How much agricultural land and how many workers laboring in agriculture does it take to support large modern cities?
How much agricultural land and how many workers laboring in agriculture does it take to support large modern cities?
Just curious, figure someone on here will know
Edit: Thank you all for the great answers.
The minimum amount of agricultural land necessary for sustainable food security, with a diversified diet similar to those of North America and Western Europe (hence including meat), is 0.5 of a hectare per person. This does not allow for any land degradation such as soil erosion, and it assumes adequate water supplies. Very few populous countries have more than an average of 0.25 of a hectare. It is realistic to suppose that the absolute minimum of arable land to support one person is a mere 0.07 of a hectare–and this assumes a largely vegetarian diet, no land degradation or water shortages, virtually no post-harvest waste, and farmers who know precisely when and how to plant, fertilize, irrigate, etc. From the FAO (the Food and Agriculture Organization of the United Nations (1993)
.5 hectare ~ 1.24 acres
This does not allow for any land degradation such as soil erosion, and it assumes adequate water supplies
That's really the problem imo, not space. Geometry is easy. It's all the limited reagents in the formula for feeding millions that's the problem.
Some back-of-the-envelope math:
There's 900 million acres of farmland in the US, producing plant-based food, but also raising livestock for meat (which makes up a majority of the farmland). The US exports about 20% of their food production, and imports a similar amount, so we'll just call it even (it's literally an apples to orange comparison anyhow, since the imports are things like fruit and liquor, while exports are mainly grain and meat). With a population 330 million, that means that the average American is eating food grown and raised on ~2.5 acres of land.
In other units: in the current American system of food production, you can feed 250 people on 1km^2 of land. Let's use Chicago as our example city, with a population of ~10 million people. They are eating food that is grown and raised on 25 million acres of land, or 100,000 km^2. That's about 2/3rds of the land in the state it resides in, Illinois. Illinois itself is only ~12 million people, so you could basically think of Illinois "carrying capacity" as being 15 million people.
This analysis is very different if you use other countries as a basis. China and India have a lot less overall useful farmland, and it's been farmed much longer, with more labor, and with less mechanization. It ends up being more productive in terms of calories per acre, but with less worker productivity.
It is also worth noting that of that 900 million acres, only a portion of it goes towards food for humans or livestock. Most of the corn and soybeans grown are used industrially for ethanol, lubricants, acids, starches, and rubber. We also grow things like tobacco, medicines, and cotton, which may be needed, but are not food. A significant portion of corn is also traded as a currency "commodity crop" in a market I don't understand at all.
If I recall correctly, roughly 40% of farmland is dedicated to food production for livestock, and 2% is dedicated to food for direct human consumption. So assuming you already have all necessities, and only need food without any change to an average american diet, we may need as little as 1.05 acres per person, following your math.
idk. Back in the day it was like .6 acres per person or something but I have no idea what crops that involved, what quality of land.
It's very complicated bc you have to take in to account soil quality, what kind of inputs like fertilizer and nutrients you've got, what crops you're growing.
I can say it's not as much as it was before the mid 20th century ag revolution, now that we can make nitrogen fertilizers and engineer high-yield crops and have a better understanding of genetics and disease and also harvester combines. harvest combines are really cool. Scythes are cool too but not compared to combines.
In modern time, we trade some space efficiency for automation efficiency, especially in the United States. Midwest USA agricultural production as an example, can feed ~1 acre per person, meat production included, and requires moderate energy input, and very little labor. But it's very possible to shrink that to ~0.1 acre per person, if you're willing to put more labor and capital investment into it, as well as changing people's diets. It just kind of depends on what you out of food production.
death rides a pale harvester combine
There are a lot of variables, but I'll focus on something others haven't yet. Compare urbanization with employment in agriculture. The developed capitalist countries have a single digit percent of their workers employed in agriculture. The developing countries are more variable but for the most part as the productive forces develop, less people are employed in agriculture. China now is down to like 17% for instance.
Havana is a relevant case study for your question. 35,000 hectares of organic urban farms produce 90% of the city's produce which is enough for 280 grams per day for each resident. Well, the data is over a decade old but it's probably not that different now. About 19% of the Cuban population works in agriculture but I don't know the stats for Havana specifically. And of course the organoponics are only supplementary to staple crops from outside the city.
So yeah, definitely depends on technological development. There's also a dialectical aspect to it... the negation of the negation I think? Someone better trained in Marxism correct me if I am wrong. But mechanization and fertilizers negated the persistent rural and famine-ridden state of humanity while also sowing the seeds for its own negation. The agricultural techniques developed under capitalism erode the topsoil, cause eutrophication in the waters, and drive climate change. This makes necessary a socialist agricultural revolution, not a return to subsistence agriculture. While the technologies are in their infancy, this form of agriculture would be way more labor efficient. The future is a couple percent of the population employed in renewable and nuclear powered agricultural bioreactor factories and highly automated farms, not a fifth of the population doing large-scale organic farming.
i don't know, but I'll comment so that the sorting algorithm sees this as more active.
if i, dumb idiot with no prior knowledge had to guess;
Several orders of magnitude fewer people (scaling slightly depending on the tools and machinery available).
Much more land than the city proper actually takes up - an order of magnitude difference at least, but possibly probably more
and since it reminded me, here's an excerpt from Terry Pratchett's Night Watch
Vimes climbed back up the barricade. The city beyond was dark again, with only the occasional removed of light from a shuttered window. By comparison the streets of the Republic were ablaze. In a few hours the shops out there were expecting deliveries, and they weren't going to arrive. The government couldn't sit this one out. A city like Ankh-Morpork was only two meals away from chaos at the best of times. Every day, maybe a hundred cows died for Ankh-Morpork. So did a flock of sheep and a herd of pigs and the gods alone knew how many ducks, chickens and geese. Flour? He'd heard it was eighty tons, and about the same amount of potatoes and maybe twenty tons of herring. He didn't particularly want to know this kind of thing, but once you started having to sort out the everlasting traffic problem these were facts that got handed to you. Every day, forty thousand eggs were laid for the city. Every day, hundreds, thousands of carts and boats and barges converged on the city with fish and honey and oysters and olives and eels and lobsters. And then think of the horses dragging this stuff, and the windmills . . . and the wool coming in, too, every day, the cloth, the tobacco, the spices, the ore, the timber, the cheese, the coal, the fat, the tallow, the hay EVERY DAMN DAY. . . And that was now. Back home, the city was twice as big . . . Against the dark screen of night, Vimes had a vision of Ankh-Morpork. It wasn't a city, it was a process, a weight on the world that distorted the land for hundreds of miles around. People who'd never see it in their whole life nevertheless spent their life working for it. Thousands and thousands of green acres were part of it, forests were part of it. It drew in and consumed . . .
. . . and gave back the dung from its pens and the soot from its chimneys, and steel, and saucepans, and all the tools by which its food was made. And also clothes, and fashions and ideas and interesting vices, songs and knowledge and something which, if looked at in the right light, was called civilization. That's what civilization meant. It meant the city. Was anyone else out there thinking about this? A lot of the stuff came in through the Onion Gate and the Shambling Gate, both now Republican and solidly locked. There'd be a military picket on them, surely. Right now, there were carts on the way that'd find those gates closed to them. Yet no matter what the politics, eggs hatch and milk sours and herds of driven animals need penning and watering and where was that going to happen? Would the military sort it out? Well, would they? While the carts rumbled up, and then were hemmed in by the carts behind, and the pigs escaped and the cattle herds wandered off? Was anyone important thinking about this? Suddenly the machine was wobbling, but Winder and his cronies didn't think about the machine, they thought about money. Meat and drink came from servants. They happened. Vetinari, Vimes realized, thought about this sort of thing all the time. The Ankh-Morpork back home was twice as big and four times as vulnerable. He wouldn't have let something like this happen. Little wheels must spin so that the machine can turn, he'd say.