Why does the answer have to forgo everything that facilitates optimal modern high-tech food production?
Gladwell's "Outliers" spent a lot of time on farming technologies thru the ages (and subsequent impact on cultural success). Japanese rice farming amounts to a sustainable long-term high-tech process making heavy use of artificial irrigation and any other suitable tech, maximizing production with limited space and growing seasons.
For starters, one could compute an outer limit of calories per square meter and match that to basic caloric needs per person: given an average solar energy concentration there is no way (unless you want to turn geothermal & fossil fuel) to produce more food (whatever manifestation) in caloric terms than sunlight provides. From there the answer requires providing assorted limiters, reducing the potential caloric output to more realistic levels based on viable technologies.
Computing from a different angle:
149M sq km total land, 15M sq km farmland, 7000M people
Dividing current farmland by population and rounding the result up a bit, each person gets a plot 47x47m for 603 sq ft for living and the rest for farmland. Assuming half the land is rank (unusable) wilderness, that roughs out to an optimistic carrying capacity of 33000M people.
Gladwell's "Outliers" spent a lot of time on farming technologies thru the ages (and subsequent impact on cultural success). Japanese rice farming amounts to a sustainable long-term high-tech process making heavy use of artificial irrigation and any other suitable tech, maximizing production with limited space and growing seasons.
For starters, one could compute an outer limit of calories per square meter and match that to basic caloric needs per person: given an average solar energy concentration there is no way (unless you want to turn geothermal & fossil fuel) to produce more food (whatever manifestation) in caloric terms than sunlight provides. From there the answer requires providing assorted limiters, reducing the potential caloric output to more realistic levels based on viable technologies.
Computing from a different angle:
149M sq km total land, 15M sq km farmland, 7000M people
Dividing current farmland by population and rounding the result up a bit, each person gets a plot 47x47m for 603 sq ft for living and the rest for farmland. Assuming half the land is rank (unusable) wilderness, that roughs out to an optimistic carrying capacity of 33000M people.