The terrestrial ecosystem has been considerably affected by global warming and historical pollution, though reduced population pressure and denser living arrangements in the modern world have tended to relieve this problem to some extent. However, children are still taught that the outside world (i.e. outside the enclosed cities and arcologies) is dangerously polluted, for reasons of social control - certainly, the existence of people who live their whole lives outside the modern world is not often discussed; when they are mentioned at all, it is usually to point out how short and miserable their lives supposedly are.

Though their population is kept in check by uMon, feral mons compete with these outsider humans and other organic life for some resources. The ability of mons to eat most organic foods (at least, after sun-drying) is actively problematic for the ecosystem; a grey goo scenario in parts of the world uMon ignores is deferred largely due to the relatively slow reproduction of viviparous mons.