Are Greenhouse Gasses Warming or Cooling?

Infrared atmospheric window to the right of the peak.
The dip under the peak is the effect of CO2 which changes very little upon doubling of CO2.
Compare with Will Happer's diagram in PS below.

This is a comment to recent posts:

The basic dogma of CO2 alarmism is that a bit more CO2 as a "greenhouse gas" in the atmosphere will have such a big warming effect that the Earth will pass a "tipping point" into a "run-away greenhouse effect" into extinction of human civilisation.

Are then the greenhouses gasses in the atmosphere (mainly water vapour and a bit CO2) warming or cooling? The answer is: they are both cooling and warming.

They are cooling in the sense of infrared radiation into outer space as emission from the "top of the  atmosphere" at an effective emission level of 5 km and temperature -18 C, balancing the radiative input from the Sun.

They are warming in the sense of allowing the Earth surface temperature, by a gravito-thermodynamic  effect with lapse rate of 6.5 C/km, to be 33 C warmer than that at the top of the atmosphere. This is then a combined total effect of thermodynamics with gravitation and radiation,
not radiation only.

The "radiation only" effect can be estimated to be 1/3 of the total effect by seeing that the radiative heat exchange between an Earth surface and top of the atmosphere is 2/3 thermodynamics and 1/3 radiation. This gives a greenhouse effect from radiation of about 9 C with thus a surface temperature  of + 6 C, which is the grey body temperature of an Earth without greenhouse gasses.

The greenhouse gasses thus have the double role of radiating into outer space as a cooling effect and together with thermodynamics+gravitation of keeping the Earth surface at a higher temperature than the top of the atmosphere as a warming effect.

To compare with an Earth without greenhouse gasses is not so relevant, but to compare with the warming effect of a fully opaque is enlightening. Recalling that the step from the the semi-opaque atmosphere of the Earth to a fully opaque atmosphere corresponds to completely closing the "infrared atmospheric window" from 5/6 shut, leaving a total effect of 9/5 thus less than 2 C. Since doubling of CO2 is far from closing the window, its effect as climate sensitivity can not be bigger than 1 C, probably much smaller.

PS Below is Will Happer's picture (from COP25 Madrid There is No Climate Emergence) of the spectrum of outgoing infrared radiation showing that doubling of CO2 as represented by the difference between the black and red curves visible only in the CO2 ditch below the peak, is at most 3 W/m2, which gives less than 1 C warming by Stephan-Boltzmann.