Earth’s Carrying Capacity. That’s a myth

Theology at the end of this blog. First, some environmental talk. I have an occupational background in environmental biology (not to mention a Master’s degree in International Development), so I understand the idea of carrying capacity. And I don’t believe in the idea that Earth has a “carrying capacity” of humans. Drawn over from environmental studies of animals in an ecosystem, the reason this is a non-starter for me in regards to human population, is that history has shown, time and time again, that people are capable of creatively adapting and developing ways to live in an ecosystem far beyond what its “previous” carrying capacity was thought to be prior to the innovation.

Estimates of the carrying capacity of the Earth (for human population) since van Leeuwenhoek in 1679, have been laughably incorrect over and over again, not to mention ranging from 1 billion to 1000 billion! The low end estimates were based on the agricultural technology of the day (tillable acres and output divided by human consumption per capita) and those estimates of carrying capacity have been repeatedly increased due to the increase in agricultural output per acre enabled by new advances in farming practices. I’m typing this on Point Loma, a very densely populated part of San Diego. The carrying capacity of this area is a million fold what it would have been for the Diegan Indios 500 years ago, but then we aren’t hunter-gatherers. I’ve lived on one of the most densely populated pieces of land in the world: Java, Indonesia. Rice terracing and fish farming have increased the food-producing capabilities of that land far beyond its natural contours. As a 2012 UN study put it, “technological advances in efficiency can be a divisor of per capita impact.” 1 When the interdependent variables in dynamic systems modeling today are applied to carrying capacity, there are so many estimates regarding future variables, the range of estimates becomes so huge as to be meaningless. A 1995 article in Science called for “extreme skepticism” regarding carrying capacity estimates for the reasons I’ve just cited. 2

A meme I saw said “God makes a world for humans – 70 % saltwater ocean.” It was witty on the surface, but it really doesn’t make the point it attempts. Humans figure out how to live in ecosystems as we go. Our ancestors walking out of Africa could not have survived near the Arctic Circle with the savannah lifestyle they knew – but the Inuit and Eskimo have learned how to thrive there for thousands of years – with only Neolithic technology! 70% of our world is indeed oceanic – but we have only scratched the surface on learning how to live there. We can learn to live in oceanic environments just as surely as we did in Arctic ones. Aquatic farming is just in its earliest stages. Not only is there plenty more for us to learn about farming Earth’s various biomes, but we haven’t even hardly started with urban farming and stackable skyscraper farms. Figures for carrying capacity are always and utterly tied to current technology and practices. Any talk of carrying capacity should start by saying “If we never, ever do a single thing different than we do today…” And that’s just silly.

But there’s a strong theological reason to question the idea of carrying capacity. For those Christians who believe we are past the carrying capacity of the Earth, we need to ask “Which of the people currently alive would the Creator God prefer had never been born?” It is theologically repugnant, from a Christian point of view, to imagine there are any. We don’t need less people created in the imago dei. We simply need what every group of people have needed (and worked out) since the digging stick was invented and there were more babies born in the tribe: new ways to find, (or in our case) increase, harvestable output.

And by the way, there is no shortage of food in the world per capita. There are local scarcities we haven’t transported to effectively. It’s not a quantity issue, it’s a transportation issue and a governance issue. Next time let’s talk about carrying capacity and pollutants in a closed system.


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Environmental Systems Calculus*

When we talk about the human habitation of Earth today, we want quantitative understandings of the planet’s carrying capacity. Materials and energy balances are key tools in achieving a quantitative understanding of the behavior of environmental systems.  They serve as a method of accounting for the flow of energy and materials into and out of a system.  Mass balances provide us with a tool for modeling the production, transport, and fate of things like pollutants or resources in an environment… examples of mass balances include prediction of rainwater runoff, oxygen balance in a stream, the temperature change in a river from the discharge of cooling water from a power plant, or the temperature rise due to global warming.

In its simplest form a materials or mass balance may be viewed as an accounting balance. For an environmental process the equation would be

Accumulation = input – output.

There are both known and unknown inputs, outputs, and accumulations in system modeling, but the mass balance should account for and solve the amount of unknown inputs and outputs.

Time is also a factor: For many environmental problems time is an important factor in establishing the degree of severity of the problem or in designing a solution. Another simple equation from environmental engineering:

Mass rate of accumulation = mass rate of input – mass rate of output

In plug-flow systems, a calculus equation can tell you how many km of pipe is needed to decontaminate a certain amount of polluted water as it flows through the pipe with a catalyst inserted. This kind of rate-of-flow-and-conversion is another calculation we need in order to understand our carrying capacity as a planet.

So, our situation is this. As human civilization has grown and continues to, we are increasing the inputs of some things in the system at a rate that outpaces the output. At the same time, we have a hard time calculating the availability and sustainability of some of the key resources – estimates have been wrong time and again. Likewise, we don’t know the tipping point of some processes, since we’ve never been to this spot before. More on what this means for our future as humans on this planet, and how theology affects our calculations, next time.

* Intro to Environmental Engineering Fourth edition (Davis & Cornwell). My family includes an environmental engineer.