Is The World Nearing Peak Population?

Authored by Bill King via RealClearPolitics.com,

I regularly talk to well-informed people who do not realize that world population growth is rapidly decelerating.

Currently, the UN estimates the most likely case is that the world’s population will top out around 10 billion in 2080 and then begin a long, slow decline. Other modelers are projecting the peak will be reached in 2060 at 9 billion and then decline more rapidly. Some scenarios predict there will be fewer people on the planet at the end of century than there are now.

UN Population Division

The United Nation’s predictions for the U.S. are similar, with our population topping out at around 380 million near the end of the century. This is consistent with the Congressional Budget Office projections, which assume the U.S. annual population growth rate over the next 20 years will decline from 0.5% to 0.2%. Without immigration, the U.S. population would begin to decline around 2035.

Congressional Budget Office

Many of us grew up reading Paul Ehrlich’s runaway best-seller “The Population Bomb,”, which predicted a worldwide apocalypse was just around the corner. The book, written in 1968, categorically predicted that “The battle to feed all of humanity is over. In the 1970s hundreds of millions of people will starve to death.” Of course, that did not happen and since around 2000, researchers have found there have been more obese people in the world than those who are undernourished.

In part, it did not happen because of an explosion of agricultural technology in the 1950s and 1960s known as the Green Revolution. But Ehrlich’s prediction also never came to pass because he missed that at the time of their book, women had already begun having fewer babies.

The critical metric for population growth is the average number of children women are having at any particular time, known as the fertility rate. Other factors, such as childhood survival and longevity, also affect population growth, but the fertility rate is the big driver. It takes a fertility rate of 2.1 children per woman to maintain a stable population, known as the “replacement rate.” Anything above that and the population will grow and below that it falls.

When ”The Population Bomb” was published, the fertility rate was stunningly high at 5. That astronomical rate would go on to cause the world population to double just 40 years later.  But what was not apparent to the author at the time was that the fertility rate had peaked about five years earlier at 5.3. That began a steady slide downward to 2.3 today, just barely above the replacement rate.

World Bank

However, a decline in the fertility rate does not show up at once. It takes a while for that lower rate to work through the generational cycle, something referred as “population momentum.” That is why you still see a hefty 25% increase in the world’s population in the projections before it tops out in 2080.

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