The following is a comment from a reader of the greatest blog ever, Mikepedia (no bias, I swear), in response to the post 'the epidemiologic transition.'
Do you know what's expected in Phase 6? Will our birth rates continue to decline, or level off... It's kind of scary to think it could continue along the current trends :s
Great question. Assuming no migration of people, the developed world would eventually die out in phase 6 using this model (as death rates would be higher than birth rates). This isn't going to happen because of immigration- the developing world (formally known as 2nd/3rd world countries) is still in phase 2- where birth rates are higher than death rates. The rise in global population in the most recent decades (and likely in decades to come) can be attributed to developing countries, not places like Canada, US or EU.
In short, thank goodness for immigrants :)
As for our national birth rates...it's a toss up. I expect that they would naturally decline as people are having less and less children. However, advancements in reproductive technologies, such as in-vitro fertilization, may actually assist many couples in having children where they would not be able to otherwise. Overall, I think the national birth rate will decline, but the reproductive biotech industry may balance some of this out.
As for death rates...this too is a toss-up. In the developed world, an aging population will likely skyrocket the death rates. However, the death rates of developing countries are generally much higher, and as medical and technological advancements reach these people, we may see a decline (somewhat) in their infant mortality rate, and perhaps an increase in life expectancy, thus contributing to a decreased death rate.
Overall, the global population will continue to grow. Overpopulation is said to be THE largest threat to human survival...not global warming, not nuclear warfare, and not availability of food or water...overpopulation will have an immense impact on our planet (and our species) by the end of generation Y's lifetime.