Hi gb

Just how much greenhouse gas are you planning on pressurising that greenhouse with? There's about 6 kg of CO2 above your head and every sq.m. of the Earth - to get the same in a greenhouse you'd be looking at quite a high partial pressure. Then there's the water vapour you'd need to match what's around you. Thus a pressure cooker like situation inside that little greenhouse to match the atmosphere's IR active gases.

When they were first measuring the amount of CO2 above Venus's clouds they had to fill a large cylinder to several bars pressure in order to replicate the air-column light from Venus had travelled through. Surprised everyone. Led a few to realise that the Cytherean surface was rather hot and under several bars worth of pressure - but World War II got in the way of further analysis. When radio telescopes turned towards Venus c.1955 the high temperatures of the lower atmosphere shone through, so by c.1960 people knew Venus was probably over 300 C, though the "hot ionosphere" model misled a few for a while.