Inspired by this thread, and the situations in Children of Men and Tepper’s Gibbon’s Decline and Fall:
If humanity stopped conceiving today, how quickly would the global population decline? Would there by any noticable difference in a week/month/year, as the ill and elderly died off and weren’t replaced?
Just wondering how quickly drastic_quench could get down to 250 million humans from 7 billion, without having to kill anyone off!
As of July 2009 the crude death rate for the whole world is about 8.37 per 1000 per year according to the current CIA World Factbook.
So it would take a while.
That number has some issues when it comes to the OP’s questions however. 8.27 per thousand per year would suggest that everyone would live to be well over 100 years old if the population were stable. We know this isn’t the case. That figure much is lower than it would be if everyone suddenly stopped reproducing because we have a growing population today and a low death rate reflects a large infusion of young people. Once you take that away, the rate would start to go up and increase drastically over time as the last of those born reach old age.
It is an interesting math problem and one that is fairly difficult to do well. I will leave that to others.
The term “zero population growth” means the number of births equals the number deaths. So by definition the population stays stable at 7 billion or whatever indefinitely.
What you really mean is “zero birth rate”.
If we take some real simple assumptions, that the average lifespan is 70 years & the distribution of all ages today is even, then about 1.5% of the population will die each year. So it’ll take about 7 years to lose 10%, then another 7 years to lose the next 10%, etc.
In reality there are a lot more young than old folks worldwide. but the youth is concentrated in poorer & middle eastern countries whereas Japan, Europe, and to a lesser degree the US are relatively more full of oldsters.
So (made up but ballpark numbers) it might take 5 years for Japan to lose 10% of their headcount, but it might take 25 years for Zimbabwe or Saudi Arabia to lose 10% of theirs.
250 million is ~4% of 7 billion. So we’re talking about losing 96% of the population. Which’d take about 96% of the average lifetime. Again assuming 70 years average lifespan & uniform age distribution today, that’d take 67 years. And at that time the youngest human on the planet would be 67 years old. In reality, given the present skew towards youth, it’d take even longer, maybe 70 or 75 years.
We’ve discussed the global-no-births scenario before. The usual concensus is that once the reality sank in, a lot of society would collapse. People would decide “what’s the point?”, or would realize there’ll be nobody young to run the world & take care of them when they are elderly. SO folks stop going to work, form weird cults, embrace anarchy, etc.
If society does collapse, even partially, that will kill a lot of people well ahead of the current statistical expectations. From starvation if nothing else as modern commerce collapses.
At this point we’re dealing in pure fantasy so there’s no way to reasonably estimate when the population would decline to any specific headcount.
Based on that figure alone, I knocked up a quick spreadsheet and it looks like it would take about 400 years to get down to 250 million. Of course in real life that rate would accelerate as the population ages and we’d be down to zero in, oh, 70-80 years or so…
See this:
Assuming everyone lives to the average age, the population decline would accelerate as time went on.
Some countries would decline faster than others, the 3rd world countries decline the slowest.
Huh? Which “figure alone”?
If you got 400 years you did something totally invalid which doesn’t pass the *this is obviously preposterous * smell test.
Indeed. With zero births, it can’t very well take more than a century for nearly everyone to be gone.
There’s a serious problem here. Suppose it takes 75 years to get down to the target 250M. But now the youngest woman is at least 75 years old, and can’t reproduce. So by then there’s no alternative than to continue on to 0.
Aside from all the social stuff, a better bet would be for your target population to reproduce at the replacement rate for that time (2.1 per woman or whatever). It will take longer to get to the target but the early part (going from billions to hundreds of millions) will be about the same, and will ensure you retain a viable breeding population.
So you are saying to pick 250 million people who are going to be the ones to breed at replacement rate and sterilize everyone else? Sounds like a plan. How do we choose? I’m out because I already have kids but my children and grandchildren should have a lot going for them. I can see some serious social tension between the ‘breeders’ and ‘non-breeders’ but, hey, they get to have all the sex they want and don’t have to change diapers or pay for college. I call it a wash.
It could easily be accomplished with a computer. And a computer could be set and programmed to accept factors from youth, health, sexual fertility, intelligence, and a cross section of necessary skills.
Stored in a giant tape memory bank.
Mr. President, we must not allow a mine shaft gap!!!
Yes, Dr. Strangelove, I *did *see what you did there.
Yup, that’s precisely what I meant thank you - must’ve been influenced by the ZPG named poster elsewhere on the board, sorry!
I love you.
I’d love to say that I planned that out from the beginning… but I never miss an opportunity when I see one.
It would not be difficult, Mein Führer!
Back when the movie was fairly new & my bros & I were roughly college age, we decided that there’s no situation in all of human existence without a relevant *Dr. Strangelove *quote.
Doesn’t matter whether you’re eating breakfast, just crashed your car, are asking a babe for a date, are playing cribbage, or are attacking a missile base; the movie has a line which fits the situation perfectly.
:Snip: At this point we’re dealing in pure fantasy so there’s no way to reasonably estimate when the population would decline to any specific headcount.
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Good thinking LSL Guy! Thanks
I understand that these are just made up numbers, but did you pick Zimbabwe for a reason? Because their life expectancy is in 34-37, so I’d guess that after 25 years they’d lose a LOT more than 10%.
Life expectancy is a complicated concept. If 9 of 10 babies die before age 1 and the rest live to be 100, the life expectancy of the entire population is only about 10 years old. Yet everybody over age 2 will live to be 100.
I picked Zimbabwe more or lesss at random as a generic African country. I was thinking mostly in terms of death at old age from more or less natural causes. What they do have is a massive youth bulge, implying that it’ll take many years-worth of relatively rare oldsters to use up 10% of the total headcount which includes massive numbers of under 25s.
You make the valid point that IF they have massive losses in the young ranks due to disease (HIV) or warfare or gangster violence, then they could lose 10% pretty quickly from that group alone.
I confess to not knowing which factor predominates in Zimbabwe as such.