In 1859, European settlers brought 24 rabbits to Australia to help colonialists feel more comfortable in this strange new land. With no natural predators, the rabbits bred like, well … rabbits, and it wasn’t long before hunters could brag of shooting 1,200 of them 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 the infamous 1,000 mile Rabbit-Proof Fence were introduced … with mixed results.

Without natural predators or other external forces to keep a species in check, its population (and consequent consumption) will often grow beyond the sustainable limit of a given area (a.k.a. “carrying capacity“) and move into what is called “overshoot” as shown in the following diagram from Rees and Wackernagel’s Our Ecological Footprint:

It’s important to note, there are no ringing bells or flashing lights to warn when a population exceeds its environment’s carrying capacity. There’s no booming voice of God yelling, “Watch out!” Instead, populations blithely continue as they have always done.  Once in overshoot, however, populations risk peaking and collapsing, often damaging their local environment in the process. 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 and the herd’s ability to rebound to its former splendor.

Got it? Okay, good. So here’s an important question….

Where do you believe humans are with respect to the carrying capacity of the planet Earth?

And, by “humans” I mean humanity as a whole, even though, of course, some of us are living larger than others.  Try to pinpoint where you believe humans are on this curve today. Are we on the upslope of the hill still with resources to spare? Are we in overshoot and nearing the peak? Are we at the top of the roller coaster looking down? Or are we in the midst of a crash?

I’ve done this exercise a hundred times and it’s always fascinating to hear how people respond, so feel free to share your ideas in the comments. Some say “We have plenty of room to grow; it’s just a problem of redistribution.” On the other end of the spectrum, some yell out “We’re crashing and burning!”  One student even replied “I don’t believe in lines.”  Okaaay….

The range of responses to this question is itself fascinating. I mean, when you get down to it, isn’t this something we should know? Isn’t this kind of basic information? Where are we in terms of the carrying capacity of the planet?

As a side note, while people are all over the map in terms of where they think we are, I have yet to find a single person (except perhaps that guy who doesn’t believe in lines) who thinks we are moving from right to left on this diagram (i.e. things are getting better). Of the thousands of people I’ve asked, everyone agrees that if we continue on the trajectory we are heading, we will eventually top out and crash. That’s an amazing consensus! The question then is not whether we need to change, but rather how we need to change and when.

But back to the original question…. When people ask me to show one image that expresses the magnitude of our global crisis, I often show the following graph from the Living Planet Report:

This graph displays our Global Ecological Footprint, which is the amount of bio-productive land and water that humanity has appropriated to support our collective lifestyles. This is shown from 1961 to 2012 in relation to world biocapacity, which (amazingly) has been increasing slightly, mostly due to increased agricultural productivity. While this graph does not include all environmental pressures (e.g. pollution and loss of habitat), it does offer insight into a basic condition for sustainability — are we living within our means.

In 1961, humanity was using around 70% of world biocapacity. This was not that long ago – a mere blink in planetary time. For most of our evolutionary history we were likely using less than 1% and it has shot up since the Industrial Revolution. Our footprint has continued to rise and best estimates are that we reached global carrying capacity around 1970. But, of course, we didn’t stop there. We kept on growing both in terms of our population and our consumption and today we are using the resources of about 1.6 planets.

Wait.  What?!  1.6 planets?! How is that even possible given we have only 1.0 planets? How are we not all dead?  I’ll give you a hint. It’s not because of social inequities and it is not because of improving technology, although both are contributing factors. Remember, this is the whole population and the whole planet, we’re talking about.

The reason we are able to live so far beyond our means is because we have been using up the planet’s built-up natural capital, primarily fossil fuels.

Think of it this way.  Imagine, every time you went to the store, in addition to your weekly groceries, you also bought a can of soup that you store away. After a few years, you’d have a pretty well-stocked cupboard. Well, this was our situation when the first modern oil wells were drilled one hundred fifty years ago. It was like opening the door to a huge pantry!  “Look at all this soup!”  The problem is, we went a bit crazy and have been gobbling up our reserves ever since. We’re now rummaging around, trying to find the few remaining cans hidden behind the cereal. But we’re also chowing down so fast it is making us sick and we’re starting to run a temperature, which is likely to get much worse.

You can see how big a proportion of humanity’s ecological footprint is from fossil fuels (i.e. carbon) in this more detailed graph from the Living Planet Report.

Now, you might well ask what burning fossil fuels has to do with our ecological footprint.  After all, CO₂ is in the air, not on the ground.  It helps to remember fossil fuels were created millions of years ago from the anaerobic decomposition of buried organic matter. This is why they are called fossil fuels. They really represent land that once existed, but is now in a different form. Recognizing this fact, some refer to these resources as “ghost acreage.” Think about that the next time you fill up your gas tank.

So, there is strong evidence humanity is now in overshoot. It’s hard to say how close we are to the top of the roller coaster, but we can say with some confidence we haven’t peaked yet since our global consumption and population continue to rise.

But let’s reflect again on that moment, around 1970, when we crossed this threshold. It didn’t shake us out of bed. It didn’t make front page headlines.  We didn’t even know it was happening at the time. But this was an amazing moment, not just in human history, but in planetary history. Never before in the Earth’s 4.5 billion years has one species exceeded the entire planet’s carrying capacity.  Not only have we done it, many of us were alive when it happened!  Sometimes I think we should restart our calendars using 1970 as Year Zero so we can always remember when humanity went into overshoot.

I realize this is a lot to take in.  I try to understand it as best I can. I read books about it. I watch documentaries. I think about it and talk about it a lot. Yet I still don’t feel I really get it. Not viscerally; not in my bones. And I wonder, I worry really, whether evolutionarily, we are equipped to understand a change of this magnitude. We evolved to understand changes in our environment that are quick and local. A lion chasing us? We get that. But issues like climate change that are drawn-out and non-local are quite difficult to grasp.

Unfortunately, as a species, we have been slow on the uptake. Look around and what do you see? Businesses, by and large, are going on as usual. Governments, at best, are thinking ahead to the next election, when they really need to be thinking seven generations ahead. Even our educational systems, with some notable exceptions, are still stuck in the industrial age and we are still training leaders with the skills, the aptitudes — even the rationales and “stories” –necessary to dig deeper and faster into the world’s resources.

As a side note, this is the core reason I founded CAPE, which develops Custom Academic Programs in Ecovillages. While not utopias, I believe these communities are the best campuses we have for training leaders for the 21^st century; for a post carrying-capacity world; for a post-carbon world.

Please share your thoughts and questions in the comments.  Thanks for reading!