The global fertility rate has fallen almost by half from 70 years ago and further declines are projected by the end of the century that will see most countries experience population declines and require societies to reorganize, according to a study by researchers at the University of Washington.
The study, published July 14 in the British medical journal The Lancet, says that 23 countries – including Spain, Japan, Thailand and South Korea – will see their populations cut in half by 2100.
"That's a pretty big thing; most of the world is transitioning into natural population decline," researcher Christopher Murray told the BBC. "I think it's incredibly hard to think this through and recognize how big a thing this is; it's extraordinary, we'll have to reorganize societies."
The study, “Fertility, mortality, migration, and population scenarios for 195 countries and territories from 2017 to 2100: a forecasting analysis for the Global Burden of Disease Study,” said women across the world were having an average of 4.7 children in their lifetime in 1950.
But that had plummeted to 2.4 by 2017, and the researchers at the University of Washington's Institute for Health Metrics and Evaluation say it will continue to fall to 1.7 by the end of the century.
Once it falls below 2.1, the world’s population will begin to decline.
The researchers predict the number of people on Earth to reach a peak of 9.7 billion around 2064, and then recede to 8.8 billion by the start of the new century.
“Our findings show that some countries with fertility lower than replacement level, such as the USA, Australia, and Canada, will probably maintain their working-age populations through net immigration,” the study says.
It predicts the United States will grow slightly from a population of 324.8 million to 335.8 million by the end of the century.
China will peak at 1.4 billion people in four years before starting to decline, but that will drop by half to 732 million by 2100. India will replace it as the most populous country, although it will fall from its current 1.38 billion to 1.09 billion by 2100.
The reason for the decline has nothing to do with biological concerns such as sperm counts.
“Our findings suggest that continued trends in female educational attainment and access to contraception will hasten declines in fertility and slow population growth,” the study says.
Among the consequences of a falling fertility rate will be the number of 80-year-olds going from 141 million in 2017 to 866 million by 2100.
“Individuals might have profound concerns over population in the future: will there be enough workers to pay taxes to support pension and health benefits for the retired?” the study asks. “Will demographic change enhance global and national security and stability or make societies more precarious?”
"It will create enormous social change,” Murray said.
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