The "plans" for Mars terraforming will probably include slamming comets into it (at low relative speeds), on the scale of 1000-10000 years. It's unlikely to involve slow-and-steady air production.
I looked into this a while ago, and a major problem with Mars terraforming is that if you add a bit of additional carbon dioxide (or water vapor), it'll mostly just get frozen and deposited onto the ice caps.
So you need to add something like nitrogen to "bulk up" the atmosphere to prevent it from freezing out. And there's just no nitrogen on Mars.
I looked into this a while ago, and a major problem with Mars terraforming is that if you add a bit of additional carbon dioxide (or water vapor), it'll mostly just get frozen and deposited onto the ice caps.
So you need to add something like nitrogen to "bulk up" the atmosphere to prevent it from freezing out. And there's just no nitrogen on Mars.