The dramatic rate of population decline has been laid bare in a new study which has found the majority of countries could be below their replacement level of fertility in the next 26 years.
According to projections by international and Australian researchers, by 2050, 76 percent of countries and territories around the world will not be having enough babies to sustain their population size.
By 2100, that number is forecasted to jump to 97 percent of countries.
The authors are sounding the alarm bells for governments to plan for emerging threats to economies, food security, health, the environment, and geopolitical security brought on by these demographic changes that are set to transform the way we live.
The fertility rate shows the average number of babies women would have in their life. The replacement rate in most developed countries like New Zealand is 2.1, which is the number of children a pair would have to have in order to replace themselves. In countries with high infant and child mortality rates, the replacement level is much higher.
New Zealand has experienced one of the most rapid transitions from replacement-level fertility to well below of any high-income country.
In 2012, the country was still at replacement fertility sitting at 2.1 births per woman, but by 2017, New Zealand had sharply dropped well below and has sat at about 1.6 births per woman since.
However, 2023 saw New Zealand birth's drop to its lowest in 20 years, plummeting the total fertility rate (TFR) to 1.56, from 1.66 in the year prior.
It's a similar picture in most countries, with the study saying global TFR has more than halved over the past 70 years, and in 2021 over half of all countries and territories are below the population replacement level.
Over the coming decades, global fertility is predicted to decline even further, reaching a TFR of around 1.8 in 2050, and 1.6 in 2100.
By 2100, only six of 204 countries and territories (Samoa, Somalia, Tonga, Niger, Chad, and Tajikistan) are expected to have fertility rates exceeding 2.1 births per female.
The researchers forecasted the fertility of countries around the world using data on a range of factors that predict how many babies a group of people will likely have including education level, contraception access, child mortality and living situation.
However, the trend will not happen everywhere all at once. Richer countries will be hit first and hardest by falling birth rates, while poorer places will maintain higher birth rates, with some increasing.
In the coming decades, it expects the majority of babies (77 percent) will be born in low and lower-middle-income countries by the end of the century. Currently, sub-Saharan Africa already contributes nearly a third of the world's babies in 2021.
"We are facing staggering social change through the 21st century," senior author Professor Stein Emil Vollset from IHME said. "The world will be simultaneously tackling a 'baby boom' in some countries and a 'baby bust' in others.
"As most of the world contends with the serious challenges to the economic growth of a shrinking workforce and how to care for and pay for ageing populations, many of the most resource-limited countries in sub-Saharan Africa will be grappling with how to support the youngest, fastest-growing population on the planet in some of the most politically and economically unstable, heat-stressed, and health system-strained places on earth."
Co-lead author Dr Natalia Bhattacharjee, of the University of Washington's School of Medicine, said the trends will completely reconfigure the global economy and the international balance of power.
"The implications are immense," Dr Bhattacharjee said.
She added that there is no "silver bullet" to fixing this threat.
"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," she said.
Dr Bhattacharjee said once every country's population is shrinking, reliance on open immigration will become necessary to sustain economic growth. Therefore, Sub-Saharan African countries have a vital resource that ageing societies are losing - a youthful population.
There is also a concern that countries may turn to more draconian measures that limit reproductive rights.
"It is well established that nations with strong women's rights are more likely to have better health outcomes and faster economic growth," Dr Bhattacharjee said.
"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."
