More than three out of four countries may have a shrinking population by the middle of the century due to "tumbling" fertility rates, research suggests.
And by 2100, more than 97% of countries – 198 out of 204 – will have fertility rates below what is necessary to sustain population size over time, according to a study published in The Lancet.
The analysis in the Global Burden of Disease, Injuries and Risk Factors study predicts that sub-Saharan Africa will account for one in every two children born on the planet by the end of the century.
Meanwhile in Western Europe, the total fertility rate – the average number of children born to women of childbearing age – is predicted to be 1.44 in 2050, dropping to 1.37 in 2100.
In the U.K., the total fertility rate was 2.19 in 1950, dropping to 1.85 in 1980 and then 1.49 in 2021. That is well below the rate of 2.1 needed to maintain a steady population without significant immigration.
By 2050, the U.K.'s total fertility rate is predicted to be 1.38, dropping to 1.30 by 2100.
The researchers said the findings pose "serious challenges" to global economic growth, especially in the midst of a shrinking workforce and aging populations.
They said that for countries with low fertility rates, social policies such as enhanced parental leave, free child care and extra employment rights may provide a small boost but most nations would remain below the levels needed to sustain their populations.
Dr. Natalia V. Bhattacharjee, co-lead author and lead research scientist from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington's School of Medicine in the U.S., said, "The implications are immense."
"These future trends in fertility rates and live births will completely reconfigure the global economy and the international balance of power and will necessitate reorganizing societies."
Senior author professor Stein Emil Vollset, from the IHME, said, "We are facing staggering social change through the 21st century."
"The world will be simultaneously tackling a 'baby boom' in some countries and a 'baby bust' in others."
The analysis predicts Niger would hold the top spot in 2050 for the highest fertility rate, with an average of five children for each woman, but this could come down to 2.7 children if universal education targets were met.
South Korea would have the worst fertility rate by the middle of the century with 0.82 children per female, according to the analysis.
The global total fertility rate has more than halved over the past 70 years, from around five children for each woman in 1950 to 2.2 children in 2021, the researchers said.
They said it will be important for countries with low fertility rates to implement policies "that support those who wish to have children and offer additional benefits to society such as better quality of life and greater participation of women in the workforce, alongside open immigration policies."
Bhattacharjee said, "There's no silver bullet."
"Social policies to improve birth rates such as enhanced parental leave, free childcare, financial incentives and extra employment rights may provide a small boost to fertility rates, but most countries will remain below replacement levels."
"And once nearly every country's population is shrinking, reliance on open immigration will become necessary to sustain economic growth."
"Sub-Saharan African countries have a vital resource that aging societies are losing – a youthful population."
"There is very real concern that, in the face of declining populations and no clear solutions, some countries might justify more draconian measures that limit reproductive rights," she added.
"It is well established that nations with strong women's rights are more likely to have better health outcomes and faster economic growth."
"It is imperative women's rights are promoted and protected and that women are supported in having the number of children they wish and pursuing their careers."