Fabricated Evidence of GHE from CO2

The blogosphere offers many attempts to explain the CO2 greenhouse effect GHE, since it is not well explained in the scientific literature and it is the basis of CO2 alarmism. We find on Barret Bellamy Climate The GH effect of CO2 the following outgoing long wave emission OLR spectra with varying concentrations of CO2 as a trace gas (from 0 to 1000 ppm with 390 the present level) computed by Modtran:

 

Figure 2APortions of the emission spectra of the atmosphere with varying concentrations of CO₂(in ppmv as indicated in each portion). The portions of Planck curves are for comparative temperatures; from the top downwards the curves are appropriate for the temperatures 300 K, 280 K, 260 K, 240 K and 220 K. The horizontal axis gives the wavenumbers in cm^-1

 

Figure 2BPortions of the emission spectra of the atmosphere with varying concentrations of CO₂(in ppmv as indicated in each portion). The portions of Planck curves are for comparative temperatures; from the top downwards the curves are appropriate for the temperatures 300 K, 280 K, 260 K, 240 K and 220 K. The horizontal axis gives the wavenumbers in cm^-1

We see the ditch around the main resonance at 667 widening as the concentration of CO2 is increasing. We see that the effect from the present 390 to a doubling of preindustrial level to 600, is very barely noticeable as a slight widening of the ditch. Barrett Bellamy offers the further remarkable information about the total emissions:

• The spectral portions show only the emissions from water vapour and CO2when it is present. Consider the emission when CO2 is absent and assume that the global mean temperature is 280 K (7°C). The radiance to space is estimated to be 286.2 W/m2, considerably greater than the value required for radiative balance (235 W/m2). 
• Adding just 1 ppmv of CO2produces a noticeable effect and the Q branch of the spectrum is particularly obvious. The estimated radiance to space is 281.7 W/m2, a reduction of 4.5 W/m2. Such an atmosphere would be radiating less energy to space and the system as a whole would be warmer. Even 1 ppmv of CO2has a warming effect!

We read that even 1 ppm (0.0001%) of CO2 added to a carbon free atmosphere would have a warming effect or "radiative forcing" of 4.5 W/m2. Amazing! 

We read that the total effect of the present 390 ppm of CO2 is about 50 W/m2, about 20% of the total forcing from the Sun. Remarkable. (It is stated that Modtran with 390 ppm gives OLR of 258.7 W/m2 to be compared with 235 for radiative balance, suggesting that something is wrong).

Both 4.5 W/m2 for 1 ppm and 50 (or 28) W/m2 for 390 ppm signal a big effect of CO2 as a trace and thus serve as the chief scientific evidence of the existence of a GHE from CO2. Not surprising it is also claimed that doubling to 600 would give a radiative forcing of about 4 W/m2, which fits with the canon  defined by IPCC.

But is the evidence credible? Well, the numbers are computed by the commercial software Modtran marketed by Spectral Sciences Incorporated. The numbers are not supported by direct observation. The numbers are surprisingly big and against all forms of physics intuition of the possible effect of an trace gas: 4.5 W/m2 from 1 ppm simply seems impossible! 

In a sequence of posts on OLR I have questioned to ability of a small presence of CO2 to block the radiation from the Earth surface in the entire interval 600 - 800 represented by the ditch. The analysis of blackbody radiation presented on Computational Blackbody Radiation suggests that CO2 even as a trace gas can absorb and emit radiation in a narrow band around its main resonance at 667, but that the emissivity is small away from 667. The analysis thus gives mathematical support of the intuitive conviction that 1 ppm of CO2 cannot cause a radiative forcing of 4.5 W/m2. 

We are thus led to suspect that Modtran does not give a correct description of atmospheric radiation, and therefore that the main evidence of a GHE from CO2 is fabricated incorrect evidence. 

A similar attempt to justify a GHE from CO2 is given on The Science of Doom.  It is a remarkable that the most serious attempts to prove GHE are those made by amateur bloggers.

It is also remarkable that virtually nobody seems to be willing to question the evidence of GHE supplied by Modtran, as if Modtran cannot be questioned. Maybe it is like Coca Cola,which with its secret recipe cannot be questioned.