How many "wake-up calls" do we need before we wake up?

I clearly remember, at age nine or ten, being stunned to learn in school that there were two billion inhabitants on Earth. Within my lifetime, that number has more than tripled. But we need not fret about the consequences for posterity of our indifference toward population control--our children's children can always rely on Famine, Pestilence, and War to restore balance.