It appears that I have wasted all week trying to explain this effect, which seems blindingly obvious to me as it fits in with everything else we know about anything and I'm pretty sure that our physics teacher mentioned it once in passing:
Earth surface temperature (as well as the surface temperatures of 5 other rocky planets in our solar system) can be very accurately determined solely on the basis of two variables:
1. atmospheric pressure at the surface, and
2. solar irradiance at the top of the atmosphere.
For sure, it is only a starting point and you will probably have to make lots of other little up and- downward adjustments, but having Googled around, as per usual anything which offers an alternative/complementary/non-GHG induced explanation for why surface temperatures are what they are gets mired in purely political controversy and nit picking.
It is even hotly debated whether luminaries such as Maxwell and Feynman supported or rejected the idea, that's how mad it is.
I don't see how hard it can be to do all the measurements of a few different planets with differing atmospheres (I'm not sure why we should restrict it to rocky planets) and settle the matter one way or another to everybody's satisfaction, but hey…