When Fortune invited my design firm, which specializes in sustainable architecture, to share our vision of a building of the future, we decided not to guess about conditions decades or centuries away. Instead, we looked at the possibilities that exist now.

Buildings consume 40 percent of our energy and can have life spans longer than humans. Because we live, work and associate with others in buildings, they form part of the fabric of human life—and thus have an enormous effect not only on the quality of individual lives but also on the state of the earth.

In the pages that follow, we have configured a structure that is not just kind to nature; it actually imitates nature. Imagine a building that makes oxygen, distills water, produces energy, changes with the seasons—and is beautiful. In effect, that building is like a tree, standing in a city that is like a forest. -- By William McDonough, founder and principal of William McDonough & Partners