What Does It Mean To Be Sustainable?

Every day we hear about topics like sustainable growth and sustainable building, but what does it really mean to be “sustainable?” The economist Herman Daly has suggested three simple rules to help define sustainability:

• For a renewable resource–soil, water, forest, fish–the sustainable rate of use can be no greater than the rate of regeneration of its source. (Thus, for example, fish are harvested unsustainably when they are caught at a rate greater than the rate of growth of the remaining fish population.)
• For a nonrenewable resource–fossil fuel, high-grade mineral ores, fossil groundwater–the sustainable rate of use can be no greater than the rate at which a renewable resource, used sustainably, can be substituted for it. (For example, an oil deposit would be used sustainably if part of the profits from it were systematically invested in wind farms, photovoltaic arrays, and tree planting, so that when the oil is gone, an equivalent stream of renewable energy is still available.) 
• For a pollutant, the sustainable rate of emission can be no greater than the rate at which the pollutant can be recycled, absorbed, or rendered harmless in the environment. (For example, sewage can be put into a stream or lake or underground aquifer sustainably no faster than bacteria and other organisms can absorb its nutrients without themselves overwhelming and destabilizing the aquatic ecosystem.)
  

From looking at Daly's definition of sustainability, we see that few things in our modern world are actually built, processed, or manufactured sustainably, including what is generally referred to as "sustainable building", and that we have a long ways to go towards actually making our modern word sustainable. Building a sustainable world is not easy, but it is doable!

The Huffington Post - What is Sustainability?
Photo credit: Simon Gray