LOL! I was thinking that too, that they probably came up with this tripe because professional horticulturists/gardeners actually pump CO2 into greenhouses to help the plants grow and the heat is magnified and trapped by the glass of the greenhouse. So some genius lib one day probably walked into one of these and said “Wow it’s hot in here! It must be because of the CO2!” That HAS to be how it started because the percentage of CO2 in the atmosphere right now is miniscule, a trace gas at 0.04%. Methane even more ridiculously small at 0.00017% and how else would they come up with that conclusion unless they got it from some ridiculous source like an actual greenhouse? To go by the numbers alone and reach that conclusion is absurd. It’s like someone peeing in a lake then coming to the conclusion that the lake will now turn yellow. It’s insane thinking, so they must have started this myth from another source: Actual greenhouses! LOL! I think Venus is another source they could have gotten it from, but I looked it up and they said Venus became a greenhouse planet from WATER VAPOR! The water vapor came first THEN it trapped the CO2 but liberals can’t regulate the ocean and clouds can they. No “evil corporations” behind that. This whole thing is the biggest scam since PT Barnum and the Cardiff Giant, it really is the only difference is back then people weren’t forced to believe in the Cardiff giant and weren’t forced to pay extra money from everything they bought from “Cardiff regulations”.
That may have augmented the original 'concept', but the original came from explaining why Mars did not have much of an atmosphere. We didn't even know what the atmosphere of Venus was really like until the Russians sent some probes there. The first ones were crushed like tin cans by the intense atmospheric pressure.