08
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    $\begingroup$ Not my downvote. My guess? Anger with the paper. It attacks mainstream science with poor experimental design. I lack enough expertise to answer, but they mix gases with a procedure too unlike that of the atmosphere to see the effect they deem exaggerated. An increased lapse rate cools the atmosphere's effective greybody surface, so Earth's poorer at radiating heat. They object to experiments with stratification and increased infrared insolation, and miss what it takes to model what's confirmed in satellite measurements of specific wavelengths' absorption. $\endgroup$
    – J.G.
    Apr 14, 2023 at 21:26
  • $\begingroup$ @J.G.: Ahh understood. I didn't realize these flaws in the paper. Whether their flawed design leads to an incorrect magnitude of effect or not, at least it seems to clearly demonstrate an effect that can't be attributed to conduction or convection like other experiments -- if you could point to other papers that do a better job I would appreciate it! With all that said my question still stands, it doesn't make sense to me how the CO$_2$ could be absorbing the infrared light but not resulting in a higher air temperature. $\endgroup$
    – Cloudyman
    Apr 14, 2023 at 21:30
  • $\begingroup$ Until someone who understands it better than me explains that, I'll share another experiment that shows a sizeable effect. $\endgroup$
    – J.G.
    Apr 14, 2023 at 23:07
  • $\begingroup$ Minor comment to the post (v2): Please consider to mention explicitly author, title, etc. of link, so it is possible to reconstruct link in case of link rot. $\endgroup$
    – Qmechanic
    Apr 14, 2023 at 23:50

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Reply to: Why did the air not heat up in this experiment demonstrating the atmospheric greenhouse effect? We got notice about some discussion on this website concerning our paper “Experimental Verification of the Greenhouse Effect” (http://hharde.de/index_htm_files/Harde-Schnell-GHE-m.pdf).

Cloudyman asked: “Why (in our experiments) did it not result in a higher air temperature corresponding to the higher heat source plate temperature?”; and: “why did the addition of the IR-interacting gas not result in any increase in air temperature (denoted by T1, T2, T3, and T4)?

First, we have to remind that our set-up reveals a temperature difference from the earth plate (upper position) to the cold plate (bottom) of more than 40°C. The sensors T1 to T4 measure the vertical temperature distribution close to the compartment walls, and with greenhouse gases (GH-gases) indeed there can and will emerge a smaller difference between the gas close to the earth plate and on the other hand to the upper wall or to the dome. But at equilibrium the gas doesn’t get warmer than the plate. The regular process is that GH-gases, different to N2, O2 or noble gases, are absorbing and radiating in the infrared and far-infrared. So, they can be excited on their absorption bands by radiation from the two plates, the walls and from neighboring molecules, which are radiating on the same wavelengths. In addition, under conditions as in the tank and in the atmosphere, they can be excited by inelastic collisions from a lower to a higher ro-vibronic state. These processes are increasing the inner energy of the molecules. On the other hand, excited GH-gases re-radiate or transfer some part of their inner energy to other molecules via superelastic collisions.

Due to the kinetic gas-theory the kinetic energy of molecules defines their temperature. At the same time this temperature also defines the relative population of the ro-vibronic states via the Boltzmann-distribution. In the presence of collisions there is a continuous exchange between the inner and kinetic energy, which also determines the strength of the re-emitted radiation, and thus, the losses to the environment. This eigen-radiation (spontaneous radiation) of the GH-gases is again partially absorbed by the earth plate and therefore reduces its own losses, till it is adjusting a new equilibrium between the gas and the plate.

Concerning the quote source, NOAA should know that the cited paragraph is more than problematic to explain absorbed radiation simply as heat. When photons are absorbed by an atom or a molecule, this is not heat, but in a first step increases the inner energy. The atoms or molecules are excited to a higher level, from where they can re-radiate by spontaneous emission. When electronic transitions are involved, this typically happens within a few nanoseconds, when ro-vibronic transitions in molecules are included, which here are only of interest, this happens within milliseconds up to seconds. Under conditions as found in the atmosphere excited molecules can transpose and share part of their inner energy or even all with other molecules via superelastic collisions. During such collisions the excited molecule undergoes a transition from an upper to a lower state, and the transition energy is transferred to the colliding molecules as kinetic energy or also partly as internal excitation. This kinetic and inner energy of the molecules determines the heat and temperature of a gas, not “electrons in those atoms resonating or moving faster than they were before”.

As the collision rates in the troposphere - and even up to the stratosphere - are orders of magnitude larger than the spontaneous decay rates of the vibrational modes, one might expect that any radiation of the molecules is completely suppressed (quenched). But in the same way as molecules are deexcited by collisions, they can also be excited by inelastic collisions (see above), which remove kinetic energy from the gas mixture and convert it back to excite the GH-gases. Thus, lower-lying energy levels are continuously re-populated, when there is sufficient thermal energy. The population density of the states is determined by the Boltzmann distribution, and thus, by the temperature (see also: Harde 2013 http://dx.doi.org/10.1155/2013/503727, Subsec. 2.3). This continuous re-population ensures that spontaneous emission occurs largely independent as thermal background radiation and parallel to the superelastic collisions (Harde 2013, Subsec. 2.5). Only the linewidths of theses transitions are significantly broadened due to the collisions and are found as an almost continuous absorption band respectively emission band around a central frequency. Over longer pathlengths as in the atmosphere or at higher mixing ratios as in our experiment the radiation can achieve the same strength as a blackbody radiator, and at thermal equilibrium this is only controlled by the gas temperature.

@J.G.: The absorption and also re-radiation depend on the product of pathlength and mixing ratio together with the local temperature. The reader of this blog may decide, if our studies attack mainstream science with poor experimental design and if we mix gases with a procedure too unlike that of the atmosphere to see the effect we deem exaggerated.

Apparently J.G. didn’t realize, what we were presenting and verifying with our set-up. He should have read more carefully, what we write under Section 6 of the shorter paper and in more detail in our original paper https://doi.org/10.53234/scc202203/10 (Section 6 and Appendix 5). There is explained, how our measurements and their simulation can directly be compared with atmospheric conditions and calculations. There, we also show that without feedbacks this exactly reproduces the basic Equilibrium Climate Sensitivity (temperature increase at doubled CO2-concentration) of ECS_B = 1.05°C, as specified in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Significant differences to the IPCC’s Assessment Reports 5 and 6 only show up, when considering feedback processes (for details see: Harde 2017 https://doi.org/10.1155/2017/9251034 and Harde 2022 https://doi.org/10.53234/scc202206/10).

Concerning J.G.’s statement: “They object to experiments with stratification and increased infrared insolation, and miss what it takes to model what's confirmed in satellite measurements of specific wavelengths' absorption”, he should also look to Harde 2013 (http://dx.doi.org/10.1155/2013/503727, Figs 21 and 22). Our atmospheric simulations, which are based on Line-by-Line Radiation Transfer Calculations with up to 100.000 lines and for more than 200 atmospheric layers, are well reproducing satellite measurements and also observations of the atmospheric back-radiation. Our calculations for the laboratory experiment were performed with up to 30.000 lines for the individual gases and in steps of 1 cm for 111 slices over the propagation path.

@FlatterMann: He writes “This sounds like horrendous nonsense to me. Most of the radiation in this geometry will simply be transported by reflection on the chamber walls. A realistic experiment just from an optical standpoint would have to have a diameter that is, at least, ten times the distance between the two radiating surfaces. Convective mixing and heat transport at such a strong temperature gradient is most likely completely uncontrolled. This does not even come close to resembling a scale model of a planetary atmosphere”.

In one aspect FlatterMann is right, most of the radiation from the warmer plate downwards and from the colder plate upwards as well as the spontaneous radiation of the GH-gases is reflected at the side-walls on the way through the gas column. This has extensively been investigated in Section 4 of the original paper without and with GH-gases. But the highly reflecting side-walls to a larger extent just compensate the radiation losses, which appear between parallel plates of larger distance than their diameter. So, for radiation from the cold to the warm plate we measure a transmission of 75% and for the emission of CO2, e.g., a fraction of 65% compared to the theoretical uptake between infinitely extended plates.

@Cloudyman: He believes that “the large effect from those type of experiments is just due to CO2’s lower conductivity than regular air making a sort of conductive/convective insulating layer above the surface, ie you would get the same effect with Argon which is not IR-active”.

Sorry, that’s the wrong interpretation, look to our control measurements with the noble gases He and Ar, He with a significantly higher thermal conductivity, Ar with a lower conductivity than air and comparable with CO2 and N2O (see https://doi.org/10.53234/scc202203/10, Section 4 and Appendix 3). Within our measuring accuracy no differences between the noble gases and air in the energy balance could be observed. Thus, based on these experiments heat conduction as a reason for the observed changes can well be excluded. Convection is well suppressed by the set-up with the warmer plate in the upper position.

In summary:

  • There is no other explanation than back-radiation from GH-gases, which is additionally heating the earth plate, respectively reducing its supplied power to stabilize the plate at a fixed temperature.
  • The measured temperatures of the earth plate or saved powers exactly reproduce the calculated warming as a function of the mixing ratio for the gases CO2, CH4 and N2O.
  • Any energy transfer in form of radiation or additional heating is finally again re-radiated by the greenhouse gases. The temperature of the gas is increasing, till the radiation losses are in equilibrium with the supplied power.
  • Radiation from a blackbody radiator with higher temperature than the greenhouse gas is absorbed on the ro-vibronic bands and results in a local heating of the gas. Net absorption only continues till the incident intensity is the same as the eigen-radiation of the gas on its transition frequencies.
  • For a gas with the same temperature as an internal or external blackbody radiator the outgoing intensity is the same as the incident intensity.
  • A larger local and global warming of a GH-gas is restricted by its own radiation. This limits the effective absorption from an IR or visible light source and impedes distinction of this contribution from the dominating waste heat when trying to verify the GH-effect by measuring the gas temperature.
  • A prerequisite for the observation of the GH-effect in the atmosphere and in the same way in a laboratory experiment is a temperature gradient in the gas, otherwise no net changes in the radiation balance can be expected.
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  • $\begingroup$ I realized the paper concedes pre-feedback warming. The problem is its case against feedback. Even without warmed air (and it only argues against direct air warming), a warmer ocean evaporates more, except into already very humid air. $\endgroup$
    – J.G.
    Apr 30, 2023 at 13:23

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