Global carbon dioxide levels set to pass 400ppm milestone

[GliderGuider]

13. According to a couple of sources, the sustainable human population is under 50 million.

In an article earlier this year I pegged the level of human population that is probably sustainable over the long term at just 20 to 50 million individuals.

An article published by the British Royal Society in 2003 (Is Humanity Sustainable?) concludes that our population is at least 190 times higher that it should be for sustainability. That puts the sustainable population at about 37 million, almost exactly halfway between my two bounds.

If human numbers are not sustainable, then they will decline at some point. It's kind of axiomatic. I haven't a clue about how that will happen, or how fast, but I expect it to happen only as a result of a global ecological crisis, not in anticipation of one. Given the remaining 20 year window I see for Business As Usual, I expect the early effects (which are already visible) to be undeniable, even by politicians, within the next decade or so.