http://www.physics.harvard.edu/%7Emotl/lindzen-nature-of-arguments.pdf

It may do for the request in comment 353 too.

Thanks

Also see “Ultimate Resource II” by Julian Simon (RIP)

One of the big problems with the UN estimates is that they assume that all countries whose population is currently dropping, will have their rates stabilize when they hit replacement. (2.1 live births per woman) Problem with that assumption is that it has never happened. To date, every country whose birthrates have hit replacement, have had their birthrates continue to fall.
The UN also assumes that countries with birthrates below replacement will over the next decade, return to replacement. Once again, that has not happened either. Countries in Europe have had their birthrates well below replacement for decades now, with no evidence that they are moving upwards. Despite growing govt efforts to increase the rates.

What we are seeing here is an accelerating trend.

My personal guess is that we will see the population peak within 10 years. We already have two major countries, Russia and Japan, with falling populations. (I’g going to leave out discussions of how AIDS is devastating many African countries, because that could turn around if a cure is found.) In Europe, birthrates have been below replacement for over a generation, only immigration keeps their populations growing. There are only a handfull of countries left with birthrates higher than 3 or 4 per woman, and even those are falling fast.

RE: “The human population, currently 6.5 billion, is predicted to rise to 9.1 billion by 2050. ”

Not! This is the problem. There is a whole subculture out there still playing the old late 1960s – early 1970s Erlichian tape. The “Soylent Green” vision of the future. They were predicting that we’d be over 10B by now (if not extinct). They sure got that wrong. They assumed that the large post WW2 families in Western countries would continue to be the norm through the end of the century and that birth control would never take hold in the 3rd world. When in fact, by the 1980s, in the West, it was already obvious we’d soon hit our peak of natural growth and start falling so rapidly that we’d hear calls to import labor to do jobs “we won’t do.” But instead of acknowledging their error, they now hang their hats on the third world. Funny thing is, beyond a handful of those countries, natural increase has also slowed much more rapidly than anyone would have ever imagined. Once a person gets a cell phone or otherwise tinged by modernity, the whole big family thing loses its appeal and bourgeoisification starts to set in. The whole world will be on the Euro like negative trend within a generation if not sooner. I expect the peak in population prior to 50.

There’s a couple of ways to estimate future populations. We have good data from 1961 – 2004. The growth rate has been steadily dropping. By my calculations, if we extend the average drop in growth rates linearly, by 2050 the population will be 9.17 billion. For comparison, the UN Median Estimate is 9.19 billion in 2050.

Or we can look at the post-1990 drop, which has been slightly steeper. Extending that drop gives us a peak in 2042, with a 2050 population of 7.88 billion The UN Low Estimate for 2050, for comparison, is 7.79 billion. So my estimates are very close to the UN estimates, which gives some confidence in the figures.

The UN high estimate is 10.76 billion, I’d throw that out as unrealistic. I’d say that the 2050 population will likely be around eight and a half billion, plus or minus a billion.

While these numbers are large, from 1961 to 2006 the world population more than doubled (~210%). There’s more than twice as many people on the planet than when I was in high school, and yet people are living better and eating better than they were in the sixties, even the poorest people.

On the other hand, from now to 2050 we’re only looking at a population increase of about 17-38%, not 210% … me, I think we’ll deal with that without calamitous problems or meltdowns, but YMMV …

w.