Population numbers are expected to peak at 9.7 billion in 2064 and then fall to 8.8 billion by 2100 - as more women access education and contraception, according to a new study.
The global population is expected to peak at 9.7 billion in 2064 before falling as more women gain access to education and contraception, a new study has found.
This has prompted concerns that some countries could target reproductive rights as a way to stop their populations from shrinking.
The study, published in The Lancet, predicts that 183 out of 195, or 94 percent, of countries will see a falling fertility rate by the latter half of this century.
Fertility rate refers to the average number of children per woman. An average of 2.1 children per woman is considered a stable rate with regards to population growth.
A higher average will result in an increasing population, while an average lower than 2.1 means a shrinking population, unless this number is bolstered by migration.
The University of Washington modelling of fertility, death and migration rates highlights 23 countries where population numbers will shrink by half, including Japan, Spain, South Korea and Thailand.
An increasingly ageing population is also forecast, where the number of people older than 65 is larger than the number of those who are 20 years or younger.
“Our findings suggest that the decline in the numbers of working-age adults alone will reduce GDP growth rates that could result in major shifts in global economic power by the century’s end,” said author Professor Stein Emil Vollset.
"Responding to population decline is likely to become an overriding policy concern in many nations but must not compromise efforts to enhance women’s reproductive health or progress on women’s rights.”
What does this mean for women’s reproductive rights?
If lower birth rates are being driven by education and access to contraception, then taking this away could be a strategy employed to increase a country's workforce.
The study's authors allude to this when they stress that the response to shrinking population size "must not compromise efforts to enhance women's reproductive health".
University of Sydney migration expert Anna Boucher said this is a concern in some parts of the world.
"It's definitely a possibility and you have seen backlash against women's movements at present,” she said.
"So I wouldn't be surprised if that was part of the agenda and obviously that is something that should be pushed back against."
The other solution put forward is investing in childcare.
"Research has shown that providing heavily subsidised childcare is a good incentive to women to have more children,” Dr Boucher said.
"When women feel they have the burden of household responsibilities and working then they effectively go on a form of fertility strike and have fewer children.
"So if we want to encourage women to have children that is really where policies around work family balance and family friendly workplaces become very important.”
Where will we see the largest population declines?
The lowest fertility rates in 2100 will be in Europe, with 1.2 children per woman in Italy and Spain and 1.17 in Poland.
But the largest population declines will come from countries with high birth rates currently, particularly in Asia.
China's population is predicted to drop from 1.4 billion to 732 million in 2100, Thailand may go from 71 million to 25 million people and South Korea could drop from 53 million to 27 million, which is similar to the current population of Australia.
Australia’s fertility rate is already in decline at 1.86, but our population trajectory is trending upwards because of migration.
Australia's population is forecast to reach 36 million by the end of the century.
The number of people in sub-Saharan Africa is expected to triple over the course of the century, but the major diver here is a falling death rate with increased access to medication.
Africa is not exempt from a falling fertility rate, for example, Niger currently has the highest rate in the world with an average of seven children per woman, but this will fall to 1.8 by 2100.
What is the burden of an ageing population?
An ageing population can slow down economic growth as it presents an increasing burden on a country's health and welfare systems.
"If you have a younger population you have more people to support elderly people in the community and also children and that's what you want in your population mix,” Dr Boucher said.
"The countries with higher population rates and a younger population - some of them are emerging economies, places like Indonesia."
But being an economic powerhouse is not driven by demographics alone.
“Population youth is not the only ingredient that you need for economic success, you also need stable government, you also need robust industry partners, so I guess that is part of the question as well," Dr Boucher said.
"It is not all about demographics when it comes to economic success for a country."
How is this likely to affect immigration policies?
Australia has been singled out as a likely success story, moving up in the global rankings due to high rates of immigration relative to population size.
“Countries bolstered by immigration that rose up in the global rankings by GDP were Australia and Israel,” the study reads.
Associate Professor of Demography at Monash University Rebecca Kippen said immigration has had a slight positive impact on Australia’s growth in the past.
“When the migrants are coming in they're also consuming the things the rest of us are consuming, they are buying products and buying houses in addition to working and adding to productivity of Australia,” Dr Kippen said.
“When you have more people working you can have more efficiencies within business.”
More liberal immigration policies are expected so countries can balance their ageing population against their workforce.
"I think a lot of countries that did not count on migration, will count on migration as they will need workers to support the aged care sector," Dr Boucher said.
"You are seeing this already, countries like Japan, that historically did not want to have any migration, now do have migration in those sectors.”
COVID-19 travel restrictions have thrown a spanner in the works, as migration, especially temporary migration, can no longer be counted upon.