Population growth doesn’t remain static. It’s not going to double in the time frame you’ve projected. In fact, it’s not going to reach that figure for much longer, if at all.

Hans Rosling’s talks (on TED and YouTube) throw a lot of light on the peak population we’d likely reach, the reasons for those and also what we can do to control it (the key is educating girls). He died some months ago, but his talks and work are engaging and illuminating.