Sustainability 101

What does Sustainability mean?

In 1983 the Brundtland commission was formed in response to a UN General Assembly resolution, and in their report, entitled Our Common Future they defined sustainable development as meeting the needs of the present without compromising the ability of future generations to meet their own needs.
A truly sustainable solution is considered one at the intersection of three realms: equity, environment, and economics.
An ecological footprint is the land (and water) area that would be required to support a defined human population and material standard indefinitely (Wackernagel and Rees, 1996).
In 2008, earth overshoot day, defined as the day of the year on which humans will have used all the resources that nature will produce for that year, occurred on September 23rd (http://www.footprintnetwork.org/gfn_sub.php?content=overshoot). Globally, we now require 1.4 Earths to support our lifestyles (although that number considers all humans - if everyone lived as we do on Mercer Island, the number would be closer to 5 Earths!)
A sustainable solution would require that we live only off of nature's interest and so do not deplete nature's capital. Nature's interest in this context includes not only regenerating biomass and animal stocks, but also the ability of the atmosphere and waterways to accommodate our wastes.