Seven billion people and shrinking?

Sometime around Halloween, the United Nations will celebrate the birth of the world’s 7th billion baby. As U.N. Secretary General Ban Ki-moon told world leaders in New York last month, the 7th billion baby will most likely be poor and will inhabit an earth buffeted by the ravages of global warming, desertification, and dwindling food shortages.

Sounds swell. Given this kind of apocalyptic rhetoric, it’s no surprise that much of the media’s focus has been on the strain of an over-populated planet, one where more than 79 million people are added each year to the human family, overwhelming already overcrowded cities, fighting it out over a dwindling pool of natural resources.

But what if the world’s population actually shrank?

While global population has tripled since the U.N.’s creation in 1945, global fertility rates over the past 100 years have steadily declined, from a high of 6 children per family at the dawn of the 20th century, to about 5 in 1950, to 2.5 today. The United Nations expects to reach a break-even replacement rate of about 2.1 children per family after 2100.

The United Nations has produced a range of scenarios showing population growing to nearly 10 billion over the next century — or even as high as nearly 27 billion, if the current rate of population growth continues through the next century (needless to say, an outcome that many demographers see as unsustainable).

More likely, according to U.N. statisticians, is that population will gradually rise to 8 billion in 2025, 9 billion in 2043, hit 10.1 billion by century’s end, and then stabilize. The so-called "medium variant" projection assumes that countries with high fertility rates like Niger, with a rate of 7.37 babies per woman, and those with low fertility rates, like South Korea, where women have an average of only 1.2 children, will ultimately converge.

That assumption, like most others, is pretty much a guess, and doesn’t take into account potential cataclysmic events, like an asteroid hurtling into earth or perhaps a more plausible scenario in which mass numbers of people die by infectious diseases. The HIV/AIDS epidemic temporarily slowed the rates of population growth in Africa, preventing the African continent from surpassing the combined population of Europe and the Americas by 2025.

"Demography is not destiny. In some ways the most implausible assumption is the idea that the entire world is going to start having 2.1 children. There is no reason to believe that is going to happen," said Matthew Connelly, a history professor at Columbia University and author of Fatal Misconception: The Struggle to Control World Population. "It wouldn’t surprise me if we have more surprises ahead."

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