The best way to define sustainability is by looking at what isn't.

With less than 5% of the world's population, the U.S. (us) uses 1/3 of the world's resources: air (yes, the same air that goes into cars and lungs, yours and mine), water, fish, trees, oil, gas, energy, metals, soil, timber, beef, food, anything.

Elementary algebra says that just two more countries of our size would consume 100% of everything.  That would be less than 15% - about 1/7 - of the world's population consuming all of the world's resources. Europe already consumes just about as much as the U.S. (us) does, and gobbles another 1/3 slice.  That leaves 1/3 of the world's resources to be shared by well over 3/4 (85%) of the world's population.

One more country the size of the U.S. (us) consuming at our present levels - which isn't terribly difficult to do as things are - and there will be nothing left to share. Elementary algebra again tells us that at current rates of extraction and consumption by developed countries (us), we would need not one, two, three, four, five, or six, but just about seven planets with the same abundant resources - air, water, light, trees, fish, beef, oil and soil - to sustain the current world population the great American way.  

In the end, we would leave those seven planets ozone depleted, warmed up, species extinct and inhabitable no doubt like we are doing to this one.

Global solutions must pay attention to the minute details that form the infinite complexity of life in all of its forms, therefore achieving the balance and harmony that are the principal characteristics of life. The way we interact and evolve in our diverse natural environments, how we inhabit, co-exist and prosper on this planet must do so without significantly altering the life systems that support all.

Life was made possible for all, not just for the exclusive realm or convenience of humans.  The perspectives of sustainability and environment must form entire, whole and functional systems, not just isolated pieces that humans can use and dispose of. The underlying principles of sustainability must be applied to economic development, the built environment, architecture and engineering.