Latest UN Population Forecast

88 thoughts on “Latest UN Population Forecast”

1. https://www.pewresearch.org/fact-tank/2019/06/17/worlds-population-is-projected-to-nearly-stop-growing-by-the-end-of-the-century/ The population would level out and the birth rate would trend to 2 kid families. You see North America (I guess that is where you live) would have a similar population. We just need to make sure those extra billions in South Asia and Africa wouldn’t have reasons to immigrate, we need to ensure their prosperity because you can’t shut off a multi-billion person mass migration if they lack infrastructure that can weather climate change (if it gets worse).

2. I agree population is an issue, although in China inland farming immigration is nearing it’s end. That means less building needing to be constructed so no need to expand. This is for most countries that are not South Asian of African whose populations will account for most of the 21 century growth, they are the ones who will need good cities so we wouldn’t have a billion+ immigration crisis. So Western and most Asian countries wouldn’t have Bladerunner or Akira levels of skyscrapers, they would be tame, although some people may move into more establised cities but it wouldn’t cause a loss of land due to leaving one piece of land to another. As for the population of South Asia and Africa, the population would level out with the world population around 11 billion by 2100 and most of those people would be in cities. This isn’t mandatory, all cities have outskirts and I bet you can still find houses in the suburbs, all I’m saying is that this is a trend.

3. Food production is a function of energy used and its price.
   With enough cheap energy we can go vertical farm up and down with ease. Increasing quality and quantity.

4. The point I was trying to make with that example is that a population can still grow while being below replacement rate (even if only temporarily), and also to explain the concepts of “doubling time” and “half-life”. I picked the simplest example I could think of to demonstrate those three things.

   As I said, in a later post (after thinking about my example more), I concluded that it wasn’t as “misleading” as I thought, but rather that it’s a long-term metric. Which is why it’s misleading if you’re only looking at the short term. Your example demonstrates that just as well as mine, but for the opposite case.

   Real populations are usually more complex than these simple examples, but the point remains: they too can grow or shrink opposite of what the fertility rate would indicate – for a while.

   I’ve since come to realize that fertility rate is analogous to a directing force, while growth rate (= birth rate minus death rate) is analogous to velocity. There is also a factor that determines how strongly the fertility rate affects the growth rate, which we can call “growth inertia”, which is analogous to mass. If you apply a force to a moving object opposite its velocity, it can take time for the velocity to change sign. Same with fertility rate and growth rate.

5. While “Impossible foods” Lab “meat” technically isn’t meat, it plays in the same market, and has already penetrated that market in small volume at a high price.

   Right now they’re benefiting from market hype that is getting people to try it, but they can probably stay in business just by targeting would-be vegetarians who really don’t want to give up on hamburgers and similar foods. It should easily displace the ‘veggie burgers’ found on lots of restaurant menus.

   If they can get the price below hamburger by ramping up volume – should be possible since the product is plant based – they might take over the budget beef market – stuff like cheap packaged pizza or pasta.

   However, to your core point, I’d agree that it is virtually certain to take at least a decade before faux-meat or cultured meat will really start to impact the beef industry and beef-feed crop farming enough to start freeing up land.

6. You might as well consider a case with 100 80 years olds and 2 young folks that will have 10 kids in 10 years while most of the elders die off. So an isolated and unnaturally skewed population can shrink dramatically in one generation despite having a very high fertility rate.

   That might be true, but is not evidence that “replacement rate” is a ‘misleading metric’ in a discussion of population dynamics, because populations generally are NOT like that.

7. Check out a book called: Empty Planet, The Shock Of Global Population Decline.

   Although the UN has been pretty good at population predictions in the past, the authors make a good case for the premises the UN uses for population projection being extremely out-of-date.

   They posit peak population around 2050, after which it begins to decline with no end to that decline in sight. Essentially, and for various reasons, city dwellers, which most people are becoming, have less kids.

   The work is somewhat biased in that the authors are very much in favor of grabbing all the immigrants they can get (the authors are Canadian), with little attention paid to how unfortunate it would be for many cultures to be entirely subsumed by immigrants. For example, I would rather Ireland become smaller in population than wind up being a satellite of some other culture and I’m pretty sure the Irish would feel the same way.

   The authors are couching it all in terms of economics, which is why countries like Japan and China, that simply don’t accept immigrants, are likely to suffer badly, in economic terms. On the other hand, as The Architect said in The Matrix Reloaded, when threatened with a severe reduction in production, “There are levels of survival we are prepared to accept.” 

   Note that international adoption, once involving a huge number of children, has shrunk to a trickle of what it was as countries, for one excuse or another, find reasons to keep a dwindling resource.

8. I consider the deaths in the last paragraph.

   You can think of it this way: the 2 boys and 2 girls were left on an uninhabited island at age 18 – e.g. washed up as the only survivors of a cruise. Now we look at what happens to the population of that island.

   The island population would start at 4 and so on. You would still see that it would double in 42 years despite being below replacement rate since the beginning.

   The previous generation were never part of that population. Never reached the island.

   I agree that if it stays below replacement rate, it will eventually start to decline. If you read my other posts, I eventually concluded that fertility rate is a long-term metric.

   What matters in the short term is birth rate vs death rate. Below replacement rate, the birth rate will gradually drop and/or the death rate will increase until they cross. But that can take a while, and until then, the population will keep growing, despite remaining below replacement level.

9. You can’t examine a population with no deaths and conclude much that is useful about overall population growth – at least barring the end of dying as a factor in population size.

   Now if you had pointed to a generation produced with above replacement birth rates, and pointed out that that ‘boom’ generation had not died off yet and was still having children and grandchildren, you might have made a sensible point regarding populations continuing to expand even after fertility rates have fallen to replacement or below.

10. But most of the world HAS embraced birth control, and their fertility rates have dropped close to or well under replacement. This includes many less developed nations.

    If we are concerned that some nations might not save themselves from Malthusian Doom, there is a very clear method to push them off that course. Dump money into female education in those countries.

    You should look for a book called “Empty Planet”. The title is hyperbole, and the text is rather repetitive, but it highlights that global population trends are the opposite of what most people tend to assume.

11. The Amish have already started migrating to other jobs – such as crafting, construction and small retail.

    Also, they tend to be big savers – so if the US farm economy tanks and farm land gets cheap for a while, you can bet they’ll be snapping up land. (E.g. if politicians finally get around to ending the corn ethanol biofuel program.)

12. I removed them because they’re not relevant to the sub-population starting with those 2 girls and 2 boys. It’s perfectly valid to discuss a sub-population, just like you can analyze a single country or city instead of the whole world.

13. China considered it and tried it. They had a bunch of problems as a result, and eventually decided to cancel it.

14. For some perspective, Shenzhen density is 6100 people/km^2. The urban part is 7400. NYC is similar. If we conservatively take 5000 as the “comfortable” limit, 100 billion people would need 20 million km^2. That’s ~13% of Earth’s land area; or ~4% of its total surface area, if we allow for seasteads by that point. (Cut that in half if you’re willing to go with 10K people/km^2.)

    However, even if we eliminate all deaths tomorrow, we won’t reach 100 billion until ~2150. By that point, both seasteading and a significant space presence are likely. If we go by O’Neill ideas (or similar), a large portion of those 100 billion may be off Earth. But even if not, 4-13% of the land area for housing (depending on the level seasteading) is doable, and would still leave a lot of area for other things, including wilderness.

    The bigger issue isn’t living area, but farm area. That’s what really eats into wilderness. There are solutions on the horizon to feed a larger population, but eventually we’d want to significantly increase food production density. At least by an order of magnitude or two. (My bet is either on tissue culture growing only the edible parts in dense factories, or some sort of synthesis technology. The former has some decades of history behind it; the latter is complete sci-fi at this point.)

15. Except that by assuming the original parents are ‘gone in some way’, you eliminated their deaths from the equation, which would have balanced the population ‘growth’.

    In fact, since the original 2 girls and 2 boys were unrelated, that would have been 8 parents for them, all of whom might be dead by the time you added 4 new people in your example. So the population would have gone from 12 originally to 8 at the end, if you’d considered it as ‘steady state’.

16. So, if you ignore ISRU, I heartily agree!

17. I was correcting a common mis-quotation of Bezos. He always sez trillions, but shows a picture of an Island 3, which alone would hold millions. Then the headline talks of millions, which is the problem.
    My mention of 2100 was to point out the authors’ blindness to O’Neill even 80 years hence! Bezos and O’Neill of course think bigger.
    “Even if millions were in space it would be an insignificant percentage.” I agree.

18. So the main takeaway is that the indian subcontinent and eastern africa are going to get very busy. This may not end well…

19. I agree densification is a fact of life and i’m glad Shenzhen is hospitable, but that is only a temporary fix because at some point population will increase and your remaining wilderness will start filling with more skyscrapers. It is mathematically unavoidable that at some point someone is going to have to put on the brakes so that future people don’t have to live in an overcrowded hell when there is no justifiable reason for it.

20. There are a lot of places in the world including the US where people live at the edge. A few degrees increase in the temperature can kill thousands.

    Last July 4th, I spend a day in the hospital emergency room. Overheated. Didn’t even notice it until I was dizzy and throwing up.

21. Don’t believe the hype. It will take decades for lab meat to penetrate the market.

22. That doesn’t seem to be the trend. The trend was to buy farm land and build suburban housing schemes. But that may be slowing down as the millenniums fled the suburbs for the cities.

23. China’s population will drop by 300 million by 2050, Russian by 40 million. US will add 100 million.

24. These population shifts are extremely likely to happen, it’s not really a question of if. These meeting are about how to house and sustain a huge population. Cities are inevitable in this equation, but it doesn’t have to be bad. I live in Shenzhen, a city of around 13 million people. Contrary to what you may be thinking it doesn’t feel crowded and there is a calmness to it all. Sure I don’t want to live with multiple people and I don’t have to, skyscrapers condense the population into a small area. It isn’t like the unsustainable urban sprawl in cities like Los Angeles, not everybody needs a house in the suburbs. I would rather be able to go camping in the wilderness outside the city rather than it being used for housing. My story isn’t anecdotal, hundreds of millions share my belief. The point I’m making is your American Suburban view is just not preferable in the long run.

25. None of this going to happen fast enough or on a large enough scale to outweigh exponential population growth. We already have the solution to these problems – the birth control pill. Why is no one considering that? Why is it a sin to even consider that we should set a limit on and regulate our numbers using mathematics and intelligence?

26. It’s alarmism, but sadly, it’s not absurd. It’s one of the somewhat lower-probability scenarios, and has been on the outer edge of my radar for three decades now. If the tundra (or ocean floor) starts to release a lot of methane, I’ll have to revisit those probability calculations.

27. Black swan events can not be calculated.
    Also its quite some time since the last major pandemic. That would be Spanish flu 100 years ago, yes it killed more than WW1 but neither did much to overall population.
    Something like the old plagues don’t work today because better healthcare, and yes they was not uncommon back from ancient time until past medieval times that they could kill 20% of population.

28. In analogy with Candide I once wrote a short article where 1000 floating mega cities lives on the oceans, energy from nuclear power from seawater food raw material from seabed until 100% urban mining. Food producing in and on the floating mega cities.

    They could be build from modern concrete with up to 1000 year life length.

    They could help people on land when they har so hard to cooperate.

    Every floating state should have people with som what the same system, not sharia and other primitiva cultures in same states.

    The seabed wait for human living and cities deep in the bedrock.

    But is the number more important than the life quality?

29. Bezos. But he’s rich! The trillions would take a while, but the pop relief easily by 2100.

30. True. Even if birth rates didn’t drop at all from current levels, and we eliminated all deaths tomorrow, it would still take ~260 years to reach just 1 trillion people in total. But I think Dan is talking about longer-term eventualities, or is maybe ignoring time frames completely. Though he did mention 2100 at the top of this thread…

31. Trillions by 2100? Um….so who’s uninformed exactly???

32. as you might see in the graph, there is a projection interval.
    bottom line: world population is growing a lot!

33. LOL. A “Projection” from the UN. What anti-American agenda are they pushing now?

34. To be clear:
    “and show zero signs of being able to launch the colossal amount of material required for an O’Neill colony of useful size to alleviate population conditions” the material is not launched from Earth. ISRU.
    We will within a few years have a vehicle that will carry 1,000 suborb, or with booster orb, assuming a place to drop them off quickly. Only 100 if the stay will be long.
    Everything else is as O’Neill described, just way delayed. Except that we use the Moon as a power sat, rather than building sats.
    http://www.searchanddiscovery.com/pdfz/documents/2009/70070criswell/ndx_criswell.pdf.html
    for more on this, which directly addresses some environmental concerns long before the pop actually starts leaving in great numbers.
    Along with that, check out Al Globus at nss.org for small, even launch, starter kit. As long as we don’t waste time and effort on Mars!

35. The UN tends to overestimate population projections by quite a bit. It makes it easier to stir up panic when asking donor countries for funding.

36. I bought the O’Neill book when it came out and was just as captivated by the concept as you are. Over the last 50 years we have only been able to send a handful of people to the moon and show zero signs of being able to launch the colossal amount of material required for an O’Neill colony of useful size to alleviate population conditions. The massive growth of 2 billion people or more in Africa will be a disaster and space colonies will not come to the rescue. Millions of people will travel north to Europe to escape and Europe will be overrun unless they stand their ground which they are already starting to do. Humanity will hang around but we are going to pay a big price in species extinction and environmental degradation. By the time we reach the peak of 11 billion or so there will be no doubt in anyone’s mind about the need to pull back to something more reasonable.

37. Very true, but most people don’t know what they like until they experience it. Most of those people were born and raised in such an environment and have only seen more sedate places in movies and pictures or driven through them. I knew a couple that both grew up in New York city and moved to Bellingham Washington. The wife as you say couldn’t stand how quiet it was but the husband felt like he’d been let out of prison. The wife complained and complained and the husband had to move back to New York or face a divorce possibly. I still believe that crowding huge masses of people together in an ant colony is not healthy or desirable over the long term.

38. Well, I wouldn’t say *all* bets. We know that current death rate is 0.8%. So we can reasonably predict that the growth rate won’t increase by much more than that if life extension therapies are widely implemented. Any higher increase would have to come from an increase in birth rate. So that still lets us project the population to 2100, just under different assumptions.

39. Fare enough.

    God bless.

40. Of course, O’Neill plan is unlimited. Bezos talks trillions, but is usually misquoted as millions, as that is per O’Neill habitat. Please be informed before displaying false assumptions!

41. Very true, if affordable life extension causes a lifespan escape velocity around 2040-50 all bets are off on 2100 numbers.

42. That’s absurd alarmism

43. Even if millions were in space it would be an insignificant percentage.

44. I actually don’t think that will be true; lab meat will massively drop farm land demand.

45. > Any longevity increase is just a temporary arithmetic increase

    That said, it can take so long for the birth rate to drop below the death rate, that the conditions can change multiple times until then.

    The graph in the post projects multiple decades ahead. In that time, there could be multiple advances in medicine and life extension, which could increase life span (longer half-life). Or there could be breakthroughs in old age fertility, allowing women to go for a 2nd child-rearing round, if they want to. That would effectively increase the fertility rate. Or there could be various sociological, cultural, and economical changes.

    In today’s world, it’s so difficult to predict beyond 10-20 years, that such long-term predictions are somewhat meaningless. That’s why I still think fertility rate is less useful. It’s a good early warning sign, but it’s too long-term to be a good prediction tool.

    For the rest of what you wrote, I mostly agree.

46. Yes, that is what I was getting at. Sorry for my misunderstanding.
    Any longevity increase is just a temporary arithmetic increase and as soon as these level off, even at a ripe old age of 120 or even 200, that effect completely ends. People eventually die.
    Whereas only birth rates have the potential for the exponential increase of a population. If birth rates get high and level off at say four per woman then the population will at least quadruple every century as it did in the 20th and this is where the book Population Bomb has some legitimacy. And, of course, if these rates decreases, as they are even in Africa and the Middle East, and does not get corrected then we are looking at much smaller populations, with its own ramifications. Certainly at time of plunging birth rates improving technology to feed and provide energy with minimal impact on ecology, overpopulation is just not the concern that it was.
    What I am even more concerned with, and what I should have emphasized from the beginning of this discussion, is polarization everywhere in the world on issues such population and ecology, and even morality. Technology has the potential to take care of some of these problems, i.e ecological effects of high population, reducing the left v. right tensions. If these tensions break out into open conflict, the first casualties will be ecology and morality, as well as population. Liberals and conservatives take note. Let’s cool our jets and work to actually fix our problems.

47. Yes, I stand corrected in my misconception of what you were saying. I realized that last night trying to get to sleep. 🙂
    I was having a very hard time even seeing the longevity thing being a big deal or the controlling factor, so I read more into what you were saying than I should have. And now I see your comment below. We seem to be understanding each other.

48. “And please don’t appeal to space travel because we can’t move the requisite numbers of people fast enough.”
    We can start. The first things done will remove much of the support effort for people into Space, so the damage goes down, starting with electric power. I agree with your observations, being even older, but you can’t just dismiss our only long term hope, our best short term hope. Other than actually eliminating all humans, staying on Earth is a disaster, as it only took 70,000 years for humans to come from 2,000 pop (that survived) to present.
    A popular O’Neill factoid is that if there were places to go, and current airliners could go to them in Space, it would take about a year to totally depopulate the Earth.
    Now, if you are not thinking O’Neill, I can understand your despair. Are you?

49. Of course, that is if you assume you are interested only in living on planets, such as the Moon is for these purposes. O’Neill (Bezos) has pointed out that we do not want to live on planets. A huge change in plans!

50. Below replacement rate you have an accumulation of older people, and relatively few younger people are added over time. So what I think will happen is the doubling time will gradually grow over time as the population both increases and ages, until the doubling time catches up to the half life, and the population would stop growing.

    This is the same as saying that below replacement rate, the birth rate can still be higher than the death rate, so the population can still grow; but the birth rate will decline (and likely the death rate will rise) as the population ages, until the birth rate and date rate become equal.

    Same result, different description, using different metrics. Eventually, the birth rate will drop below the death rate, and the population will start declining. So come to think of it, replacement rate (or more correctly, fertility rate) is more telling than I thought, it’s just that it’s a long-term metric. It may take a while for the population decline to materialize. The birth rate and death rate are short-term metrics.

51. I didn’t say “per generation”.

    As a simple example, let’s say we have two girls and two boys, same age, not blood related. We’ll ignore their parents for simplicity (suppose the parents are gone in some way). So starting population is 4. At age 20, one of the girls has a girl, and the other has a boy. Those are their only children. This boy and girl have their own two children at 20 and 22. Now we have 4 grandparents, aged 42, still alive; 2 parents, aged 22, still alive; and 2 kids, a two year old and a newborn. Total population is 8.

    The number of children per woman is 4/3 = 1.3, well bellow replacement rate. Yet the population has grown. Not only has it grown, it doubled in 42 years. That’s the doubling time.

    The half-life is defined as the time until the population is halved (borrowed from physics), which we can’t calculate form the above numbers. We’d need to know the life expectancy. I think you’d also need to ignore new births for the half-life calculation, and only calculate it for the original population, otherwise you may not get a logical result.

    So in the above example, let’s say the life expectancy is 70 years. So on average, we expect two of the original 4 to die before 70, and the other two to die after. That would place the half-life at ~70 years. So we have a doubling time of 42 years, and a half-life of 70 years. The population doubles faster than it halves, so it accumulates even though the number of children per woman is below replacement rate.

52. Not necessarily, since Mars has no oceans and its land is more-or-less equally livable. But there are many other obstacles to overcome…
    The Moon is a better near term choice and far more accessible.

53. The U.S. makes it onto the list, barely, because of net migration to it. Of course, that means other countries have “lower” growth because they are exporting people to the U.S., so it is a bit misleading, for example, to say Latin America is not growing as fast as the U.S., or many of the other countries of the world where a record number of refugees are fleeing – 70.8m: https://www.scmp.com/news/world/africa/article/3015162/world-refugee-count-hits-grim-milestone-708-million-major-powers
    Even so, many of the countries are still on the list that are in refugee lists too: Nigeria, DNC, etc. It’s hard to see where they get the time/wherewithal to reproduce.

54. What about the mass pandemic… like Ebola jumps a ride on the bird flu …. it’s like the plague that killed half the population in Europe in the Middle Ages…

55. 50%increase in US population despite low US fertility rates can mean only one thing… immigration from countries with too much population growth…. I think the future reincarnation of trump would be having his worst nightmare coming true in that case… there’s no way anybody is going to agree with replacing 50% of the us population with India, Nigeria, Pakistan, just to be number 6 in the list…. I think by that time we will be instituting the “Superman” gene codex program… and dividing everybody in “vex” and “el” clans…

56. This sort of question should not be hard to answer. 80’s radar tech is well understood, and solar panel goodness can only get better. When I hear such objections, they often seem to be ways to avoid the question, often being covered in the proposed offer. Surely someone has wondered about that!

57. Believe it or not, many people move to the big cities because they like be around so many people.

58. Understand that USA has been growing due to immigration in the past but that is drying up with the wall etc.

59. Yes, odd about Musk SSO. Especially since he owns a rocket co and a solar co and wants to save the planet. He says it’s inefficient with so many energy conversions photons to electrons to photons to electrons. Makes me question it’s viability. Of course he thinks Mars is a good idea and terraformable so hard to say.

60. To have a doubling of population per generation you need a birth rate of 4 not 2. Birth rate refers to women only. Half of those born are male so each woman needs to give birth to 4 to double. That ain’t happnin anytime soon.

61. I have trouble w/ *this* editor when going from email link. See if this works. Firefox on Ubuntu. Anyway:
    Janov’s accidental discovery of repression was in the stores in 1969, even tho the C is 1970. The Primal Scream. John Lennon an early patient is how many hear of it. So, think of an exception in computer. The main program stops, and control is transferred somewhat peacefully. Overloading a vulnerable paranate or infant with incredible pain will ,IF bad enuf, cause such a thing in primates. Jane, my fantasy love, observed this in chimps. The experience itself is simply stopped, as in when an exception is thrown. But it is still there, actively repressed as a life-preserving emergency action, so the *program* can continue. (space bar seems to cause failure, but reboot of everything?)
    A Primal is the experiencing of this repressed experience, slowly perhaps, by the adult, who can now integrate it into normal memory, freeing the load of repression. Dramatic epigenetic changes happen to such adults, permanent physical changes that could only come from the cellular level were reported by Janov long before epigenetics was discovered. Thus the health and longevity advantages to not having repression in the first place would seem to follow, but it takes longer to do the experiment.

62. With most farmers using ever more efficient technology, and an eventual fall in population (i.e.. consumers) we might see cheap farm land be MORE available.

63. The USA is still growing because of immigration, and the point Michael K explains.

64. Sorry, I’m not understanding what you mean by “repression”.

65. Agree totally! Did not know Musk had any thoughts on SSP. Seems quite odd!
    Growing out of debt is about our only chance, and Space seems the only way to do that with scale needed for far future.

66. Well, the number is wrong, it was just an example a nurse thru out a few days ago. Certainly there are areas of exceptional average longevity, her topic. Is it how they are born and treated as infants? The load of repression is a huge life threat. Janov points out that cancer and heart disease (I would add suicide) are not the major killers they are thought to be-repression is.
    Much greater life length, with better health thru the whole life, is the result of removing (well proven in 50 years of experiment) or, better yet, not causing, birth trauma.
    Now, this effect on longevity should not matter, if we go to Space!

67. I like Bezos’ O’Neill idea better than Mars. Musk is also very down on Space Solar Power. Population aside, if we are doing such large things out in space this does mean our economy will be much larger and this has always been a way out of debt, to grow the economy until it outsizes the debt. And certainly AI and robots along with reusable rockets could vastly accelerate all that beyond the current paradigm. So far though all debt has just increased compared to GDPs along even with large growth. We will see.

68. The issue is not whether we are technically capable of supporting massive numbers of people but whether it is desirable. If you adopt a 24hr schedule in your house and allow each person to have 20min/day in the bathroom you could support 72 people in your house. Is that the way you want to live? Man is not immune to population collapse and I do not understand people who think growth is no big deal. Many current problems would not exist at all had U.S. population never risen above 150 million. We would not need to develop robotic cars for traffic congestion and California would not be facing water shortage because of too many people. I do not understand this mentality that says we must mindlessly increase our numbers to no specific end when there would be so much more natural beauty available if we backed off. The optimists among you are to me like a person who sets off driving across the country with an 8th of a tank of gas with no plan for what to do if another gas station does not appear on the road, and the whole time you tell your passenger that there will always be a gas station because there was one before. I grew up in the 60’s and 70’s and I have witnessed nothing but steady decline in natural beauty and wilderness. Where is the technology to increase land area my friend? And please don’t appeal to space travel because we can’t move the requisite numbers of people fast enough.

69. There are small pops where *many* people live well until120. Janov sez healthy birth process will make this universal, for those so born. Really!

70. We should grow into Space, as that will pay off the *growth* Ponzi looking debt, which makes sense if the growth happens! Baby boomer social security is (temp) problem with lack of growth.
    But debt repay is not a good justification for population on planet. Move to O’Neill Space and have the Earth as a park, eventually. Bezos and Space Solar Power are the right direction. Musk has good rockets, but Mars is way too small to help with this.

71. LOL! Yes, as this debt keeps piling ever higher it does start resemble that. There is still a sliver of a chance it will get paid back and no sign that confidence in the Japanese bonds is faltering. So all is good. The way these things work, people are willing to keep buying a govement’s bonds … until they don’t.

72. Pretty sad talking about pop in 2100 w/o mentioning O’Neill. How stupid can the authors get!

73. The US Census Bureau projects 9.5 billion in 2050, or about a quarter billion less people. So there is some uncertainty in these projections.

74. “…but so can too little as most advanced countries are experiencing while trying to finance their government debt and pension liabilities…”

    You make it sound like a huge ponzi scheme.

75. When the wetblub temperature reachs the limit of human survival most of the population will die. So no the population won’t be 14 billion in 2100. More likely it will be 1 or 2 billion.

76. Not to worry, many flee the orthodoxy. Also the Amish need cheap farm land and the supply of that will diminish with time.

77. It is called natural deaths and below replacement birth rates. Most everyone alive at the beginning of the century will be dead by the end of it. Unless they are replaced by new births, the populations will be smaller. World birth rates are dropping below replacement, therefore …

78. Replacement rate is a misleading metric, because while a woman is still alive, her children will (usually) have children, and their children could have children, and sometimes even theirs have. So the population can still grow below replacement rate.

    You can sort of think of it as doubling time vs half-life. If the doubling time is shorter, the population will accumulate. If the half-life is shorter, the population will decline. That’s why birth rate and death rate are more useful to predict population growth.

    The replacement rate is more useful when discussing how the population ages. Below replacement rate the population will tend to grow older on average.

79. Yes, I understood your meaning. These calculations’ merits rest solely on how accurately they factor in trends. I am saying that these trends have been factored in as best as they can be, including decreasing death rates. Of course, a black swan event could make all such calculations a bunch of garbage, but such is life. 🙂

80. My point is that the death rate is and will be dropping too. I’m sure they accounted for the current death rate, since that’s the basic calculation: growth = birth – death. But did they account for the future drop in death rate? My guess is they very likely underestimated it.

    Also, the population can’t level or begin to drop unless the birth rate drops to and below the death rate. But since the death rate is dropping too, it’s a moving target.

81. Death rates are factored in and they are, indeed important to the calculation. But given that most of the worlds countries are experiencing below replacement birthrates and the world birth rate is dropping, the population will level off and begin to drop due to the inescapable math of demographics.

82. Dear god, it won’t, it simply will not.

    Where on earth you came up with that gibberish but wow. The population at the start of the century was 6 billion. How, without a war or pandemic does the population decrease to that level in 100 years?

83. God knows where the hell this crap comes from but Australia increased in population by 420k in less than 12 months. Get a grip Brian, jesus.

84. Due to tecnogical advancement plus high education starndard the population will remain same at the end of century

85. When I was a kid the big worry was the “Population Bomb” https://en.wikipedia.org/wiki/The_Population_Bomb based on a book by that name published in 1968 which advocated draconian world government intervention to stave off disaster by famine. This was just a rehash of outdated, discredited Malthusian population theory from the 1700s. Both then and now there was a pessimistic under-appreciation for the coming advances in technology (which is weird because it was technology that enabled the populations to grow in the first place and this technology has much more potential for growth than the population). In the 1970’s there was the “Green Revolution” https://en.wikipedia.org/wiki/Green_Revolution where technology provided more than enough extra food for the growing population, defusing the “bomb”, and this revolution is now experiencing its second wave https://en.wikipedia.org/wiki/Green_Revolution#The_New_Green_Revolution, which focuses on reducing the inputs needed, exactly what developing countries need.
    In short, our worries about population are overblown and ultimately, if the green revolution reaches its full potential, it could make people the solution to the environment rather than the problem. ( This is because the largest vector on the carbon cycle https://en.wikipedia.org/wiki/Carbon_cycle is land based plants that grab CO2 from the atmosphere, of which, through our farming to feed our population, we have direct control. )

86. With all that population growth in Africa, I really hope they can get their agricultural productivity up. They have a lot of room for improvements; for example, the average corn yield across Africa is less than half of what the Brazilians manage.

    And for some more long term concerns after that: with birth rates falling all over the world, going below replacement level once a certain level of development is hit, well what happens next? Does the world population dwindle until humans go extinct? Or do minority groups that reject a lot of modern developments manage to keep up their birth rates, and end up the majority? Somewhat silly example here, but if the Amish manage to keep up their current birth rates they will be a majority of the US population by 2200. And a majority of the world population by 2300.

87. The problem we are facing is actually too LITTLE population growth not too much. Wikipedia has a list of all nations by birth rate.
    https://en.wikipedia.org/wiki/List_of_sovereign_states_and_dependencies_by_total_fertility_rate. The replacement rate is 2.1 or 2.2 (2 births for every woman to replace every man and woman who eventually dies plus a little extra for those who die before reproducing). Notice that most all the world has less than replacement levels, including China and the US. (I don’t know why the US is mentioned as having a significantly growing population in this article since its rate is about 1.8, ranking about 140th of all countries). These rates are still falling and there are very few examples (Russia) of anyone being able to reverse this trend.
    Yes, too much growth can be a problem, but so can too little as most advanced countries are experiencing while trying to finance their government debt and pension liabilities. This is most prominent with Japan, google “japan debt world financial stability”. With the imminent population implosion and with of all the new technologies coming on line, 4th generation nuclear, solar power, the second green revolution, any one of which can solve our food, energy and ecological concerns, a 180 degree turn in our population policy is long overdue. We need to look ahead.

88. In the graph where they project the population growth rate going toward zero, I wonder if they account for reduction of death rate. Just the top 10 leading causes of death account for ~0.4% death rate. There could be a lot of progress on preventing those deaths by 2100, which would add much of those 0.4% to the growth rate.

    If there’s also progress on life extension, we could see as much as ~0.7-0.8% added. Current death rate is 0.8%. There’d still be accidents and injuries, but they only account for less than 0.1% death rate, and there could be progress on treating more serious injuries and preventing some of the fatal ones.

    On the other hand, we should also see progress on reducing our environmental footprint and developing space. We won’t be constrained to Earth for much longer, though the number of off-worlders by 2100 may still be quite small.

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