The research, published in Environmental Research Letters, concludes that humanity has already surpassed Earth's sustainable carrying capacity. Scientists say continued population growth combined with current levels of resource use will place even greater strain on ecosystems and societies around the world.

The study examined more than 200 years of global population data and identified a major turning point in human population trends that began during the mid twentieth century.

Lead author Corey Bradshaw, Matthew Flinders Professor of Global Ecology at Flinders University, says the findings reveal a clear sign that humanity is operating beyond the planet's natural limits.

"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.

Population Growth and Earth's Limits

The international research team, which included the late Professor Paul Ehrlich, analyzed historical population records and used ecological growth models to study changes in both population size and growth rates over time.

Researchers compared trends across different world regions and examined how population growth related to climate change, carbon emissions, and ecological footprints. Their goal was to better understand how rising human numbers contribute to environmental stress.

According to the study, population growth accelerated before the 1950s as the number of people increased worldwide. More people led to greater innovation, increased energy use, and technological advances that helped support further growth.

That pattern changed in the early 1960s. While the global population continued rising, the rate of growth began slowing.

"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."

Fossil Fuels and Ecological Overshoot

Professor Bradshaw says this level of population growth is only possible because societies have relied heavily on fossil fuels and consumed natural resources faster than Earth can replenish 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 gap between that sustainable estimate and today's global population of 8.3 billion highlights the scale of worldwide overconsumption.

According to the study, dependence on fossil fuels has temporarily hidden the effects of ecological overshoot by supporting food production, industrial growth, and energy supplies. However, the same processes have also intensified climate change, pollution, and environmental degradation.

The researchers also found strong links between population size and rising global temperatures, growing ecological footprints, and increased carbon emissions during the negative demographic phase. The study concluded that total population size explained environmental changes more strongly than per capita consumption alone.

Professor Bradshaw says both population growth and consumption patterns are increasing pressure on the planet.

"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."

Risks to Climate, Food, and Human Stability

The researchers emphasize that the study does not predict a sudden collapse of civilization. Instead, they describe it as a realistic assessment of the growing pressures shaping humanity's future.

Among the risks linked to exceeding Earth's "biocapacity" are worsening climate impacts, biodiversity loss, declining food and water security, and increasing inequality.

Professor Bradshaw says societies will need to rethink how land, water, energy, and raw materials are used if future generations are to live safely and sustainably.

"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 researchers hope the findings encourage governments, organizations, and communities to focus on long term planning, recognize environmental limits, and support strategies that stabilize population growth, reduce consumption, and protect natural systems.

"The choices we make over the coming decades will determine the well-being of future generations and the resilience of the natural world that supports all life," concludes Professor Bradshaw.

The project received support from The Kids Research Institute Australia and Population Matters.

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.