There is no scientific basis for the claim that the earth could sustain 100+ billion people. These types of unsubstantiated claims are not just false but dangerous, as they suggest there is no need for significant action and change.
IMO, the claims that population is the problem is far more dangerous. Population growth is mostly a solved problem. All population growth models have the growth being much slower over the next 50 years than it was over the past 50. Most viable models actually show the growth reversing, and some even show it peaking near current levels.
Does that mean we've fixed the problems? Far from it.
The number of people is only a really small factor in the damage that people do. One jet-setting westerner does many orders of magnitude more damage than the typical subsistence farmer; and the damage done by subsistence farmers varies quite widely. (Some are causing desertification and chopping down trees)
And of course there are some people doing more good than harm, reducing the population reduces those people too.
No matter what the population is, we have a lot of work to do. Greenhouse gases are the most visible problem; there are lots of others.
I didn’t make the claim that population is the biggest problem. I responded to the incorrect suggestion that population size is not a problem (which you repeat without offering any evidence that we could sustain ourselves). Growth is by no means a “solved” problem. Growth is expected to slow, but even at our current population size we are consuming an unsustainable amount of resources. And growth will slow as a result of increased wealth > higher consumption. Given that we live within the finite ecosystem of of our planet, this means we need to make significant changes and we need to make them now.
I think that's making the assumption that having 100 billion livestock + the current human population is sustainable. Even if that were the case, humans consume a lot more resources than animals living on factory farms.
I think the point was that if humans were vegetarians we wouldn't need 100B livestock. And since a cow needs quite a lot more food than humans do, if we could transition 1:1 to a human-edible crop then we have plenty of food to support humans.
Whether or not the earth can sustain 100 billion humans was the scope of the statement, so I don't think resources other than food is a separate issue.
I agree with the assertion that humanity is more sustainable (all other things being equal) vegan or vegetarian rather than omnivorous, but it's going to far to suggest we could just swap in humans for livestock.
Where is the logic in your statement? That makes absolutely no sense. You honestly think the world can support the same number of humans as it can chickens? And even if it did, do you want to live the way those chickens live?
TLDR : 100+ billions is a hard reach today, but 50+ billions might not impossible
There is approximately 63,824,448 km² or liveable land on earth today.[1]
Let's cut that in half to account for farms/land lost due to global warming/industries/etc... We get 31,912,224km² of land usable for habitation.
Let's assume we cover the remaining with a huge city with the density of Hong Kong (6,690 people/km²). This is for the whole city, not the most populated quarters.
We arrive at a population of 213,492,778,560 people, so twice as much as the parent's estimate, with half of the remaining liveable land usable for farms/industries/wildlife parcs/inefficiencies of repartition...
Would that be enough ? According to a Sweden study [2], we use 1.6 billion hectares (16,000,000 km²) of farmland today, for approximately 7 billions people. It means that for 200 billions, we need 486,857,142 km². That's a huge increase, and currently the Earth can only sustain 44,000,000km² (same source as earlier, FAO), so an order of magnitude lower.
According to a study on the effect of diets on land [3], switching to a vegetarian/vegan (not much change in the result) diet allows to cut the land use by ~4.
So we're left with 121,714,285 km² of required land : a bit better, but we still fall way short. That's going to be our actual bottleneck.
Let's cut population by 3, and we arrive at ~40,000,000 km² of required land for 66 billions people.
It would be a pretty grim dystopia, that's for sure.
Most of nature would be erased, there would be a lot of natural catastrophes, and clearly the Earth would be way less welcoming than it is now.
But 66 billions people on Earth, given 'sufficient' technological (and most notably political) advancements is not completely out of whack, especially if we manage to produce clean energy (or at least clean on Earth) and to radically improve our crops (with genetic engineering, hydroponic culture, exploitation of oceans maybe ?)
Bottom line : this is napkin calculation, a lot of factors have been left out (water to give a main one)
Since you nerded out on this enough to do the math, you might actually be interested in this video. The only real bottlenecks to getting to these numbers are first, power and second the elevator conundrum. Solve for those and you can have quite a substantial population. Go big enough and the only bottleneck, if you want to stay a single planet species, becomes black body radiation. Check it out
Interesting, I've never heard about this before! But isn't it basically just the question of private vs public transport (cars vs underground), but in vertical dimension?
Not only is it not a good argument. It is a dangerous argument. We need innovation and maybe it will come in the form of “whacky” ideas, but please don’t replace the work that climate scientists have been doing for decades with a few “back of the napkin” calculations.
At those levels of scarcity, the economics of farming will likely change enough that hydroponics could (would?) become far more commonplace. That drastically cuts down on the amount of land needed, as you're no longer limited to ground surface area for growing crops.
In fact, there's a growing trend of combining fish farming with hydroponic vegetable farming; circulating water between the plants and fish tanks, monitoring nutrient and bacteria levels, can allow for a non-vegetarian diet.
Granted, they're not going to be the tastiest fish- think tilapia, not salmon. There's a CSA farm doing exactly that in a relatively densely populated suburb not too far from me.
I'm not normally a picky eater, but seafood in general is one thing I have a really hard time bringing myself to enjoy. Also, from my very limited understanding, tilapia is fairly delicate to begin with, so it's more about making sure your cut doesn't include much of the grey fat.
With all of that said, I'm sure that for people who do enjoy seafood, it'd be quite tasty. The business near me was put together with eco-conscious people in mind, so the care they put into farming- nutrients, food for the fish, etc. I'm sure the difference between their fish and wild fish is a good deal smaller than stereotypical farm-vs-wild-caught salmon or what have you.
