We're already over the carrying capacity if the world wants first world lifestyle.

Only if they want a first-world lifestyle, though.

Cut out meat, suburban lawns, and the cars that go with them, and the earth could support 10B people right now, at the living standards of a typical Millenial in a cosmopolitan metropolis.

Unfortunately, there's pretty good indications that most people on earth want those meats, suburban lawns, and cars, so I think it's more likely we'll get war instead. But it's totally doable, at a standard of living that people will grumble at but could abide.

Viable meat replacements are right around the corner. I don't think this is a blocker.

> meats, suburban lawns, and cars

Can I opt out of the coming war if I don't want these things?

If you can get enough of your like-minded friends to settle an area that doesn't have many of the desirable resources that'll be fought over (water, fertile land, nice climate) and doesn't have many people who do want those things, probably. Just be Switzerland.

Debatable, a large issue is land use and for all the land we have here in the US alone large swathes of it are used for single family homes promoting horrible density. We dump carbon into the air, have less arable land, and destroy more natural habitats than necessary because of poor planning and regulation.

There is more issues to be solved, yes - but reversing wasteful land use is a HUGE component of preserving our planet and quality of life.

If you think we can't sustain every couple/person on earth having a single family home then you're agreeing with my statement.

What is "first world lifestyle"?

The life style of a well-to-do member of America or Western Europe.

I think you'll find that not everyone wants this lifestyle, and trying to force everybody into it because you want it is a silly form of reductionism.