Worrying about ecological self-sufficiency and sustainability at a smaller than planetwide scale is essentially throwing away the entire advantage of how much our massive global logistics network has shrunk the world in recent decades.
Relying on the massive global logistics network to support massively nonequilibrium populations in highly infertile land is counting on a patently unsustainable level of resource use to create a massive risk.
It's one thing to have local shortfalls of food or water of a few percent which can be satisfied with largely local imports of a few hundred kilometers (say, Germany, which is roughly 90% self-sufficient for food production). It's quite another to require massive imports of food and fresh water.
Economic efficiency is directly opposed to sustainability and risk.
> [...] is counting on a patently unsustainable level of resource use to create a massive risk.
Can you please elaborate? We sit on a giant ball of matter, and there's enough energy coming in from the sun (or via nuclear power) to last us a few billion years.
(And for anyone stumbling on this comment in the future -- I'm planning on substantially reorganizing that Wiki page though it should link to the appropriate sections).
The major issue with tapping solar power for high-grade electrical energy is whether or not it's possible to do so in a manner that sustains the ability to create that solar energy infrastructure and support technological life. EROEI, capital and maintenance requirements, and other resource limits all come into play.
The last time humans had a sustainable-energy based economy was 1700. The state of technology was markedly lower. If we return to that energy state, we should continue to have the benefit of scientific understanding gained since then (engineering, germ theory, metalurgy, sanitation, evolution, steam power, thermodynamics, electricity, chemistry, relativity, quantum mechanics, atomic physics, astronomy, electronics, pharmacology, aviation, rocketry), though how much of it we'll have the techological stack to support is another question.
Joseph Tainter, Charles Hall, Robert Ayres, Donna & Dennis Meadows, and William Stanley Jevons would make for some interesting reading.
Oh, and you've only got 800 million - 1 billion years: solar flux and/or C4 synthesis will mean the end of life as we know it. Life on Earth is past middle age. Even allowing for the lignin revolution and decomposer lag, that's barely sufficient time to replenish fossil fuel stocks for a do-over should humans fail.
The timescale of human evolution to date is on the order of 2 million years or so since we branched from our common ancestor with chimpanzees.
Somewhere around 80,000 years ago (plus or minus) we seem to have reached modern levels of cognitive ability, specifically, the capacity to keep 7 +/- 2 things in mind at the same time, as evidenced by the anthropological record -- stone artifacts and such.
Written history and most civilization spans roughly 6,000 years.
So, if you're looking at what "sustainable" might mean, I'd argue for somewhere within that timeframe. A minimum of 6,000 years, a reasonable upper bound of about 2 million.
