> Fresh air is created by plants and CO2 is taken from the air by plants

Plants can be net CO2 consumers, but they burn O2 to CO2 just like you. Tropical forests are net CO2 producers for most of the day, except for a few hours around noon, but that's enough to become net consumers averaged over the day. Occasionally someone fills their room with plants, and then puzzles over having high CO2 levels.

I imagine it's not much different from a regular residential greenhouse, in which case the plan is to throw a sufficient number of cats in there.

Not sure people in glass houses should be throwing cats.

Mine would love that environment I’m sure though.

They are somewhat softer than stones, but yes, cat throwing is rarely called for.

My mother has a decent sized greenhouse. Her cats spend most of the winter in there by choice - they love it.

The plan: https://i.imgur.com/XcJSDlE.jpg