[mattmanser]

Most of the developed world has now got a lower than replacement birth rate (except, typically, the US):

http://en.wikipedia.org/wiki/Sub-replacement_fertility

Can't we extrapolate and say that in a few decades that's going to happen to the developing world too?

In other words, that graph is nonsense?

[pchristensen]

Usually wealth, education, and women's rights lead to a drop in fertility, so if you're worried about population growth your #1 priority should be to help poor countries get richer. Ditto for pollution.

[cbr]

"Ditto for pollution"

I believe pollution per capita is highly correlated with per capita wealth (or income).

[pchristensen]

Pollution drops rapidly after household income (or was it GDPPC) rises above $5000, because people have more acute problems taken care of and start to care more about clean air, water, etc. Essentially poor countries use "pollution acceptance" as an asset to grow richer, until they earn enough to spend buy pollution acceptance from someone else.

[byrneseyeview]

But pollution per marginal dollar of GDP per capita is lower. That could just be an artifact of the rich world relatively de-industrializing: as the US gets more Facebooks and Starbuckses, China gets more steel mills. But it also seems that one luxury rich countries pay for is lower pollution relative to GDP.

[xiaoma]

I don't think it's set in stone. Some countries which previously had very low fertility rates have seen a recent upswing, notably France and a few Scandinavian countries.

[byrneseyeview]

Is this accounting for immigration? The US has the same issue: the white population reproduces at barely above or barely below replacement (it varies), but immigrants have much higher fertility. And, weirdly enough, comparable infant mortality.

[nobody314]

It typically takes two generations. The first generation of women that have the chance of higher education and a professional job have a much lower birth rate. Then once these women get into positions of power they show that it's possible for women to have children and a career introduce maternity leave, women's rights etc and the birth rate recovers with the next generation.

It's interesting to plot the position of each country in Europe in this cycle, from Scandanavia through Italy/Spain to Greece/Portugal.

For the 3rd world or 'human resource rich countries' - it's different. You have to look at the population in the industrial revolution 200years ago. People living on farms in the countryside had lots of children to run the farm, to provide for them in their old age and because many wouldn't survive. They move to the cities and have the same number of children - but more of these survive (however bad conditions in the 18C towns were - they were better than the countryside!)

Then as people become more prosperous they have less children and the population stabilizes - but at the new higher level

[tokenadult]

The United Nations has made world population projections to the year 2300 under varying assumptions,

http://www.un.org/esa/population/publications/longrange2/Wor...

as I mentioned in a different recent thread here on HN about the current world population count.

[epscylonb]

I heard population is expected to rise to about 9 billion at which point it will start falling.

[wallawe]

It will have to be checked one way or another. Either we as humans will have to (as in the case of China) or nature will take its course in checking the population. We can't grow at the rate that we are, while consuming the resources at the rate we do for much longer. Check out economist Thomas Malthus' "Malthusian Theory:"

http://en.wikipedia.org/wiki/Malthusian_catastrophe

[T-hawk]

Malthus has been debunked plenty of times. The school of thought has been predicting overpopulation disaster for 200 years which hasn't come close to materializing. The key point is that resource production also increases -- all those extra humans have a way of figuring out how to produce the resources they need.

Okay, eventually there's a hard cap on resource production, limited by the total insolation energy to Earth or perhaps that which can be captured with space power satellites or a Dyson sphere. And you can continuously predict Malthusian disaster until that comes true. But that's a bit like predicting "recession!" for every year from 1992 through 2001 and then claiming in 2001 that you were right.

[wallawe]

Your response conveys that you have a fundamental misunderstanding of what the theory even describes. It has not "been predicting overpopulation disaster for 200 years" on a continual basis as you make it seem by your analogy in the second paragraph.

The theory merely maintains that population increases ‘geometrically’ or exponentially and that subsistence increases arithmetically. Thus, population increases along the order of 1, 2, 4, 8, 16, 32..., whereas subsistence limps along at the rate of 1, 2, 3, 4... You are correct that this has been debunked in the past in many ways due to technological and agricultural developments, changes in societal organization.

But it has been revived recently. What you don't take into account is that fact that we are only approaching 7 Billion which is sustainable currently but is expected to double within the next 100 years if not checked. Also, the problem has changed as agriculture is no longer the main concern; Oil and energy are. Peak Oil production has, or will have been reached within the next 10 years which presents an entirely new and much more serious problem for world economies. We are already seeing some of the beginning effects that depletion is having.

Don't get me wrong, I believe humans are ingenious and can move to solve problems when cornered, but I don't think you can argue that at the growth rate we are seeing today, that there will not be any sort of check necessary whether it be natural or imposed by man.

(and i don't think a downvote was necessary, as I was merely stating opinion, as you have as well)