I think there are two theories regarding the human population explosion:

1. More the merrier. Some say the probability of geniuses rise with increasing population and that such people will find innovative ways to maintain the balance between humans and the rest of the biosphere.

2. Too many cooks spoil the broth: Some say that the above is NOT a plan. It's predicated on random chance and is not the way we should approach the problem. Also, it could be that no amount of technology can reverse or stop the downward spiral towards global extinction.

Personally, I'm a fence sitter. I don't know which of the two is true. Let's see.

This is a good topic. I wanted to open the same topic here. I think the population will become a major issue when oil finishes.

The people who think it's a problem tend to live in Western countries whose native populations are declining. Population growth is occurring primarily in the third world, especially Africa.

That said, the world's total fertility rate has been declining for some time and will continue to decline, so the world's population is not expected to continue increasing at an exponential rate for very much longer.

That said, the world's total fertility rate has been declining for some time and will continue to decline, so the world's population is not expected to continue increasing at an exponential rate for very much longer. — Thorongil

We're supposed to top out around 10 billion at mid century, so it becomes a question of whether Earth can support 10 billion for the second half of the century.

If we were much more efficient and more focused on sustainable technologies, then I think the answer would be yes. But so far, we've been very wasteful and uneven in resource distribution. Maybe that will change in the future out of necessity.

If everyone wants to live like Americans and Europeans (and given the choice or opportunity they apparently do) then that would put a terrible strain on the Earth's natural resources. Perhaps a mitigating factor is that countries with such high standards of living also tend to have lower fertility and population growth rates. Perhaps with education, opportunity and family planning services it will turn out all right after all. Remains to be seen, in any event not much to do except the above.

[Delete] @Baden

In those groups where growth is the highest, I believe the primary motivation to have children is still economic survival. If no government will take care of them in old age then their children will. That is a difficult mindset to regulate or reverse.

https://www.census.gov/popclock/

Most arguments for or against the problem revolve around physical and material variables. There is not (usually) an acknowledgement of the psychological variables associated with the problem. Here is a good, short link on it: http://bigthink.com/scotty-hendricks/why-overpopulation-is-more-than-just-a-material-problem

We know our numbers are going to increase in the short term. We also know that the bulk of the population is clustering into cities. We can see empirical behavioural differences between rural and urban dwelling populations when it comes to the "tooth and claw" side of nature - one is more likely to die of violence in a city than in a rural setting. That means, unlike ants or bees which are controlled chemically, the more we pack in, the more we are affected by our own psychological underpinnings. All the variables of course are part of the equation like resources and adaptations through social evolution and technological advancement, but all of those are driven by our psychological and behavioural underpinnings. You can't do science that saves the world from overpopulation if most of the governments of the world aren't going to pay for it (or for each other). That part alone, at least to date, seems to be true. Even the Paris agreement on climate - if we look at the "official numbers" for greenhouse gases emitted - any one government's self reported emission numbers may look great. But if we measure emissions independently, we get a different story.

But, going back to the point about psychology and behaviour, if you take a look at the different periods marked in the Calhoun experiments, can we note possible parallels between the mouse populations and the human populations? For example:

Days 315-600: The “Equilibrium” period. It was here that the social roles of mice began to break down. Mice born during this period found they lacked space to mark out territories in, and random acts of violence among the mice began to occur. Many males simply gave up on trying to find females. These males retreated into their bedding and rarely ventured out. Simply eating, sleeping, and grooming.

What would these actions "look like" in human populations? Random violence, complacency, reproductive and mating changes, etc. When "humanized" into a "social issue", how and where do these "signals" show up? Can we see them happening today in areas where humans are similarly packed together (like modern urban centers)? How about this part "... retreated into their bedding and rarely ventured out. Simply eating, sleeping, and grooming." - can we add "shopping" and "surfing the net" as a couple of items?

Days 600-800: The “Die” phase. The population, which maxed-out at 2,200, began to decline. No surviving births took place after day 600, and the colony ultimately died out. Individuals removed from the colony and placed in similar units continued to demonstrate erratic behavior and also failed to reproduce. The mice were remarkably violent at this time, for little reason.

Same set of questions - what do the human versions of these behaviours look like? And, can we see them happening today?

and then, the really ominous part:

He felt it was plain that the problem was having too many individuals for meaningful social roles, saying that after that point: “only violence and disruption of social organization can follow. ... Individuals born under these circumstances will be so out of touch with reality as to be incapable even of alienation. Their most complex behaviors will become fragmented. Acquisition, creation and utilization of ideas appropriate for life in a post-industrial cultural-conceptual-technological society will have been blocked.”

Imagine a world where there are 10+ billion people.
* 75-90% of which live in medium to large, polluted urban conglomerates and centers.
* Technology and automation (and potentially A.I.) remove "work" for the bulk of the population.
* Cooperation on climate change, per the usual Prisoner's Dilemma outcome, is rendered ineffectual.
* Scientific advancement to mitigate negative factros is curtailed by social and economic upheaval.
* Social upheaval and climate change create mass migrations.
* Mass migrations create and exacerbate existing social and economic upheaval.
* Mass population collapse. Even survivors of city and urban areas are so psychologically damaged they don't survive and don't reproduce.

I don't see humans going extinct as a certainty, but unlike the Ice Ages - there probably won't be much of the natural world still present to support the remainder.

The camp that puts all chips on science saving the day for the bulk of the human race I think forget that "science" is really two things - a philosophical methodology (which can offer solutions through observation, experimentation, and cooperation) but also it is a social venture (cooperation in and out of the scientific community). I heard it like this somewhere that makes it short and sweet: "No buck$, no Buck Rogers". If there is no social fabric to uphold the scientific endeavor, then science can't "save the day" and humans find themselves constrained by brute fact and the laws of biology.

I also think that for science to save "us", we have to redefine what the "us" is. For example, we could genetically engineer ourselves to be "super socials" like ants or bees - but take the consequences that our lives are determined by self-engineered chemical controls and lifelong "roles" in a manner foreign to what we humans already have and live under and by subconsciously. Our conceptual view of ourselves will have to radically change...if it even can.

When I think about the likely rather dystopian future coming down the pike, I am glad that I am 71 and not 21 years old. I expect to be dead of natural causes in 10 years, give or take a few.

* 75-90% of which live in medium to large, polluted urban conglomerates and centers.
* Technology and automation (and potentially A.I.) remove "work" for the bulk of the population.
* Cooperation on climate change, per the usual Prisoner's Dilemma outcome, is rendered ineffectual.
* Scientific advancement to mitigate negative factros is curtailed by social and economic upheaval.
* Social upheaval and climate change create mass migrations.
* Mass migrations create and exacerbate existing social and economic upheaval.
* Mass population collapse. Even survivors of city and urban areas are so psychologically damaged they don't survive and don't reproduce. — Uneducated Pleb

We don't know how certainly inevitable all this is. It is conceivable that wise, thoughtful, scientific and socially enlightened solutions could be devised which would render these calamities moot. What is much, much less conceivable is that "wise, thoughtful, scientific and socially enlightened solutions" will ever see the light of day, much less be implemented.

Still, some progress is being made. Population has stabilized (not shrinking, though) in much of the world. Some areas are still growing way too fast. The means of generating fairly clean energy from nuclear, solar, and wind are available. Having people clustered in cities is more efficient than having them spread out across the countryside, ruining essential farm land.

The cities can be cleaned up; they don't have to be smoky, filthy, garbage-strewn shit holes, to use a famous phrase. A major piece of that is not using cars to move people around. Do it with mass transit, foot traffic, and bicycles.

The dystopian stuff is mostly going to be the result of climate change, and we just aren't doing nearly enough for carbon dioxide and methane abatement. We have probably passed the point at which we can do some things easily. For some time, ever solution has been getting more difficult, and they will keep getting more difficult.

Human responses to stresses aren't quite the same as they are for rat populations; we (presumably) have more flexible response capability that rats. But yes, there is no doubt that after a certain amount of environmental degradation and crowding, people's behavior tends to become more disorganized.

not only the oil, also food, water, metals, etc. — René Descartes

Particularly fresh water for drinking and agricultural needs. Peak oil, peak water, peak metal, peal lots-of-stuff probably has already passed.

Mass population collapse. — Uneducated Pleb

As the population grows this century and as temperatures, humidity, disruptive storms, droughts, floods, and other disasters become more intolerable, we will reach a crunch where a lot of people are going to die off.

Predictions are that the lands adjacent to the equator will become too hot to maintain normal habitation. It will be too hot to work outside in the daytime, and perhaps too hot to work for long periods at night. Much of Africa, South America, and S and SE Asia would be most adversely affected. Areas as far north as the Southern US would be affected.

Unpleasant Questions: Is a massive die-off among the poorer populations (who simply can not keep body and soul together under the stresses of population and climate change) part of the solution? Should we let this happen or not? Is there anything we might do to stop it, once it began? What if there are, simply, too many people?

[Delete] @Baden

[Delete] @Baden

[Delete] @Baden

In Global Problems and the Culture of Capitalism Richard H. Robbins shows that it is governments in the West who have been the alarmists about human population growth and overpopulation. It is not the potential ecological consequences that motivate such alarmists. What motivates them is that they are scared to death of the national security implications of extremely large populations in the non-West.

In those groups where growth is the highest, I believe the primary motivation to have children is still economic survival. — Monitor

Not necessarily.

According to Wealth Flows Theory, in traditional societies wealth flows from children to parents, therefore it is in people's best interest to have large families. Probably everybody reading this knows that in industrialized societies the opposite is true: wealth flows from parents to children (saving for one's children's college education, for example). Therefore, in industrialized societies it is in people's best interest to have small families.

In Global Problems and the Culture of Capitalism Richard H. Robbins gives at least one example of Wealth Flows Theory inspiring and informing a program that successfully led to people having smaller families, if I recall correctly.

I should add that the incentives in traditional cultures to have large families also explain why giving those people modern birth control technology does not lead to smaller families.

Perhaps a mitigating factor is that countries with such high standards of living also tend to have lower fertility and population growth rates... — prothero

But that high standard of living depends on a large supply of cheap manual labor in the Global South. If everybody in the Global South is suddenly in an air-conditioned building with amenities like a cafeteria and an exercise room and in a cubicle doing paperwork, who will there be to assemble the iPhones and Nikes for pocket change and with barely a bathroom break?

If automation replaces those humans as the source of cheap labor, why should we believe that those people will suddenly live like the American middle class? Many of them are young people who were taken away from their families and moved to cities. How do we know they won't go back to the villages they came from and return to peasant life and culture?

Perhaps with education, opportunity and family planning services it will turn out all right after all. Remains to be seen, in any event not much to do except the above. — prothero

Or perhaps overconsumption in the Global North continues, increases, and/or is increasingly exported to places like China and India, and no change in global fertility can make up for that.

That is what almost always seems to be ignored in the narrative about the problem of population growth: overconsumption.

[Delete] @Baden

One interesting angle to this problem is one that considers it'll self-solve (if that's a word). We don't need to care about it at all. Just like bacteria in a petri dish nature will find the balance automatically. We just have to go on doing our thing - living our lives the way we do.

[Delete] @Baden

We don't know how certainly inevitable all this is. It is conceivable that wise, thoughtful, scientific and socially enlightened solutions could be devised which would render these calamities moot. — Bitter Crank

I was not trying to present it as inevitable, just from a synthesis of my own study on the issue - this is what is most probable (in my opinion). The more up in the air question for me is the timeline. Climate change is the big variable.
As far as scientific solutions - I hold to my original premise that "science" is a business and social enterprise that is mainly funded for military purposes or for market goods by specific corporations. The other issues with the "science solution" include the fact that a solution to each of the problems mentioned would each take a multinational approach, perhaps on the order of CERN or more in levels of cooperation, which, as part of the social deterioration forecast for the future conditions, cooperation is a victim.
As far as "socially enlightened" solutions - I won't hold my breath. Have we ever seen, in the sum of human history, an "enlightened solution" which originated from one country (or a group) and then was implemented on the scale needed to stem something like climate change? Will the middle class of the United States fund the application of a climate solution for Africa? I doubt it. We are within the game theory, multiplayer version of the Prisoner's Dilemma (in this multiplayer version - the Tragedy of the Commons). It is simply too easy for one group to defect, which then leads to the domino effect.
If you take a look at the polling done in all countries of the world on the issue of climate change - you will see low to middling levels of "awareness" of the problem, an average of half of the people who are aware thinking that humans have even caused it, and less than half that think it is a threat (especially within the so called 2nd and 3rd world countries whose populations are rising and who want a piece of the 1st worlds pie).

The means of generating fairly clean energy from nuclear, solar, and wind are available. — Bitter Crank

Yes they are, but are they "market" worthy? Also, the net energy use to mine, manufacture, and implement these solutions, plus the fact that the energy needs of the world is going to go through the roof (even by todays standards), these technologies will be hardpressed to meet those needs.

The cities can be cleaned up; they don't have to be smoky, filthy, garbage-strewn shit holes...A major piece of that is not using cars to move people around. Do it with mass transit, foot traffic, and bicycles. — Bitter Crank

Getting the political will, the funding, and then the incentives to remove the population from their cars and make them share buses and trains more so than already done - that would be a neat trick. What would you propose? What would you do for people that refuse to do so because simply because it is their right to drive their car where they want and how much they want? If that gets done, say in the US, would the same pressures work for China? For India? For Iran? Too many players, too many chances to defect from the game.

Human responses to stresses aren't quite the same as they are for rat populations; we (presumably) have more flexible response capability that rats. — Bitter Crank

That is true - they are not the same. But, as you noted, we do have limits. We are constrained by Nature and her biology. The question is - what are the responses? And, are we already seeing them? From work done by Stanley Milgrim, by Philip Zimbardo, and others we are shown that we can easily culturize and adopt the worst tendencies simply from social roles in a conducive environment for "evil", but in the end, they are evolutionary adaptations (that are not so savory or noble) that, given the right conditions, become part of culture. Between the work of psychologists and game theory, at least in my reading of them, the problem of climate change is going to be a reality with the same effect on people and populations as the Ice Ages but done in a shorter timeframe than the onset of an Ice Age. It will be an evolutionary bottleneck for our species...but as the optimist I am, I think we will survive it as a species. I liken it to the Ice Age meets the Dark Ages with the addition of, at the beginning, the Rwandan Genocide.

Unpleasant Questions: Is a massive die-off among the poorer populations (who simply can not keep body and soul together under the stresses of population and climate change) part of the solution? — Bitter Crank

I read somewhere that when the social class of elites gets a sniffle and cough, the poor die of pneumonia. When you say "solution" it sounds as though it is a planned, meditated response. From what we have observed in nature - those individuals and groups that have "lesser status", or less access to land and resources, are the most likely to die off first when there are stressors in and of the environment. So, I don't think it is part of "The Solution", but I do think it is going to be a fact regardless of any solution put into place or not.
I also believe there to be a few paradoxical points on this topic within the issue. If and when the climate creates problems to the point of food, water, and power generation of more "civilized" countries - who will be able to navigate survival better? A middle class family with the minivan and office jobs? Or a migrant family used to hardship and living off the land? I think in the beginning we will see the poor dying off from being crowded into pockets by the more elite countries, but that will change when the elite countries get hit themselves with things like famine, water shortages, and energy discruptions. Then, it will be the civilized countries that turn into bloodbaths and cemetaries, ripe for the poorer to move in and take over. I think of it this way - if we all lost power today the Inuit and the Aborigines would not be so worse off than they are now. But if we lost power today, New York and Los Angeles would see millions die. Perhaps there is a biological lesson in the quote - the meek shall inherit the Earth.

Should we let this happen or not? — Bitter Crank

I am not sure it is a question of "letting it happen" or not. Look at past history and all that is happening now as far as displaced populations - the Rohingya, the Syrians, the Mediterranean migrant ships. All of these people leaving lands that will be most affected by climate change in the future - what are the results of the mass flow of people now? Political (and military) upheaval in the countries these populations are escaping to. Now multiply that problem to the entire or bulk of the populations of those countries and I think we get an idea of, based off today's responses, what we can expect in the future but with an exponentially more drastic response.

Is there anything we might do to stop it, once it began? What if there are, simply, too many people? — Bitter Crank

In order to stop it, once it began, we would have to know "when it began" and "what it looks like" first, would you agree? What line would be drawn, when is the category created, of "climate induced die off" or even "climate induced famine/migration"? One of the thoughts behind the Syrian civil war was the fact that the country experienced a climate change exacerbation of a natural drought cycle, which then sent all the farmers (young men) into the cities looking for work. Upon not finding that work, unrest followed and was then met with severe reprisals from the government. Then, floods of refugees of the war - but couldn't you also say that all the Syrian refugees are really "climate refugees"? The war was the reason they left, but the mechanism behind the war would be labeled as climate change. How do we tell the difference between war induced migration and climate induced migration?
That question is one I have been focusing on recently...human awareness of and internalization of external factors affecting and generating behaviour and what those behaviours are labeled as in "expression".

but unlike Bacteria, humans keep finding new ways to allow for further population growth and to exploit nature. Humans adapt the environment for themselves. I'm slightly skeptical about the comparison. — René Descartes

What is the difference between bacteria and humans when it comes to "finding new ways" to increase populations? There is a loooong bacterial history, both in depth and scope of "changing environments" in order to adapt. In these regards, bacteria are actually better than humans and have a longer evolutionary history that places the high score firmly in their column. I think you give bacteria too little credit, they are (so far) the clear winners of evolution (adaptation to conditions, exploitation of resources, and adaptation of the environment itself). Hell, without bacteria, humans would not be able to do anything we currently do, including digesting a meal.

That is what almost always seems to be ignored in the narrative about the problem of population growth: overconsumption. — WISDOMfromPO-MO

I think because, in part, the definition is slippery and differs between groups. Even the vegan, bicycle riding minimalist in the West will have different ideas of what "overconsumption" is than someone like a San hunter.

Also, "overconsuming" tends to be associated with that which affects the economies of the group defining it. Ask the normal person on the street what we are "overconsuming" in the West and the answer tends to stick to things like oil or plastic or even large amounts of smaller junk-cluttering their apartment or houses. What is not in awareness are arable land, water, construction materials for suburban and city housing, and all the electricity from non-renewables needed to run it all, metals for the iPhones, etc. The environmental familiarity and awareness of an indigenous aboriginal used to living within their climate is simply greater than the typical Westernized climate-concerned citizen, but that awareness comes at the cost of hardships which cost them their lives and the lives of their children.

I get a perverse pleasure in asking the hardest flag waving environmentalist what phase of the moon we are in, when was the last time they actually saw the moon, what constellations are in the sky, what birds are appearing in the trees around them, which plant on the ground in front of us is native and which is invasive, and other details that an indigenous would have at the forefront of their consciousness. Many in the West are so concerned with the "knowledge" about the "environment" they are fed from the "top down"- yet have zero clue about their own immediate ecosystem. It is a gross mismatch of awareness. Without knowledge of the local ecosystem and what current changes are happening and what they might mean, it is hard to imagine people actually know what "climate change" actually looks like until it is upon them.

Indigenous people tend to look upon the materialism of the West (in my reading and very small experience) and generally tend to admire it. They see lives made easy from all the "stuff". Given the chance, they too will "overconsume" as it is part of our evolved nature to exploit and compete for resources. Would the most ardent and concerned climate change activist ever intentionally adopt a lifestyle with the footprint of a San member? I tend to doubt they would, but maybe I'm wrong.