U.S. researchers say world population will continue to grow at a vigorous pace in decades to come, even as overall global fertility rates continue on a downward trend.
The Population Reference Bureau projects world population at 9.3 billion by the middle of this century, a 45 percent increase over today's tally of roughly 6.4 billion. That is despite a global average fertility rate that has dropped from more than five children per female in the 1950s to 2.8 today, and is expected to decline further to less then 2.5 in years to come.
Where will the population growth occur?
"Here is the prospect for the developed countries: basically no [population] growth," said Demographer Carl Haub. "And remember the only industrialized country that is really growing is the U.S., which is keeping it [the overall figure] from going down further. The developing countries: all the growth. Basically 99 percent."
To illustrate his point, Mr. Haub points to two countries with starkly different population projections: Nigeria and Japan. He notes that, today, the two countries have similar populations: 137 million for Nigeria and 128 million for Japan.
"But if we look at a projection for the population of both countries, look where they wind up: Nigeria three times the size of Japan," said Mr. Haub.
By 2050, Nigeria's population is expected to reach 307 million, while Japan's population is projected to decline by 22 percent to 100 million.
Mr. Haub notes that fertility rates are highly uneven in the developing world, with Thailand currently averaging 1.7 births per female as opposed to eight births for Niger. He says fertility rates will likely decline in Africa as they have done elsewhere. But he admits that it is impossible to say precisely how fast and how far the rate will drop.
Of one thing he is certain: the median age difference between the industrialized world and the developing world will continue to grow, with European and North American populations becoming more "aged" as a whole, while developing nations become more "youthful". This, he says, will have important economic consequences for the future.
"There is a real shift in population, not just in terms of numbers, in total size, but in age. The youthful population today is more and more becoming that of the developing countries. These are the people who are setting up families, household formation. They are buying things. That is where I think the more vibrant markets are going to be," he predicted.
Carl Haub says, when it comes to population trends, the United States is in an enviable position relative to its industrialized peers. He says, while Japan and Germany fret about a fertility rate that is below replacement, 1.3 for both countries, the United States enjoys a steady and sustainable fertility rate of two births per female. In addition, he notes that the United States benefits from a regular infusion of working-age people thanks to the 1.3 million immigrants who arrive in the country each year. U.S. population is expected to swell to more than 400 million by 2050.