There is a simple formula our understanding of the greenhouse effect (GHE) is based on.
((1-0.3) * 342 / 5.67e-8) ^0.25 = 255K
0.3 = albedo
5-67e-8 = SB (Stefan-Boltzman) constant
0.25 = 4th root, representing the SB law according to which radiation emitted as a function of temperature by the power of 4. And if you start out with radiation given you will have to invert it to get to the temperature.
If we compare this theoretical temperature to the average observed surface temperature of Earth, about 288K, we find a difference of 33K. So that is the GHE. Or that is what it should be. So far so simplified.
The above formula is not quite complete. The term 1-0.3, or 1 minus albedo has a name on it's own, which is absorptivity. Indeed the absorptivity of planet Earth is about 0.7. Yet absorptivity has a little brother called emissivity, which is equally important to calculate the temperature of any surface with given insolation. What we actually need to do is to divide absorptivity by emissivity. So how does the above formula yet yield the right result? Quite simple, it is being assumed emissivity was 1, and dividing any term by 1 will not change the result.
With that knowledge in mind and a given surface temperature of 288K, we can determine the actual emissivity of Earth relative to its surface temperature. We can solve the following equation for x = 0.614.
(((1-0.3)/x) * 342 / 5.67e-8) ^0.25 = 288K
All other things held constant, the surface temperature of Earth is a function of Earths emissivity. We know that with the given temperature emissivity must be about 0.614, or 61.4%. And with an emissivity of 1 the temperature would only be 255K.
That brings up the question what causes emissivity to be so much lower than 1. "Climate science" has a very strict position on this.
Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C 1
The claim is, that without GHGs Earth would be a perfect emitter. All the substantial deviation in emissivity from 1 was ONLY due to GHGs. Of course it as position totally indefensible. There are a number of other factors reducing emissivity apart from GHGs. The surface is NOT a perfect emitter, clouds reduce emissivity and even aerosols. Clouds btw. are not a gas, but either droplets of water or ice crystals, and they are meant to net cool the planet. So they fail any thinkable definition of a GHG.
GHGs have serious competition and the true denialism is about denying this inconvenient fact. The GHE has NOT a magnitude of 33K, and more importantly, GHGs do not provide some 33K of warmth to the surface. The big taboo, the unseen gorilla in the room so to say, is the question how much competition there is, and what role actually remains for GHGs. It is a question that not just poses a threat to the global warming agenda, but potentially might even doom it.
There is a myriad of tricks and excuses to fool around this problem, you would not believe it. It is like a needle to a balloon, and "climate science" does its best to keep the two separated from each other. The scope of this site will be no other than bringing them together..