Billed as the world's largest scientific instrument, Biosphere 2 was built in the Arizona desert outside of Tucson in the late 1980s/early 1990s to model Earth, the first biosphere. Constructed by a private company looking to study space colonization technology, it was a project somewhat akin to miniaturizing the planet within a test tube, albeit a very large one -- three acres --with an equally large price tag of more than $150 million.

Eight biospherians entered this living laboratory in 1991 to reside within its sealed-off environment for two years. They wanted to demonstrate that humans had the biological and engineering know-how to build a self-contained system resilient to unpredicted challenges and capable of sustaining life over an extended period. It stands today as the first real-world, large-scale attempt to build a resilient, sustainable community and study it scientifically as a complex system in operation.

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Aside from space colonization, a primary purpose for Biosphere 2 was to gain a better understanding of the simultaneous interactions among air, water, soil, buildings, plants and people as a way to improve the quality of life in communities right here on Earth. Sustainability and resilience were incorporated as central themes in the design, construction and operation of Biosphere 2: a system capable of generating its own food, replenishing its atmosphere and recycling its waste under controlled scientific research conditions.

As such, it served to demonstrate a fundamental of sustainability: "The crucial fact about sustainability is that it is not a micro phenomenon: there can be no such thing as a 'sustainable' house, office building, or household appliance, for the same reason that there can be no such thing as a one-person democracy or a single company economy," wrote David Owen in his book Green Metropolis. He added, "Every house, office building, and appliance … is just a single small element in a civilization wide network of deeply interdependent relationships, and it's the network, not the individual constituents, on which our future depends."

Much like a city nested in and dependent on resources from its region, state and country, Biosphere 2's ongoing existence relied heavily upon a vast array of equipment housed beneath its rainforest, desert, savannah grassland, ocean, mangrove wetlands, agriculture fields and living areas. This "technosphere," as it came to be called, consisted of thousands of miles of wiring, pipes, ductwork and air handlers. A nearby energy center provided continuous power, supported by backup systems. (During summer monsoon seasons, power outages were frequent and a loss of power as short as 20 minutes could have irreparably damaged the plants in the structure.)

The sealed, self-contained phase of Biosphere 2's history wrapped up in 1994. Today it is owned by the University of Arizona, whose College of Sciences administers it as an Earth systems science research facility. It has been repurposed as a platform for the university to conduct collaborative, multidisciplinary studies, host conferences, support innovative product development and teach systems science to a new generation of students.

Like the founders of Biosphere 2, cities across America have made huge investments in infrastructure. Expensive to build, these roads, bridges, transit networks, public buildings, and water and sewer systems can't be changed overnight. However, just as the University of Arizona developed new purposes for Biosphere 2, existing city infrastructure can be continually repurposed to fulfill future needs.

Recognizing this, the term "Cities 3.0" has been coined to describe cities that use systems thinking to guide the renovation of their infrastructure. In effect, Cities 3.0 will generate flexible infrastructure platforms allowing for modification, rather than wholesale rebuilding, in response to changing social, economic and environmental demands. Cities 3.0 will provide multimodal, smart transportation options and decentralized energy generation with micro grids to enhance resilience. They will make greater use of local water resources and maximize materials recovery from their waste streams.

Sustainability, as David Owen noted, "is a context, not a gadget or a technology." Successful Cities 3.0 will strategically incorporate this concept in their planning. Biosphere 2 not only provides context but also shines a spotlight on the importance of building cities as integrated systems capable of making adaptive use of existing resources, increasing resilience and sustaining life far into the future.