The Earth has already exceeded its ability to support the global population sustainably, with new research warning of increasing pressure on food security, climate stability, and human wellbeing. However, slowing population growth and raising global awareness could still offer humanity some hope.
Published in Environmental Research Letters, the study shows that humans have pushed well beyond the planet's long-term capacity and that continued growth under current patterns of consumption will intensify environmental and social challenges for communities worldwide.
The research examined more than two centuries of global population data and uncovered a major shift in human population dynamics that began in the mid-twentieth century.
Lead author, Matthew Flinders Professor of Global Ecology Corey Bradshaw, from Flinders University says the trend reveals a clear biological signal that humanity is living far beyond what the Earth can support.
"Earth cannot keep up with the way in which we are using resources. It cannot support even today's demand without major changes, with our findings showing that we are pushing the planet harder than it can possibly cope," says Professor Bradshaw from the Global Ecology Laboratory in the College of Science and Engineering.
The researchers, including distinguished Professor Paul Ehrlich who recently passed away, analysed more than two hundred years of global population records and used ecological growth models to track how population size and growth rates have changed over time.
They tested the direction of these trends and compared results across world regions. They also measured how population size has historically aligned with changes in climate, emissions, and the ecological footprint to understand how human numbers cause environmental stress.
The study found that before the 1950s, global population growth actually sped up as human abundance increased. More people meant more innovation, more energy use, and more rapid technological development that supported further expansion.
However, this pattern broke down in the early 1960s when the global growth rate began to fall even as the population continued to rise.
"This shift marked the beginning of what we call 'a negative demographic phase," says Professor Bradshaw.
"It means that adding more people no longer translates into faster growth. When we examined this phase, we found the global population is likely to peak somewhere between 11.7 and 12.4 billion people by the late 2060s or 2070s if current trends hold."
Professor Bradshaw says this upper limit is dangerous and has only been possible to date because human societies have relied on fossil fuels and drained natural resources faster than nature can replace them.
"The truly sustainable population is much lower and closer to what the world supported in the mid-twentieth century. Our calculations show a sustainable global population closer to about 2.5 billion people if everyone were to live within ecological limits and comfortable, economically secure living standards," he says.
The researchers say the enormous gap between that sustainable number and today's population of now 8.3 billion highlights the scale of global overconsumption. They argue that this overshoot has been hidden for decades by heavy reliance on fossil fuels, which boosted food production, energy supply, and industry, but also accelerated climate change and pollution.
The study shows a strong link between increasing population size and rising global temperatures, larger ecological footprints, and higher carbon emissions during the negative phase. Total population size explained more variation in these environmental indicators than per-capita consumption.
Professor Bradshaw says this highlights how both human numbers and consumption patterns jointly intensify environmental stress. "Humanity's current path will push societies into deeper crises unless we make major changes," he says.
"The planet's life support systems are already under strain and without rapid shifts in how we use energy, land, and food, billions of people will face increasing instability. Our study shows these limits are not theoretical but unfolding right now."
The researchers stress that the study does not predict sudden collapse, but instead offers a realistic assessment of the long-term pressures shaping humanity's future. The consequences of overshooting Earth's 'biocapacity' include stronger climate impacts, declining biodiversity, reduced food and water security, and widening inequality.
Professor Bradshaw says society must rethink how it uses land, water, energy, and materials if future generations are to live safe and stable lives.
"Smaller populations with lower consumption create better outcomes for both people and the planet," he says. "The window to act is narrowing, but meaningful change is still achievable if nations work together."
The team hopes the findings encourage governments, organisations, and communities to plan for the long term, recognise Earth's environmental limits, and focus on strategies that reduce consumption, stabilise population, and protect natural systems.
"The choices we make over the coming decades will determine the wellbeing of future generations and the resilience of the natural world that supports all life," concludes Professor Bradshaw.
Acknowledgements:
The Kids Research Institute Australia and Population Matters supported various aspects of the project.
The paper, ''Global human population has surpassed Earth's sustainable carrying capacity' by Corey J.A. Bradshaw, Melinda A. Judge (University of Western Australia), Daniel T. Blumstein (University of California, USA), Paul R. Ehrlich (Stanford University, USA), Aisha N. Dasgupta (University of Cambridge, UK), Mathis Wackernagel (University of California, USA), Lewis J.Z. Weeda (University of Western Australia) and Peter N. Le Souëf (University of Western Australia) was published in Environmental Research Letters. DOI: 10.1088/1748-9326/ae51aa
