How overpopulated is the planet, really?

[GliderGuider]

19. Because my definition of "sustainability" is too strict to allow for technological renewables

Basically, anything but a hunter-forager puts too much indirect stress on the ecosystem in one way or another. For example, we would have to mine and refine the materials and then manufacture the equipment for renewable energy technology, regardless of where we put the resulting gear. And you have to grow food to feed the extra people that result from having the energy (resulting in habitat destruction) and give them some level of infrastructure (more impact) etc. etc.

Here's how I explained it in the FB comment thread:

Ever since agriculture began, we've been strip-mining the soil. That's where the extra energy to boost the population - as well as the initial planetary damage - first came from. If we'd stuck to doing it with oxen and sticks, it might have been tens of thousands of years before the negative effects became visible. But we didn't.

I use a very strict definition of sustainability - something like, "The ability of a species to survive in perpetuity without damaging the planetary ecosystem in the process." This principle applies to a species' own actions, but not to external forces like Milankovich cycles, asteroid impacts, plate tectonics, etc. In fact, in order to completely fulfill this definition, even my numbers could be too high by up to an order of magnitude.

I've traditionally used an estimate of 1 billion. Numbers like that require much shorter time horizons for planetary damage to become visible. Remember that 1 billion people was the world population in 1800. Were we "sustainable" in 1800 by any reasonable definition of the word?

The other, unstated implication of the analysis is that if we drop from 7 to 1 billion, we'll be in population free-fall. As a result, we will likely keep falling until we hit the bottom of Olduvai Gorge again. My numbers are an attempt to define that landing point.

I figure if I'm going to draw a line in the sand, I'm going to do it on behalf of the plant's entire ecosphere.