Constructed Climates

I’ve covered many factors that connect to urban environmental issues, including energy and carbon, air, heat, water, nature, and the health and welfare of people, as well as the effect cities have on regional and global climatic patterns and the changes imposed on other species. Cities, by their very definition, involve natural lands turned into rain-repelling, impervious surfaces — roofs and parking lots — filled with people and cars. As cities become bigger and denser, impervious surfaces increase while trees, forests, parks, and grass decrease.

People in cities use an unusually large amount of energy and water in limited spaces, and the resulting problems include air and water pollution, heat and health problems, and reduced benefits from natural ecosystems. Cities create many environmental problems.

Despite these problems, an economy of scale provides an effective argument for bigger, denser cities. Urban states have lower per capita energy use than rural states: With high densities come reduced individual transportation demands and lower electrical transmission line losses. Extending this argument, if vegetation and forest remnants serve no function in urban settings, cities should increase densities as high as possible, creating square kilometers of contiguous multistory enclosures with internal moving sidewalks transporting the people within. At this limit, cities would become vast “underground” bunkers—land-based cruise-ships — with small portals for food provided by rural areas and air exchange for oxygen provided by external forests. Their green coverings could collect all their water from rainfall and all the electrical power they need from solar energy, with, perhaps a baseball and soccer field here and there.

At the other extreme, people could spread out as much as possible while attempting to reduce urban environmental issues associated with aggregating impervious surfaces. Unfortunately, there’s not much room to spread. Suppose Durham County, North Carolina, citizens were removed from cities and dispersed evenly across the county. The density would be 1.35 people per acre. Suppose North Carolinians were removed from cities and dispersed evenly across the state. The density would be one person per 3 acres. For all Americans there’d be one person per 8 acres. For all humans, there’d be about 5 acres per person. Ignoring deserts and counting only the world’s arable land, the 10% of the land surface where crops can grow, that number drops to half an acre per person. We have such a large human population that we can’t live without cities.

Another possibility is to imagine a local region divided into three parts: agricultural; forested watersheds with no impervious surfaces; and cities built out to 100% imperviousness and maximum population density. In this situation the issue becomes that of where a small forest parcel would be best placed: within the city as a small urban patch, or as part of an imperceptibly larger contiguous forest at the city’s edge. Placement also depends on the anticipated function of that forest fragment, the function or functions that defines the term best in the previous sentence.