Debunking the Latest CO2 "Saturation" Paper

A paper published earlier this year is the latest in the long history of attempts to show that CO2 is already "saturated" in the atmosphere, and therefore increased CO2 cannot cause any more warming. The latest in a series of these kinds of papers from Kubicki et al 2024[1] attempts to make this point by modeling the atmosphere in a couple different experiments. The result of their experiments suggested to them that we should question whether "additionally emitted CO2 in the atmosphere is indeed a greenhouse gas," since their experimental results, "unequivocally suggests that the officially presented impact of anthropogenic CO2 increase on Earth's climate is merely a hypothesis rather than a substantiated fact." But de their experiments actually justify this claim?

The Greenhouse Effect

In order to see if their experiment indeed challenges accepted science regarding the Greenhouse affect, we should first explain how increasing CO2 is expected to cause an increase in GMST - that is, we need to understand how the Greenhouse Effect (GHE) works with respect to CO2. Broadly speaking, increasing CO2 pushes climate towards warming for two reasons:

1. As CO2 increases, the altitude at which upwelling longwave radiation (LWR) can escape into space moves higher into the atmosphere, where the air is both colder and thinner. As this altitude gets higher, it also gets colder, and colder air is a less efficient emitter than warmer air, so overall more heat is trapped in the atmosphere, and the surface warms according to the lapse rate. This would continue to be true even if CO2 were "saturated" near the surface relative to upwelling radiation.
2. The central and primary wavelength absorbed by CO2 is at the 15 micron band, but as atmospheric CO2 concentrations increase, more absorption occurs at the "wings" - that is, at wavelengths outside of central wavelength of LWR absorption. The increasing importance of the wings as CO2 increases means that CO2 is not actually saturated at all relative to upwelling radiation.

I go into more detail about these reasons in another post, so I won't say more here. But any proper test of the GHE with respect to CO2 must be able to simulate the impact of increasing CO2 on that altitude at which LWR finally escapes into space, which becomes progressively higher and therefore colder and thinner as concentrations increase. The test should also evaluate the relative impacts of the central 15 micron band and the wings as CO2 increases. 

Kubicki's CO2 Experiment

Kubicki's first test of the GHE was to use an oil-filled "glass vessel" as a "source of radiation" with oil temperatures of 78.6°C and 109.5°C; a graphite layer was added to the glass vessel to emit thermal radiation. They say this was done according to one of their 2022 papers, so I checked that paper[2] and found that the "graphite emissive surface applied to a copper plate adjacent to the flat surface of a glass vessel with heated oil." So they simply attached this "emissive surface" to the outside of a glass container. To simulate the atmosphere, they used a 1 meter long and 150mm diameter PVC pipe with polyethylene film windows on either end of the pipe. At the far end of the pipe was a "radiation power meter." They "injected" CO2 into the PVC pipe according to the diagram below.

Figure 7

A few things should become immediately obvious:

1. Since glass is opaque to IR light, and since the "graphite layer" was simply fixed on the side of the heated glass vessel, the radiation emitted from the vessel would not contain much LWR at wavelengths absorbed by CO2. Since the graphite layer was fixed to the glass surface, heat would transfer to it by conduction, but this is a poor experimental design.
2. The heat that is emitted from the vessel would warm the PVC container, which would then heat the air inside the container by conduction, meaning that it's not testing the GHE very well at all.
3. Since the PVC pipe is only 1 m long, there's absolutely no way it can test how the greenhouse effect increases with elevated CO2, which works on an atmosphere several kilometers thick that becomes both thinner and cooler at higher altitudes.

This experimental set up is not designed properly to test the GHE, and it certainly cannot detect if there is a saturation point that limits warming above a certain concentration or "saturation mass."

Kubicki's Moon Experiment

Kubicki then attempts to construct an experiment based on a telescope pointed towards the moon. He estimates that the sunlit portion of the Moon's surface is 110°C, and that emitted LWR from the Moon's surface must travel through the Earth's atmosphere to get to the surface. They reason if you point a detector at the Moon, you should see a "dip in the spectrum of this radiation, reducing its overlap with the absorption spectrum of CO2, and consequently, the absorption of this radiation by additional carbon dioxide should decrease." So they set up a two-stage experiment in which they first pointed telescope at a "lunar simulator" (by which they mean an object heated to 110°C) and put one of two cuvettes between the lunar simulator and the telescope, one with air and one with CO2. They saw 14% absorption of radiation when using a CO2 cuvette. Then they used the same set up and pointed it at the Moon instead of a lunar simulator, and they observed that "the absorption of this radiation in carbon dioxide in the cuvette was practically negligible." They conclude, "additional carbon dioxide does not absorb thermal radiation that has been emitted from the heated surface of the Moon and has passed through the Earth's atmosphere."

Figure 11

But how much thermal radiation originating from the Moon would you expect at the Earth's surface when compared to the downwelling LWR already in the atmosphere? In the first part of the experiment, the temperature of the "lunar simulator" may be the same as the Moon, but it's also much closer, so more of the LWR radiating from the simulator would reach the telescope than LWR emitted from the Moon. The amount of LWR from the moon reaching the Earth's surface would be practically negligible, and we wouldn't expect to see a difference between the air cuvette and the CO2 cuvette.

Let's do some simple math. The Sun and the Moon are about the same angular size (the Moon is much smaller but also much closer), and the Sun (5,772 K) is about 15x hotter than the Moon (110°C or 383 K), so if total solar irradiance (TSI) is 1361 W/m^2, then "total lunar irradiance" (TLI) would be 1361/15^4 = 0.027 W/m^2. The radiative forcing at the Earth's surface (assuming an albedo of 0.3) would be 0.027*(1-0.3)/4 = 0.005 W/m^2. But the average downwelling LWR at the Earth's surface from the atmosphere is about 333 W/m^2. Why do the authors of this study to think a change of 0.005 W/m^2 from what is otherwise 333 W/m^2 would be anything other than "practically negligible?" This is a dumb experiment, and the results they observed were precisely what we'd expect if increasing CO2 has a significant impact on global temperatures.

Humlum Redivivus

Much of this paper is just rehashed from previous papers they wrote, and there's not much new in this paper. But following their failed experiments described above, they rehashed an old argument from 11 years ago published by Ole Humlum.[3] That paper argued that temperature causes CO2 to increase, not the other way around. That paper was debunked in several comments to the original paper.[4][5] Among its many flaws, Humlum took the derivative of CO2 and temperature, essentially detrending CO2 and temperature and removing the long-term effects of CO2 on temperature, then argued that temperature caused the long-term increase in temperature. In fact, all he succeeded in doing is showing that ENSO has a significant impact on variability in the increase in CO2 on an annual basis. This is neither new nor interesting, and it doesn't support the argument of the paper. I shared my own debunking of this paper in another post, so I won't repeat myself here.

Conclusion

There is nothing in this paper that qualifies as an experimental test either of the greenhouse effect or of the possibility that CO2 is "saturated" in the atmosphere. There is nothing in this paper that warrants the conclusion that there is a "need for continued and improved experimental work is suggested to ascertain whether additionally emitted carbon dioxide into the atmosphere is indeed a greenhouse gas." The authors clearly don't understand how the greenhouse effect works, and so their experiments have nothing to do with the actual greenhouse effect. As I was writing this, I came across a new video by Sabine Hossenfelder, who came to similar conclusions (I have one trivial gripe about her video, but it's not worth mentioning). Needless to say, we can file this paper away as yet another in the long tradition of scientists writing outside their field of expertise in low-to-no impact journals with challenges to climate science based entirely on bad experiments.

References:

[1] Jan Kubicki, Krzysztof Kopczyński, Jarosław Młyńczak, Climatic consequences of the process of saturation of radiation absorption in gases, Applications in Engineering Science, Volume 17 (2024), 100170, ISSN 2666-4968, https://doi.org/10.1016/j.apples.2023.100170.

[2] J. Kubicki, K. Kopczyński, J. Młyńczak. Absorption characteristics of thermal radiation for carbon dioxide. IAPGOŚ, 12 (2022), pp. 4-7, 10.35784/iapgos.2998

[3] Ole Humlum, Kjell Stordahl, Jan-Erik Solheim, The phase relation between atmospheric carbon dioxide and global temperature, Global and Planetary Change, Volume 100, 2013, Pages 51-69, ISSN 0921-8181. https://doi.org/10.1016/j.gloplacha.2012.08.008.

[4] Richardson, M. (2013). Comment on “The phase relation between atmospheric carbon dioxide and global temperature” by Humlum, Stordahl and Solheim. Global and Planetary Change, 107, 226–228. doi:10.1016/j.gloplacha.2013.03.0

[5] Masters, T., & Benestad, R. (2013). Comment on “The phase relation between atmospheric carbon dioxide and global temperature.” Global and Planetary Change, 106, 141–142. doi:10.1016/j.gloplacha.2013.03.010