From 2 billion people to 7 billion in how long??

A week ago we hit a world population of 7 billion people.

ABC's Radio National must-hear weekly science wrap The Science Show interviewed Paul Ehrlich, author of The Population Bomb (1968) and life-long population campaigner.

Why his focus on population? Because he was the 2 billionth person born - in just 1932 - he claims, meaning that 5 billion people have been added in his lifetime alone.

Wikipedia claims we hit 2 billion in 1927, but regardless, it does give a horrifying insight into what a huge problem we face.