Shock predictions for global population
More than 23 countries could see their populations halve by the end of the century according to a fascinating new study of population, fertility and migration.
The University of Washington's Institute for Health Metrics and Evaluation's findings showed that global fertility rates will nearly halve from 2.4 in 2017 to 1.7 in 2100 - largely due to factors such as the availability of contraception and women in education and careers.
The results up-end current expectations and suggest that "once global population decline begins, it will probably continue inexorably."
"Our findings suggest that, because of progress in female educational attainment and access to contraception contributing to declining fertility rates, continued global population growth through the century is no longer the most likely trajectory for the world's population," the authors said.
It states 23 countries including Japan, Spain, Italy, Thailand, Portugal, South Korea and Poland are expected to see their populations halve by the end of the century.
For example, Japan's population is projected to fall from a peak of 128 million in 2017 to less than 53 million by 2100. Italy is expected to drop from 61 million to 28 million over the same period.
The world's most populous country, China, is expected to peak at 1.4 billion people in four years before falling back to 732 million by 2100 with India becoming the largest nation.
Sub-Saharan Africa, meanwhile, will triple in size to some three billion people, with Nigeria alone expanding to almost 800 million in 2100.
Australia's population is due to peak at 36.38 million in 2096, with growth being sustained due to net migration rather than replacement fertility rates, the authors said.
"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.
"Our forecasts for a shrinking global population have positive implications for the environment, climate change, and food production, but possible negative implications for labour forces, economic growth, and social support systems in parts of the world with the greatest fertility declines."
Australia will also rise up the economic ranks before the end of the century from being the world's 12th biggest economy in 2017 to the eighth by 2100 putting it just behind the UK.
The US is expected to retain its status as the world's largest economy until 2050 when it will be overtaken by China. However this will then reverse, with the US the world's largest by 2100 the report states.
"By the end of the century, the world will be multipolar, with India, Nigeria, China and the United States the dominant powers," said The Lancet editor Richard Horton, describing the study as outlining "radical shifts in geopolitical power."
As fertility falls and life expectancy increases worldwide, the number of children under five is forecast to decline by more than 40 per cent, from 681 million in 2017 to 401 million in 2100, the study found.
At the other end of the spectrum, 2.37 billion people - more than a quarter of the global population - will be over 65 years old by then.
Those over 80 will balloon from about 140 million today to 866 million. Sharp declines in the number and proportion of the working-age population will also pose huge challenges in many countries.
- with wires
Originally published as Shock predictions for global population