Take a look at the world populace and how long it took to double the last time. Well, that's going to happen again. It's not slowing down. The states with the highest level of income have taken the population of this planet to be an important issue. The third world never will.
The only reason the UN would dare make such a stupid prediction is because they are pefectly happy with the third world overpopulating at the expense of the western world. That is exactly what is happening.
When my first wife was pregnant with our children, she was ignored by all men except one group. When she was nearly full term, she was still getting harassed by hispanic men who would make cat calls and try to pick her up. I can't explain it. Wouldn't even attempt to. I'm just telling you what she experienced.