Humanity may have entered an unprecedented demographic era, with global fertility falling below the level required to replace each generation, according to a new study warning that population decline could begin within decades.
Terra Incognita: The Economics of a Shrinking World, by University of Pennsylvania economist Jesús Fernández-Villaverde and Northwestern University researcher Patrick Norrick, estimates the global fertility rate at no more than 2.19 children per woman, marginally below the roughly 2.2 replacement threshold.
Examining 236 countries and territories between 1950 and 2023, the researchers found fertility declined in 219 and said there was little evidence of the trend stabilising. “As of 2026, humanity is likely to be below replacement level,” they wrote, describing it as something that has “never happened before in our history as a species, not even during wars or pandemics.”
Population growth could nevertheless continue for around three decades because of demographic momentum, with the researchers estimating a peak of roughly nine billion people around 2056 before numbers begin falling.
They warn that shrinking younger generations could leave fewer workers supporting increasingly elderly populations, placing greater pressure on pensions, healthcare, government finances and economic growth.
Fertility declines are also increasingly evident outside wealthy Western countries, with particularly low rates estimated in Thailand, Colombia, Iran and Brazil. Elon Musk, a longstanding critic of falling birth rates, responded to the findings by saying, “I’ve been warning about this for years.”
He has previously argued that “population collapse due to low birth rates is a much bigger risk to civilization than global warming” and more recently declared that “Low birth rates will end civilization.”
The study comes as UN population projections have also been revised substantially downward, although the UN still forecasts a later population peak than the researchers, currently projecting about 10.3 billion people in the mid-2080s before a gradual decline.
I’ve been warning about this for years https://t.co/kHFPFjNkE7
— Elon Musk (@elonmusk) August 23, 2026
