A very interesting look at where all of the earth’s billions of people are now, and where the population is heading. Projections place the occurrence of the world population of humans passing 7 billion at some point between 31 Oct 2011 (UN estimate) and March 2012 (US Census Bureau estimate). The most interesting piece of this article is the pointing out that the rate of increase is now slowing. (The second derivative is now negative, for my math inclined readers.) Where the fertility rate is high, and where it is low, helps to predict the economic future of countries around the world. The pertinent section follows this graph of fertility rates (live births per woman).

The low-fertility countries face the biggest demographic problems. The elderly share of Japan’s population is already the highest in the world. By 2050 the country will have almost as many dependents as working-age adults, and half the population will be over 52. This will make Japan the oldest society the world has ever known. Europe faces similar trends, less acutely. It has roughly half as many dependent children and retired people as working-age adults now. By 2050 it will have three dependents for every four adults, so will shoulder a large burden of ageing, which even sustained increases in fertility would fail to reverse for decades. This will cause disturbing policy implications in the provision of pensions and health care, which rely on continuing healthy tax revenues from the working population.

At least these countries are rich enough to make such provision. Not so China. With its fertility artificially suppressed by the one-child policy, it is ageing at an unprecedented rate. In 1980 China’s median age (the point where half the population is older and half younger) was 22 years, a developing-country figure. China will be older than America as early as 2020 and older than Europe by 2030. This will bring an abrupt end to its cheap-labour manufacturing. Its dependency ratio will rise from 38 to 64 by 2050, the sharpest rise in the world. Add in the country’s sexual imbalances—after a decade of sex-selective abortions, China will have 96.5m men in their 20s in 2025 but only 80.3m young women—and demography may become the gravest problem the Communist Party has to face.

Many countries with intermediate fertility—South-East Asia, Latin America, the United States—are better off. Their dependency ratios are not deteriorating so fast and their societies are ageing more slowly. America’s demographic profile is slowly tugging it away from Europe. Though its fertility rate may have fallen recently, it is still slightly higher than Europe’s. In 2010 the two sides of the Atlantic had similar dependency rates. By 2050 America’s could be nearly ten points lower.

But the biggest potential beneficiaries are the two other areas with intermediate fertility—India and the Middle East—and the high-fertility continent of Africa. These places have long been regarded as demographic time-bombs, with youth bulges, poverty and low levels of education and health. But that is because they are moving only slowly out of the early stage of high fertility into the one in which lower fertility begins to make an impact.

At the moment, Africa has larger families and more dependent children than India or Arab countries and is a few years younger (its median age is 20 compared with their 25). But all three areas will see their dependency ratios fall in the next 40 years, the only parts of the world to do so. And they will keep their median ages low—below 38 in 2050. If they can make their public institutions less corrupt, keep their economic policies outward-looking and invest more in education, as East Asia did, then Africa, the Middle East and India could become the fastest-growing parts of the world economy within a decade or so.

Demography, though, is not only about economics. Most emerging countries have benefited from the sort of dividend that changed Europe and America in the 1960s. They are catching up with the West in terms of income, family size and middle-class formation. Most say they want to keep their cultures unsullied by the social trends—divorce, illegitimacy and so on—that also affected the West. But the growing number of never-married women in urban Asia suggests that this will be hard.If you look at the overall size of the world’s population, then, the picture is one of falling fertility, decelerating growth and a gradual return to the flat population level of the 18th century. But below the surface societies are being churned up in ways not seen in the much more static pre-industrial world. The earth’s population may never need a larger island than Maui to stand on. But the way it arranges itself will go on shifting for centuries to come.

Here are a couple more helpful graphs of the world population and world fertility rate.

World Population Graph: Note the change in concavity in the last few years.

The Declining World Fertility Rate

You can read the rest here.