In recent years it has become self-evident to many of us that we need to protect and restore our changing environment. By “environment” we are generally referring to our surroundings—our biophysical environment, which in earlier times meant the four classical elements, earth, fire, water, and wind, and later came to include the quintessence or the aether—air or space. Today we tend to refer more to the nitrogen, carbon, and hydrologic cycles. Also, today we consider our environment to additionally mean the exchange of mass energy or other properties that affect our life cycle and that of other organisms. But in our everyday world there is another environment—the built environment—which encompasses the design, construction, management, and use of buildings, neighborhoods, cities, parks, and systems that provide our individual and global surroundings, and the setting for all sustainable human activity. As all built environments depend upon energy, water, and other natural resources from the earth's biophysical environment for their very existence, it might be hoped that our biophysical and built environments (see Figure 1) can coexist in some form of commensal symbiosis, whereby we humans and our built environment benefit while the biophysical environment is unaffected. However, unless significant global positive change comes soon, it is looking increasingly like a parasitic relationship, where humans collectively benefit at the expense of the natural world.

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