An important question about sustainability, Part I


I’d like to ask you an important question, but before I do, I first need to explain something. This question depends on a concept called carrying capacity so I want to make sure you understand this term. Basically, carrying capacity is the maximum population of a given species that could survive indefinitely in a given area.  Think of a forest with defined edges.  Given the available food, water, habitat and other resources in that forest, how many deer could live there?  This maximum population is the carrying capacity for deer in that forest.

Now let’s consider rabbits in Australia.  In 1859, 24 rabbits were successfully introduced by European settlers for game and to help the colonialists feel more comfortable in this strange land.  With no natural predators, the rabbits did what rabbits are wont to do and it wasn’t long before hunters could brag of shooting 1,200 rabbits in just a few hours.  By 1996, Australia was estimated to be home to around 300 million rabbits and drastic measures such as anti-rabbit viruses and over 1,000 miles of fence (the infamous “Rabbit-Proof Fence”) were introduced with mixed results.

Without natural predators or other forces to keep a species in check, its population and consequent consumption will often grow beyond carrying capacity and move into what’s called “overshoot” as in the following diagram from Rees and Wackernagel\’s Our Ecological Footprint:


It’s important to understand, there are no bells that ring and no lights that flash when a population has exceeded its environment’s carrying capacity.  There’s no booming voice of God yelling, “Watch out!”  And that’s too bad.  Because beyond this point, a population moves into dangerous territory and risks topping out and crashing.  If a population declines precipitously enough, it may even take down carrying capacity with it, so its numbers might never rebound to its former splendor.  For example, as a herd of deer overshoots the carrying capacity of a forest, their preferred food becomes scarce and they may start browsing on acorns and saplings, thus diminishing the forest’s ability to flourish.

Got it?  Okay, good.  So here’s the important question….  Where do you believe humans are with respect to the carrying capacity of the planet Earth?  Seriously.  Where are we?  Do we still have room to grow?  Are we in overshoot and heading uphill?  Are we at the top of the roller coaster looking down?  Or are we in the midst of a crash? See if you can pinpoint where you believe humanity is on this curve at this moment in time. Recognize I’m talking about right now with our present technology and culture and about all of humanity, even though, of course, some of us are living larger than others.

I’ve done this exercise literally hundreds of times with groups ranging in size from 5 to 500.  Often I will move my finger (or laser pointer) along the curve and ask people to give a quick clap when we reach that point where they feel we are.  It’s always fascinating to see how people respond.  So, please feel free to share your ideas in the comments. In addition to where you think we are, I’m also curious how you made this determination?  Was it just a gut feeling?  Did you read something or watch a movie that led to your conclusion?

In my next post, I will offer some evidence that clarifies this question and further explore this question and what it means for creating a more sustainable future.

Thanks for your interest and please share your thoughts and questions in the comments.