In New York City, 66 year old Michael Sorkin – architect, urban planner, and critic – runs Terreform, a non-profit devoted to architecture that is both urban and green. Two years ago, Terreform began a project called New York City (Steady) State, which investigates the possibility of “urban self-reliance.” Its goal is to figure out what a sustainable New York might look like.

By imagining an ideal city, the thinking goes, you make a better one more likely. How would such a city function? And what would it be like to live on its leafy and fruitful streets?

When we say “green” today, most people think of renewable energy and recycling trash. But Sorkin and his group focus instead on something even more basic – food. In their city of the future, fruits and vegetables grow on the tops and sides of buildings. They also fill our public parks and other urgan greenspaces. Walking city streets, we would be like insects looking up at a welter of stems and leaves. Livestock would grow on rooftops, not on factory farms 10 states away.

Green growing things have several benefits. They absorb carbon dioxide from the air. They provide shade. They help control rainwater runoff from buildings. And they add insulating power to the walls and roofs of buildings. In Paris, a new law requires all new roofs within the city to be covered either in plants or solar panels.

In Sorkin’s vision, one parking lane on each street could be converted to green space and used for gardening. It could even have a “pneumatic disappearing device” into which trash could be deposited. Sorkin believes that imagining an alternative, however idealistic it may be, serves an important purpose: “It gives you a more self-sustainable, more egalitarian vision of what the city could be.”

Sorkin’s concepts are based on the writings of Lewis Mumford, an architectural critic who published his seminal work, “The City in History: Its Origins, Its Transformations, and Its Prospects,” in The New Yorker in 1961.

He wanted cities to be more unified with their environments. In an ideal urban landscape, economic considerations would be secondary to an organic relationship with nature. Mumford’s ideal city was localized rather than sprawling. It used clean energy. It had more trees and fewer cars.

San Francisco may be the American city that is closest to Mumford’s ideal. With the assistance of geography, it is many cities in one, from the heights of Nob Hill to the ethnic anomaly that is Chinatown. From The Castro to Haight-Ashbury and Golden Gate Park to Noe Valley, it is more like a collection of urban communities than one homogeneous city and that disparity has a lot to do with its reputation as a charming and peaceful place to live.

Over the past half century, Mumford’s dream has been almost overwhelmed by the influx of more and more cars. Los Angeles and Phoenix are examples of 24 hour a day gridlock. But slowly, there are signs that things are changing. Multiple studies show that there are significant health benefits that flow from reconnecting with nature.

New York has re-purposed an old elevated freight railroad into The Highline, a beautiful outdoor park that parallels the Hudson River. A city wide bike sharing program is encouraging bicycle commuting not only within the city but from cities across the Hudson in New Jersey.

Sorkin says China is doing the best job today at re-imaging sustainable cities, but he attributes much of that success to the enormous power of the central government to mandate the policies it approves. In the city of Wuhan, the world’s tallest building is under construction. When it is done, it will not only be energy self-sufficient, it will actually help purify the environment around it.

Sorkin is optimistic about the changes that are coming. But he realizes that those changes won’t come if the people of the city don’t agitate for them. “We as a body politic have a responsibility to protect the different qualities of a neighborhood,” he says. It helps to dream big. His final comment to the New Yorker is, “I love it when people of faith and good heart collude in this collective work of art we call the city.”