What’s the carrying capacity of the Earth?

You started thinking of a number, right? Most people start thinking of some number around ten billion, within a factor of two or so.

I meant, what does the concept mean. Most people don’t think of what it means. I didn’t until recently, and realizing what it means changes how I think about it a lot more than I expected.

Wikipedia says

The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water, and other necessities available in the environment.

If you think the carrying capacity is how many people the Earth could sustain living like you do, you’re not close, especially for nearly all Americans or readers of this blog. We use far more resources than necessary.

So getting the “maximum population size” means everyone would have to use less resources. I think I use a lot less resources than most, but I still could use less.

What is the minimum anyone would materially need? We aren’t talking about TVs and microwaves. Minimum resources mean clean water, air, and space. If the air or water is cleaner than necessary, we could still put in more people to pollute it more. If you have any privacy, we could pack more people in the space available.

So what sets the limit on pollution and space? To reach the carrying capacity, we’d have to be at the limit where any more pollution would kill more people than it would allow. A friend of mine who looks at these things from a purely engineering standpoint puts it this way:

The carrying capacity limit is where everyone is indifferent between living and committing suicide.

Approaching the carrying capacity of the Earth means approaching living with minimal resources.

By contrast, living below the carrying capacity means having more resources for everyone. There would remain the economic challenge of distributing the resources, which we have challenges doing, but at least we’d have spare resources to distribute. Business people who understand operations also know the benefit of running below peak efficiency also allows for more slack if there are problems. A factory running at peak efficiency that hits a problem, no matter how small, has to stop completely. One running below peak efficiency can absorb problems in some places and catch up without shutting down.

In the context of factories lowering production we mean it produces less. In the context of populations at peak efficiency having problems, we risk innocent people dying. Allowing more slack in the system can save lives.

When people think of the carrying capacity of the Earth, they generally think of the human carrying capacity. Other species that use similar resources as us lower our capacity, so more humans mean fewer other species. Historically, humans arriving in a new land mass have led to extinctions of most animals of around our size. We’re killing of more species all the time, however indirectly.

So approaching the human carrying capacity of the Earth also means causing more extinctions. Probably no dogs, cats, cows, pigs, sheep, and other mammals around our size.

When you consider what the Earth’s carrying capacity is for humans, keep in mind what approaching it means to people living in such a world—with the absolute minimum sunlight, fresh air, clean water, and so on to live.

Do you want to approach such a world? When I say you don’t want to know the Earth’s carrying capacity, I mean you probably want to live far enough below it that we never narrow our uncertainty because we still have enough material abundance to enjoy things like national parks and air and water without mercury in it, or at least not much more than we’ve already put there.

There is also the concept of overshoot. Our population may be over the carrying capacity now, using some resources unsustainably, which would lead to population decline when the stores we’re living on run out, but I’ll save that topic for another post.

• ← Why Sriracha Hot Sauce tastes good
• Thoughts about thoughts →