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There's rarely such a clean example of Dunning–Kruger in action, but this is a good opportunity to remind people how the greenhouse effect works. What Don has shown (not with a climate model, but a basic radiative transfer program) is in fact consistent with everything we know. https://twitter.com/KeillerDon/status/1355089596711919617
What he is showing is the upward infrared flux that would be "seen" by an observer in space (well, 70 km altitude) looking down. This is a representative tropical atmosphere without clouds and with a prescribed vertical temperature structure (again, not a climate model).
These are the same plots except with two numbers changed. One is CO2 (40 to 400 ppm) which is input by the user, and the other is the upward IR Heat Flux (from 312 to 298 W/m2) which is calculate by the radiative transfer model.
In this program, the user specifies the ground temperature (it's not calculated) and the upward and downward radiative fluxes are calculated according to the given atmospheric composition. The reduction in upward IR flux, that Don himself found, is because of the increased CO2.
The ocular manifestation of the CO2 in the atmosphere is that big dip in the upward IR flux around 666 (heh) inverse centimeter wavenumber. Actually, there's a wider wavenumber regime affected. As CO2 rises, it's harder IR to escape to space from the surface and lower atmosphere.
In this not-a-climate-model, the outgoing radiation is reduced by about 15 W/m2 (this would be what we call "radiative forcing"), which of course means there's a big radiative imbalance that needs to wiped away by the surface-atmosphere system warming up to emit more!
