Lemme guess, you caught this from http://xkcd.com/1331/ too?
Fascinating - and I think humanity is "winning"
How 'bout that for the correlation=causation folks!
The historical preindustrial peak human population was around 500-800 million. Maybe we'd be lucky and be able to sustain somewhat more than that, say 2 billion. I have a hard time seeing much more given energy and resource limitations.
Prediction's hard, especially about the future, but I suspect we're looking at a crisis well within 100 years. Possibly a few decades out, if that.
Look up Limits to Growth.