Synopsis: The growth brakes are applied, but an instant stop is problematic.
It turns out that some things are really difficult to stop immediately. No matter how hard you press the brake pedal on a car, there is still a stopping distance. The only way to stop immediately is to hit a wall, and then everyone in the car dies.
There are some parallels with population growth. You can apply the brakes by ensuring families have an average of 2 or less children, but stopping that way still takes 3 generations, as explained here:
- Two children per family will stop growth, but it still takes 3 generations to stop population growth.
Without understanding this principle, it would seem that population growth would only still be happening if people were still having too many children. But an understanding of this population ‘pipeline’ that explains the delay between applying the brakes and growth coming to a coming, reconciles the world having reached was at ‘peak child‘ with the current generation of children no larger than their parent’s generation, with the facts that populating is still growth, but growth is projected to soon end.
So, this answers why population growth continues even when births per woman, is now at a sustainable level. It more answers: “what is not enough to stop population growth immediately, even though you might think it would be enough?” The original question remains:
In summary, that answer turns out you could, but it is the equivalent of using a brick wall to stop the car immediately, in that people get hurt, and it makes no sense. Stopping immediately requires only allowing one birth for every death, and it turns out that means each year the same number of babies born as there were around 75 years earlier, and it turns out that is an equivalent to crashing into a wall once every 75 years, and a cycle like ‘Groundhog Day’ with 75 years in place of one day!
So, just maintaining “peak child” takes 3 generations to stop, and an instant stop is too draconian. But there is another strategy:
Yes, this was followed in China, and any “one child policy” only remains at the “one” level for a limited time.
However, Japan managed to end population growth even earlier:
Clearly, Japan shows that holding ‘births per woman’ significantly below 2.0 is a viable alternative to the “one child” stragey, although it can be worryingly difficult to control.
The next question is:
With the last question being:
Overall, it does appear inevitable that population will not only end growth but even have a period of contraction. That is, if anything is dependable in a world facing climate change and threats of global conflict.
Two children per family will stop growth, but it takes 3 generations to stop.
At first glance, it would seem logical that families had one child for each parent, then population numbers would be stable.
Unfortunately, it is not that simple, and while this works eventually, it takes 3 generations to end previous population growth, as there is a population ‘pipeline’.
This can be illustrated by considering a simplified model society. In this simplified model, people all live to around the global average life expectancy of around 75 years, and people have their children when aged 25. So, with these simplified rules, people become parents at 25, grandparents at 50, and become great-grandparents at 75, when they at that age of 75 then conveniently die to make way for the new generation of children.
The grandparents at the start of the generation would be great-grandparents by the end of the generation, etc.
To illustrate the principle, consider what happens with one family tree.
For this example, we can assume all adults about to become parents will from now have 2 children, but the previous two generations, each had 4 children per couple which meant previously the population was doubling each generation, as was happening in the real world in around 1970.
| Generation – Step | grandparents to great-grandparents | parents to grandparents | kids who grow up to be new parents | planned children of new parents | population (before children) * |
|---|---|---|---|---|---|
| 1 | 2 | 4 | 8 | 8 | 14 |
| 2 | 4 | 8 | 8 | 8 | 20 |
| 3 | 8 | 8 | 8 | 8 | 24 |
This illustrates the population pipeline, and with the ‘two children per family’ rule applied when the population of the family tree is 14, the population still grows to 20 in 25 years when the children become parents of the next generation.
Then it grows again to 24 in another 25 years when the next generation has children. The number of children has remained constant all three generations, but the number of elderly people dying to make way for those children gradually increased, until even the elderly age group is ‘full sized’ cohort. This was also demonstrated by the late great Hans Rosling, as shown in the video here.
Peak child is the beginning of the end for population growth, but the actual end only comes with ‘peak elderly’.
What would be required to stop population growth immediately?
Simple maths reveals that stable population will result with births equal deaths. Looking at the previous two children per family analysis, it becomes clear that stable population requires the “planned births” value match the “grandparent who will become great-grandparents and then die” column. Do so then produces this table:
| Generation | grandparents to great-grandparents | parents to grandparents | kids who grow to be new parents | planned children of new parents | population (before children) * |
|---|---|---|---|---|---|
| 1 | 2 | 4 | 8 | 2 | 14 |
| 2 | 4 | 8 | 2 | 4 | 14 |
| 3 | 8 | 2 | 4 | 8 | 14 |
| 4 | 2 | 4 | 8 | 2 | 14 |
Population is stable, but the rules are strange to say the least. Once every 75 years, there is a generation who must go back in time, and have only “one child per two families”, with half of all families not being permitted any children. Then, there are two generations who could go back to having enough children to again grow the population.
In the simple model for one family, the boundary between generations is clear, but in the real world with children born every year, there is no clear boundary between generations. In practice it would require looking at the records for the number of people born around 75 years earlier and declaring that number as the limit to how many babies are permitted to be born over the next year. Every 75 years or so there would be generation able to very few children to correct for the growth years.
Further, while there would be stable total population, no age group would have stable population. Things like schools would be continually adjusting up and down in the number of students who would attend. Clearly, changing from a growing population to an absolutely fixed population size is unworkable.
The first model, “peak child” allowed 3 generations of population growth but was entirely feasible. This model has zero generations of population growth but is completely unworkable. There is a possible compromise, which has even been applied in the real world.
The compromise “stop fast” solution: A limited time “One Child Policy”.
So, if just relying on “peak child” is too slow, and “immediate stop” too draconian and unworkable, is there a mix of the two that is less draconian but applies the brakes faster?
One alternative is to apply a “one child policy” for a limited time, and then have an ongoing “two child policy”. Applying the “one child policy” for only one generation, produces this result in the simplistic model:
| Generation | grandparents to great-grandparents | parents to grandparents | kids who grow to be new parents | planned children of new parents | population (before children) * |
|---|---|---|---|---|---|
| 1 | 2 | 4 | 8 | 4 | 14 |
| 2 | 4 | 8 | 4 | 4 | 20 |
| 3 | 8 | 4 | 4 | 4 | 20 |
| 4 | 4 | 4 | 4 | 4 | 16 |
The first generation has only 1 child per couple, resulting in one generation half the population size of their parents’ generation, and from that point on the “peak child” pattern where the generation of children matches the size of the generation of parents can be followed. The result is a “population bubble” of in the example 8 people in one generation, which ripples through the age-groups, producing at one point an “aging population” maximum.
In the real world, China implemented something like this for its population. The “one-child policy” was considered draconian, and required exemptions due to gender balance issues, and never quite applied to everyone, which resulting in needing more like 2 generations before moving to the two-child, “peak child” plan, only for China to then find the “two-child” may not even be what people seek anymore.
However, by any measure, the policy did reduce the population of China relative to what it would have been without restrictions, and in turn, this has slightly reduced the world population today.
A better strategy: How did Japan end growth even before China?
Japan has already ended national population growth and has not needed to enforce the reduction of births to 1 per family and has a more reasonable 1.4 average births per women.
How?
The secret is Japan achieved this by starting to reduce family sizes even earlier than China. While the two children per family model can take 3 generations, 1.4 children per family does reach the target of stopping growth much sooner and has the benefit that remaining at that level can provide a period of population correction. Note Japan has already had around 40 years of a decreasing number of children born every year.
The graphs on this page tell the story of ending population growth:
- 1960s world graph from the time of fast growth.
- 2020 world graph from the start of ‘peak child’.
- 2020 Japan graph with population correction starting, after 40 years of reduced birth rates.
The big difference between Japna and China, is that while China implemented a “one child” policy the people did not necessarily agree with, the birth-rates in Japan feel without any direct government planning. In fact, this has been happening globally, without even any official explanation that fits with what is happening.
So, when will populating growth end then?
The accepted number crunching.
The graph here show actually births vs deaths up to 2020, and estimates into the future. Of course, the future is not locked in, and the entire premise is what is needed to create a specific, and different, future.
From the data, in 2020, globally there were 140 million births and 59 million deaths, which is a population increase of 81 million! Even halving the number of children born would not stop population growth immediately, even though ‘births per woman‘ is less than 2.4.
How does this make sense?
The births were children born to parents centred around the 25–29-year age group, and the deaths were to people centred around the 75–79-year age block. Yes, there are parents and deaths from outside these age blocks, but as the median age group, these blocks give the best indication of the relative sizes of the group typical of children, vs the group with an age most typical of those dying.
The world population pyramid for 2020 reveals 598 million people in the 5 year age group aged 25-29, which on average rounds to 120 million parents for those 140 million children. More than 2 children per couple, and equating to 2.33 children per woman, which is overall the number for a stable population in the long term.
The problem is, right now, there are not enough people in dying, the peak age group were born 75 to 79 years ago, when the world population was less than 1/3rd of what it is now.
The number of 75–79-year-olds on the current population pyramid is even smaller than the base to calculate from, as this is the typical age, and some have already died. Go back 60 years, and these people would have been 15-19, and it is that population that should be used.
From back in 1960, there were 258 million in the correct age group, which suggests approximately 52 million per year, would be expected to be dying per year now. Reasonably close for an approximation, given the years of death have an even bigger spread than peak years for being parents.
It becomes clear that even a global 1 child policy is not enough to stop population growth immediately, but it would be most likely close enough, and within a few years as the elderly grow in number, we would very soon move from halting growth, to rapid population correction.
But there is a more realistic picture.
Many, including those predicting the future at Deustche Bank, predict the population will stop sooner, and call into question UN projections.
The example provided by Japan shows that birthrates can and do fall even lower than UN estimates, and that the results can be a quicker end to population growth than may expect.
Globally, births per woman is currently still at around 2.3, having fallen from around 6.0 prior to 1900, when infant mortality was still high. We have had a population explosion triggered by a fall in infant mortality, but the explosion is now ending.
If the word follows the path of Japan, it could still take another 35 years before the population is decreasing, and if we follow some UN projections where having fallen to 2.3, births per woman stops falling, it population growth could persist until the end of the century, provided the resulting numbers themselves don’t cause a disaster.
Realistically, even if you do not accept that as we are unable to exist sustainably so far, proves we are currently overpopulated , without a massive intervention, the very fact that population of elderly people is so much smaller because they were born when population was smaller, means population keeps growing for at least another 10 years.
All projections are theoretical for an ideal world.
Then there are predictions “the sky will fall” in the form of catastrophic impact from global warming, another pandemic, or global conflict.
Personally, despite that I do believe we are already overpopulated, I also believe any disruption so severe as to halt growth immediately, is likely to reduce the planet’s carrying capacity of humans. Thus any catastrophe would make overpopulation an even worse problem, even if it does reduce the number of people.
Ending growth smoothly in 10 or even 20 years I think is the best we could hope to achieve.
What about all those predictions of perpetual population growth?
There are loud voices calling for perpetual population growth as the only economic solution. Cries that ‘ageing population‘ will be too expensive, and other stories that make no sense when examined properly.
But consider the comments of Jeff Bezos on returning from his trip to space. His wealth results from all the people in the world who buy from Amazon. If there were less people in the world, he would have less wealth.
Jeff Bezos gave a heartfelt thanks to Amazon employees and customers following his record-setting trip to space Tuesday — noting that they “paid for all of this.”
“I … want to thank every Amazon employee, and every Amazon customer because you guys paid for all this,” the 57-year-old Amazon founder told reporters after returning from his trip to the edge of space.
“So seriously, for every Amazon customer out there, and every Amazon employee, thank you from the bottom of my heart, very much. It’s very appreciated.”
Jeff Bezos thanks Amazon workers, customers for bankrolling trip to space
But it not just those few billionaires for whom it is “more people equals more wealth”. The same applies to companies such as Apple, Facebook, Google and Amazon. Not that any of these companies is in a position to influence how people think… oh wait, they are valued at trillions of dollars on the basis of their ability to do just that, and can even get people to believe the Earth is flat. Ok, so admittedly it is that small minority with the greatest ability to influence opinion, just happed to the ones who benefit from population growth. And yes, you would think that in an equitable world, more people would also mean more shares and shareholders for these global companies, so the individual share price and wealth of each shareholder would not change as population increases. But it just may be, we don’t live in that equitable world quite yet.
“Anyone who believes in indefinite growth in anything physical, on a physically finite planet, is either mad or an economist.”
Attributed to Kenneth Boulding in: United States. Congress. House (1973)
Updates:
- 2023 March 22 nd: Synopsis added.
