If you want to assume a specific power density (239.7 W/m2) and use the S-B equation to calculate the temperature, you are actually calculating a temperature that provides an outgoing radiation from a surface. The sun's short wave radiation hitting the earth would correspond to an earth temperature of -18C only if you do not assume anything else, such as an atmosphere.
Equilibrium requires that the input from the sun is balanced by the output of the earth. So the calculated -18C is the temperature the earth would be if there were no atmosphere at all.
Just how stupid are you really wuwei?....see this graphic..it is the one rocks posted...the one that I responded to...see the text in the box at the bottom of the picture?...see where it says clearly....assuming no atmosphere?....radiation in...radiation out...no atmosphere
see this graphic...see right there in the middle of the graphic on the right side....ATMOSPHERE...that is because that graphic is modeling the greenhouse effect with the atmosphere...note that the 239.7 wm2 remains unchanged...they just add in another 239.7 wm2 from the atmosphere....then using the Stefan Boltzman equation...they ADD the two radiation outputs together...and then calculate a radiating temperature of 303K....using the SB equation, when you have two radiators, you subtract the two which gives you a radiating temperature somewhere in the middle of the two radiators..you don't add them together to get a radiating temperature that is higher then either....are you really this far behind the curve?...got to admit, for a while there, you had me fooled...no longer...
The basic flaw is to think that the outgoing LW radiation from the -18C surface of an airless planet has anything to do with a computation involving the GHE.
No..there are three basic flaws...and both are yours...the first one is not recognizing that the graphic clearly denotes the earth's atmosphere...and the second is that using the SB equation, they added the output of the two radiators together to get a radiating output when they were supposed to subtract and get a temperature somewhere between the two...not a temperature higher than either...and the third basic flaw is that you believed the bullshit of the greenhouse effect in the first place...
You know...I copied some of your comments and ran them by a MSc in applied mathematics...he got a big old bellylaugh...so don't fret over being so far behind the curve here...you are still bringing sunshine into peoples lives...laughter is a much needed commodity in the world and if you can make people laugh like that...then you are doing a real service......even if you can't manage to understand a simple graph and grasp very simple equations...