We are now ready to take the final step in the evaluation of the main scientific evidence underlying CO2 alarmism, which consists of outgoing long wave radiation OLR spectra produced by a combination of mathematical software (Modtran) and measurement of the line spectrum of atmospheric CO2 (IRIS interferometer).
The warming effect or "radiative forcing" of CO2 is seen as the area of the ditch in the OLR spectrum in the wave number band 550 - 800 containing the line spectrum of CO2 around the main resonance 667, which by Modtran is predicted to increase by 3.7 W/m2 upon doubling of the concentration of CO2 to 600 ppm from preindustrial level of 300 ppm, which is commonly translated to a global warming of 1 C. Starting from the present level of 395 ppm Modtran predicts a global warming of 0.5 C from radiative forcing of 2 W/m2.
Global warming of 0.5 C is too small to be observed and thus cannot give rise to alarm. In any case CO2 alarmism starts from 1 C warming from doubled CO2, which is then inflated to 3 C by postulated feedback effects for which scientific evidence is missing.
The scientific evidence of the warming effect of CO2 thus boils down to the Modtran prediction of 3.7 W/m2 upon doubling to 600 ppm as the increase of the ditch area. Inspection of the OLR spectrum produced by Modtran shows that bottom of the ditch is connected to temperature 220 K which is the minimum temperature of the troposphere with top at 10 km and the constant temperature in the tropopause between 10 and 20 km. The increase in ditch area is thus seen to come from the shoulders of the spectrum around wave number 600 and 800 containing weak spectral lines of CO2.
This effect can be studied by the Gas-Cell Simulator by Spectral Calc with a free version online, which is similar to Modtran. Spectral Calc shows to produce atmospheric CO2 spectra with a simple dependence on the parameter p x L, where p is the partial pressure of CO2 (bar) and L is the path length (m). The switch from transparency to opaqueness shows to occur for p x L ~ 1, which indicates that the effective emission altitude on the shoulders could increase by 1000 m upon doubling of CO2. With a lapse rate of 6 C/km and a width of the shoulders of 100, this can be estimated to a radiative forcing of the same size as the 3.7 W/m2 by Modtran.
We have now decoded the radiative forcing of 3.7 W/m2 from doubled CO2 predicted by Modtran as the result of a very simple model of line broadening of the weak spectral lines of CO2 on the shoulders of the line spectrum around the main resonance 667. The effect could as well be 2 W/m2, or 1 W/m2, in which case CO2 alarmism would have nothing to start from.
Increasing CO2 beyond 600 ppm lifts the effective emission altitude of the main resonance of CO2 at 667 into the warmer stratosphere with a cooling effect, which may dominate the warming effect from the shoulders. The same evidence in the form of Modtran predicting 1 C warming by an increase from 300 ppm to 600 ppm, thus may give cooling under further increase.
It is mind-boggling to realize that the scientific basis of CO2 alarmism asking for a complete transformation of human civilization into a carbon-free society, consists of simple ad hoc model of broadening of a CO2 line spectrum predicting global warming of 1 C from radiative forcing of 3.7 W/m2 by doubled CO2, which could as well be instead 0.5 C, too small to be observed.
The mantra of 3.7 W/m2 will certainly be repeated in the upcoming IPCC 5th report as the foundation of the house of cards of CO2 alarmism. The time of reckoning is here as soon as leading climate skeptics (finally) realize and articulate the weakness of the 3.7 W/m2 card.
PS1 World Leading Swedish Meteorologist Lennart Bengtsson is now switching from warmist to skeptic and will have to retract his support to IPCC expressed in a statement by the Royal Swedish Academy of Sciences, which will change Swedish climate politics.
PS2 The falling house of cards is now creating head lines in the press.
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