OK, let's talk numbers for a moment. I know you are correct when you stress that there will continue to be substantial population growth in the future. That is why I wrote, in my first missive, "We're due for at least an additional 2 billion people by 2050, even in the United Nations' Low Variant projection."
But let us not forget that, ultimately, numbers flow from rates. On that front something is going on that has never--repeat, never--happened before. Until quite recently demographers drew neat charts that showed rates going down to the 2.1-children-per-woman replacement level and staying there, more or less forever. They were pretty charts. Everyone would live happily ever after.
But here's a shocker: Young men and women conceiving children, or not, often in a darkened bedroom, aren't thinking about pretty charts or about an invisible line called "replacement." They are thinking about a good life for themselves, in quite new, modern circumstances. Their recent collective actions, in just about all the developed nations and in a growing number of less developed nations, have had the effect of slicing through the invisible line of replacement like a laser through grits.
Fertility went down to the 2.1 replacement rate all right, and then, in the developed countries, kept going down, down, down. And has stayed down. As mentioned, the Total Fertility Rate in Europe is about 1.5 children per woman, in Japan about 1.4. This has never happened before. In talking to European and Japanese demographers, most of them see no particular reason that these rates will turn upward any time soon and plenty of reasons that they will stay low.
Here's how numbers flow from rates. The numbers you cite for the year 2050--a global population of 9.4 billion people, up from the current 5.9 billion--come from the so-called Medium Variant of the U.N. projections.
The crux of the current argument concerns precisely that so-called MV. It's wacky. Garbage in, garbage out. For example, the MV takes the more developed regions, with a current TFR of 1.59 children per woman, and raises that rate to 2.05 by 2050. That's about a 30-percent increase. Why? Almost all the arrows point the other way: more contraception, more women working, later marriage, legal abortion, the continued move from rural to urban, and the fact that rates in the modernized nations have fallen significantly in the 1990s from the already low levels of the 1980s.
The current MV also deals with the Less Developed Countries in a bizarre way. There are already 19 LDCs with below-replacement fertility--but the MV raises them to 2.1. (For example, Thailand, now at 1.74, has fallen from 6.11 in 1965-70, and yet the MV takes it back up to 2.1. Why?) Moreover it doesn't allow any LDC that is now above replacement to go below it. (Brazil was at 6.15 in 1960-65, and it's at 2.17 now, but the current MV freezes it at 2.1 through 2050. Why?)
In short, the current MV basically visualizes a 2.1-replacement-level world, re-creating those pretty charts where everyone lives happily and neatly ever after. Because the MV appears to be the Baby Bear, just-right scenario between High and Low, it is also often regarded as the "most likely" scenario. It's not, as the United Nations makes very clear.
There is an existing alternative U.N. Low Variant projection with at least as much U.N. blessing behind it. It does not yield anywhere near a population of 9.4 million. It comes in at 7.7 billion people in 2050 and shrinking. Repeat: shrinking. By how much? By a lot, and relatively quickly: down to about 6 billion in 2100 and 4.3 billion in 2150, according to long-range U.N. projections. (A bust, like an explosion, moves in a geometric progression.) The central assumption in the existing Low version is that the global TFR will drop to 1.6 children per woman. Unlike the 2.1 figure, this is not an abstract construct. It is the current rate in the developed nations. The assumption is that as nations modernize, they will behave like modern nations. Even if you split the difference between the 2.1 and the 1.6--at 1.85--population tops out at 8.5 billion, and then starts shrinking.
Ken, this may sound like the screed of a statistical malcontent. But the United Nations is on my side. It recently called a meeting of leading demographers to offer advice on how to lower the assumptions in that MV to reflect more accurately what has been going on in the more developed regions. That revised version will appear late this year. There is every reason to believe that as the years go on, the United Nations will be dealing with other anomalies in the MV.
Why? Because something very big is going on that has never happened before.
Perhaps we can talk next about what that means, for good and for ill.
P.S. I don't think I was wrong about Japan. I was there recently and spoke to Noahiro Ogawa, one of the leading Japanese demographers, who said this: "If current fertility rates continue in Japan, in 60 years the population will be cut from 120 million to 60 [million]." (That is, if the current rate was maintained, it "would cut the Japanese population in half by the middle of the next century"--which is what I said in my opener.)