I can speak out of personal experience when it comes to sustainable cities. The city I live in is very sustainable. There is about 30 houses and 30 mobile homes. The only other buildings are a school and a post office, no factories or businesses to creating greenhouse gasses. No one drives that much because the next town over where people can get food and clean water is in walking or biking distance. All the water comes from a well. All the electricity comes from generator power or solar panels, decreasing the carbon footprint of the lights and other appliances in the households. A lot of the food that the people eat is grown or hunted in the town, promoting sustainability by taking the transportation out of the picture. The humans in the town have not shaped the land, or cut down any trees, so the ecosystem and the water, nitrogen, and carbon cycles thrive.

I agree that it lowers emissions drastically, but that way of living is unreasonable. The fact that you have to travel to a different town to purchase consumer goods is just as bad. Not everyone bikes or walks to the next town over for simple necessities. Does everyone bike or walk over. Highly unlikely. People still drive. How do you use the generator? Fuel, which is burned by the generator to produce the electricity. You say that the landscape is unaltered. Impossible, why? It is impossible because you had to build the roads into the town which means that they had to have trimmed down trees. It may not seem like the residents have had any impact, but you have. You still drive a car, you still produce garbage. All in all, no city is actually sustainable.