Surface heat loss by moist convection dominates over radiative heat loss from the surface. If somehow you could switch off convection then surface temperatures on Earth would need to rise by about 60 deg.C to bring the atmosphere into a pure radiative equilibrium with space.
I became fascinated by an article written by Richard Lindzen about 10 years ago  in which he wrote, when discussing the greenhouse effect on Earth.
When all these things (greenhouse gases,clouds, water vapour) are accounted for in sophisticated radiative transfer models, the equilibrium surface temperature works out to be 350K or about 80C. But the equilibrium temperature decreases rapidly with height reaching a minimum of 210K (-60C) about 8 miles above the surface…. But the rapid decrease in temperature with altitude cannot be sustained because it is unstable to convective overturning.
In the absence of convection the surface could only cool through radiation alone. A pure radiative equilibrium on Earth would then result in a much larger greenhouse effect with a surface temperature of 350K !
Convection, evaporation and the environmental lapse rate reduces the greenhouse effect on Earth because they act somewhat like a “release valve” moving heat up more efficiently through the atmosphere to then radiate out to space. The more humid the air the less steep the lapse rate and the less effect any increases in CO2 will have on the surface temperature. Just how important convection is to the Earth’s climate can be seen in Figure 1. I ran my radiative transfer model for the CO2 15 micron band first for the observed surface temperature and lapse rate shown in black, and then a second time for the pure radiative energy balance and steeper lapse rate shown in red.
Convection is mainly determined by gravity and the heat capacity of gases in the atmosphere, modified by latent heat of water.
But supposing that the atmosphere was stratified in some way to stop convection – something like a series of transparent shells blocking air movement vertically but still transmitting radiation both up and down. In such a hypothetical case the surface could only cool through radiative transfer. The surface would then heat up enough to sustain a temperature gradient for 100% radiative cooling reaching a surface temperature of 350K.
Convection and evaporation really do moderate the greenhouse effect.