It's not only because cities outsource carbon intensive activities. Sure, there's some of that with farming, mining, etc. that must be done elsewhere. But there

It's not only because cities outsource carbon intensive activities. Sure, there's some of that with farming, mining, etc. that must be done elsewhere. But there's also lots of savings from things like residents walking/biking/using public transit instead of driving, living in more efficient apartments, etc. The suburbs are pretty wasteful, they don't generate anything unique and they just waste more resources.