The first question you should ask is: Is the world overpopulated? See especially the link at the bottom: What is Overpopulation? (Population Reference Bureau)
As far as I can determine, the main cause of population increase (in recent decades) has been greater life expectancy. That means our overall population keeps getting older and the rates of growth will correspondingly decline, as they are doing now in most countries of the world, some even with negative growth rates.
Fr. Phil Bloom