Wanna go green? Witold Rybczynski says you gotta get back to the concrete jungle:

Architectural journals and the Sunday supplements tout newfangled houses tricked out with rainwater-collection systems, solar arrays, and bamboo flooring. Yet any detached single-family house has more external walls and roof—and hence more heating loads in winter and cooling loads in summer—than a comparable attached townhouse, and each consumes more energy than an apartment in a multifamily building. Again, it doesn’t really matter how many green features are present. A reasonably well-built and well-insulated multifamily building is inherently more sustainable than a detached house. Similarly, an old building on an urban site, adapted and reused, is greener than any new building on a newly developed site.

A Thoreau-like existence in the great outdoors isn’t green. Density is green. Does this mean that we all have to live in Manhattan? Not necessarily. Cities such as Stockholm and Copenhagen are dense without being vertical. And closer to home is Montreal, where the predominant housing form is a three- or four-story walk-up. Walk-ups, which don’t require elevators, can create a sufficient density—about 50 people per acre—to support public transit, walkability, and other urban amenities. Increasing an area’s density requires changing zoning to allow smaller lots and compact buildings such as walk-ups and townhouses.

In other words, being truly green means returning to the kinds of dense cities and garden suburbs Americans built in the first half of the 20th century. A tall order—but after the binge of the last housing boom, many Americans might be ready to consider a little downsizing.