This article was written by Alex Steffen in February 2008. We're republishing it here as part of our month-long editorial retrospective.
Sometime in the latter half of this century, human population will peak. Having swelled to a bit over nine billion people, our numbers will begin to drop as people age and women worldwide pass through the urban transition, gain control over their own life-choices and have fewer children.
After that, population will proceed to decline by the middle of the 22nd century to a number somewhere between 8.5 billion and 5.6 billion (depending it seems largely on whose assumptions about longevity growth you find most credible).
That's pretty much the consensus position among demographers (though there is a range of belief about when the peak will happen and whether we can expect to more or less plateau at 8.5 billion or experience a long bumpy slope to a stable-state population of about 6 billion). Note that we don't need to assume any sort of apocalypse here: this is the orderly progression of human beings passing through a post-industrial demographic threshold you can already see in cultures from Japan to Italy to Finland.
Note, too, that the major difference, if I'm reading the studies right, between a 22nd century with 8.5 billion people and one with 6 billion is the number of old people. We live now on a planet of children and youth, with a world median age (in 2000) of about 26. By 2100 it will be 44 years, if U.N. demographers (PDF) are correct. If that median age continues to rise because life expectancies continue to rise, we'll end up with a flatter global population including a lot of people who are by today's standards extremely old; if the growth in life expectancy levels off, we'll see a gradual decline in population (and I suppose it is even possible that radical life-extension could mean that population continues to grow... which could have very grave consequences).
But let us, for the sake of argument, take a middle ground position. Let us assume that human population peaks about 2070, that we experience modest but constant life-expectancy gains and low fertility rates, and we end up with, say, a little over 7 billion people sharing the planet by the middle of next century. Why does this matter?
We'd have two essential tasks here: the first is a well-understood challenge of seeing humanity to that peak with the least possible permanent damage to the planet and vital human institutions -- essentially, building a bright green future 9 billion people can share; the second is one I don't think I've heard any discussion of, which is planning that bright green future with the different needs in mind of the shrinking, aging population to follow.
We might think of this a two-stage process: working to see a young humanity safely through the shoals of this century while preparing the groundwork for a more mature humanity to live happily in the centuries to come.
How we design our answers to the immediate crisis will have, it seems to me, much to do with the conditions faced by our great-great grandchildren in the next couple centuries. Just as we're learning that the Great Wager is a one-time shot (that we only have enough resources and biocapacity to build this new civilization once, so we'd better get it right the first time), barring some magical technological breakthrough (and pinning our hopes on that seems a bad bet for reasons we'll pick up another time) those to follow after probably will have, to some large extent, work within a tighter set of ecological limits and with the already-embedded energy and resources of the civilization we design this century. It seems to me extremely unlikely, in other words, that humanity in the 22nd century will be in a position to toss it all and start over (instead, their frontier may be the ruins of the unsustainable aspects of the world we're building today, their resource base our dumps and disaster zones).
Thinking about this reality might, I suppose, bum out some folks who place their faith in a future human transcendence of natural limits and human shortcomings. If you can't imagine any worth in a future that lacks free energy, nan-fabs, super-intelligent AI and immortal people, the 22nd century as it may well shape up might seem pretty lame. But this is stale thinking in my opinion, Industrial Age ideas of the linear progress of our ability to conquer nature, the future projected as a replay of the past, with no limits.
But limits are reality. We live on a finite planet, one whose workings we understand only poorly. Everything else is very far away. And by the time the people of the 22nd century get their turn, the Earth will be a much smaller place, in terms of ecological utility, than it is today.
The standard response to these facts is that some new technology will "save" us, and make limits irrelevant. But I am consistently impressed, when I speak with folks who are hard at work in the fields of biotechnology, molecular engineering and software design, at how real a sense of limits actually exists among the smarter ones. There are things we don't know how to do now and may never (in any foreseeable time span) know how to do; there are others that seem like good ideas until you start doing them and encounter the unintended consequences; there are still others that work, but work in ways that mean something different than we expected. Where in the 90s we expected emerging technologies to unleash the boundless, more contemporary thinking about these technologies seems to me to be all about seeing them not as magic but as tools: profoundly useful, if used right, but perhaps far less transformative than once we hoped. They may greatly extend the range of actions we can take within the fundamental limits we face, but they most likely won't change the limits themselves.
Given that, I've been thinking, that we might begin to imagine our responsibilities in a slightly different light. It seems to me we might imagine a series of nested challenges:
1) The meeting of the immediate crisis. Before global population peaks, we need to have one-planet models of prosperity, and we need to make sure people embrace them (and have the opportunity to embrace them), so that we head off the disaster-spirals that await us if we continue to overshoot the Earth's biological capacity. The meeting of this crisis allows us to imagine stability returning in the 22nd century, and is vital.
2) The preservation of long-term legacies: the maximum possible number of species, the most stable climate possible and as many of the great human legacies -- from languages to learnings, seeds to world heritage sites -- as we can. The preservation of these legacies expands choice for future generation, and is vital.
3) The design of answers to 1) and 2) that themselves think ahead. We will be designing, for instance, cities to house billions more people over the next 50 years... but then most of those cities will become shrinking cities, home to far fewer people in the next century: can we design cities that can shrink gracefully?
Can we imagine designing all our buildings and infrastructure for eventual disassembly, reuse or recycling, so that the no-longer needed urban fabric of these shrinking cities becomes not waste material but the resource feedstock of the cities of the future? Can we imagine, now, designing loops and closed systems which will leave our great-great grandchildren not with the vast toxic legacy of corrupted waste we are currently amassing, but with healthy, useful stockpiles of materials which we have used, enjoyed and then left for re-use?
Can we plan beyond the peak? If we spent even 1% of our money and effort to plan into our systems and designs more of the needs of people 150 years from now, we might find that the pay-off to future humanity could be really vast.
Well, re-reading this, I'm not sure I've arrived at the points I most wished to make. Somewhere in my mind is a larger point about the nature of sustainable design, and how we ought to be working as hard as we can to imagine our current stock of resources as the only stock of resources -- the stock of resources to which future generations of our children will be largely limited -- and to work a bit harder at building our cities and systems to have the flexibility of re-use, disassembly, etc. that will allow future generations to re-make their world out of the pieces of our own.
Furthermore, I suspect, without an entirely coherent argument to back myself up, that thinking about our work in this way might actually greatly accelerate sustainable prosperity in our own day, that pairing flexibility and one-planet limits may be part of what lets us reimagine the good life along radical new lines that fix the future we're passing on while making our own stay on the planet as bright as possible.
But I don't really have the words yet. Perhaps others have ideas along these lines?
What are the Sustainability Implications of Peak Population? is part of our month long retrospective leading up to our anniversary on October 1. For the next four weeks, we'll celebrate five years of solutions-based, forward-thinking and innovative journalism by publishing the best of the Worldchanging archives.