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Comment by jniedrauer | Hacker News Reader

> it should be noted that the Earth has been here before and come back from it

There weren't 7 billion humans back then. My big concern is that we're well above the pre-green-revolution carrying capacity of Earth and it wouldn't take all that much to put us in a position where we can't feed 3 billion people. It's possible that a greenhouse earth will give us more arable land to work with, and we'll be just fine. It's likely that things will become ugly during the transition, as formerly arable land becomes desert, the oceans stop providing food, and mass migration causes global unrest. A lot of people are going to starve.

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For those that want to dive deeper it looks like this meta-analysis might be a good starting point for the human carrying capacity of the earth.

https://academic.oup.com/bioscience/article/54/3/195/223056

> When taking all studies into account, the best point estimate is 7.7 billion people; the lower and upper bounds, given current technology, are 0.65 billion and 98 billion people, respectively.

> the lower and upper bounds, given current technology, are 0.65 billion and 98 billion people, respectively.

The answer is "anywhere from a tenth of the people currently alive to 13.5 times as many as are currently alive." Absolutely useless. A range covering more than two orders of magnitude. May as well say, "We don't know."

> Absolutely useless

Not at all. To say "we don't know" might mean that we don't know the order of magnitude. Order of magnitude estimates to the first or second decimal place are oftentimes more than enough to hone in on a solution. In this case the two orders of magnitude set a clear bound (assuming the capacity estimate are accurate) for the near future at the high end and provide a warning sign for the present.

This is a meta-analysis. They reference many different papers. Many of them come to different conclusions. If you want more certainty you can get it by starting to read the papers the reference and deciding which ones you think are reasonable.

Seems like this calculation completely disregards the emotional effects of that many people in such close proximity.

Well if we have 98 billion people on earth - lets see how dense we get. This [site](http://www.zo.utexas.edu/courses/thoc/land.html) argues there's about 24,642,757 square miles of habitable land on Earth - this is discounting deserts and mountains, and of course oceans.

That puts about 6 people per acre in all the habitable spots on the globe.

To put that into perspective, Manhattan has about [27,000](https://www1.nyc.gov/site/planning/data-maps/nyc-population/...) residents per square mile - or 42 people per acre. There are other, denser cities out there as well. People-dense parts like this make other parts more people-sparse.

I'm sure by the time (if) we have 98B people - Manhattan will be much more people-dense, and many more cities will be similarly dense. So it may be that 50B people live in massive, dense cities, leaving the other 50B to be in more suburban-yet-still-dense zones.

However, this is the 'idea' case of all habitable land being used for habitation. There is also the need for farms and industrial land, and all manner of other places for human activity, and the vast things needed to support it. Ideas like vertical farming solve for some of these, but are not perfect.

98B might be possible if we did everything perfectly efficiently and optimized every single part of the planet leaving absolutely nothing allocated for the bare essentials to keep people living. The reality is we would never get anywhere close to that level of efficiency and would destroy the planet much sooner.

At Dutch population density (1,312 people per square mile[1]) that would be 32 trillion people so even 100 billion people should leave plenty of space.

[1]http://www.worldometers.info/world-population/netherlands-po...

Would AR/VR help with this at all? I was thinking that with the earlier article about Japan's micro apartments, if having the walls covered with 3D screens (or even mirrors) would give a bigger sense of space and help with mental well being.

I can say from experience that VR absolutely helps dispel cabin fever. I once lived in a fairly small apartment in a dense city. Turning on a big box fan in my VR area and then going out to wide open spaces like the mountains in Skyrim VR made me feel better almost instantly.

Seems likely, if you decided to dive into the various papers they are pulling from I'd be really interested to hear about which ones consider sociological problems like emotional effects of over crowding!

And heading to 10 billion. On the back of unsustainable use of soil, water, fish, natural resources in general, antibiotics, antifungals, etc. That worries me too.

It's pretty easy to turn energy into food, in large quantities in small areas, even in incredibly hostile environments. (AKA greenhouses). We don't do so only because food and arable land is so incredibly cheap that it's not worth it.

Farming is only 0.07% of the US economy. A small increase in food prices would vastly increase supply. Africa would probably be screwed, but that would have nothing to do with our ability to feed them and be solely due to economics not making it profitable.

Is farming 0.07% of the US economy or of the US workforce? Those are totally different things. Its certainly not 0.07% of US arable land

There were bread and rice riots around the globe just 10 years ago.

https://en.wikipedia.org/wiki/2007%E2%80%9308_world_food_pri...

> Is farming 0.07% of the US economy or of the US workforce?

0.07% of GDP. It's a higher percentage of workforce, but still under 1% directly employed. Land area is irrelevant to my argument -- greenhouses can feed a lot of people in a small area.

> There were bread and rice riots around the globe just 10 years ago.

All that says is that Capitalism does a really bad job of supplying stuff to people without any money.

Well, the Earth doesn't care about humans, per se.

So the Earth will still come back from it. And even the human species will likely come back from it. But technological society? That's a lot more iffy.

But a lot of people starving will probably help the coral reefs recover since there will be fewer people using energy and polluting.

I don't think many people are seriously thinking that starving is the next problem. These days it seems like war comes before people start starving to death.

https://www.nytimes.com/2015/03/03/science/earth/study-links...

No-one studying coral reefs now thinks they have much chance of surviving beyond mid-century given already baked-in ocean heating.

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