Basic physics shows that doubled CO2 will have little effect on ‘global warming’

French scientist summarizes the findings of physicist William Happer in a single figure

By Prof. Jean N., Faculty of Sciences, European University, June 2022

Originally published in French on Science, Climat, Energie.

When we talk about the greenhouse effect and the level of atmospheric CO2 there are three categories of scientists: 

(i) those who accept this greenhouse effect and who think that the increasing rate of CO2 will have major effects on the temperature of the lower troposphere; they are generally the partisans of the theses of the IPCC

(ii) those who accept the idea of ​​a greenhouse effect but who believe that the warming will be modest or even non-existent; they are scientists qualified as climato-realists or climato-skeptics; we can, for example, place in this category physicists and climatologists such as William Happer , Herman Harde , Roy W. Spencer , John Christy or Richard Lindzen

(iii) and finally those who do not accept the idea of ​​a greenhouse effect, for various theoretical reasons, and for whom inevitably there will be no effect of the increasing rate of CO2 . The latter scientists are also referred to as climate-realists or climate-skeptics; we can for example cite Gerhard Gerlich , Ralf D. Tscheuschner , Jack Barrett (at least in his 1995 article) and Georges Geuskens. Note that scientists in the above three categories generally do not deny slight global warming. Finally, there are also undecided scientists.

This article explains the vision of William Happer , a physicist belonging to category 2.

Happer’s ideas are clearly summarized in the figure below (Figure 1) , taken from his 2020 work with his colleague William Wijngaarden ( here ).

This figure represents the quantity of infrared emitted by the Earth according to their frequency (from the ground and/or from the atmosphere), at the altitude of the mesopause (86 kilometres), if a spectrometer were positioned at this altitude and pointed towards the ground.

Figure 1 shows four curves: three in the presence of various atmospheric compositions (black, red and green curves) and one without any atmosphere (blue curve). It should be emphasized that all these curves are the result of calculations and have not been measured at an altitude of 86 km.

Figure 1. Calculated radiation emitted by Earth at 288.7 K (15.5°C). Source: Happer & Wijngaarden (2020). The area under the plunging CO2 line (black and red) indicates less heat in Watts per square metre escaping into space, as calibrated on the vertical axis to the left. Any line under the blue line indicates less heat escaping into space than would be the case if there was no atmosphere (blue line).

To construct this figure, Happer and Wijngaarden used the HITRAN line-by-line molecular absorption and transmission database maintained at Harvard University ( Wijngaarden & Happer, 2020 ). HITRAN is an acronym coming from the English terms “high-resolution transmission.” This database compiles spectroscopic parameters that computer programmers can use to model the transmission and emission of light in the atmosphere. Importantly, Happer and Wijngaarden do not consider the effect of clouds. We will come back to that later.

The blue curve of Figure 1 represents the infrareds emitted by the surface of the Earth (the ground) towards space if the Earth did not have an atmosphere, for the temperature of 288.7 K (15.5°C) . It is a curve that can be calculated with Planck’s equation. The total energy emitted to space is the area under this blue curve.

The black curve in Figure 1 represents the infrared emitted by the Earth towards space with the current atmosphere, comprising 400 ppm of CO2 (at the time of writing), still for the temperature of 288.7 K (15.5°C). This is also a calculated curve using the HITRAN database.

We see that less energy is emitted to space because some atmospheric gases absorb infrared (and therefore the area under the black curve is smaller than in the previous case). The names of these gases are shown in Figure 1.

Note that this black curve is relatively close to the experimental curves observed by spectrometers placed in orbit around the Earth, at various altitudes. This is called in English the “Outgoing Longwave Radiation,” or OLR. A good example of a publication on this subject is that of Harries et al. (2001). All this seems to validate the method based on the HITRAN database.

The red curve in Figure 1 represents the infrareds emitted by the surface of the Earth towards space with an atmosphere identical to the current one but containing 800 ppm of CO2, again for a temperature of 288.7 K (15.5°C ). It is also a curve calculated with the HITRAN database. 

Here we see the most important point of Happer’s ideas: the difference between the black curve and the red curve is minimal , whereas the CO 2 level has been doubled! According to Happer’s calculations, the difference between the two curves is only 3 W/m2. In terms of the greenhouse effect, this 3 W/m2 corresponds to an increase in surface air temperature of only 1.4°C to 2.2°C (without the intervention of clouds). In other words, a doubling of CO2 caused warming of no more than 2.2°C, and as little as 1.4°C.

Finally, the green curve represents a hypothetical atmosphere, similar to the current atmosphere, but which would not contain any CO2 molecules . We see here that the area under the curve is larger than in the previous two cases.

We can therefore see that atmospheric CO2 absorbs the infrared emitted by the Earth well, but that currently, with 400 ppm, we have almost reached saturation. Indeed, if we add CO 2 to the atmosphere, it will hardly absorb any more infrared rays emitted by the Earth . And if one day we reach 800 ppm, the difference with the current situation will only be 3 W/m2.

What to Conclude?

The major conclusion is the following: if William Happer is right, the effect of a doubling of the CO2 rate on the temperature of the globe (from 400 to 800 ppm) will be minimal because CO2’s ability to deflect infrared radiation is already “saturated.”

But what would happen in the presence of clouds, which Happer doesn’t discuss? Considering that the current net effect of clouds is to cool (see here), and that it seems likely that the total water vapor in the atmosphere will decrease or remain stable (see here), Happer’s results suggest that we really don’t have to worry about rising CO 2 levels in the atmosphere.

This article originally appeared on the Friends of Science website.

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