MercoPress. South Atlantic News Agency

Earth will be home to 8.8 billion people in 2100, two billion less than current UN projections

More than 20 countries - including Japan, Spain, Italy, Thailand, Portugal, South Korea and Poland - will see their numbers diminish by at least half

The Earth will be home to 8.8 billion people in 2100, two billion fewer than current United Nations projections, according to a major study published on Wednesday that foresees new global power alignments shaped by declining fertility rates and graying populations.

By century's end, 183 of 195 countries - barring an influx of immigrants - will have fallen below the replacement threshold needed to maintain population levels, an international team of researchers reported in The Lancet.

More than 20 countries - including Japan, Spain, Italy, Thailand, Portugal, South Korea and Poland - will see their numbers diminish by at least half. China's will fall nearly that much, from 1.4 billion people today to 730 million in 80 years.

Sub-Saharan Africa, meanwhile, will triple in size to some three billion people, with Nigeria alone expanding to almost 800 million in 2100, second only to India's 1.1 billion.

“These forecasts suggest good news for the environment, with less stress on food production systems and lower carbon emissions, as well as significant economic opportunity for parts of sub-Saharan Africa,” lead author Christopher Murray, director of the Institute for Health Metrics and Evaluation (IHME) at the University of Washington.

“However, most countries outside of Africa will see shrinking workforces and inverting population pyramids, which will have profound negative consequences for the economy.”

For high-income countries in this category, the best solutions for sustaining population levels and economic growth will be flexible immigration policies and social support for families who want children, the study concluded.

“However, in the face of declining population there is a very real danger that some countries might consider policies that restrict access to reproductive health services, with potentially devastating consequences,” Murray cautioned.

“It is imperative that women's freedom and rights are at the top of every government's development agenda.”

Social services and healthcare systems will need to be overhauled to accommodate much older populations.

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.

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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.

By 2050, China's gross domestic product will overtake that of the United States, but fall back into second place by 2100, they predict.

India's GDP will rise to take the number three spot, while Japan, Germany, France and the UK will stay among the world's 10 largest economies.

Brazil is projected to fall in ranking from eighth today to 13th, and Russia from the number 10 spot to 14th. Historical powers Italy and Spain, meanwhile, decline from the top 15 to 25th and 28th, respectively.

Until now, the United Nations - which forecasts 8.5, 9.7 and 10.9 billion people in 2030, 2050 and 2100, respectively - has virtually had a monopoly in projecting global population.

Founded in 2007 and supported by the Bill and & Melinda Gates Foundation, the IHME had become a global reference for health statistics, especially its annual Global Burden of Disease reports.