Quick facts:

  • Humanity’s impact on the environment is a product of our population and our environmental footprint per person. Our footprint is, in turn, a product of our consumption pattern (affluence) and the way we achieve it (technologies, behaviours and institutions). This is often summarised in the “IPAT” equation: I = P x A x T (Impact = Population x Affluence x Technology)
  • Humanity’s impacts on the biosphere are now so profound that geologists have labelled the current period the “Anthropocene”, meaning the era shaped by humans.
  • Global warming is one feature of the Anthropocene. Others include species extinctions, persistent pollutants, loss of forests and other natural habitats, soil erosion, freshwater diversions, ocean acidification and overloading the environment with nitrogen and phosphorus.
  • We are in the middle of the planet’s sixth great extinction event, in which the number of species on earth is greatly reduced. Species extinctions are now happening many times faster than they were over thousands of years before the industrial revolution. Humans are the cause.
  • While some of the impacts of the richest billion people are avoidable (either frivolous or wasteful), the poorest half of humanity need more access to the resources of nature in order to attain a reasonable quality of life. The quality of life they will be able to achieve depends greatly on how many people there will be.
  • “Carrying capacity” is the number of people who can live, in the way they happen to be living, without damaging the environment or diminishing its ability to support people in the future.
  • Humanity has been exceeding the sustainable carrying capacity of the Earth since 1981, according to the Global Footprint Network.
  • We can increase (and have greatly increased) the planet’s carrying capacity by doing things in less impactful ways. But population growth undoes all the efforts we make to have less impact per person, or to deliver better access to food, water, energy and services per person.
  • The lower the peak global population, the more likely that humanity can achieve a peaceful and sustainable future




  • Australia State of Environment 2021 Report.  The SoE 2021 report acknowledges that human population growth contributes to pressures on Australia’s environment and, in particular, that it has ‘very high impact’ on biodiversity.   SPA wrote a Media Release,  “Population growth has ‘very high impact’ on biodiversity” in response
  • SPA supporting document to the “Parliamentary Joint Standing Commmitee On Migration.”  Earlier in 2023,  SPA made a submission to the Joint Standing Committee on Migration inquiry into Migration, Pathway to Nation Building,  to which SPA was invited to a public hearing.  A question from the committee chair, “what do you ultimately see as the sustainable population level for the country?” inspired an answer in writing.   The attached documents states that: “SPA believes Australia’s population may already exceed a sustainable long-term level. We advocate for stabilisation below 30 million people because this is readily achievable and would minimise the further escalation of risks. However, a fully precautionary approach, reducing future risks still further, would then allow the population to decline gradually, at least until State of the Environment reports show predominantly improving trends in environmental health.”
  • Lane, M. (2017). Exploring short-term and long-term time frames in Australian population carrying capacity assessment. Population and Environment, 38(3), 309-324.  A recent study of Australia’s carrying capacity at Queensland University of Technology estimated that it ranges between 9 million and 40 million people, depending on what time scale was assumed. If long term sustainability were the aim, then the study found carrying capacity would
    need to be towards the lower end (9 million).
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