Thomas Palm wrote:

Multiply the population density of Biosphere II, which could probably
work at that population density, with the area of the earth, and you
get 200 billion.


Biosphere II was never self-sufficient but relied heavily on energy import,
and against the rules had to replace the atmosphere when CO2 levels got too
high.

There's nothing wrong with energy import. The earth wouldn't survive
for long without energy import.