9 ms·

Peak Population Projections

34 points by sjmulder 2y ago

cl42 2y ago
I was just emailing a few folks in the insurance industry about demographic decline. I can't find any good economic analyses on what will likely happen to our economies when populations start to decline. This will happen given the projections and the fact that we can't force people to have babies 2, 3, 4, 5 years ago. Has anyone come across anything good that isn't a 'popular press' book? I'm looking for deep analysis.
- bryanlarsen 2y ago
  Japan's population has been declining for ~15 years. It's hard to disentangle from the aftermath of their bubble collapse in 1991, but it does appear that while demographic collapse isn't great for an economy, it's also not the doomsday that many predict.
  - lotsofpulp 2y ago
    It’s not the first derivative that is usually a problem, it’s the second derivative. The rate of decline is important to monitor for the purposes of managing expectations of supply and demand in the markets.
  - edmundsauto 2y ago
    It’s also a decent indicator whether the economy is working well for the people. I think too often the tail wags the dog.
  - cl42 2y ago
    Do you think it's different when global growth declines, or when there's a large group of countries going throughs population stagnation or decline? One can say that Japan's economy was still buoyed by global population growth, export growth, etc.
  - tuatoru 2y ago
    In demographics the units of time are generations. It takes several of them for the effects of shock to be fully felt because generations overlap, about a century. Japan's TFR fell below replacement around 1973, iirc. So we should wait at least till 2070 before making assertions about the severity or otherwise of the issue. In the mean time, it sure looks serious. Japan has been propping up its economy with debt. It has the highest public debt to GDP ratio in the world. Is that sustainable if interest rates climb? I don't know.
- deleted 2y ago
  [deleted]
- JamesLeonis 2y ago
  This might be difficult to come by. It was only recently the zeitgeist shifted from Overpopulation to Underpopulation. As another commenter mentioned, Japan is an example of a possible future for many advanced economies. https://www.cambridge.org/core/journals/japanese-journal-of-political-science/article/japan-the-harbinger-state/2A9123B64A04C480B1BC5669FC2C8AF3 https://www.cambridge.org/core/journals/japanese-journal-of-... previous discussion: https://news.ycombinator.com/item?id=34486824 https://news.ycombinator.com/item?id=34486824
  - toomuchtodo 2y ago
    Which is strange, because population momentum is still pushing us towards a much higher global total population number by end of century. What are potential reasons for the change in narrative from the media, as well as economic and political interests?
    - Balero 2y ago
      The global population may be growing, but for developed countries where we get most of our news (I assume, at least I do), they're just starting to tip over into the shrinkage and dealing with the bulge of elderly people. The narrative is right for the political and economic interests that we hear from. I imagine if we were consuming news from India, Egypt or Nigeria it would be a very different story.
    - somenameforme 2y ago
      The good faith answer is that they believed their own projections. This article mentions that the UN projections just somehow assumed everybody's fertility rates would decline and then kick into a mediocre but closer to sustainable level for a slow bleed. This topic has been a pet obsession of mine for years now because these data made no sense. Why would everybody's fertility rates suddenly trend to 1.69, as per the article's numbers? The more logical path has always seemed an ongoing extrapolation of current trends, and that leads to quite terrifying outcomes on very short timeframes. And as more people seem to realize that's where we're indeed headed, it's long since past time for a sharp 180 on this topic. On top of incorrect projections, I also think most don't understand the math of how fertility rates affect populations. It's an exponential system, so extreme outcomes are entirely possible with rates that seem 'bad' but not that bad, like e.g. a fertility rate of 1. Such a fertility rate, if shared among an entire population, would result in an exponential 50% decline in your population per 20 years. And alongside that you get social chaos, screwed up age ratios, economic chaos, and more. All on an extremely rapid timeframe. I think this is a self correcting problem, but it's likely far wiser to fix it before it starts fixing itself.
- tuatoru 2y ago
  The primary reason that deep analysis is close to non-existent is that fertility is coded as a right-wing issue, and discussing the decline is unacceptable in today's academic social sciences. "You want to force women to be baby-making machines", and more vitriolic rhetoric, and loss of tenure, is what happens when someone raises the issue. I think of this as one of Iain Banks's "Outside Context Problems", something that our society cannot (allow itself to) understand or even see, so it cannot begin to solve it.
  - jiggawatts 2y ago
    I’m very left-leaning and so is almost everyone I know, but we’re aware of the problem and concerned about the implications. The right wing so far hasn’t provided any solutions. I have one child. I would prefer to have two, but I can’t afford it. For reference: my income is in the top 2% for my country and the top 5% in the affluent part of the largest city. I literally cannot afford to buy a house big enough for a growing family unless my partner also works full time. That’s nuts.
    - nojvek 2y ago
      Seems about right for most OECD countries. To have kids you need a large enough house and ample financial security / schools / daycare etc. Doesn’t make sense to have kids when both parents have to work full time to barely make it.
    - tuatoru 2y ago
      No one has any solutions. The solution is to make parenthood high prestige, higher than doctor or lawyer or CEO or rapper or billionaire. Then everyone will want to do it. A pity that despite a hundred years of marketing we are clueless about how to do that. There are 'hygiene' actions like getting rid of credentialism, so lowering the perceived-to-be-required investment in each child, and decreasing density (which inversely correlates with number of children independently of other factors, and giving people an optimistic life plan and expectation, and changing marriage/partnering back from being a capstone (something you do once you are established) to being a cornerstone (something you do at the start of adulthood, to build your lives on). But ultimately it's about the social prestige. Try saying "she's a soccer mom" in tones of awe and respect, out in public, and watch the funny looks you get.
- Supermancho 2y ago
  (Almost) no country is going to leave a terminal decline unchallenged. In North Dakota, new single moms can qualify for a large number of assistance (https://singlemothersgrants.org/single-mothers-assistance-in-north-dakota/ https://singlemothersgrants.org/single-mothers-assistance-in...). Imagine this for any new mom, per child. Once the economics of incentivized population growth kicks in, I think there will be rapid change. Can it be sustained? Probably not, but that's an easier problem...ie Repeat programs every X years.
  - lotsofpulp 2y ago
    No country has successfully increased fertility rates, so there are no known figures on the economics of incentives sufficient to increase fertility rates.
    - Supermancho 2y ago
      > No country has successfully increased fertility rates, What's your point? Ostensibly, modern countries have not yet suffered the predicted population crash that might incentivize more aggressive baby bonuses (https://en.wikipedia.org/wiki/Baby_bonus https://en.wikipedia.org/wiki/Baby_bonus). This has been a thing for awhile (https://www.npr.org/sections/money/2011/11/03/141943008/when-governments-pay-people-to-have-babies https://www.npr.org/sections/money/2011/11/03/141943008/when...). It's a likely strategy to be extensively employed in the future, if the trends are realized. It's reasonable to expect there is an economic inflection point, where the program(s) would be successful.
      - lotsofpulp 2y ago
        Paying women to have babies does not incentivize what a society wants, which is kids who are properly raised and contribute to society. That requires many years of effort, something I don’t think that can be incentivized by a cash gift or tax credit. The only economic incentivize I can think of that might work is to remove all old age benefits and require people to depend on descendants, but that is not going to be politically palatable until there is no choice because the system fell apart.
PKop 2y ago
We live in a finite world, with finite resources, and particularly finite space. Take a look at the massive population increase especially in some countries in 50 to 100 years, even ones without huge amounts of land..population density has skyrocketed vs historical norms. It is no wonder that eventually this puts pressure on birth rates, and some of the lowest birth rates are found in places with some of the highest population densities. Cost of living and real estate has risen, and it will be a good thing for this to reverse or slow. And some foolish leaders want to short circuit this natural correction by importing new people to compete with local citizens for real estate and resources. Not smart. It will only depress domestic birth rates further.
- oceanplexian 2y ago
  The world is finite but the amount of resources are astronomical. In the United States 75% of the population lives on 2.7% of the total land area. And in the last century we figured out how to harness unlimited energy, produce as much clean drinking water as we could ever need, practically unlimited food production, raised the quality of life for the average human a thousand times over, not even getting into the fact that we are on the cusp of cheap, reusable access to space. I would consider the human population unbounded.
  - kibwen 2y ago
    > practically unlimited food production Our aquifers are being permanently drained, our most productive regions are rapidly desertifying, our growing seasons are becoming increasingly unstable as the climate shifts, our crops are genetically homogenous and therefore catastrophically susceptible to disease, our rampant use of pesticides is unraveling the food chain, we're 100% reliant on the use of artificial fertilizers which is dependent on functioning global supply chains and fossil fuels, and even if you can grow the food there's no guarantee that you have the logistics network necessary to distribute it before it rots. Which is all to say, food is far from a solved problem. And there's nothing in space that's going to address that particular need.
- MostlyStable 2y ago
  We live in a finite world, but almost all of humanities improvements have come not from using more stuff, but from using the same stuff more efficiently. To be clear, I'm not saying that we aren't using more stuff, we very obviously are, but merely that the majority of improvement in quality of life has come from increases in efficiency. There is no indication that we are anywhere near the end of those efficiency gains. To your point of housing: that is the most clear example of a thing that is artificially constrained by policy. The reason there are housing shortages has absolutely nothing to do with resource constraints and everything to do with terrible policy decisions.
bkandel 2y ago
It's a bit strange that the author doesn't mention the population projections published in The Lancet a few years ago (https://www.thelancet.com/infographics-do/population-forecast https://www.thelancet.com/infographics-do/population-forecas...). They note a lot of the problems with the UN projections, which include the modeling but also include other factors, like the effect of female education. In the few years since their study came out, their numbers appear to be more accurate than the UN approach of assuming fertility ends up at 1.69 everywhere.
- hscontinuity 2y ago
  1.69 That tracks.
xnx 2y ago
It seems none of these projections are expecting people to start living to 120 or longer, which seems like something that could happen in the next 50 years.
- dijit 2y ago
  last thing i heard was that life expectancy was actually dropping in the developed world. Due in part to underinvestment in health services and exacerbated by COVID.. However that could have been UK specific data. *EDIT*: It was global, data comes from the Lancet, which is considered a strong source by many: https://www.thinkglobalhealth.org/article/global-life-expectancy-declines-first-time-30-years https://www.thinkglobalhealth.org/article/global-life-expect...
- datadrivenangel 2y ago
  Average life expectancy is what matters. We'll probably have more outliers of wealthy/healthy people living longer, but poor management of broader access to basic health and education may not result in that drastic an increase in overall average results.
- somenameforme 2y ago
  This, extremely counter-intuitively, doesn't actually change anything at all in terms of population change. All it does is cause some brief noise as you hit the 'equilibrium point.' It's easiest to explain this with an example. Let's take it to a ridiculous extreme and say people live to 200 years old, yet otherwise maintain the same general fertility trends of having about 20 years of peak fertility. And to keep things simple, we'll assume a fertility rate of 1, which means the total population would halve every generation. We'll also assume everybody has all their children at age 20, and then dies at age 200. So start at the bottom. And say we have exactly 2 twenty year olds. Since there are 2 twenty year olds there must be 4 forty year olds, 8 sixty year olds, and so on. This generalizes to there being a total of (2^n) people of age (20*n). So there are 512 people of age 180. The entire population is 512 + 256 + 128 + ... 1 = 1023. So what happens when this 180 year old generation dies? Your population declines by half. What happens twenty years later when the 256 population group dies? Your population decreases by half. So each generation, you start seeing an exponential halving of your population. So how long people live doesn't actually matter. All it does is add some noise/delay as you shift from an equilibrium between fertility rates. And once that equilibrium is reached, your population will shift by a factor of fertility_rate/2 every breeding generation (~20) years. This holds true whether people live for 40 years, or 40,000. So with a fertility rate of e.g. 1 your population will exponentially decline by 50% every 20 years, until you go extinct or start having babies.
fred_is_fred 2y ago
The UN has done nothing but downward revisions in the last 10+ years. They consistently overestimate birth rates and underestimate how quickly they are falling especially in the developing countries. This itself is a trend that says the UN is overly optimistic here in terms of population growth and max/max year. The 2019 to 2022 revision went from population max of 10.88B in 2100 to 10.4B in 2086. I didn't find the 2024 data yet but would expect another "our numbers were too high" again.
- lainga 2y ago
  > This itself is a trend that says the UN is overly optimistic here Who benefits?
  - fred_is_fred 2y ago
    I've been wondering but didn't come up with anything. I don't think the world economy as a whole is ready for a decline. For countries like the US or for example Australia, I think population will not decline due to net immigration, even as the world as whole declines. For the rest though, it cannot be good for an economy.
- tuatoru 2y ago
  The very latest 2024 update (not yet on their website) is apparently a small increase, because they expect a slower rate of fertility decline in sub-Saharan Africa. (I think I read about this on the IIASA website.) Time will tell.
AtlasBarfed 2y ago
Population does not matter .what matters is population and the average resources footprint. China and India having 2.5 billion if they are subsistence farming is a much faster different thing that China and India with some approximation of western lifestyles. Demographic decline does seem endemic to urbanization, but urbanization is hand in hand with western consumption rates. Net economic activity will probably increase in net, but with, uh, bumps.
- tuatoru 2y ago
  There are several factors that operate successively and in combination to reduce fertility: infant survival (low infant mortality); secularisation (loss of religion); urbanisation (or more accurately neolocality, the practice of moving away from family at the time of marriage); education, particularly of women; and stronger government (stability and military defence, universal application of the law, protection of property rights (perhaps counterintuitively)).
  - AtlasBarfed 2y ago
    IMO urbanization broadly includes secularization (consumer culture), education (needed for urban jobs), education/empowerment of women working (two jobs to survive rather than one, women work to survive in cities rather than stay in extended family homes) But of course you are correct. Urbanization is responsible for the largest population migrations and geographic redistributions of the last century. I consider it the major factor in the demographic birth rate declines.

34 points by sjmulder 2y ago

cl42 2y ago

I was just emailing a few folks in the insurance industry about demographic decline. I can't find any good economic analyses on what will likely happen to our economies when populations start to decline. This will happen given the projections and the fact that we can't force people to have babies 2, 3, 4, 5 years ago. Has anyone come across anything good that isn't a 'popular press' book? I'm looking for deep analysis.

bryanlarsen 2y ago
Japan's population has been declining for ~15 years. It's hard to disentangle from the aftermath of their bubble collapse in 1991, but it does appear that while demographic collapse isn't great for an economy, it's also not the doomsday that many predict.
- lotsofpulp 2y ago
  It’s not the first derivative that is usually a problem, it’s the second derivative. The rate of decline is important to monitor for the purposes of managing expectations of supply and demand in the markets.
- edmundsauto 2y ago
  It’s also a decent indicator whether the economy is working well for the people. I think too often the tail wags the dog.
- cl42 2y ago
  Do you think it's different when global growth declines, or when there's a large group of countries going throughs population stagnation or decline? One can say that Japan's economy was still buoyed by global population growth, export growth, etc.
- tuatoru 2y ago
  In demographics the units of time are generations. It takes several of them for the effects of shock to be fully felt because generations overlap, about a century. Japan's TFR fell below replacement around 1973, iirc. So we should wait at least till 2070 before making assertions about the severity or otherwise of the issue. In the mean time, it sure looks serious. Japan has been propping up its economy with debt. It has the highest public debt to GDP ratio in the world. Is that sustainable if interest rates climb? I don't know.
deleted 2y ago
[deleted]
JamesLeonis 2y ago
This might be difficult to come by. It was only recently the zeitgeist shifted from Overpopulation to Underpopulation. As another commenter mentioned, Japan is an example of a possible future for many advanced economies. https://www.cambridge.org/core/journals/japanese-journal-of-political-science/article/japan-the-harbinger-state/2A9123B64A04C480B1BC5669FC2C8AF3 https://www.cambridge.org/core/journals/japanese-journal-of-... previous discussion: https://news.ycombinator.com/item?id=34486824 https://news.ycombinator.com/item?id=34486824
- toomuchtodo 2y ago
  Which is strange, because population momentum is still pushing us towards a much higher global total population number by end of century. What are potential reasons for the change in narrative from the media, as well as economic and political interests?
  - Balero 2y ago
    The global population may be growing, but for developed countries where we get most of our news (I assume, at least I do), they're just starting to tip over into the shrinkage and dealing with the bulge of elderly people. The narrative is right for the political and economic interests that we hear from. I imagine if we were consuming news from India, Egypt or Nigeria it would be a very different story.
  - somenameforme 2y ago
    The good faith answer is that they believed their own projections. This article mentions that the UN projections just somehow assumed everybody's fertility rates would decline and then kick into a mediocre but closer to sustainable level for a slow bleed. This topic has been a pet obsession of mine for years now because these data made no sense. Why would everybody's fertility rates suddenly trend to 1.69, as per the article's numbers? The more logical path has always seemed an ongoing extrapolation of current trends, and that leads to quite terrifying outcomes on very short timeframes. And as more people seem to realize that's where we're indeed headed, it's long since past time for a sharp 180 on this topic. On top of incorrect projections, I also think most don't understand the math of how fertility rates affect populations. It's an exponential system, so extreme outcomes are entirely possible with rates that seem 'bad' but not that bad, like e.g. a fertility rate of 1. Such a fertility rate, if shared among an entire population, would result in an exponential 50% decline in your population per 20 years. And alongside that you get social chaos, screwed up age ratios, economic chaos, and more. All on an extremely rapid timeframe. I think this is a self correcting problem, but it's likely far wiser to fix it before it starts fixing itself.
tuatoru 2y ago
The primary reason that deep analysis is close to non-existent is that fertility is coded as a right-wing issue, and discussing the decline is unacceptable in today's academic social sciences. "You want to force women to be baby-making machines", and more vitriolic rhetoric, and loss of tenure, is what happens when someone raises the issue. I think of this as one of Iain Banks's "Outside Context Problems", something that our society cannot (allow itself to) understand or even see, so it cannot begin to solve it.
- jiggawatts 2y ago
  I’m very left-leaning and so is almost everyone I know, but we’re aware of the problem and concerned about the implications. The right wing so far hasn’t provided any solutions. I have one child. I would prefer to have two, but I can’t afford it. For reference: my income is in the top 2% for my country and the top 5% in the affluent part of the largest city. I literally cannot afford to buy a house big enough for a growing family unless my partner also works full time. That’s nuts.
  - nojvek 2y ago
    Seems about right for most OECD countries. To have kids you need a large enough house and ample financial security / schools / daycare etc. Doesn’t make sense to have kids when both parents have to work full time to barely make it.
  - tuatoru 2y ago
    No one has any solutions. The solution is to make parenthood high prestige, higher than doctor or lawyer or CEO or rapper or billionaire. Then everyone will want to do it. A pity that despite a hundred years of marketing we are clueless about how to do that. There are 'hygiene' actions like getting rid of credentialism, so lowering the perceived-to-be-required investment in each child, and decreasing density (which inversely correlates with number of children independently of other factors, and giving people an optimistic life plan and expectation, and changing marriage/partnering back from being a capstone (something you do once you are established) to being a cornerstone (something you do at the start of adulthood, to build your lives on). But ultimately it's about the social prestige. Try saying "she's a soccer mom" in tones of awe and respect, out in public, and watch the funny looks you get.
Supermancho 2y ago
(Almost) no country is going to leave a terminal decline unchallenged. In North Dakota, new single moms can qualify for a large number of assistance (https://singlemothersgrants.org/single-mothers-assistance-in-north-dakota/ https://singlemothersgrants.org/single-mothers-assistance-in...). Imagine this for any new mom, per child. Once the economics of incentivized population growth kicks in, I think there will be rapid change. Can it be sustained? Probably not, but that's an easier problem...ie Repeat programs every X years.
- lotsofpulp 2y ago
  No country has successfully increased fertility rates, so there are no known figures on the economics of incentives sufficient to increase fertility rates.
  - Supermancho 2y ago
    > No country has successfully increased fertility rates, What's your point? Ostensibly, modern countries have not yet suffered the predicted population crash that might incentivize more aggressive baby bonuses (https://en.wikipedia.org/wiki/Baby_bonus https://en.wikipedia.org/wiki/Baby_bonus). This has been a thing for awhile (https://www.npr.org/sections/money/2011/11/03/141943008/when-governments-pay-people-to-have-babies https://www.npr.org/sections/money/2011/11/03/141943008/when...). It's a likely strategy to be extensively employed in the future, if the trends are realized. It's reasonable to expect there is an economic inflection point, where the program(s) would be successful.
    - lotsofpulp 2y ago
      Paying women to have babies does not incentivize what a society wants, which is kids who are properly raised and contribute to society. That requires many years of effort, something I don’t think that can be incentivized by a cash gift or tax credit. The only economic incentivize I can think of that might work is to remove all old age benefits and require people to depend on descendants, but that is not going to be politically palatable until there is no choice because the system fell apart.

PKop 2y ago

We live in a finite world, with finite resources, and particularly finite space. Take a look at the massive population increase especially in some countries in 50 to 100 years, even ones without huge amounts of land..population density has skyrocketed vs historical norms. It is no wonder that eventually this puts pressure on birth rates, and some of the lowest birth rates are found in places with some of the highest population densities. Cost of living and real estate has risen, and it will be a good thing for this to reverse or slow. And some foolish leaders want to short circuit this natural correction by importing new people to compete with local citizens for real estate and resources. Not smart. It will only depress domestic birth rates further.

oceanplexian 2y ago
The world is finite but the amount of resources are astronomical. In the United States 75% of the population lives on 2.7% of the total land area. And in the last century we figured out how to harness unlimited energy, produce as much clean drinking water as we could ever need, practically unlimited food production, raised the quality of life for the average human a thousand times over, not even getting into the fact that we are on the cusp of cheap, reusable access to space. I would consider the human population unbounded.
- kibwen 2y ago
  > practically unlimited food production Our aquifers are being permanently drained, our most productive regions are rapidly desertifying, our growing seasons are becoming increasingly unstable as the climate shifts, our crops are genetically homogenous and therefore catastrophically susceptible to disease, our rampant use of pesticides is unraveling the food chain, we're 100% reliant on the use of artificial fertilizers which is dependent on functioning global supply chains and fossil fuels, and even if you can grow the food there's no guarantee that you have the logistics network necessary to distribute it before it rots. Which is all to say, food is far from a solved problem. And there's nothing in space that's going to address that particular need.
MostlyStable 2y ago
We live in a finite world, but almost all of humanities improvements have come not from using more stuff, but from using the same stuff more efficiently. To be clear, I'm not saying that we aren't using more stuff, we very obviously are, but merely that the majority of improvement in quality of life has come from increases in efficiency. There is no indication that we are anywhere near the end of those efficiency gains. To your point of housing: that is the most clear example of a thing that is artificially constrained by policy. The reason there are housing shortages has absolutely nothing to do with resource constraints and everything to do with terrible policy decisions.

bkandel 2y ago

It's a bit strange that the author doesn't mention the population projections published in The Lancet a few years ago (https://www.thelancet.com/infographics-do/population-forecast https://www.thelancet.com/infographics-do/population-forecas...). They note a lot of the problems with the UN projections, which include the modeling but also include other factors, like the effect of female education. In the few years since their study came out, their numbers appear to be more accurate than the UN approach of assuming fertility ends up at 1.69 everywhere.

hscontinuity 2y ago
1.69 That tracks.

xnx 2y ago

It seems none of these projections are expecting people to start living to 120 or longer, which seems like something that could happen in the next 50 years.

dijit 2y ago
last thing i heard was that life expectancy was actually dropping in the developed world. Due in part to underinvestment in health services and exacerbated by COVID.. However that could have been UK specific data. *EDIT*: It was global, data comes from the Lancet, which is considered a strong source by many: https://www.thinkglobalhealth.org/article/global-life-expectancy-declines-first-time-30-years https://www.thinkglobalhealth.org/article/global-life-expect...
datadrivenangel 2y ago
Average life expectancy is what matters. We'll probably have more outliers of wealthy/healthy people living longer, but poor management of broader access to basic health and education may not result in that drastic an increase in overall average results.
somenameforme 2y ago
This, extremely counter-intuitively, doesn't actually change anything at all in terms of population change. All it does is cause some brief noise as you hit the 'equilibrium point.' It's easiest to explain this with an example. Let's take it to a ridiculous extreme and say people live to 200 years old, yet otherwise maintain the same general fertility trends of having about 20 years of peak fertility. And to keep things simple, we'll assume a fertility rate of 1, which means the total population would halve every generation. We'll also assume everybody has all their children at age 20, and then dies at age 200. So start at the bottom. And say we have exactly 2 twenty year olds. Since there are 2 twenty year olds there must be 4 forty year olds, 8 sixty year olds, and so on. This generalizes to there being a total of (2^n) people of age (20*n). So there are 512 people of age 180. The entire population is 512 + 256 + 128 + ... 1 = 1023. So what happens when this 180 year old generation dies? Your population declines by half. What happens twenty years later when the 256 population group dies? Your population decreases by half. So each generation, you start seeing an exponential halving of your population. So how long people live doesn't actually matter. All it does is add some noise/delay as you shift from an equilibrium between fertility rates. And once that equilibrium is reached, your population will shift by a factor of fertility_rate/2 every breeding generation (~20) years. This holds true whether people live for 40 years, or 40,000. So with a fertility rate of e.g. 1 your population will exponentially decline by 50% every 20 years, until you go extinct or start having babies.

fred_is_fred 2y ago

The UN has done nothing but downward revisions in the last 10+ years. They consistently overestimate birth rates and underestimate how quickly they are falling especially in the developing countries. This itself is a trend that says the UN is overly optimistic here in terms of population growth and max/max year. The 2019 to 2022 revision went from population max of 10.88B in 2100 to 10.4B in 2086. I didn't find the 2024 data yet but would expect another "our numbers were too high" again.

lainga 2y ago
> This itself is a trend that says the UN is overly optimistic here Who benefits?
- fred_is_fred 2y ago
  I've been wondering but didn't come up with anything. I don't think the world economy as a whole is ready for a decline. For countries like the US or for example Australia, I think population will not decline due to net immigration, even as the world as whole declines. For the rest though, it cannot be good for an economy.
tuatoru 2y ago
The very latest 2024 update (not yet on their website) is apparently a small increase, because they expect a slower rate of fertility decline in sub-Saharan Africa. (I think I read about this on the IIASA website.) Time will tell.

AtlasBarfed 2y ago

Population does not matter .what matters is population and the average resources footprint. China and India having 2.5 billion if they are subsistence farming is a much faster different thing that China and India with some approximation of western lifestyles. Demographic decline does seem endemic to urbanization, but urbanization is hand in hand with western consumption rates. Net economic activity will probably increase in net, but with, uh, bumps.

tuatoru 2y ago
There are several factors that operate successively and in combination to reduce fertility: infant survival (low infant mortality); secularisation (loss of religion); urbanisation (or more accurately neolocality, the practice of moving away from family at the time of marriage); education, particularly of women; and stronger government (stability and military defence, universal application of the law, protection of property rights (perhaps counterintuitively)).
- AtlasBarfed 2y ago
  IMO urbanization broadly includes secularization (consumer culture), education (needed for urban jobs), education/empowerment of women working (two jobs to survive rather than one, women work to survive in cities rather than stay in extended family homes) But of course you are correct. Urbanization is responsible for the largest population migrations and geographic redistributions of the last century. I consider it the major factor in the demographic birth rate declines.