Earth’s Sustainable Population May Be Limited to 2.5 Billion

A new scientific study suggests that the Earth may no longer be able to sustainably support its current population. Published in Environmental Research Letters, the research estimates that the planet’s long-term carrying capacity is around 2.5 billion people—significantly lower than today’s global population of over 8 billion.

Led by ecologist Corey Bradshaw from Flinders University, the research team analyzed more than 200 years of population data using ecological growth models. Their findings show that until the mid-20th century, population growth followed a self-reinforcing pattern, where more people led to increased innovation, energy use, and further expansion.

However, this trend began to shift in the early 1960s. While the global population continued to grow, the growth rate started to decline. Researchers describe this transition as a “negative demographic phase,” where adding more people no longer accelerates growth but instead places increasing strain on global systems.

According to the study, if current trends continue, the global population could peak between 11.7 and 12.4 billion by the late 2060s or 2070s. The gap between this projected peak and the sustainable level of 2.5 billion has been bridged through intensive resource extraction, much of it driven by fossil fuel use.

The researchers argue that Earth’s natural systems are no longer able to keep pace with human demand. While fossil fuels have temporarily masked the scale of ecological overshoot, the limits of this model are becoming increasingly apparent.

The study also highlights the environmental implications of population growth. It found that total population size plays a more significant role in rising global temperatures, carbon emissions, and ecological footprints than per-capita consumption alone. This underscores the need to address both population dynamics and consumption patterns together.

Consequences of exceeding the planet’s biocapacity include biodiversity loss, declining food and water security, and growing inequality. The research team includes contributors from Stanford University, University of Cambridge, and University of California, including the late biologist Paul Ehrlich.

Importantly, the authors emphasize that their findings do not predict an imminent collapse. Instead, they call for urgent and coordinated global action, particularly in energy systems, land use, and food production. While the window for meaningful change is narrowing, they stress that a sustainable future is still within reach if nations act together.