Sustainable Means What?

Sustainable, carbon-neutral, self-sufficient and similar terms get thrown around and used somewhat interchangeably in the press and on the internet. For the purposes of this blog, I will use the term sustainable to refer to a process that can be carried out indefinitely. This can only happen when that process consumes resources slower than those resources are replenished (or at the same rate).

A simple example is collecting dead fall from the forest floor to make a camp fire to roast marshmellows. As long as you collect the wood that falls from the trees to make your fire and don't cut any live trees, you can do this for a very long time (generations, centuries, etc.) The trees will continue to grow and produce wood for your camp fires indefintely. But as soon as you collect all the deadwood and decide to start cutting down trees to burn, you have started a non-sustainable process because you are consuming the wood faster than it is being replenished.

All human activity can be examined through the lens of sustainability similar to this method. The complexity arises in the many different inputs required for most of our activities and analyzing whether each one of its resources are being consumed slower than they are being replenished.

There is one extreme example that I want to get out of the way for any critics who find issue with my definition of sustainable processes. Sunlight is for all intents and purposes a sustainable energy source even though we all know that the sun is slowly consuming its vast store of hydrogen and fusing it into helium in a non-sustainable process. I think any resonable person will agree that 4-5 billion years is such a vast amount of time beore this resource runs out that it is effectively infinite.

On the other hand, fossil fuels are not infinite in supply. We are close (10-50 years depending on who you ask) to consuming 50% of all of the easily accessible petroleum on the planet. That is a timeframe that most of us alive today will live to see. After that point (called peak oil) the demand to consume oil each year will exceed the supply, likely resulting in wild price flucuations (remember the price of oil in the summer of 2008?). This is a common response in complex systems to restricted supply of resources.

So why is all this important? If a process is not sustainable, at some point it will stop (because there will be no more resources to keep it going). In our campfire example, no more trees (think Easter Island), no more roasted marshmellows.

For all of human history our resources have been effectively infinite (like the sun's supply of hydrogen). At the end of the 20th century I belive human beings entered a new era where on a global scale we are starting to exhaust the resources upon which we depend for everything from growing our food, to generating our electricity to building our cities. History is littered with the ruins of civilizations that collapsed because of the over-consumption of local resources. For the first time in history we are going to have to contend with the consequences of over-consumption of our resources on a global scale.