The warming effect of atmospheric CO2 as a "greenhouse gas" is evidenced by the atmospheric radiative transfer computer code Modtran based on the high-resolution transmission molecular absorption data base Hitran, while direct observational evidence is lacking. CO2 alarmism is thus based on Modtran/Hitran.
In a previous post I noticed that Modtran assigns 1 ppm of CO2 a radiative forcing or warming effect of 6 W/m2. A very big effect from a very small cause! It is indeed very difficult to believe that one CO2 molecule per one million of O2/N2 molecules can change anything observable. This is like changing one grain of sand in the above picture!
Clive Best shows in The CO2 GHE Demystified using a radiative transfer model similar to Modtran a radiative forcing effect upon doubling of CO2 from 300 ppm to 600 of 3.52 W/m2 in close correspondence with the 3.7 W/m2 put forward by IPCC. The radiative forcing is shown to result from an increase of the effective altitude of radiation around wave numbers 600 and 750, which are far out on the "shoulders" of the CO2 spectrum centered at the main resonance 667. This is again a big effect of a small cause, since the spectrum on the shoulders is very sparse. The model further shows that the main emission from the band around 667 without shoulders occurs from altitudes of 30-40 km in the very thin stratosphere.
In both cases CO2 is attributed strong absorptivity away from the main resonce at 667, with very sparse spectral lines depending on concentration. Both results are most remarkable as a big effect of a small cause and as such call for a thorough investigation of the validity of the underlying radiative transfer model as concerns the effect of an atmospheric trace gas.
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