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What are the Sustainability Implications of Peak Population?
Alex Steffen, 10 Feb 08

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?

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Bird flu and natural disasters will strike before we reach that peak. Floodings and draughts are to be expected with global warming as are tornadoes and hurricanes. Moreover, we have several VERY densely populated areas on top of earthquakes waiting to happen. Add that more and more viruses are resistant to penicillin and we will be back to the "good old days" in no time.

Posted by: B on 10 Feb 08

I have no choice but to agree that development progress is terribly slow, on all levels except for entertainment it seems... But personally, I do give some hope to emerging technologies, only that, we should have excepted them a good decade ago, or perhaps had been insightful enough to see the good in some, half a century ago (Porsche hybrid anyone ?) but as this article was oriented to the future, there is little sense for myself to dwell in the past then. As I said, technology can provide us with salvation, if we were to have enough prudence, or heck, at least imagination, to see it. As long as there are people who flinch at electric cars because they don't fart thunder like a gas guzzling V8, the situation is obviously not that bad...everywhere. Merely a lone example. Personally I think politics are a great barrier in such thought. We are one species, until we start behaving like that, until borders become meaningless, we will not improve...

Posted by: Igor on 10 Feb 08


"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...."

What if world pop goes higher and higher, and never goes down? Maybe 10 billion and then 15 billion? Where do you get those rosy figures for pop decline? Yes, Japan and Italy, but not India or China or many other nations...

Posted by: Danny Bloom on 10 Feb 08

Hmmm, is there something in the water around here? :-)

I kind of picture the post-peak future as looking something like the world depicted in Sterling's Holy Fire.

Posted by: Stefan Jones on 10 Feb 08

LES gets award for longest blog post ever. Take heart - the Bush administration is soon over. But given the fact that federal politics increasingly equals corporate control, I'm not sure we're going to find the answers (action) we need in Washington, on either side of the isle. (e.g., Al Gore had to leave Washington to achieve what no politician could have dreamed of doing.)

Alex, I love that you're engaging the biggest ideas over the longest spans. But you know how "futurism" works - things rarely turn out as we predicted. Did you catch Paul Saffo at Long Now and his "cone of uncertainty" principle?

Your post reminds me a talk I saw at Columbia by Nobel laureate / physicist Richard Smalley (whose Nanotech group is now chaired by my old friend Jim Tour, after Dr. Smalley passed away). In Smalley's talk, he lists our most pressing structural issues.

And what were his top two structural issues? Energy and population. What's interesting is that he saw these metrics as interchangeable - that since 1900, population effectively equals energy. Like unchecked microbial systems that use every bit of energy in their path, humanity has grown from 1 billion to 6 billion - soon 9 billion - entirely as a result of access to concentrated stores of energy.

Remove our access to fossil fuels and population falls back to a far smaller sustainable number. But this brings up myriad questions that quickly spiral into Saffo's cone of uncertainty.

I think your last statement nails our focus -- to recognize the exceptional opportunity NOW to "greatly accelerate sustainable prosperity in our own day." And this, alas, is the essence of good futurism - while giving us a better chance of grasping the profound issues which await future generations, it awakens latent sensitivities which inform our decisions in the here and now.

Posted by: John L on 11 Feb 08

that's "aisle".. though sometimes it does seem that our government exists on some distant and detached isle.

Posted by: John L on 11 Feb 08

Thanks for the comments. I've moved Les' incredibly long and off-topic comment to unpublished. You're welcome to your views about the Nazis and the Bush administration, but this post is really not the forum for discussing them.

Note re: China and India- the same dynamics of lower birth rates is observed pretty much universally when women gain reasonable economic security, education and access to family planning. Chinese and Indian women are no different.

Note re: disasters and the "good old days". Natural disasters don't put much of a dent in human population, even bird flu in the worst case scenario wouldn't behave like the black death. In addition, when people are freaked out, we tend to have more kids. Sorry, but the apocalyptic population drop is unlikely.

Nor is it desirable. Violent/disastrous population decline is worse for everyone involved -- people, critters, systems -- than gradual decline after a peak.

Posted by: Alex Steffen on 11 Feb 08

Alex, would you mind to comment about these thoughts I have? I view humans as animals, operating mainly from a biological imperative. We use whatever means are available to massively kill one another--and its always been so. It seems to be built into our psyche to 'wipe out the other guy.' Could this be a 'built-in' (biological) plan for population control that has been over-ridden by all the other factors in our civilizations/cultures/tribes?

Posted by: Tanya Henrich on 11 Feb 08

I've seen this plateau scenario for 20 plus years. Is there any evidence that world population has actually passed the inflection point, the point when the rate of increase begins to decline? If not, we can't begin to predict when world population will level off. So, the question: how can we engender world-wide political will to establish a sustainable/livable population policy. How can all people see our danger?

Posted by: Geo Donart on 11 Feb 08

I hope you are right about India and China. What I see is increasing population there, and world pop going from current 6 billion to 10 billion by year 2099 and then continuing to increase to 15 billion. There are billions who want want what the West has created and they will stop at nothing to get it. And they want it with same kind of expectations that Westerns had when we first wanted this "stuff". Again, I hope you are right. But I think you are wildly optimistic. The pop plateau has not even started yet, and won't until a long long time in the future. Population limits IS a major issue. The planet cannot carry so many people in a healthy way. Which leads us to warming.

Posted by: Danny Bloom on 11 Feb 08

Geo- The demographic transition that happens as women's prospects improve has so far held true in essentially every case, as I understand the literature on the subject.

Danny, Tanya, I have to admit I find your tone frankly a bit creepy here: murder as "a 'built-in' (biological) plan for population control"? "they will stop at nothing to get it"?

I think it might be worth stepping back a bit and really thinking about these statements.

Posted by: Alex Steffen on 11 Feb 08

Danny and Tanya's take on humans being natural born killers spookily parallels another discussion I've been having about whether or not delinquency is a survival trait in a ruptured environment where social systems are disrupted to a point where offspring don't receive effective parenting. An interesting idea, except the other guy has this notion that savagery may be the natural human state.

I say no: civilisations arise too spontaneously for this to be so. In fact, it occurs to me that civilisations may be our *natural* reaction to increased environmental pressures: too many people? Shall we knock a few off, or organise ourselves more efficiently?

As to population peaks, the birth rate has halved since 1963

As Alex says, there is no reason to expect that China and India won't follow the same trend as for other developing nations. However, this doesn't get us off the hook since the improved expectations of people in those developing nations needs to be provided for. The barrel may be well scraped by 2070.

Posted by: Tony Fisk on 11 Feb 08

The median age is rising even in *Somalia*. China is forecast to do the demographic transition very soon and very fast (the one child policy is a success; maybe a catastrophic success a la Rumsfeld).

Posted by: Alex on 12 Feb 08

Re China and India, the fertility rate (children per woman) has halved in both countries in the last 30-35 years.


Posted by: sabik on 12 Feb 08

I am a lanscape architecture graduate student and stumbled across your blog while researching "Design Like You Give a Damn," edited by Architecture for Humanity.

I just finished "The World Without Us" by Alan Weisman, which takes a theoretical look at what the world would be like if humans were suddenly removed from the planet. In the last chapter he addresses human population. He proposes that as humans become less numberous they become more valuable. The care of each child becomes more deliberate. When we begin to value people more than money, convience and comfort we will have accomplished much.

This is contrasted with the caption of "The Sea Wolf" by Jack London, who states that while he can't easily replace the ships riggings, humans are infinately replaceable. Frightening philosphy.

In the hopes of bringing about a better future, perhaps we should all begin to design like we give a damn. Design our lives so that we each make a positive contribution and minimal negative impact. Make that which should be permanent, permanent, and that which should not be, reusable. Grandma's advise of waste not want not was most profound.

Posted by: Rhonda on 14 Feb 08

Something is happening that many too many people appear not to be seeing, I suppose.

Scientific evidence is springing up everywhere that indicates the massive and pernicious impact of the human species on the limited resources of Earth, its frangible ecosystems and life as we know it.

Guided by mountains of carefully and skillfully developed research regarding climate change, top rank scientists like Dr. Rajendra K. Pachauri, Dr. James Hansen, Dr. Hans J. Schellnhuber and Dr. Christopher Rapley issued a Climate Code Red emergency declaration this month to leaders of governments and to the family of humanity proclaiming the necessity for open discussion and action by politicians and economic powerbrokers.

From my humble perspective, many leaders of the global political economy are turning a blind eye to human over-consumption, overproduction and overpopulation activities that can be seen recklessly dissipating the natural resources and dangerously degrading the environs of our planetary home. The Earth is being ravaged; but it appears many leaders are willfully refusing to acknowledge what is happening.

Because the emerging global challenges that could soon be presented to humanity appear to so many fine scientists as human-induced, leaders have responsibilities to assume and duties to perform, ready or not, like them or not.

Perhaps leadership in our time has too often chosen to ignore whatsoever is somehow real in order to believe whatever is politically convenient, economically expedient, socially agreeable, religiously tolerated and culturally prescribed. When something real directly conflicts with what leaders wish to believe, that reality is denied. It appears that too many leaders are content to hold tightly to widely shared and consensually validated specious thinking when it serves their personal interests.

Is humanity once again finding life as we know it dominated by a modern Tower of Babel called economic globalization? That is, has human thinking, judging and willing become so egregiously impaired by our idolatry of the artificially designed, manmade, global political economy that we cannot speak intelligibly about anything else except economic growth and profits without sounding like blithering idiots?

Posted by: Steven Earl Salmony, Ph.D., M.P.A. on 15 Feb 08

I have a very different take on the future population levels of humankind than presented here. The lack of availiblity of cheap energy and continuing climate change will cause a food crisis throughout the world starting in the next couple of decades. Humankind will be forced to adapt this century to a world of limits, and by 2100 will live almost entirely on the annual solar budget. Historical records are quite clear what the world can support in a stable climate. About one billion people. In a unstable compromised climate how many will it support? Less than one billion to hazard a guess.
I see the people of this century as witnessing a dramatic and wrenching population de-explosion.
God help them.

Posted by: Dan Kislinger on 15 Feb 08

RE: Alex said:

"Danny, ...[and Tanya],.... I have to admit I find your tone frankly a bit creepy here: murder as "a 'built-in' (biological) plan for population control"? "they will stop at nothing to get it"?
I think it might be worth stepping back a bit and really thinking about these statements."

Good point. I will step back a bit and think over what I wrote. I didn't mean to say murder as a built-in plan for pop control, but if it came out that way, then I do need to step back and check it over again. Thanks for the note. -- Danny

Posted by: danny bloom on 17 Feb 08

I see now. Tanya's comment was the murder one, my comment was the "they'll stop at nothing to get it" one. Still, good to take a step back and think about it again. I will. -- Danny

Posted by: danny bloom on 17 Feb 08

Alex, you inspired to write a little essay up about peak population and planned obsolescence. Here's an excerpt:

1. Businesses as usual – Disaster! As populations shrink, buildings become abandoned and investments become unsustainable.
2. Everyone gets more personal property – It might just be my opinion, but I think to accomplish our goals of heritage preservation we need to focus on urban density. We should maximize the amount of green, common space combined with dense urban environments with quality of life amenities.
3. Unused built environment is converted to functional public space - Planned obsolescence; for once, it's a good thing.

The full article is here:

Posted by: Matthew Petty on 27 Feb 08



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