United Nations demographers have been anticipating since last year that the world population could stop growing by 2,100 as fertility rates decline, projecting a peak of 10.9 billion people by the end of the century, compared to approximately 7.8 billion now.
But a study published Tuesday in The Lancet, the medical journal, has challenged that forecast, with major economic and political implications. The study stated that the world population could reach a maximum of 9,700 million in 2064, almost four decades earlier, and decrease to 8,800 million in 2100.
Furthermore, the study concluded, the elderly will account for a larger share of the total than expected in the UN forecast, and the populations of at least 23 countries, including Japan, Thailand, Italy and Spain, could be reduced by more than 50 percent . The study also projected significant declines in the working-age populations of China and India, the two most populous countries, heralding a weakening in their global economic power.
The study’s projections, if confirmed, also have significant consequences for the United States, whose economy is expected to follow the size of China by 2035. As China’s working-age population declines in the second half of the century, according to the study, United States States could claim top economic position by 2098, if immigration continues to replenish the US workforce.
“The continued growth of the world population throughout the century is no longer the most likely path for the world population,” said Dr. Christopher Murray, director of the Institute for Health Measurement and Assessment at the Faculty of Medicine of the University of Washington, who led the study.
Dr. Murray said the study “gives governments in all countries the opportunity to start rethinking their policies on migration, the workforce and economic development to address the challenges of demographic change.”
An important underlying reason behind the findings is the improved access to modern contraception and the education of girls and women, which according to the study “would accelerate fertility decline and slow population growth.”
While the most recent United Nations population forecast, made in June 2019, also noted declining fertility, the new study said the consequences would be felt much sooner and with greater impact.
John Wilmoth, director of the population division of the United Nations Department of Economic and Social Affairs, which produces the organization’s projections every two years, said Tuesday that he had not yet fully read the study. But he said he had made some assumptions about fertility, mortality, and migration that helped shape the conclusions.
One of the most important assumptions, he said in a telephone interview, was that countries with low fertility rates would do nothing to increase them from now until 2100.
“It is an extreme assumption to think that countries are not going to think about getting out of the problem for the next 80 years,” he said.
Mr. Wilmoth also said that the United Nations had been following population trends for 70 years and that its projections “represent a vision of consensus” among demographers. Still, he said, “I’m glad for this kind of creative research into other ways of looking at these things.”
The prognostic methodology used in the study found that by 2,100, 183 out of 195 countries would have total fertility rates, the average number of children a woman gives birth to during her lifetime, below the replacement level of 2.1 births. That is the level necessary to prevent population decline.
The study also suggested that the decline could be offset by immigration, with countries promoting liberal immigration policies better able to maintain their populations and support economic growth.
Some countries with fertility rates below replacement level, such as the United States, Australia and Canada, are likely to replenish their working-age populations through net immigration, the study said, although it noted uncertainty about such a forecast. The United States’ backlash against immigration, according to the study, could threaten “the country’s potential to sustain population and economic growth.”
