Global fertility may have fallen below replacement level, threatening workforces, aging societies, and mounting economic pressure within roughly one generation
Global fertility may have fallen below replacement level for the first time in human history, putting the world population on course for decline within roughly one generation, a new study has warned.
The paper, Terra Incognita: The Economics of a Shrinking World, published earlier this month by economics professor Jesus Fernandez-Villaverde of the University of Pennsylvania and Northwestern University researcher Patrick Norrick, warns that prolonged low fertility could shrink workforces, rapidly age societies, and strain economies and welfare systems.
The researchers estimate that humanity is likely already below replacement fertility – the average number of children per woman needed for each generation to replace itself. The global threshold is around 2.2, while the study puts the current rate at no higher than 2.19, suggesting the world may have only just crossed it.
“As of 2026, humanity is likely to be below replacement level: we are having fewer births than we need to keep population constant in the long run… this has never happened before in our history as a species, not even during wars or pandemics,” the authors stated.
The analysis covers 236 countries and territories from 1950 to 2023, with fertility declining in 219. On average, countries have lost around 0.062 births per woman annually, and there is little evidence the trend is leveling off, authors note.
The global population is not shrinking yet because large generations born in previous decades are still having children, but the researchers estimate this effect could sustain growth for only another three decades, with population peaking at around 9 billion in 2056 before declining.
The authors note the trend has spread well beyond rich countries, with fertility rates in 2025 estimated at just 0.87 in Thailand, 1.01 in Colombia, 1.35 in Iran and 1.52 in Brazil. They say there is no automatic mechanism driving fertility back toward replacement level because there is no single explanation for falling birth rates: while housing and childcare costs, economic insecurity, contraception, and changing social norms may all contribute, none fully explains the global trend.
The economic consequences of the looming population decline could be far-reaching, the study warns. Smaller generations mean fewer workers supporting growing elderly populations, straining pensions, healthcare, and public finances while slowing growth. In the US, the authors estimate that 2% annual productivity growth combined with a 0.5% contraction in the workforce would reduce long-term GDP growth to roughly 1.5%.
UN demographic forecasts have also shifted sharply downward over the past decade. In 2015, the organization projected more than 11.2 billion people in 2100, with no peak before the end of the century. Its 2024 revision instead projected that the population would peak at around 10.3 billion in the mid-2080s before declining slightly to about 10.2 billion by 2100.
The world’s population crossed the 8 billion mark in 2022, according to UN estimates, and currently stands at approximately 8.3 billion.
Musk weighs in
US tech billionaire Elon Musk, who has repeatedly warned about falling birth rates, reacted to the study after an X user described its findings as an “existential crisis.” “I’ve been warning about this for years,” he wrote.
Musk, who has 13 children, has repeatedly described declining birth rates as one of the greatest threats to civilization. In 2022, he wrote that “population collapse due to low birth rates is a much bigger risk to civilization than global warming.” Last year, he warned that “Low birth rates will end civilization” and called for the issue to be treated as a national emergency, while suggesting Europe could “die out” unless birth rates recover.
Last weekend, commenting on a paper outlining ancient Rome’s attempts to boost its population, Musk wrote: “The reason Rome fell was because they stopped making Romans.”
Russia’s demographic challenge
Russian officials have long warned about the country’s demographic challenges. According to state statistics agency Rosstat, Russia’s total fertility rate fell to around 1.305-1.374 children per woman last year, alongside some of the lowest monthly and quarterly birth figures in modern Russian history.
Moscow has introduced childbirth payments, expanded maternity benefits and other family support measures to reverse the trend. It has also revived the Soviet-era “Mother Heroine” title, which provides financial rewards to women with ten or more children, and discouraged the promotion of “child-free” lifestyles.
Russian President Vladimir Putin has repeatedly stressed the importance of improving economic and social conditions in order to promote larger families and make parenthood a widely supported choice. He has backed a national family support service and established a presidential council on family and demographic policy in 2024.
