Image from Harry Cunningham via Pexels.

Bill Rees uses the term overshoot to describe how unconstrained population and economic growth are unsustainable on a finite planet. It’s an argument he’s often made and, as a sustainability-focused academic, I’m a receptive reader. Mostly.

On population, I appreciate his pushback against the oft-heard argument that a declining (or even stable) population will be economically disastrous for individual countries like Canada, and ipso facto disastrous globally. The reality is that each human consumes material inputs, produces wastes and occupies space, meaning that a rising global population exacerbates the sustainability challenge. If, instead, population is stable or declining, there will be challenges no doubt. But the need for workers to support an older population will incentivize innovations in sectors like health care and elder care, while also enabling some willing people to apply their skills in the workforce well beyond conventional retirement age.

I diverge somewhat from Rees when he inextricably links population, economic output (GDP), material inputs and wastes. Historically, these four attributes have been linked, as our growing populations and economies consume more resources and produce more wastes. But what if our policies finally constrained our economic system to recognize planetary limits? Would economic growth inevitably stop? Or, instead, would the character of that growth change? Rees implies that the Tikopians, with a fixed land base, will never develop environmentally benign innovations that provide them with greater value from constant or fewer material inputs and less waste.

In describing the economic process, Nicholas Georgescu-Roegen once noted that its “true product is not a material flow but a psychological flux: the enjoyment of life, which cannot have room in any material matrix.” The enjoyment of life would improve dramatically for billions of people in the global South if their economies and governments provided them with more nutritious food, quality health care, basic education, adequate shelter, clean environments, minimal corruption and reduced natural and human-caused threats to security. Much of these improvements would show up in national accounts as a rising GDP – ergo economic growth.

To achieve this while sustainably using material inputs and preventing environmental calamity is a huge challenge. But in applying his “ecological footprint” concept, Rees makes it even more difficult. By his accounting method, the resource use and waste stream of each location must not exceed the ability of “productive ecosystems … to produce the renewable resources that the population consumes and to assimilate its carbon wastes” (such as CO₂).

But the current output and waste assimilative capacity of productive ecosystems is an artificial constraint, and humans have long shown they can innovate beyond this limit. We’ve added water to exceed the bioproductivity of arid lands. We exploit various forms of solar energy (sunlight, wind, hydro, biomass) that can exceed the energy productivity of photosynthesis in ecosystems. And as we increasingly focus, by necessity, on the limits of a finite planet, our innovations are likely to continue this trend. To name just a few innovation paths, humans are likely to:

• exploit the chemical energy from fossil fuels while increasingly returning its carbon into the sedimentary layers from which we extracted it,
• develop an array of energy storage options that enable vastly greater exploitation of solar and wind,
• develop nuclear fission variants that are more sustainable in all respects,
• develop nuclear fusion that revolutionizes our energy systems,
• produce goods where all byproducts from production and use are either recycled or can assimilate benignly, and
• structurally shift our economies from material throughput–based economic value to services that provide “enjoyment of life” for young and old.

I agree with Rees that our odds aren’t good for avoiding major calamities related to overshoot. But if we want to improve these odds, we should not tell everyone to stop all forms of economic growth – a global North perspective if there ever was one. Five billion people in the global South need a lot more economic growth, of the right kind.