The time of growing human populations may be ending, a new study shows. And that move will affect society, the economy and the environment.
Today, the world is home to about 7.8 billion people. The study found that the world’s population may top out at 9.7 billion on or around the year 2064. But researchers think it could shrink to 8.8 billion by the end of the century.
The findings appeared in the medical publication The Lancet.
The numbers come from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington in Seattle. Those estimates disagree with the findings of the United Nations Population Division. Its experts expect the population in 2100 to be 10.9 billion and rising.
U.N. Population Division chief John Wilmoth has called the new estimates "extreme."
If the study proves to be correct, however, the changes brought on by a shrinking population could be great.
"I think this is one of the more profound changes that's faced humanity ever," said Chris Murray. He is the director of the IHME and a co-author of the study.
The new estimates would be great news for the environment. Fewer people would make fewer pollutants, for example. This would lower demand for food, reducing the demand that agriculture puts on land and water.
But a shrinking population could be very bad for the economy.
Decreasing populations mean fewer people are working, which means lower gross domestic product (GDP). It also means fewer people are able to buy things, and buying things is the basis of the international economy.
"What happens when you don't have young people buying their first house…buying the first car?" asked Darrell Bricker. He is co-writer of the book, "Empty Planet: The Shock of Global Population Decline." Bricker was not involved in the study.
Also, populations age as birth rates fall.
"This is actually more serious than just simple population decline," said Zhenchao Qian, a sociology professor at Brown University in Rhode Island. He was also not involved with the research.
A smaller workforce would be supporting a larger population of older adults, Qian said. He added that this puts great demands on paying for healthcare and social programs.
Population decreases could also have geopolitical affects. Fewer workers also mean fewer soldiers, Murray said.
"The balance of power between nation-states has always been related in some ways to the size of the working-age population," he said.
Female empowerment
Birth rates have been decreasing worldwide because women are getting more education and face fewer restrictions on birth control.
"It's really a story about female empowerment," Bricker said.
The main difference between the IHME estimate and the U.N. study is what researchers expect will happen after birth rates hit bottom.
Population numbers change little when women have about two children each. This is known as the replacement rate. Across wealthier countries, the average birth rate is more like 1.6.
The U.N. believes birth rates will rise again over time to 1.75.
But Chris Murray disagrees.
"We see no sign of that," he said.
He believes that decreasing birth rates in places like Japan and parts of Europe will expand to other countries.
By 2100, his group estimates that nearly every country in the world would be below the replacement rate. Populations in 23 countries, including Japan, Thailand and Spain, would be half what they were in 2017.
But only if Murray and IHME researchers are right.
'Great uncertainty'
The U.N.'s John Wilmoth notes that both groups are basing their projections on "what's still early experience in the lives of a few countries. So…there's great uncertainty about that," he said.
"We will know much more about that in 10 or 20 years," he added. "But for now, we're both guessing.”
Murray said countries will have three ways to keep their populations from decreasing.
"One is to make it easier for women to work and have children," he said.
Most countries have policies to help working mothers, he added, but that alone does not bring the birth rate to the replacement rate.
The second way is to open their borders to immigration. But many governments, including the Trump administration in the United States, are not open to increased immigration. Anger about the European Union’s migration policies was a major issue in Britain’s vote to leave the EU.
Ibrahim Abubakar is director of the University College London Institute for Global Health. In an opinion piece published in The Lancet, he wrote if the IHME’s estimates are only 50 percent right, migration would be necessary for all nations.
Finally, some countries might decide to take away women's reproductive health rights in an effort to pressure them to have more children. He called that third way "very undesirable."
I’m Susan Shand.
VOA’s Steve Baragona reported this story. Susan Shand adapted it for Learning English. George Grow was the editor.
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Words in This Story
profound - adj. deep, dramatic
author - n. one who writes an essay, book or article
gross domestic product - n. the total value of goods produced and services provided in a country during one year.Compare with
geopolitical - adj. relating to politics, especially international relations, as influenced by geographical factors.
decline - n. a decrease or lessening
