Here is an interesting excerpt from Sir Ken Robinson's book The Element that talks about world population. See what you think.
"At the beginning of the Industrial Revolution, there was hardly anybody around. In 1750, there were one billion people living on the planet. It took the whole of human existence for the world population to reach one billion. I know that sounds a lot, and we've agreed that the planet is relatively small. But it's still big enough for a billion people to spread out in reasonable comfort.
In 1930, there were two billion people. It took just one hundred and eighty years for the population to double. But there was still plenty of room for people to lie down. It took only forty more years for us to get to three billion. We crossed that threshold in 1970, just after the Summer of Love, which I'm sure was a coincidence. After that came spectacular increase. On New Year's Eve 1999, you were sharing the planet with six billion other people. The human population had doubled in thirty years. some estimates suggest that we'll hit nine billion by the middle of the twenty-first century."