We’re at 8 billion people. Obtain 3% annual population growth and continue for 20 years you’re already at 14 billion. 30 years you get to 19 billion. If those numbers don’t seem like they’re within the limits to growth as you see them, keep adding decades and soon you’ll reach a number that probably is. The point here being that the limits may be far away numerically, but at modest growth rates we will hit any conceivable one. We are going to have to adapt to stable or declining population rates at some point, and this seems like a particularly good time to do it.