A train of thought is that a lot of our problems could be solved by reducing our numbers. For this question I am limiting it to environmental changes. For example: a successful species will increase its population until their natural resources are consumed. In the case of humanity: people attempt to be 'green', some people choose to be vegan and so on, with the intent of reducing ones footprint on the planet. However, our numbers keep increasing, which could mean that it might still be a 'half-measure' and eventually we still will use up all our 'footprint-space' or natural resources. Our population limit will just be greater that it would have been when using bigger footprints. This would make us live in a more crowded manner.

I am pondering a limit to the population (say 3.5 billion, 1 billion, even less...). Not to allow us to use ridiculously large footprints, but to artificially stop us from using up everything while maintaining our current standards of living. My question has two parts:

1) What would be the environmental consequences of a hard-limit on our population? (Deforestation, wildlife, pollution,...)

2) Is this achievable through birth-control, single-child-policies and the like? To achieve this, should we stop attempting to longen the average lifespan even more? Should we make a point to drop it by 10 years?

Some related topics :

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    $\begingroup$ sorry if this is nitpicking, but what do you mean by saving the planet? The planet will be fine long after humanity has disappeared. And new species will develop in the wake of our demise. For the planet this is just a regular thuesday in a long lifespan of seeing massextinctions come and go. $\endgroup$ – Martine Votvik Jun 14 '16 at 10:58
  • $\begingroup$ @MartineVotvik: I agree fully, but try seeing 'saving the planet' as how organisations like greenpeace or gaia would see it. Meaning: drastically reducing our own impact on the natural resources. $\endgroup$ – Bjorn Jun 14 '16 at 11:35
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    $\begingroup$ Last time I proposed ending the lifespans of 50% of the human population, people were yelling at me. I don't know why. $\endgroup$ – Damon Jun 14 '16 at 12:37
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    $\begingroup$ A one-child policy has been tried before, in China. It was a massive failure, creating widespread discontent within China, setting up skewed demographics (as male children are seen as more valuable than female children in Chinese culture, selective abortions (and occasionally even darker practices) were frequently done to make sure the one child would be a boy, leading to a severe gender imbalance in the current population) and making the rest of the world laugh at them. The policy has since been discontinued by the Chinese government. $\endgroup$ – Mason Wheeler Jun 14 '16 at 14:47
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    $\begingroup$ @Damon: Why stop at 50%? Have you ever read "Tom Clancy's Rainbox Six"? It's the best manual how to eradicate humankind and humanity. $\endgroup$ – Alexander Jun 14 '16 at 17:20

Population reduction has ethics nightmare written all over it. Do we let people die when we have the technology to save them for the sake of reaching depopulation quotas? What do we do with people who keep making children against the law? If it comes down to it, who gets the right to reproduce and who doesn't? Are you prepared to fight the people to make this change happen?

There is a fun fact that even if we suddenly had zero impact on the environment, temperatures would continue to rise thanks to all that the oceans have accumulated. Eventually, the system would stabilize, but it would take about half a century if I remember correctly. So simply reducing the population will only slower the rate at which we destroy our environment, not invert the process.

To make things even better, the more we have, the more we use. Reducing population would mean we have more resource per capita, so less incentive to waste them. And we already waste a lot. We may consume less overall, but we may also consume way more per capita. That isn't positive change in my opinion.

If you want to save the planet, you have to change our relation to our environment. You have to transition our society away from individualism, and you have to fight for change. You won't make a revolution without breaking eggs.

Alternatively, you could bet on technology and our capacity to bend our environment and adapt it to us. Remember, it's not about saving the planet, it's about saving ourselves. HVAC is one way to cancel temperatures rising, right?

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    $\begingroup$ Playing the devils advocate: I agree that ethically this is a nightmare. On the other hand, China's one-child policy is very well known, I agree that just letting people die is also terrible. But there are many cases that might be over the top, a 95-year old getting a third bypass for example, or people in long-term comas. Why do we necessarily need to all have a life expectancy of 90 years? Is our quality of life at that point really worth it? Last time I visited a retirement home quite a few couldn't recognize the nurses they see every day. None of them are able to survive on their own. $\endgroup$ – Bjorn Jun 14 '16 at 9:15
  • $\begingroup$ My point would be to bet on technology to allow us to have the 'current western lifestyle', with a minimal environmental impact. I would not want to use a small population as an excuse to consume or waste more. I would want to keep the standards we have now, combined with even cleaner cars, more energy-efficient solutions and so on.. $\endgroup$ – Bjorn Jun 14 '16 at 9:19
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    $\begingroup$ @Bjorn The most basic article of human rights is that we are all equal. If you posit older people have less of a right to survive, you are attacking human rights. Hence ethics kerfuffle. Though to be fair, ultimately every solution is imperfect. $\endgroup$ – AmiralPatate Jun 14 '16 at 9:37
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    $\begingroup$ Not quite every solution is imperfect. If you don't pick and choose which humans live, and just kill them all, then everyone gets the same treatment. (Note: Do not try this at home.) $\endgroup$ – Frostfyre Jun 14 '16 at 12:12
  • $\begingroup$ @AmiralPatate If all humans are equal, then why am I not allowed to go to elementary, while my nephew is? $\endgroup$ – Alexander Jun 14 '16 at 17:23


In fact this is already happening. enter image description here https://en.wikipedia.org/wiki/File:Countries_by_Birth_Rate_in_2014.svg

  • $\begingroup$ I agree. But still, in the purplest areas we also have overpopulation issues. 'Unavoidable' traffic jams (Belgium, London,...), skyscrapers worth of flats of people living small and on top of eachother and so on. $\endgroup$ – Bjorn Jun 14 '16 at 8:37
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    $\begingroup$ that birthrate graph needs to be tempered by the deathrate, otherwise its just a bit misleading. $\endgroup$ – gbjbaanb Jun 14 '16 at 12:17
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    $\begingroup$ @Bjorn: traffic in London is due to the population of London and its immediate surrounds. If you kill 6/7 of the UK population there's no guarantee that the remaining 9 million people won't still all want to live in London. You can't really put London's congestion down to world population. $\endgroup$ – Steve Jessop Jun 14 '16 at 12:29
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    $\begingroup$ Education is the answer. If we could uniformly educate the worlds women and offer them the same career paths as men, they would defer child birth and the worlds population would begin to decline. Sustainment birth rate is 2.2 kids/couple, many western couples don't reach that. $\endgroup$ – Jason K Jun 14 '16 at 12:39
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    $\begingroup$ yes birth rate graph is not a good example. but to clarify the idea, which is good if he had elaborated, most first world countries have negative population growth, including US, England, and I believe most of northern Europe? Though it's not just education, as death rate (amongst the very young) goes down births drop, as people don't feel the need to have dozens of children just to ensure a few survive to adulthood. It should be noted first world countries still have a larger footprint, each individual consumes far more resources then individuals in third world countries. $\endgroup$ – dsollen Jun 14 '16 at 14:23

The number of people who can enjoy a contemporary western standard of living sustainably, or with a minimal impact environmentally, is going to be pretty small. Before industrialisation the world's population was almost always under 500 million. That was largely because of both a lack of food and medicine. You need to consider that the problem now isn't the size of the population per se, but rather the minority who are using the majority of the world's energy - I'm talking about you, dear internet user!

Either you strictly keep economic development to an absolute minimum, and can have more people, or you have a good standard or living and have far fewer people. Fortunately there's already plenty of analysis written on these issues. I however would err on the side of the most pessimistic figures. Unless we can develop cheap and plentiful energy (like fusion or something) then that's always going to be a problem because right now development and consumption is not sustainable. So your figure is probably going to be less than two billion people.

A 2012 UN report summarised 65 different estimated maximum sustainable population sizes. The most common estimate was eight billion, a little larger than the current population. But the estimates ranged from as few as two billion to, in one study, a staggering 1,024 billion.


Of course that's the optimistic view, for the pessimistic you may also want to investigate "ecofascism". Pentti Linkola's ideas are pretty much as extreme as they come. He advocates the mass murder of most of humanity, firstly by using WMD upon cities, and then enforcing strict controls over the economy and population growth via an ecological dictatorship. And stuff like migrating people from the developed world to the less developed world, and vice versa, to thin the population averages. Basically he's a green Pol Pot.

His motivation being the idea that capitalism and industrialisation cannot be separated from the destructive effect they have on the planet. Therefore radical action is required to deindustrialise humanity. This will reduce the maximum human population to at best half a billion, but if you want to encourage reforesting to encourage biodiversity it's going to be much lower still to reduce the demand for farmland.


Given this context, in answer to your question. Firstly, you'd need to enforce serious quotas on land and resources (like fishing) to preserve them. Which would help biodiversity return as pollution and exploitation is reduced. You'd also need to go with technologies which reduce strain on resources; like having lab grown burgers, or simply having people develop a taste for fried crickets rather than steak. As in terms of energy efficiency, the land and energy required to raise cows and chickens and such required for slaughter is non-trivial; like you mention vegetarianism for social reasons.

Secondly, you'd very much need an iron fisted political regime to enforce both technological advancement (green technologies, lab burgers, fusion, etc) and also to reduce population growth and energy use. This will also probably require social changes, like aforementioned change in taste of food, and also for people to become more energy efficient in how they live... like opting to live in flats rather than sprawling suburbia. You might have to enforce changes like banning home and land ownership. You'll definitely need to throw everything you've got at reducing the population. Child quotas, contraceptives/sterilisation, and importantly good comprehensive sex and relationship education. Possibly yes, encouraging euthanasia at a certain age, which reminds me of an episode of Star Trek TNG where they came across a society where almost everyone chose to die come age 65. Bottom line, you'll have to do radical changes one way or another in almost every aspect of society as we know it.

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    $\begingroup$ And in addition to this iron-fisted political regime, you need something that humanity has never succeeded in devising: A way to ensure that the people who wield this power do so from the "right" motivations, and that the power does not corrupt whatever noble ideals. As things stand, it is nothing but a recipe for another Holocaust or Holodomor. $\endgroup$ – EvilSnack Jun 14 '16 at 12:37
  • $\begingroup$ I don't think the iron fisted regime is necessary for that; just following Linkola's ideas will do something much worse. But the argument that power corrupts tend to seem an insufficient argument. Power naturally attracts the corruptible. It's possible to have a system recruit and filter based on values. You see examples of that from Quaker bankers, to soldiers fighting to the death, and rulers lacking corruption. I don't think it's helpful to say people are always corrupt with power because it's not true. It depends. Also, I approve of your acknowledgement of the holodomor! $\endgroup$ – inappropriateCode Jun 14 '16 at 13:17

I'll address point 2 about extreme population reduction first(dropping the population by 50% or more). If you try to do this slowly, over many generations, priorities will change and the original policies will become less strict or will be dropped. If you try to do it quickly, over a few decades, you will have to take measures that are at best highly dubious from an ethical standpoint.

As to consequences: it will be complicated. Depending on how and over what time line the population reduction was achieved, standards for quality if life could rise or fall. Here are a few scenarios.

1) Everybody's rich. Let's assume everybody in the world now has an American standard of living (probably the most resource intensive in the world). Even with a severely reduced population this would be difficult for the earth to support long term, and the environmental outlook would end up quite similar. Maybe you'll get a few more decades out of the situation, maybe a few less. The current western lifestyle is not at all environmentally friendly, and the few measures you mention would be as effective as emptying a reservoir with a coffee mug. Maybe if you dropped the population to a few million or so it would be more sustainable.

2) Everything is like Detroit. Due to quickly reducing the population, you have problems. You have buildings and even cities with no one to occupy them, your policies to reduce the population had unintended negative consequences, and now crime is high and employment is low. With all the poverty, though, you are doing much less damage to the environment. Lots of abandoned neighborhoods are being reclaimed by wilderness and with the major industries gone, overall pollution has plummeted. Of course, no one cares because they are more concerned about not being robbed or killed during the riots.

3) It's the future, baby! Your powerful political rhetoric caused everyone to suddenly agree on what approach would best solve all the world's problems, and your solution works! You focused all economic resources on finding ways to sustain the current western standard of living using only 1% of the resources. Real beef tenderloin has nothing on vat grown beef flavored yeast! Due to the extreme economic investment, nearly all the major pollution problems have been solved, and the earth can now support a population of 10 billion without strain. Hey look, Honey, we can start having kids again! A hundred years or so later the same overpopulation problem rises again.

4) Not quite the Matrix. You set up a long term enforcement method to make sure your ancestors cannot expand the population or use more resources than the hard limit you set. Let's say it's a computerized overlord who ensures all women are sterilized after child number two, that shuts down or destroys any facility breaking the pollution laws, and does the same to any groups breaking the nature preservation laws. In this case, you have centuries of environmentally friendly living ahead of you, until something happens that either destroys your enforcement mechanism, or something happens that your enforcement can't handle. At that point, after a few years or decades of chaos, humanity will go right back to using available resources in an unsustainable manner.


1) Due to automation, technically a single person could hypothetically cause all the pollution we're causing now. Footprint is heavily affected by the people's lifestyles. If everyone lived pre-fire tribally, cows would be a bigger cause of environmental shift. Population reduction of a percentage of population and its effect is drastically affected by which population groups that 50% comes from. If that 50% was solely from US, China, and Europe, you'd probably completely see an end to most ongoing environmental damage. If it was all from Africa, the world would barely notice.

2) Single Birth worked moderately well in China but came with noticeable social impacts. Birth control methods could also work. (Paying money to opt into sterilization?) Honestly though, people like to breed, so it's a hard thing to do. Honestly, the easiest route is probably building space elevators (to make travel to space dirt cheap) and just getting people to move off-world. An orbital ring could support a much higher population than Earth for a fraction of the resources (and resources that don't necessarily have to come from Earth.)


I see 2 ways of achiving this

1) Force population control

The government forces you to have less than 2 child per family (1 or 0). The one child policy was effectively implemented in China. It s a controversial policy but the goal of curbing the population was reached so in that sense you could say it s a success. You could also sterelize people based on some criteria. It could be a lottery, based on some skill test (only the smart/strong ones get to reproduce) or any other mean society agrees upon.

2) Make the alternative of being childless very attractive

In developped countries, for certain categories of people, having children can competely ruin your lifestyle (think party animal or carrer focused person). If society is build in a way that makes having children uninteresting, then people will naturally choose not to have children. You can see that happening in Western civilization, especially in big cities.

And of course, the solution everyone wants to avoid: war and genocide. Eventually if Earth's population becomes completely unsustainable and climate change/war/poverty forces millions of people to migrate to other countries, the receiving countries will eventually react violently to protect their own people and it ll end in war/genocide.

Sadly since not many countries are implementing 1) and 2) it think we are heading toward that...


"2) Is this achievable through birth-control, single-child-policies and the like? To achieve this, should we stop attempting to longen the average lifespan even more? Should we make a point to drop it by 10 years?"

Well, I'd say that trying to impose such policies would indeed be a good step towards reducing world population really quickly. Unless one has a totalitarian gov (like People's Republic of China), such policies are straight way to a revolution. Thus within a few years of implementing such policy the population would be reduced because:

-temporary reduction in birth rate

-death of all people who were enforcing the policy

-high losses among people who were overthrowing their gov

-collateral damage (people who just got hit by stray bullets)

-people who got killed by boost of crime caused by temporary collapse of law and order (it's usually a neglected category, while in many revolution that body count is the highest)

The ecological impact is based on exact technologies used in the conflict. Firearms are the most ecological choice. Nuclear warheads leave serious fallout (plus there is controversy about risk of nuclear winter). It is unclear with WMD, because some of them degrade quite easily after a few days of exposure to UV.

Anyway, at least such war would cause ideological backslash, the world would return to long term trends of decreasing fertility rate, which already in big part of developed world put it below replacement level.


If people will not find a good way to solve overpopulation problem, planet will do that for them.

Scientists now say that we need to lower CO2 in the atmosphere to 360ppm. We are over 400. On this trajectory, glaciers will melt, increasing sea level by almost 100 m (300 ft). Which will drown big part of agricultural lands, severely decreasing population which can survive. Deserts in Africa expand. Food productivity of oceans decrease (hotter water holds less oxygen, and more acidic water dissolves shells of smallest sea creatures, which form base of food chain).

If you think that forcing single child policy is hard, just wait until Netherlands will sunk under waves of the rising oceans and hundreds of millions inhabitants of Africa will flee the drought to Europe. What use will have oligarchs running fully automated factories for these hordes of unskilled labor? How high will taxes of working population will have to rise to support hundreds of millions of ecological refugees? Interesting times ahead.

BTW, planet will be just fine. It will take about 20KY to more acid rains to bind the extra atmospheric CO2 back to minerals (I asked a geologist), which will lower greenhouse effect and allow glaciers to start forming, lowering the oceans. But those 20K years might be rough on survivors.


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