But insufficient thermodynamics virtuosity to try for anything quantitative (and it also seemed that such an estimate might need some 'quantitative' application of Chaos Theory,
which AFAIK is not quite utile for real numbers either.) Declared self incompetent, lazy or both.
Hmmm - DRL?

Nice that others are tackling such a massive Q. -- for which they shall have to invent a whole new map on which to hang their experiments. TANSTAAFL again?
Every science-iggerant political hack will be demagoguing this idea and all related.

(And.. what IF it turns out that techno-civilization, with all the perks we now take for granted as perpetually increasing [Hah] can 'work' only for a Population of N [excessively-comfortable bipeds] ??)
And we're already at ... say, 1.5 N ??
Will the Pope acquiesce on that 'be fruitful and multiply exponentially' thing, in the interest of having Any new acolytes at all, as Rome broils in the winter?

One thing is already clear: even at present world population, there is No Way that everyone-not-Murican can ever spend the KW-hours-per-perp that we have spent as we, all along, encouraged regular waste
(as a means to make more profits via replacements -- the usual mercantile mindset of Reddy Kilowatt et bizness-alia.)

No wonder everyone else will be really PISSED when there's enough data to prove: TANSTAAFL IS.
The last people all-the-rest will want to hear from, about 'frugality': would be .... US, methinks.

{sigh} Seems that Slaughterhouse Five's errant rocket pilot (the one who pushed the wrong button and offed the local Universe) just might have been a Murican, at least in spirit.

'Course it would be bad form to utter any such wonderments to the tykes, especially clever ones ... for all obv psyche reasons :-/

Is it time for Mahler's Sixth -With Feeling- yet?