“Population reduction” again? It might be the most politically expedient option, but the planet isn't overpopulated. We're just polluting way too much. If you model a back-of-the-envelope sustainable civilisation, you'll find we're nowhere near any sort of fundamental population limit.

As a species, our median per-capita pollution is okay. It's the mean per-capita pollution that's the issue.

> If you model a back-of-the-envelope sustainable civilisation, you'll find we're nowhere near any sort of fundamental population limit.

How did you model it? I'm curious about the assumptions you made and how you came up with your conclusion.

I lost the envelope (it was a while ago (and also not a literal envelope)), but I'm pretty sure I just drew a circle somewhere reasonably habitable in Europe, filled it with a decent population density to roughly non-capital city population, placed enough high-density farmland around it to produce double the necessary food (in crops), put in eight radial train tracks and some roads leading to those train tracks, surrounded the whole thing by enough 20%-efficiency solar panels to power the city (peak 300W per person, at 10% electricity losses) then multiplied up to nine billion people.

I assumed all in-city transport was manual or electric (and hence covered by the solar panels), all trains and food transport was diesel (even though electric trains are realistic), that the roofs of the city were covered in 20% efficiency solar panels (at 0% loss, due to proximity), that all long-distance transport was done with cargo ships (no aeroplanes) and there was a tenth the shipping of what we've actually got.

The vast majority of the planet was completely untouched by my hypothetical civilisation. I know I missed out a lot of stuff (e.g. how goods get from ports to people and back), but I don't think my conclusion was that far out – especially since “tile the world with solar panels” isn't an efficient renewables strategy.

You don't need skyscapers. You need the density levels of Paris. Six-story walkups. The concrete can be put into 5/2 urban buildings, or it can be put in to driveways, pools, and sidewalks no one will ever use.

Pretending that urbanism is somehow remotely equivalent is naive at best.

Exactly -- most "urban" areas in the USA are actually sprawling car-dependent suburbs that use far more resources of all kinds per capita than a true urban area.

What's more, is that we've forgotten that you don't need to build suburbs around cars. You can have pleasant suburbs with offices, shops, schools, and other non-residential buildings mixed into the neighborhood. Where people actually walk and cycle because the streets feel like they were made for it.

There's a massive gap between the population density of 60000 people per square mile you might find in an urban center, and the approximately 1,500 people per square mile you get in a typical suburb.