New Study Says Earth Can Sustain Only 2.5 Billion People

The Earth can no longer sustain its current human population, according to a study published Monday in Environmental Research Letters by an international team of researchers. The paper concludes that the planet's sustainable carrying capacity is roughly 2.5 billion people — less than a third of today's 8.3 billion — and that decades of fossil fuel dependence have masked the true scale of ecological overshoot.

A Biological Turning Point

Led by Flinders University ecologist Corey Bradshaw, the research team analyzed more than two centuries of global population records using ecological growth models. They found that before the 1950s, population growth accelerated as human numbers rose — more people meant more innovation and energy use, which supported further expansion. That pattern reversed in the early 1960s, when the global growth rate began to fall even as the population continued climbing.

"This shift marked the beginning of what we call 'a negative demographic phase,'" Bradshaw said. "It means that adding more people no longer translates into faster growth." The study projects that if current trends hold, the global population will peak between 11.7 and 12.4 billion by the late 2060s or 2070s.

The gap between that trajectory and a sustainable level of about 2.5 billion has been bridged only through intensive extraction of natural resources, the researchers argue. "Earth cannot keep up with the way in which we are using resources," Bradshaw said. "It cannot support even today's demand without major changes."

Environmental Links and What Comes Next

The study found that total population size explained more variation in rising global temperatures, ecological footprints, and carbon emissions than per-capita consumption alone — underscoring the combined role of both human numbers and consumption patterns. The consequences of overshooting the planet's biocapacity, the researchers warned, include declining biodiversity, reduced food and water security, and widening inequality.

The co-authors include the late Paul Ehrlich of Stanford University, as well as researchers from the University of Western Australia, the University of Cambridge, and the University of California. The team stressed the study does not predict sudden collapse but urged governments to pursue rapid shifts in energy, land use, and food systems.

"The window to act is narrowing, but meaningful change is still achievable if nations work together," Bradshaw said.