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Comment by holoduke | Hacker News Reader

People who claim the world is overpopulated probably live in a big city and never really travelled the world. Because there are vast remote places thousands of miles across without anyone living. I believe the world can easily hold 100 billion people without issues. And besides, downscaling the world is not an option. Every organic structure needs to expand indefinitely. The only reason you would have decrease in population is world scale war. Sure we don't need that.

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Not really, not all land can be used to host people. We need space to grow food, produce energy, have factories and offices, infrastructures... We're already using more than what the entire emerged land can provide us each year (with the help of massive supplies of fossil fuel and derived products, which will eventually run out).

If we want to offer everyone a western lifestyle while being sustainable on the long run, the optimal world population is indeed estimated at around 1.5-2 billions (world population of 1950), and definitely under 3 billions.

https://www.theguardian.com/environment/2012/apr/26/world-po...

Or just Google "Optimal world population".

Currently 60% of landmass is being used by humans directly (human habitat, pastures, crops). Of remaining 40% about a half is still being continuously influenced by humans (residential forests, patches of land between roads, etc.). And the land is being used unsustainably and almost all unused land is beyond the polar circle. So no, the Earth can not hold 100B people with current level of consumption.

And generally you don't want current consumption level, you want much higher standards, because majority of world's population is living in poverty. Which means that Earth can't hold 8B people either unless humans improve their land use efficiency significantly, which is unlikely.

[1] https://www.mdpi.com/2073-445X/9/5/129

You know, it's possible to convert ground dedicated to cattle or agriculture and develop that into cities. That's historically how we always do it. It's not like housing developments can only happen on land that no one owns and that isn't being used for anything at all.

What we do is change what the land is used for. So I don't think this argument holds any water, TBH.

By the time the frontier was closed -- say late 1800s, pretty much all US land was owned by someone and ostensibly dedicated to some use. Yet we managed to increase our population quite a bit since then.

All European land was spoken for by the early middle ages. Yet they managed to grow their population too.

Sorry if it wasn't clear, but the problem of land use is not legal. Indeed you can build your city whenever you have enough will to and it has never been a problem. The problem is that humans destroy the ecosystem of the place they live in. And if humans use 100% of landmass then 100% of planet ecosystems are destroyed.

> it's possible to convert ground dedicated to cattle or agriculture and develop that into cities

Unless you find a way to generate food out of thin air, it's not possible. People living in the cities need to eat something.

For most of the Western United States --- points west of the 100th latitude --- the limiting factor is not land but water.

The city of Los Angeles has a watershed which extends 1,500 miles eastward, to the western extent of the Rocky Mountains. The reason much of the Western US appears more as an island archipellago than a continuously inhabited terrain is because there simply isn't enough water to fill taps, flush toilets, and run showers, let alone grow food or provide range for livestock on an unirrigated "dry-land" basis. Even attempting that proved a major environmenal disaster, the Dust Bowl of the 1920s and 1930s.

No way 60% is used by people. Can you provide some sources on this.

the link is right in the comment

In many cases the very reason why some places aren't populated is that living there is difficult (lack of water/arable land, weather conditions...), and in many cases they are useful (as forests, grasslands...) for living beings thriving elsewhere.

Joel E. Cohen is the Earth's leading authority on the question, and lives and works in New York City, which I strongly hope is not too rural for your taste. He's the first to say that the question and answer are complicated, but that does not mean that there are no limits.

For a brief introduction to his research, see "How Many People Can the Earth Support?" https://www.nybooks.com/articles/1998/10/08/how-many-people-...

Paywall: https://archive.is/E5AB8

He makes a much more complete exploration in his 1995 book, How many people can the earth support?, Cohen visits many estimates and/or claims regarding carrying capacity and explores the assumptions or logic behind many of these, which range from a low of about 100 million to highs over 12 trillion. Most such estimates cluster around 1--10 billion, and seem more credible than outliers, especially of the high-end group.

https://www.worldcat.org/title/how-many-people-can-the-earth...

https://archive.org/details/howmanypeoplecan00cohe

There are also a few articles discussing the question, though not with the detail of the book. Most are either paywalled or in PDF formats (which seems to strongly discourage online readers). Their quality and expertise strongly reward expended effort, do please read these if you're genuinely interested in the question.

https://lab.rockefeller.edu/cohenje/assets/file/257bCohenHow...

http://www.oneonta.edu/faculty/allenth/Class-Readings-Passwo...

A review of Cohen's book, "On Human Carrying Capacity: A Review Essay on Joel Cohen's: How Many People Can the Earth Support?"

https://www.jstor.org/stable/2137692 (http://libgen.rs/scimag/10.2307%2F2137692)

And a hearty recommendation from science fiction author Kim Stanley Robinson:

https://www.theguardian.com/books/2020/oct/12/there-is-no-pl...

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