ABSTRACT
In 2009, humanity crossed into a new experience—it became an urban species. For the first time in history, more people now lived in cities than in the countryside. In the next three decades it is expected that 70 percent of the world’s population will live in cities. At low densities, cities sprawl across the landscape consuming farmland, habitat, water, energy, and materials. As densities increase, individual dwelling units become smaller, and transportation and amenities are shared by more people, thus lowering the per capita consumption of resources. A New York City subway train achieving 540 passenger miles per US gallon (229 passenger kilometers per liter) during rush hour can be 20 times more efficient than commuting by automobile, which typically struggles to achieve better than 22 passenger miles per US gallon (10 passenger kilometres per litre) during the rush hour, thanks to most cars carrying only one commuter. Tall buildings tend to be integrated into tighter, more efficient utility infrastructures, and can rely on efficient district heating and cooling systems that are not economically feasible at lower densities. This is the context in which tall buildings have the potential to be truly sustainable.
