When I described the boardgame Terraforming Mars to someone a couple months back (I forget who, sorry), the first thing they asked was “What about atmospheric pressure?”
I hadn’t thought of that question, but it seemed like an excellent question after they raised it. Presumably you would need to significantly increase atmospheric pressure to make Mars habitable by unprotected humans.
I’ve been meaning to post that question for ages, but didn’t get around to it until tonight. And tonight I figured I would do a quick search on the topic before posting, and I found this interesting 2016 thread on boardgamegeek, where someone named Andy Daglish objects to the game’s lack of handling of atmospheric pressure, and the game designer, Jacob Fryxelius, responds in a fair bit of detail.
I don’t really understand all of the science in the thread, and if I’m understanding right, Daglish remained unconvinced by the end of it. But I think the essence of Fryxelius’s argument is that (a) what he had in mind is scientifically possible (over a multi-generation timescale), and (b) it would result in an atmosphere that would be (more or less) breathable by humans, and (c) he simplified and combined some concepts to improve playability.