Earth’s limits test growth model

Humanity is consuming resources at a rate the planet cannot sustain, a new peer-reviewed study has warned, placing pressure on food systems, climate stability, biodiversity and living standards as the global population moves deeper into ecological overshoot.

Researchers led by Corey J. A. Bradshaw of Flinders University found that the world’s population has already surpassed Earth’s sustainable carrying capacity, with today’s 8.3 billion people well above the level that could be maintained over the long term without depleting ecosystems. Their paper, published in Environmental Research Letters, analysed more than two centuries of population data and linked demographic trends with climate, emissions and ecological footprint indicators.

The study challenges the long-held assumption that human ingenuity and technology can indefinitely offset rising demand. It found that before the 1950s, population growth was reinforced by expanding energy use, technological development and wider economic activity. That pattern began to change in the mid-20th century, and by 1962 the world had entered what the researchers describe as a “negative demographic phase”, where additional population no longer translated into faster growth.

Bradshaw said Earth “cannot keep up” with the way resources are being used and warned that even today’s demand cannot be supported without major changes. The study estimates that a sustainable global population under comfortable and economically secure living standards would be closer to 2.5 billion, far below current levels. It also projects that, if present trends hold, the global population could peak between 11.7 billion and 12.4 billion in the late 2060s or 2070s.

That forecast is higher than the latest UN central projection, which places the world population at about 8.2 billion in 2024 and sees it rising to around 10.3 billion in the mid-2080s before easing slightly by 2100. The gap reflects differences in modelling approach: the UN focuses on fertility, mortality and migration trends, while Bradshaw’s team applies ecological growth models to assess the relationship between population size, resource use and environmental stress.

The warning comes as multiple environmental indicators point to sustained pressure on natural systems. Earth Overshoot Day fell on July 24 in 2025, marking the date when humanity’s annual demand exceeded what ecosystems could regenerate within that year. Global Footprint Network estimates that humanity is operating well above the planet’s biological budget, drawing down resource stocks and adding carbon dioxide to the atmosphere.

The planetary boundaries framework has also moved further into danger territory. The Stockholm Resilience Centre says seven of nine boundaries have now been transgressed, including climate change, biosphere integrity, land-system change, freshwater use, biogeochemical flows, novel entities and ocean acidification. Ozone depletion and aerosol loading remain within the safe zone, though aerosol risks vary by region.

The new study is likely to sharpen debate over population policy, consumption patterns and economic models built around continuous expansion. Its authors argue that fossil fuels have helped societies mask ecological limits by allowing higher food production, faster transport, industrial growth and urban expansion, but those gains have come with climate and biodiversity costs. The findings also suggest that population size explains a large share of changes in global temperature anomaly, ecological footprint and total emissions, though per-capita consumption remains a central factor in wealthier economies.

Demographers and sustainability researchers have long cautioned that global averages can obscure sharp inequalities. High-income countries account for a disproportionate share of consumption, while many lower-income regions have younger populations, higher fertility and lower per-capita emissions. The Bradshaw study notes that the negative demographic phase emerged earlier in higher-income regions and later in lower-income, higher-fertility regions, underscoring the uneven timing of demographic transition.

Policy responses remain politically sensitive. Measures that improve education, expand access to healthcare, reduce child mortality, support women’s economic participation and widen voluntary family-planning access have been linked to lower fertility over time. At the same time, reducing waste, changing food systems, restoring ecosystems, improving water management and accelerating clean energy deployment are seen as essential to easing pressure without placing the burden solely on population control.