All the graphs below are from Populationpyramid.net and are available to be shared under a Creative Commons license They have not been modified in any way.
I remember reading Paul Ehrlich’s “The Population Bomb” as a kid. I also remember the Club of Rome’s prediction of the inevitable population apocalypse, “The Limits to Growth.” As a naive young kid, I was quite frightened by all this. Nuclear war started looking like a good alternative.
One can make a good case that the amount of carbon released into the atmosphere is proportional to the population. You also make a good case that the ability to remove carbon from the atmosphere decreases with increased population. More people certainly means declining fishing stocks, less farmland, less open space in general, more vulnerability to natural disasters and epidemics, and more air/water pollution. It is also my opinion that individual freedom inevitably becomes more restricted as population density rises.
Gentle curves and waves are to be expected. Sudden spikes that appear in one cohort and disappear in the next are suspicious. Something big happened. Or maybe the data is bad.
Males and females are generally graphically symmetrical, with a slight advantage to males at birth and a slight advantage to females starting to appear and grow in late middle age.
If you pick a level, as that cohort ages into older age brackets you can start making predictions. Those cohorts can never get bigger – except for immigration. Those children are the foundation for your reproductive and economic future. If you have fewer people in the 0-4 group than in the 20-24 group, you’ll have fewer females to have babies 20 years from now. There is nothing that can change that. Your population will continue to shrink. You’ll have fewer people entering the workforce, fewer available for military service, and so on. At the same time those folks in the 48-52 group? They will be leaving the workforce and beginning to see medical issues pile up.
What happens when many people retire in countries with long life expectancies, and fewer younglings come online to replace/support them?
Population in most countries is shrinking.
Fewer people make for less carbon, meaning less climate change. Going ahead, this would mean more resources per person and more preexisting infrastructure per person. Housing becomes cheap, traffic flows better, and backyards become more common. If businesses REALLY need more workers they can start investing in recruiting and training impoverished young people instead of demanding that the government fix things for them. A lower population could be a good thing overall. What matters is how you get there.
Higher population density itself militates for smaller families because suburbia becomes an expensive dream and apartments keep shrinking in size. Living cheek to jowl in high-rise rabbit warrens is not good for a species that evolved to live in the wilderness.
The transition to a lower population can be managed. Workers can stay in the workforce longer if working conditions are improved. Individual workers can become more productive if they control the tools instead of being the tools themselves. The higher the level of technology the average person can leverage, the more possible this becomes. AI and automation can replace workers in most low-end jobs.
Japan, S. Korea, Taiwan, and Germany are in the process of working things out. Their very low fertility rates make the change rapid, a crisis even. The problem is that there simply aren’t enough worker bees to support the older generations. But we should not conflate “difficult” with “can’t be done.”
The US population decline will be more gradual, and it will benefit from other countries’ experiences.
When looking at population change, the important number is the fertility rate. That’s the average number of live births per female. Another number to look at is childhood mortality. That gets subtracted from the fertility rate. In a modern western society that means replacement is 2.1 children per female. In completely undeveloped societies, it is childhood mortality that keeps the population in check. Because of this, the world’s population increased extremely slowly up until the 19th century and exploded in the 20th thanks to modern medicine.
In an agrarian society, one has lots of children to work the fields and support parents in their old age. There is normally a lot of infant mortality, but as antibiotics and vaccines and nutrition improve, the children mostly survive. Niger has a fertility rate of 6.82. If most of those survive, it would eventually have a population of several hundred million. Nigeria has a birth rate of 4.62. With a current population of 200 million, it would be the most populous nation on earth sometime in this century. Something will give, and it won’t be pretty.
In an industrial society, children are an economic burden. Government programs, personal savings, and pensions are what support you in old age. Women have other things they need to do other than raisng babies. The problem with an excessively low birth rate is that those benefits are paid for by younger people still in their productive years. Too few worker bees and the standards of living of everyone start to decline. Someone needs to support the elderly no matter what the level of technology is. Or you could just let them sink into poverty and die.
Another economic impact of an aging population is that retired and soon-to-be-retired people tend to sit on their savings. Very few are affluent enough to go on world tours or buy expensive items. Most put their savings in the most secure investments possible (which happen to give the lowest returns) and hope the markets don’t crash. We sell our houses and move to cheap accommodations – sometimes involuntarily. We don’t vacation a lot or throw parties. At any minute an unexpected medical expense not covered by Medicare could zero out a lifetime of savings. It is an insecure time.
OTOH the 25-55 age range is where the most money is spent. In an industrial society, 20 to 35 are where most of the babies are produced. These people are consumers, not savers. Peak net worth is 55-68 This is where – hopefully – the bills are mostly paid, and we start socking away every free penny for retirement.
An aging population reduces the amount being spent overall and this screws with economies built on consumer demand. All of our economic theories – communism, socialism, capitalism, mercantilism, and others – assume an expanding population. These are uncharted waters. Nobody knows what to do when 60-year-olds outnumber 20-year-olds.
Industrialization is not the only reason for declining birth rates. It was made possible by the invention of the birth control pill in 1960, potentially the single most important event of the 20th century. A decline in traditional religiosity contributes. Also, feminism redefined women’s roles in society so that many women no longer see childbearing as their destiny. Big cultural changes – even good ones – always have unanticipated and often painful knock-on effects.
Most of Europe has a fertility rate of 1.5-1.7. France has the highest of 2.07. Spain and Italy have around 1.25.
Taiwan has the world’s worst fertility rate at 1.08, very slightly lower than South Korea. If China doesn’t collapse first from internal issues, they’ll win Taiwan by simply waiting for it to depopulate.
Russia and China, are also facing a spectacular drop in fertility. Both countries have a problem of not being well developed. And nobody wants to emigrate there.
On the left, we have the population pyramid produced by the official census in China. It is a lie. On the right is Hong Kong. Very strange.
China (Official fertility rate of 1.45. Unofficially as low as 1.15) has about 2-300 million people living at western economic standards, almost all near the industrial east, and another billion-plus living in 2nd and 3rd world conditions. Further, they’ve been living under a one-child policy until only recently. There is an imbalance in favor of males due to the selective abortion of females. Due to political issues, their official data is suspect. There are probably a hundred million fewer children than the census would predict, with most of the missing being female. “Officially” they are on course for a halving of the population by 2100. Unofficially by 2070 or even 2050, depending on who you listen to.
Look at the population pyramid on the right for Hong Kong. That male-to-female imbalance is not possible. No war suddenly killed off millions of young men 25-50 years ago. The trend stopped abruptly 20 years ago with it returning to symmetry. Hong Kong’s fertility rate was 0.7 and may rapidly depopulate. The number of children under 20 only makes sense if there were far fewer women in the 25 to 50 range. That data is FUBAR.
Russia (fertility rate 1.6) is a nation in population decline. It also just took a major hit in their fertility because over a million people – mostly young and well-educated – fled due to the Ukraine War. (Also 15,000 millionaires!) Their official numbers are also suspect. They just “found” a million children they hadn’t noticed in the official census. Much of the reason Putin launched his war now is that in another decade he won’t have the spare military-aged men to do it. Putin is also propping up his population by relocating Ukrainians to Russia and having orphaned Ukrainian children adopted into Russian families.
Ukraine (fertility rate of 1.56) is also screwed because many of their fertile women have left the country to escape the war. There will be very few babies made until it is over. OTOH, there is usually a big jump in fertility right after a war. The US owes much of its relative stability to the post-WWII baby boom.
Even India is currently at 2.1. Since India has a higher childhood mortality rate than the West, its population will still decline, just very, very slowly. It appears from the numbers that almost all of the world’s population growth will take place in subSaharan Africa. (See the above population pyramid for Niger.)
It is also true that whichever element of the population has the highest birth rate will soon come to dominate the demographics. (I think some people are afraid of these racial/ethnic/religious/etc. shifts in culture.) That will slow the decline. The political system will become more conservative. There is less youthful idealism if there is less youth. (Personally, I think that’s a bad thing.)
At least in the US, (fertility rate 1.81) immigration is expected to keep the population almost constant. Canada (fertility rate 1.57) and the UK (fertility rate 1.63) need a lot of immigration if their populations are to stay steady. Even Mexico is shrinking at a 1.68 fertility rate. Africa is where those immigrants have to come from. Everywhere else is shrinking.
Whatever the results are, I think the decline is inevitable. Our fate was sealed in 1960 by Searle Pharmaceuticals. (They had no idea how many different social and economic tidal waves they’d send thru the world!) The number of new babies is limited by the number of reproductive females and the proportion of these interested in having kids.
Even if we started encouraging more babies right now (in a way that worked) we wouldn’t see those new worker bees come online for another 20 years. If you could coax fertility up to 2.1, even then no cohort in the future will be any bigger than that of today’s young people. The population of the developed world cannot do anything but drop, Africa’s will boom, and the average age cannot do anything but get older.
It will be a rough ride until everything stabilizes.