Consider a city of roughly 1 million people, Adelaide, Australia for example [Calgary, Canada; Bonn, Germany; Tuscon Arizona; or Bristol in the UK would do equally well]
Adelaide has two Australian Football League teams, a pro soccer team, two professional basketball teams, three Universities, a cathedral, numerous hospitals, many shopping malls, around 440 schools, an International airport, and a zoo.
There are over 400 suburbs arranged around a CBD that has high-rise office blocks that provide a common destination for a metropolitan public transport system includes a fleet of over 1,000 buses.
There are doctors, dentists, lawyers, Artisans and actors; and enough skilled tradesmen to build or engineer almost anything.
In short, Adelaide is a self-contained community surrounded by enough farmland to feed everyone.
Put all the people who live in Adelaide in one place and it would be quite a spectacle. It is hard to imagine what it would look like.
There would people as far as the eye could see. Lay them down head to toe and the line would stretch 1,800 km — 400 km further than a road trip from Adelaide to Sydney.
Stand these people in single file and the line would be 30 km long, similar to the queue at the post office.
Now having conjured the image of so many people in your mind’s eye put them all onto commercial aircraft.
Because 1 million is roughly the number of human beings who are, at any one time, airborne in commercial airliners making vapor trails around the globe.
And we wonder why we have environmental issues?