text: Now, the average of this system, the whole atmosphere and surface included together, is what should have the global average temperature of -18 degrees C, and it does, because the temperature goes from warm (+15 degrees C) at the bottom of the atmosphere, to cold (-70 degrees C) at the top of the atmosphere, and measured from space it is -18 degrees C on average. The bottom of the atmosphere is warmest because that is where the Sun does the real-time physical heating in the first place. The temperature decreases with altitude because the heat dissipates outwards from the ground and cools down, and also because of the natural adiabatic gradient. The amount of water vapour in the air-column reduces the adiabatic gradient and it also reduces night-time cooling, because of latent heat which is trapped and then released by the H2O molecules. -And to be sure, those H2O molecules wouldnt be able to get into the air-column if sunshine was freezing cold at -18 degrees C!- Finally, the natural existence of the adiabatic gradient (that is, the fact that the air has to cool with altitude), means that the bottom of the atmosphere must be warmer than top and therefore the bottom must also be warmer than the average. If the average has to be -18 degrees C, then this average has to be found between the bottom (warmest) and the top (coldest), and the bottom will naturally be warmer than that average. Its all totally sensible when you do the physics correctly, and no greenhouse effect is needed to be invented.