How Atmospheric Gases Absorb Heat
Aleksandr Zhitomirskiy
April 14, 2025
This article considers the position of the absorption bands of the main greenhouse gases within the spectra of incident solar radiation and terrestrial radiation. The presence of absorption bands for CO, HO, CH, and NO in the near-infrared range of solar ₂₂₄₂ radiation may indicate that these gases impede radiation from reaching the Earth's surface. However, the fact that one of the main absorption bands of CO (4.3 μ) falls ₂ within a section of minimum energy for both solar and terrestrial radiation, and the other band (15 μ) is significantly removed from the peak of the terrestrial radiation curve, does not support the proposed role of this gas in absorbing energy emitted by the Earth. Furthermore, the theory of the greenhouse effect overlooks the inverse square law regarding the decrease in the intensity of radiated energy with distance from the emitting object—the Earth's surface. The attempt to explain the heating of "non-greenhouse" gases through energy transfer from "greenhouse" gases is unsustainable and contradicts the established principle of independent heating of any substance by any energy source. Therefore, the hypothesis regarding the existence of "greenhouse" gases is inconsistent with the observed facts.
Introduction
Most modern climatologists attribute the increase in the average global temperature of the atmosphere and the Earth's surface to the greenhouse effect. The essence of this effect, as described in numerous publications by the IPCC, NOAA, NASA, and individual authors, is the retention of heat in the atmosphere due to its absorption by so-called greenhouse gases. These gases, also referred to as "trace gases" due to their low atmospheric concentration, are said to absorb infrared radiation emanating from the Earth, which the greenhouse effect theory equates to the absorption of thermal energy. These same gases allegedly emit the absorbed energy back towards the Earth (reverse radiation), leading to additional heating.
Several questions arise when considering the facts related to this described process. First, it is unclear how the atmosphere as a whole absorbs heat, given that it mainly consists of gases transparent to infrared radiation (non-greenhouse gases). Second,
how can we isolate the contribution of greenhouse gases to atmospheric heating via radiative absorption from other mechanisms that determine heat absorption by nongreenhouse gases? And lastly, what evidence demonstrates that infrared absorption causes heat absorption? To answer the first question, we need to understand how the atmosphere interacts with solar radiation.
Solar radiation and heating
The fact that the surface of the earth and water is heated by incident solar radiation is obvious and indisputable. At the same time, there is no direct experimental evidence that this radiation, passing through the atmosphere, heats atmospheric gases along the way. Physical theory also does not give a detailed description of this process, only general ideas are known. According to J.C. Maxwell, in the process of radiation "the hotter body loses heat and colder body receives heat by means of a process occurring in some intervening medium which not itself become thereby hot” [1, p.10]. The concept of "intervening medium" strictly speaking refers to a vacuum, and Max Planck applies it to the atmosphere with significant reservations: "There is but one medium that is diatermanous for all kinds of rays, namely, the absolute vacuum, which is to be sure cannot be produced in nature except approximately. However, most gases, e.g., the air of the atmosphere, have at least they are not too dense, to a sufficient approximation the optical properties of a vacuum with respect to waves of not too short length” [2, p.53]. The physical theory of radiation since the time of Maxwell and Planck has not clarified in detail the interaction of radiation with gases. Any hypothesis must be based on established facts. The idea of the interaction of solar radiation with the atmosphere is based on known data on the upper layers of the atmosphere. In the ionosphere, X-rays and high-energy ultraviolet radiation knock electrons out of gas atoms and molecules, turning them into ions. The radiation energy is converted into chemical energy. The reverse process of converting ions into atoms and molecules is exothermic, i.e. accompanied by the release of heat, which is found in the thermosphere (part of the ionosphere). A similar process occurs in the stratosphere, with the difference that the rupture of bonds in molecules (primarily oxygen) requires less energy than ionization, and is carried out due to UV radiation in the middle range (200-280 nm). The release of heat is confirmed by the higher temperature in the stratosphere compared to the tropopause located below.
The facts mentioned relate to the transformation of radiant energy into chemical energy and then into thermal energy, but not to the direct heating of atmospheric gases by radiant energy. Direct confirmation of such heating has not been obtained in laboratory experiments and does not follow from observations. At least, it does not agree with the regular decrease in air temperature with height above the surface. The absence of an observed effect may be due to the relatively low density of the Earth's atmosphere. According to D. Singh [3], on Venus, where the atmospheric pressure is 92 times higher than on Earth, only 2.5% of solar radiation energy reaches the planet's surface. It follows that the atmosphere of Venus is mainly heated by incident solar radiation, although the role of the planet's volcanic activity cannot be ruled out. The heating of any substance by radiation depends on the nature and intensity of the radiation, as well as on the nature of the substance absorbing the radiation. Consider these issues in more detail with respect to atmospheric gases.
Heating power of radiation and properties of gases
It has long been known that different types of radiation have different heating capabilities. High-energy radiation, as far as we know, does not create a direct thermal effect. When undergoing a medical examination on an X-ray machine, we do not feel the heat, just as we do not feel it in the dentist's office when checking the condition of teeth using X-ray film. Researchers who have worked with radioactive substances know that a container with an ampoule of cobalt-60 (gamma radiation energy 1.3 MeV) does not differ in the temperature of the outer wall from other objects in the laboratory. Obviously, high-energy radiation hitting a material object is not converted directly into thermal energy. As J.C. Maxwell noted, “...the blue and green rays have very little heating power compared with the extreme red” and “heating rays are far beyond the end of the red” [1, p.233]. Unfortunately, as 150 years ago, we have neither a quantitative estimate of the relationship between the characteristics of radiation and the "heating power", nor knowledge of how far the action of thermal rays extends "beyond the end of the red". We actually know no more about heat rays than that, according to Planck, they “are identical with light rays of the same wavelength” [2, p.4] (by light rays is meant not visible light, but any radiation). Thermal rays, interacting with matter, accelerate the vibrational motion of atoms in the structure of a solid body and the motion of molecules in a liquid. In the case of gases, the kinetic energy of the translational motion of molecules under the action of radiation should also increase. The problem is that it is unknown how to separate the effect of direct action of radiation from the transfer of heat
to the gas from a solid and liquid substance heated by radiation. What properties of gases are associated with the absorption of thermal radiation? - In essence, the exact answer to this question is unknown. We know that the absorption of thermal energy is determined by the heat capacity and thermal conductivity of any substance, regardless of the nature of the source of this energy. All substances, both "greenhouse" and "non-greenhouse" gases, have these properties.
Gas Concentration, vol. % Heat capacity, J mol-1 K -1 Thermal conductivity, W m-1 K-1
The values gas concentration are given in terms of dry air. The volume (molar) concentration of water vapor in the air varies from 4.5% to hundredths of a percent, its molar heat capacity is 33.5, thermal conductivity is 0.025. It is obvious that the thermophysical characteristics of "non-greenhouse" (N2 , O2, Ar) and "greenhouse" (H2O, CO2 , CH4) gases are of the same order of magnitude and are in no way related to the ability of gas molecules to absorb infrared radiation. It follows that all atmospheric gases can absorb and transfer heat by the mechanism of conduction and convection, while the mechanism of heat absorption by radiation remains unclear.
The greenhouse effect theory states that heat absorption is carried out by greenhouse gases due to their absorption of infrared radiation emitted by the earth's surface. In this regard, questions arise: a) what part of the radiation is absorbed by greenhouse gases, b) how this radiation is converted into thermal energy, c) how is energy transferred from greenhouse to non-greenhouse gases.
Sun radiation and infrared spectra of gases
Publications on the greenhouse effect usually consider the absorption by greenhouse gases of infrared terrestrial radiation from the earth. However, in the spectra of the main greenhouse gases - water vapor and carbon dioxide - there are absorption bands in the near infrared region of incident solar radiation.
Sun Irradiance [4] Spectrum of carbon dioxide Spectrum of water vapor
Wavelength range, μ
W/m2
μ
1.000 – 1.705
– 2.390
– 4.000
[5]
2.013, 2.060 [5]
[7]
2.734 [6]
Some other greenhouse gases also have absorption bands in the near infrared region, corresponding to incident solar radiation. Methane has a broad absorption band with many peaks in the range 3.200 – 3.500μ, and N2O has a narrow band near 2.900μ (NIST).
If gases, as the greenhouse effect theory claims, absorb thermal energy by absorbing infrared radiation, then in the region of the spectrum of incident radiation they, at least, partially absorb part of the flux falling on the earth, thereby reducing the heating of the surface. As far as is known, this paradox has not been discussed in the literature and it is unclear what the resulting effect might be. Let's see which regions of the Earth's (terrestrial) radiation correspond to other gas absorption bands in the infrared spectrum.
Terrestrial radiation
For radiation emanating from the surface of the land and water (terrestrial radiation), the energy values at different wavelengths (λ) and temperatures (T) are usually determined by calculation based on the Planck equation: E λ = c2 h λ-5 [exp(ch/kλT) – 1] -1 , where c = 2.998×108 m/s, h = 6.626×10-34 J s, k = 1.38×10-23 J/K. At the same temperature, the wavelength value corresponding to the maximum energy on the Planck curve E λ = f (λ) is determined by the Wien equation λ max = b/T (b = 2898μ K), which is also derived from the general Planck equation [2]. The energy values E λ calculated using the Planck equation have the dimension J c-1 m-3 or W m-3 and when multiplied by the value 2 π meters, correspond to the values found using the Stefan-Boltzmann equation for a given temperature T: E = σ T 4 (σ = 5.67× 10-8 W m-2 K-4 ) .
Calculations based on these equations cannot be considered completely accurate, since, strictly speaking, the theory describes the radiation of an absolute black body into a vacuum. Naturally, the Earth cannot be considered a black body, especially since the difference between different parts of the surface and the ideal black body is not the same. As for the difference between a vacuum and an atmosphere, Planck suggested that “radiation in the
air is approximately identical with the radiation into vacuum” [2, p. 75]. However, this does not agree with the idea of partial absorption of radiation by gas molecules: in a vacuum, no absorption of radiation is possible. However, let us try to ignore these problems and, in accordance with the greenhouse effect theory, compare the black body radiation spectrum with the infrared spectra of the main greenhouse gases. The curves E λ = f (λ) for the temperature range of the usual on most of the earth's surface (273 - 303 K) have maxima at wavelengths of 10.6 - 9.6 μ, reach zero E λ near 3μ and decrease to very small E λ values at λ > 50 μ [8]. The main greenhouse gas CO2 has two absorption bands in this region: an intense one (transmission close to zero) at 4.2 - 4.4 μ and a less intense one (transmission about 0.4) at 13.8 - 16.1 μ with a sharp peak at 15 μ [7]. The first of these bands falls within the interval where both the energy of the terrestrial radiation and the energy of the incident solar radiation are close to zero. The second band is relatively far from the maximum of the terrestrial radiation and calculation of the area under the Planck curve for this band [8] shows that the absorption of energy in this region will be less than 15% of the total value. It is therefore unclear where carbon dioxide gets the energy to act as a greenhouse gas.
In the literature on the greenhouse effect, as far as we know, the question of the change in the intensity of terrestrial radiation with distance from the surface has not been considered. Meanwhile, for any radiation, the law of decreasing intensity holds true proportionally to the square of the distance from the source [9]. In the case of incident solar radiation, the thickness of the earth's atmosphere is negligibly small compared to the distance from the Sun to the Earth, so it can be assumed that the amount of energy measured at the top of the atmosphere will be the same at the surface of the Earth (naturally, minus the energy absorbed by the atmosphere with clouds and aerosols). However, in the case of terrestrial radiation the situation is completely different. When we stand barefoot on a hot sunny day on the beach, our feet feel the hot sand, while our face feels much cooler air. A simple calculation shows that at a height of 100 m from the ground, the radiation intensity will be 10,000 times less than at a height of 1 m. It follows that gases that are lighter than air (e.g. methane) are practically unable to absorb terrestrial radiation due to
its negligible intensity at practically low altitudes. Accordingly, there is no point in talking about the greenhouse properties of ozone, the main amount of which in the atmosphere is located at a distance of over 15 km from the surface. From the above it follows that we have no reliable facts confirming the absorption of thermal energy by greenhouse gases either in the area of solar energy falling on the earth or in the area of earth radiation. Nevertheless, let us imagine that the greenhouse effect theory is correct and see how in this case the absorption of heat by the atmosphere as a whole can be explained.
Absorption of heat by non-greenhouse gases
Non-greenhouse gases allow infrared radiation to pass through freely, since there is no vibrational motion of atoms in the molecules of these gases. The main non-greenhouse gases in the atmosphere are nitrogen, oxygen and argon, which, calculated on a dry air basis, make up 99.95% of the total volume of the atmosphere. If we imagine that the absorption of thermal energy in the atmosphere is caused by the absorption of infrared radiation by greenhouse gases, then the greenhouse gases must somehow transfer this energy to the non-greenhouse gases. The question of the mechanism of energy transfer is not addressed either in the IPCC reports, which describe the essence of the greenhouse effect, or in the courses on atmospheric physics.
An explanation of such a mechanism was proposed in a discussion article by R. Wentworth [10]. The author writes: "And in the case of CO, each air molecule collides ₂ with 2500 other molecules about every 0.4 microseconds. So, heat in air can be distributed to and from CO very quickly ₂ and efficiently (i.e., within 0.4 microseconds)” (paragraph 8, p. 4). The ratio 1:2500 is considered based on the volume (molar) concentration of CO2 in the air of 0.04%, the time of collisions can be calculated from the data on the free path of molecules in the air (depending on temperature and pressure). However, this description raises at least two questions. The first of them concerns the theory of probability. What is the probability that the CO2 molecule (the only energy carrier?) will each time collide with exactly that one of the 2500 non-greenhouse gas molecules with which it has not collided before? Obviously, such a probability must decrease rapidly with time. The second question concerns the amount of energy that the CO2 molecule allegedly transfers to all 2500 other molecules. If such a transfer can provide heating of a certain volume of air, say, by 0.5 K, then to what temperature can pure CO2 be heated? The decisive argument against the idea of energy transfer from
greenhouse gases to non-greenhouse gases through molecular collisions is the fact that any substance, separately, is heated by any heat source. B. MacDonald proposed to consider nitrogen and oxygen as greenhouse gases, based on the fact that vibrational modes for these gases corresponding to wave numbers of 1556 cm-1 and 2330 cm-1 were detected in the Raman spectra of these gases [11]. Accepting this idea makes senseless the struggle of modern climate scientists to reduce greenhouse gas emissions. However, from a scientific point of view, the connection between Raman spectra and heat absorption seems as controversial as in the case of infrared spectra. The Raman effect is an inelastic scattering of photons of a molecular bond, and the characteristic frequencies observed in the Raman spectrum correspond to the vibration frequencies of the molecular bond. Excitation of this vibration cannot change the kinetic energy of the molecule's motion in space, which is directly related to the gas temperature. Naturally, there is no experimental confirmation of the connection between Raman spectra and the absorption of thermal energy. The author's statement [11] that "all substances have thermal absorption properties, as measured by their respective heat capacities" is absolutely correct. This statement corresponds to the theory of heat, and Raman spectroscopy is not needed to substantiate it.
Conclusion
This article examines the position of the absorption bands of the main greenhouse gases within the spectra of incident solar radiation and the Earth's infrared radiation. Carbon dioxide exhibits five absorption bands, and water vapor has two in the near-infrared region (wavelengths less than 4 μm) of incident solar radiation. If, as posited by the greenhouse effect theory, the absorption of infrared radiation is equivalent to the absorption of thermal energy, then these greenhouse gases would reduce the potential heating of the Earth's surface. The spectrum of Earth's radiation, calculated using Planck's law under the blackbody assumption, spans the region from 4 to 50-60 μ, with the peak emitted energy occurring between 9.5 and 10.5 μ for temperatures ranging from 303 to 273 K. The central wavelengths of the main CO absorption bands in this region ₂ are 4.3 and 15 μ. The 4.3 μ band corresponds to a spectral region where both incident solar and terrestrial radiation energies are negligibly small. The 15 μ band falls within a region distant from the peak energy and encompasses only a minor portion of Earth's radiation. These observations do not support the notion of a significant role for carbon dioxide in trapping Earth's infrared radiation.
The greenhouse effect theory typically treats greenhouse gases (excluding water vapor) as "well-mixed" and assumes they absorb infrared radiation energy according to their spectral characteristics. This approach neglects the inverse square law, which dictates that the intensity of radiation from the Earth decreases proportionally to the square of the distance from the emitting surface. Consequently, in reality, significant radiation absorption would likely be limited to heavier gases (CO, NO, CFCs, etc.) near the Earth's surface, and less so for ₂₂ lighter gases like methane at higher altitudes.
All atmospheric gases possess specific heat capacity and thermal conductivity values of similar orders of magnitude for both greenhouse and non-greenhouse gases. Therefore, all atmospheric gases can absorb and transfer thermal energy through conduction and convection. The attempt to explain heat absorption by nongreenhouse gases via energy transfer from greenhouse gases is unsustainable, as it contradicts the fundamental principle that any substance can independently absorb heat from an energy source.
In conclusion, the analysis of available evidence suggests that the hypothesis regarding the existence of greenhouse gases as primary drivers of atmospheric warming is flawed.
References
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