Experts say we'll need to "reorganize societies" to respond to a "jaw-dropping" decrease in the number of Earthlings being born. To keep a steady population, a woman needs to have 2.1 children on average so as to account for infant mortality and childless women. Women were having an average of 4.7 children in 1950. But the global fertility rate fell to 2.4 in 2017, per the BBC, and researchers at the University of Washington expect it to drop to 1.7 by the end of the century. As a result, the global population is expected to peak at 9.7 billion around 2064, then drop to 8.8 billion by 2100. Nearly all countries—183 of 195—are predicted to have a fertility rate below the replacement level. Some 23, including Japan and Italy, will see their populations drop by more than 50%, while 34, including China, will see a drop of more than 25%, per CNBC.
In 2017, there were 681 million people under the age of 5, and 141 million over the age of 80. By 2100, experts predict 401 million people under 5, and 866 million over 80. With fewer young people to care for the elderly, "we'll have to reorganize societies," Christopher Murray, whose research is published in the Lancet, tells the BBC. He predicts "frank competition for migrants," particularly from sub-Saharan Africa, which is expected to triple in population size to more than 3 billion people by 2100. But migration isn't going to help once most countries experience population decline. "If you can't [find a solution], then eventually the species disappears, but that's a few centuries away," Murray says. Others seem more hopeful, noting healthy life expectancy is increasing, allowing people to work longer, meaning more money paid into health care systems, per the BBC. And a lot can change in 80 years. (Read more population stories.)