Apologies...

Since this is kind of an "open thread", perhaps you won't mind me posing this question here. When I was a kid, a hotly debated scientific debate was on "over-population". In fact, the proponents seem to have been largely correct.

In just the past 30 years the earths population has increased by 50%. So I'm wondering why it's hardly talked about in the scientific community anymore. It would seem that those of you who deal with diseases would be particularly concerned. Does anyone know what current statistical trends show for the coming century?

My guess is because human overpopulation is not going to be the cataclysmic disaster once imagined in movies like Soylent Green. Why? There are numerouse reasons from the green revolution to forced birth control but the one I find most interesting is the observation that as countries get richer and populations move from the country to the city the birth rate drops dramatically until it falls below the replacement level. An interesting letter about this can be found here (http://www.sciencemag.org/cgi/content/full/sci;304/5668/207c). For those without a subscription, the letter has a single graph that shows that sometime in 2003 the world crossed a point where 50% of the world's population procreates at less than the population replacement level of ~2.1 child per couple. In the 1950s there were no large populations that had a fertility level below 2.1. At the current rate it is estimated that the world population will stabilize at around 10 billion then begin a slow decline.

I think that the US is the only developed Western nation that has an overall fertility level above 2.1. This is mostly due though to our high level of immigration and the high fertility amongst recent immigrants.

Of course, if the worst predictions of global warming turn out to be true then the population could begin declining much sooner than that.

"Does anyone know what current statistical trends show for the coming century?"

Try the population reference bureau. www.prb.org

Mike

Here is another good site for population stats.

http://esa.un.org/unpp/

D

DDS - the site you gave me only gives projections up to 2050, but based it that, population increases are going to have to tail off SHARPLY to keep the planet under 10 Billion humans by the end of the century. We don't do the greatest job taking care of 6.5. I hope we are able to contend the extra 3.5 billion (or more).

I would think there is a lot to be worried about other than simply whether or not it becomes apocalypic. Part of the problem with trying to find positive trends of growth stabilazation is that it doesn't factor in the weight of the groups that aren't (extremely poor people in 3rd World countries).

John,
To be honest, I only barely believe the predictions out to 2050. I am very skeptical of our ability to predict anything out that far. Not from lack of brain or computer power but rather from a lack of a deep understanding of nature.

I agree that there is a lot to be worried about with 10 Giga humans on the planet. Everything from environmental degradation to new infectious diseases to hunger, war, etc. My guess is that the intractable overpopulation question has been divided into dozens of "merely" extremely difficult subquestions.

As for positive trends for growth stabilization that is what I liked about the Science paper I referenced above. If you can't get it I'll send it to you by E-mail.

Also in the executive summary from the UN site is this bullet point.

"Future population growth is highly dependent on the path that future fertility takes. In the medium variant, fertility is projected to decline from 2.6 children per woman today to slightly over 2 children per woman in 2050. If fertility were to remain about half a child above the levels projected in the medium variant, world population would reach 10.6 billion by 2050. A fertility path half a child below the medium would lead to a population of 7.6 billion by mid-century. That is, at the world level, continued population growth until 2050 is inevitable even if the decline of fertility accelerates."

This is where I got my 10 billion number from. It is in fact a pessimistic number.

I should add a disclaimer that I am not a demographics expert, just an interested lay person. There could be major issues of which I am not aware.

D