There's no law of physics that says we have to be an unsustainable society - in fact, quite the opposite. The planet's ready to work with us if we're ready to think differently, but we do have to make that jump and start to do things in new ways.
The brutal reality is that newer, more sprawling suburbs - and especially the cheap boom-years exburbs - aren't just a bit unsustainable, they're ruinously unsustainable in almost every way, and nothing we know of will likely stop their decline, much less fix them easily.
For carbon-neutral cities, there are things worth talking about in how our consumption patterns can change - sharing goods, etc. - but those are a fraction of the impacts of transportation and building energy use. If we need to choose priority actions, the most important things are to densify, provide transit, and green the buildings.
When the Internet really first started to hit, people felt this would be the death blow: after suburbs and long commutes and television and the death of the family dinner, this would be the last straw that would totally break society.
In almost all city governments in America, the small group of people who don't want change are able to block change.
There's no really rosy scenario ahead, where climate change just doesn't happen, but I believe we don't have the ethical right to throw our hands up in the air and say, 'Game over.' Whatever pathway we choose, our descendants will be dealing with that reality for centuries to come.