Pretty well crap, because it assumes that current trends will continue unchanged even if circumstances change. The birth-rate is falling in most areas of the world. But it still has not fallen, worldwide, to the "replacement level" of about 2.2 children per woman. It is expected to fall to about that level somewhere around 2050. But the population will continue to rise because many of the women at that time will still be young and will not have had their children yet. The world population is expected to stabilise (barring disasters etc.) in about 2100, at nearly twice the current level. If current trends continued unaltered, it would then start falling. But the reason people are having fewer children is that they can see the world is already heavily overpopulated. if the population started falling dramatically, I am sure people would start having more children. People are not unthinking machines - they make their own decisions. When people have emigrated to new and "empty" countries, they immediately start having larger families. As a matter of fact, it would be a good thing for the world to have a lot fewer people. If the population fell, naturally and by people's free choice, to perhaps quarter of a billion, I think that would be a very good thing.