There is a big spectrum of possibilities between "everyone having a typical American suburban home with an extra room for their office" and "pitch a tent in the open space". Walkable dense cities is one such example. It is no surprise that NYC's carbon footprint is 11 MTCO2 per person while the number for the overall US is ~14.5 MTCO2. Or, NYC gives you almost one-fourth reduction in the carbon footprint per capita.