Originally published in French on Science, Climat, Energie.
When we talk about the greenhouse effect and the rate of atmospheric CO 2 know that there are three categories of scientists : (i) those who accept this greenhouse effect and who think that the increasing rate of CO 2 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 CO 2 . 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, and finally note that there are undecided scientists.
The purpose of this article is to present to you the vision of William Happer , a physicist clearly belonging to category 2.
- The ideas of William Happer summarized in a single figure
W. Happer’s ideas are clearly summarized with the Figure below (Figure 1) , taken from his 2020 work with his colleague William Wijngaarden ( here ). This is a figure representing 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 km) . Just as if a spectrometer were positioned at this altitude and pointed towards the ground. Figure 1 actually shows us 4 curves: 3 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 in no way been measured at an altitude of 86 km.
Figure 1. Calculated radiation emitted by Earth at 288.7 K (15.5°C). Explanations in the text below. Source: Happer & Wijngaarden (2020) .
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 later.
The blue curve of this Figure 1 represents the infra-reds emitted by the surface of the Earth (the ground) towards space if the Earth did not have an atmosphere , and this for the temperature of 288.7 K (15.5°C) . It is of course a curve that can be calculated with Planck’s equation. The total energy emitted to space is simply 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 CO 2 , still for the temperature of 288.7 K (15.5°C). This is also a calculated curve, here with 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 . But we let you judge for yourself by consulting the cited article.
The red curve in Figure 1 represents the infra-reds emitted by the surface of the Earth towards space with an atmosphere identical to the current one but containing 800 ppm of CO 2 , always for the 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/m 2. If we talk about the greenhouse effect, this would correspond to an increase in surface air temperature of only 1.4 to 2.2°C (without the intervention of clouds).
Finally, the green curve represents a hypothetical atmosphere, similar to the current atmosphere, but which would not contain any CO 2 molecules . We see here that the area under the curve is larger than in the previous two cases. We can therefore see that atmospheric CO 2 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/m 2 .
We are not going to describe here all the results obtained by Happer and Wijngaarden and we simply refer you to their publication ( here ). To fully understand their results, you can also use the article published here .
- Who is William Happer?
Let us now briefly introduce William Happer. He was born in 1939 and spent a large part of his career at the famous Princeton University in the USA. Under the direction of Professor Donald Hamilton of Princeton, he obtained his doctorate in physics in 1964. His thesis focused on measurements of spins and magnetic moments of radioactive nuclei. He then began his academic career in 1964 at the Department of Physics at Columbia University where he became interested in the applications of optically polarized atoms. W. Happer's early work focused on the spin polarization of alkali metals (sodium, potassium, rubidium, cesium). He was one of the first to study the effects of light with a wavelength slightly different from atomic resonance, and he studied several effects, including the rotation of the polarization of light and Raman atomic transitions. These have become the pillars of modern atomic physics. In what has become the hallmark of all his research, Happer combined experimental measurements with the development of rigorous theoretical models and simple intuitive explanations. He also investigated the unique properties of spin-relaxation collisions between alkali metal atoms, which led, 30 years later, to the development of precision clocks and magnetometers. In addition to his scientific work at Columbia and Princeton, he served as co-director and director of the Columbia Radiation Laboratory.William Happer is the author of over 200 scientific publications and has received numerous awards for his research. For more information just check out his page at Princeton University ( here ). You can also listen to him speak in several short videos like here . William Happer should therefore know what he is talking about when he talks about the absorption of infrared by molecules like CO 2 because spectroscopy is his field of research.
3. What to Conclude?
– The major conclusion is obviously the following: if William Happer is right, the effect of a doubling of the CO 2 rate on the temperature of the globe (400 to 800 ppm) will be minimal because we have almost already arrived at a “ saturated”.
– But William Happer did not consider the clouds. What would happen in the presence of clouds? 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.
– Note that William Happer did not carry out field measurements with spectrometers placed on satellites. Its conclusions are therefore based on theoretical calculations.
– Finally, note that the article by Wijngaarden and Happer has not yet been officially published since it is a pre-publication deposited on the arXiv platform . It is therefore a work in progress. This is not a poor quality proof, because physicists and mathematicians very often proceed in this way. A famous example of an original result posted on arXiv is the proof of Thurston’s conjecture, involving the Poincaré conjecture (one of the seven millennium prize problems) as a special case, posted by Grigori Perelman in November 2002, work whose validity was officially recognized in 2006, which led to Perelman being awarded the Fields Medal (which, however, he declined).
As a final conclusion, let’s take the time to read and understand the objections and arguments of scientists from the three aforementioned groups . And once your decision is made, do not believe that you will never change your mind!
WA van Wijngaarden, W. Happer (2020) Dependence of Earth’s Thermal Radiation on Five Most Abundant Greenhouse Gases. arXiv:2006.03098 [physics.ao-ph]