The major development underpinning the prospect for an early-century peak in human population and even earlier peak in civilizational power is a rapid and seemingly unexpected decline in fertility rates across the world. All regions except Africa are now below the replacement rate, and still falling.

This short post—probably my last on the population topic for a while—is centered on the following animated GIF showing how the United Nations’ demographic models have expected total fertility rate (TFR) to evolve into the latter part of this century.

U.N. TFR projections from 2010, 2012, 2015, 2017, 2019, and 2022.

Every few years, the U.N. releases a demographic projection model that includes an expectation of how TFR will behave going forward.  I have already pointed out the glaring discontinuity (kink) at 2020 in the latest projection and a gallery of systematic major misses at the country level.  What the animated GIF above helps us see is how stubborn the imagined far future is—consistently aiming for a one-size-fits-all convergence.

I have referred to the notional TFR endpoint as a “magnet,” acting like a theoretical convergence point to which all regions are attracted.  We see how persistently influential this magnet is on projections in the sequence above.

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Image by StockSnap from Pixabay

Readers may have noticed that I’m on a bit of a demography kick of late, and this post is no different.  Several reasons contribute to this focus.  First, human population is an extremely important factor in the future health of this planet.  Second, I am fascinated by the prospect that population growth may not turn out to be as crushing as I had previously believed.  Third, having developed a tool for demographic projection, I want to get my money’s worth before scooting off to something else.

The first post in this series examined the unexpected realization (on my part) that current trends could put us on track for a global population peak in the next few decades—maybe deflating the population balloon before something pops. In the process of investigating how this squared with most projections that show a late-century peak, I came to understand the theoretical biases—especially in fertility—employed by United Nations demographers. This first post also explored possible implications of an early peak: how modernity would cope with such a major, unprecedented, and rather prolonged period of declining population. The second post sketched out a reasonably sophisticated demographic propagation tool I constructed tracking six regions of the world so that I might reproduce the U.N. projections and explore what I considered to be plausible variants in terms of both fertility evolution and survival/medical trends.  I also wedged in a bonus post exposing the repeated systematic failure of demographic projections to capture recent rapid trends in declining birth rates.  The models apparently don’t incorporate whatever drives this major phenomenon.

In this post, I examine a few implausible scenarios for the purpose of isolating and better understanding factors at play. I think of it as answering “What If” questions (calling to mind Randall Munroe’s excellent What If series of outlandish yet illuminating questions). What if fertility around the globe suddenly locked at the replacement value? What if things stayed exactly as they are today? How much earlier would population peak if Africa’s fertility fell as rapidly as other recent precedents? What if we suffered a pandemic or global resource war?

The first few of these explorations are not intended to be realistic as much as they are illustrative of the relative importance of various factors. I learned from the exercises, at least, and hope you will, too.

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Image by Anne and Saturnino Miranda from Pixabay

The word “whiff” is used in baseball to describe when the batter swings and makes no contact with the pitched ball. The term presumably derives from the sound of hitting nothing but air.

This off-sequence post acts as a brief update that I wanted to present, without making a full-fledged blog post out of it (in hindsight, I may have failed). In the last two posts (here and here), I noted that recent rapid drops in child birth around the world could conceivably put us on track for an earlier population peak than previously anticipated—possibly as early as 2040 vs. the 2080–2090 timeframe.

That would be big news, and makes me continually ask myself: where is the disconnect? Is it possible that demography models are that wrong? I have discussed already (and will revisit in the next post) some of the potential blind spots for how this century develops. But here I look backwards to see if the recent drop in child births was itself a surprise to the demographers. If so, then it speaks to dynamics at play not captured in demography models, and that’s important.

I used the 2022 United Nations World Population Prospects (WPP) data (public) to build a list of countries that had the largest fractional declines in total fertility rate (TFR) from 2010 to 2019 (pre-COVID), and that also had projections in previous U.N. WPP products back to 2010. I show how (not) well the U.N. expectations match the actual story for these cases. I also throw in a few other countries of interest, including the three most populous ones.

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Last week, I reported the surprising realization that official population projections from the United Nations adhere to a notion of future fertility that appears to be immediately at odds with present real trends. The recent rapid decline in population growth—even pre-COVID—suggests that a population peak prior to 2050 is not outlandish, provided that current drivers continue to apply.  Recent declines in fertility rates, together with a flattening age distribution of young folks, combine to set the stage for population peak and decline.

In the previous post, I performed two embarrassingly crude projections of recent trends (simple curve fits) to demonstrate that a population peak as soon as 2042 or even 2033 should not be ruled out, and in fact seems to be where we’re heading if present trends continue.

I mentioned that I was working on tooling up a more sophisticated model to do some exploration of my own. The goal was to track the nuances of actual age distributions across the world, together with alternative ideations of fertility evolution (greater weight on what is actually happening lately), and allowance for non-monotonic evolution of medical care and life expectancy going forward. It was a daunting task, but I was consumed with curiosity and powered through the exercise over a few intense days.

In this post, I will give an overview of what goes into my demographic projection model, why I believe it works well enough to be useful, and what top-level questions we can explore using it.

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