Depends on where people want to live and work.

But a big part of why lower density is bad is because it leads to lots of commuting.

Commuting is no doubt a large contributor to carbon emissions. But, suburban and rural living lead to car-centric lifestyles in general. Driving to school, to the grocer, to entertainment and dining, etc. Plus all the infrastructure to support that - more roads, giant parking lots, etc.

Yes, perhaps. So a carbon tax is still a good idea. (And so is removing things like minimum parking requirements.)

I live in NYC and don't own a car. All my errands are done on foot and by bike, and I'm using relatively little power because I live in a big apartment building.

If I lived in the suburbs and had to use a car for most trips, then my carbon footprint would be substantially higher, even without having to commute. This map gets to the heart of the issue: https://twitter.com/TheJakeSchmidt/status/142478272240963174...

Yes. Though I would hope that some people would use remote as an opportunity to work from other cities, and not just from the suburbs.

(I work from Singapore for a London based company, for example.)