The world’s population is likely to peak in 2064 at about 9.7 billion, and then decline to about 8.8 billion by 2100 – two billion lower than some previous estimates, according to a major study published in the Lancet
Improvements in access to modern contraception and education for girls and women are generating widespread, sustained declines in fertility, it concludes.
Researchers from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington used novel methods for forecasting mortality, fertility and migration.
By 2100, they conclude, 183 of 195 countries will have total fertility rates (TFR) – the average number of children a woman delivers over her lifetime – below the replacement level of 2.1 births per woman.
The forecasts contrast with projections of “continuing global growth” by the UN population division and highlight huge challenges to economic growth from a shrinking workforce.
It predicts Ireland’s population (4.9 million in 2019) will peak at 5.8 million in 2057. The Republic’s population is predicted to decline to 4.82 million by 2100, assuming adoption of UN sustainable development goals on educational attainment and “meeting contraceptive need”.
With an estimated 2.37 billion individuals globally over 65 in 2100, compared with 1.7 billion under 20, the study underlines “the need for liberal immigration policies in countries with significantly declining working age populations”.
The study was part funded by the Bill & Melinda Gates Foundation.
"Continued global population growth through the century is no longer the most likely trajectory for the world's population," said IHME director Dr Christopher Murray, who led the research.
Lancet editor-in-chief Dr Richard Horton said the research "offers a vision for radical shifts in geopolitical power, challenges myths about immigration, and underlines the importance of protecting and strengthening the sexual and reproductive rights of women".
The 21st century would see a revolution in the story of human civilisation, he predicted. "Africa and the Arab World will shape our future, while Europe and Asia will recede in their influence. By the end of the century, the world will be multipolar, with India, Nigeria, China and the US the dominant powers."
The global TFR is predicted to steadily decline, from 2.37 in 2017 to 1.66 in 2100, with rates falling to about 1.2 in Italy and Spain. Ireland's TFR is predicted to reduce to 1.57 by 2100; it was 1.84 in 2017.
Much of the decline is predicted in high-fertility countries, notably in sub-Saharan Africa where rates are expected to fall below replacement level for the first time. Nevertheless, its population is forecast to triple to 3.07 billion in 2100, as death rates decline and an increasing number of women enter reproductive age.
‘Fewer workers’
North Africa and the Middle East is the only other region predicted to have a larger population in 2100 (978 million) than in 2017 (600 million).
Many of the fastest-shrinking populations will be in Asia and central and eastern Europe. Populations are expected to more than halve in 23 countries and territories, including Japan (from 128 million people in 2017 to 60 million in 2100), Spain (46 to 23 million), Italy (61 to 31 million), Portugal (11 to 5 million) and South Korea (53 to 27 million). China's population is predicted to reduce from 1.4 billion in 2017 to 732 million.
"While population decline is potentially good news for reducing carbon emissions and stress on food systems, with more old people and fewer young people, economic challenges will arise as societies struggle to grow with fewer workers and taxpayers, and countries' abilities to generate the wealth needed to fund social support and healthcare for the elderly are reduced," noted first author Prof Stein Emil Vollset.
Sub-Saharan Africa is likely to become an increasingly powerful continent as its population rises. Nigeria is projected to be the only country among the world’s 10 most populated nations to see its working-age population grow over the century, supporting rapid economic growth.
“For high-income countries with below-replacement fertility rates, the best solutions for sustaining current population levels, economic growth, and geopolitical security are open immigration policies and social policies supportive of families having their desired number of children,” Dr Murray said.
In a commentary, Prof Ibrahim Abubakar of University College London said the findings indicate the need for "a fundamental rethink of global politics".
“Nations would need to cooperate at levels that have eluded us to date to strategically support and fund the development of excess skilled human capital in countries that are a source of migrants,” he believed.
An equitable change in global migration policy would need the voice of rich and poor countries, he said. “The projected changes in the sizes of national economies and the consequent change in military power might force these discussions.”
“The choice we face is whether we improve health and wealth by allowing planned population movement or if we end up with an underclass of imported labour and unstable societies,” he said.
With challenges such as climate change and greater global migration, “the distribution of working-age populations will be crucial to whether humanity prospers or withers”, Prof Abubakar added.
