Imagine, as a thought experiment, that everyone on the planet had the same share of the world’s resources. It turns out your share is about six acres (2.5 hectares) of dry land.

Now imagine if that were your whole world. How would you treat it?

Thinking in small numbers

It’s difficult to think in extremely large numbers. Suppose, for instance, the U.S. government spends around \$100 million on climate models per year. (I believe this is about right.) That sounds like a big number! Much too big, perhaps? Well, if you are an average American, it’s 33 cents out of your pocket every year. Is that a good deal? Too much? Too little? The pentagon spends \$450 billion per year. Is that a lot? That’s about \$1,500 per American. Expressing numbers in per-capita terms puts them into perspective.

I have been thinking about this in the context of the big question of our time, which as Jeffrey Sachs points out, is not about terrorism or islamo-fascism or even oil or climate. It is about whether all of us can fit comfortably on this planet. It is a big population and a big planet, so thinking quantitatively is daunting.

Fortunately, per-capita thinking can put matters into a more familiar perspective, make them more palpable and less mathematical.

The little prince to the rescue

Consider the world of The Little Prince by Antoine de St. Exupery.

The Little Prince of the story is a child living alone on a small spherical asteroid, his only companion a single flower. He consoles himself by the fact that it is always a short walk to a sunrise or a sunset.

Let’s tell a slightly different story, with a similar asteroid, a per-capita world. Instead of being one of six billion people on a big planet, let’s suppose you were alone on a comparable asteroid. We’ll give you your six-billionth share of the surface area, your six-billionth share of each of the major landmasses and biomes, your own six-billionth scale Africa, your own little Australia. In other words, you will have exactly the average resource ownership of everyone else on earth.

Your little asteroid has a six-billionth of the earth’s total surface area. It is a sphere with a radius of 82 meters, and with a surface area of about 85,000 square meters. That, depending on how you prefer to think about it, is almost exactly 21 acres, or 8.5 hectares. In more urban terms, that is 19 American football fields, or about 12 English football (professional soccer) fields.

Just over 70 percent of your 21 acres is covered by salt water. If it were to freeze over, you could walk from any point to any other point at a leisurely pace in under ten minutes. Since the ocean covers fifteen acres, the land surface covers the remaining six acres.

A vast variety of soils and climates are arrayed about your 6 dry acres. According to the CIA, the area under cultivation is a bit under 5 percent of the total land area, or a bit over a third of an acre. If you push matters to less valuable soil, you might be able to grow things on as much as an acre, but most of your 6 acres are desert or tundra. You even have some substantial ice sheets on your land. There is also the problem that you have built your house, your workshop, your garage, your driveway and many of your industrial outbuildings on the best farmland.

About a third of your land under cultivation is irrigated, much of it using depletable groundwater. Some of the groundwater is being contaminated by some of your industrial processes. To a lesser extent, your soils are also being contaminated, but a bigger problem is that as you till them for food they erode much faster than the natural rate of replenishment.

You also like to eat fish, but most of your ocean does not naturally support large fish. From the few areas that do, you have been eating the fish faster than they reproduce. This would astonish your great-grandparents, but of course they lived on a larger world. (Their per capita share was bigger with a smaller population.)

Still, you live much better than your great-grandparents, because you have found ways to dig up fossil fuels and use them to power heavy machinery to do your bidding. Some of your machines are quite advanced, but some of them are crude and nasty. All your raw materials are dug out of the ground and refined. You produce a fair amount of industrial waste along with household waste, but you do not attend to it very carefully.

You currently use a bit over a ton of fuel per year, producing 4 tons of CO2. (This is based on world average; note that the typical North American emits about five times this much!) It seems from direct measurement that about half of this (two tons per year) stays in the atmosphere, with the rest ending up in the ocean and the soil. While this is a fairly small fraction of your atmosphere’s total mass of 880,000 tons, you are wondering whether this has anything to do with a certain slushiness you are starting to see in your ice sheets.

Your little world is a model of the sustainability problem. In some ways it is a fantasy, but the scales and constraints are real, expressed not as huge global numbers but as per capita quantities.

You are using fuels that are not replaceable. We can come up with some numbers for groundwater reserves and fuel reserves on the same basis. Your world is smaller than your ancestors’; your use of resources is more intensive and accelerating.

There is no replacing your six acres, no frontier. No amount of human ingenuity will make your world’s surface bigger.

Is your little world big enough to sustain you indefinitely? Are you past the point of permanent damage from which no amount of future cleverness can recover?

You may be considering resolving your problems by increasing energy intensiveness. Indeed, some of these problems can be solved with more power. You can desalinate sea water, for instance. However, more energy use puts demands on other parts of the system, causing other problems.

Increasing wealth won’t make your asteroid any bigger; indeed, it seems only to create more byproducts you have to put somewhere. Meanwhile, the little asteroid keeps shrinking (representing your declining average share of the land as the real world’s population increases).

Whether by design or by circumstance, sooner or later you will run up against limits. It is hard to argue that you can avoid big changes forever, all the while becoming wealthier.

The global village

As you contemplate your little asteroid, keep in mind that the intensiveness described there is a worldwide average, including many poor people who have much smaller impact than almost everyone who will read this. Most of the world’s population aspires to at least a European standard of living.

Whether we have enough resources for that goal is limited by factors not conventionally dominant in economic thinking. Economists will dislike the lonely asteroid model, since economics has been totally factored out. In some ways, I think this is a good approach. There is an economics-free view of sustainability that the tiny asteroid brings into focus. No matter how clever our advances, we will never have more than an acre to feed us. (I was actually rather surprised, in composing this article, to find out how small my fair share is.)

Economics only complicates matters and seems to be a constant distraction from the baseline question: can we continue to provide, indefinitely? The fact that the planet is finite can’t be treated as a minor factor in this crucial question: how well can we sustain ourselves, meaning a modern society of six to ten billion people?

Optimists argue that progress will prevail. Pessimists argue that progress is an illusion. I think progress is possible, but not automatic. When I contemplate my asteroid, I suspect I can manage, but I don’t think I can afford overconfidence.

I think we can prevail, but we will have to be clever about how we do it, and can’t rely entirely on individuals acting from self-interest without careful collective attention to how we set up the reward structure.

Like the Little Prince, we find ourselves rather lonely imagining this solitary little world. Our relationships to each other are crucial to our circumstances, and in the end, economics and politics are crucial components of our strategy.

In a future essay I will consider a different way of scaling the problem, to the village level rather than the individual level. We will reconsider everything scaled to a village of six thousand people on a larger asteroid. We will have to deal with rather larger numbers, but will be able to consider human relationships as part of the model.