[nateberkopec]

If what you care about is climate change, you should be in favor of cramming people into the smallest possible spaces in urban areas, not putting them in rural areas where they have to drive 20 minutes to get to the grocery store.

The carbon footprint of your average city dweller is far lower.

[Kretinsky]

It's not only about climate change, most of the effects are to be seen on the biodiversity, the beauty of the countryside (yes, it's important), agricultural production and water supply, as concrete reduces a lot water absorbtion.

Lyme disease outbreaks can be attributed in part to the increase in rodents population, which is due to the urban sprawl and the increased difficulty for predators to hunt in suburban areas.

[kajaktum]

Or provide better public transportation?

[dagw]

Public transport is only more environmentally friendly if people actually use it. Out where my parents live it was not uncommon to see busses driving for miles with 0-2 passengers. The problem was that providing good enough public transport that you didn't need a car at all is basically impossible. And since everybody had a car, the number of people that wanted to spend 60+ minutes taking a buss that went 3-4 times a day into town, instead of driving 30 minutes, was basically zero. They eventually cancelled the bus line since it was just too expensive and inefficient to run. The alternative of trying to provide a truly useful public transport service (say 2 buss lines running every 30 mintues) would have been extremely expensive and would have meant even more empty busses.