What about exploring the trend: the difference between T measurements in the higher (mountains) regions vs the lower (close to the sea level)? If the CO2 is forming a thicker membrane around the Earth to capture the heat - the higher level measurements should go up relative to the lower above Earth surface levels? Hot air is going up, no radiation of heat upwards - sort of a heat pump. Any thoughts?
Your question is interesting - lowest average, which should be night time normally, would give a good idea imo. That considering the observation on the vapour contribution, which is normal as it is the main green gas on the planet with its large wave absorption/reflection range (unlike the CO2).
