The Overpopulation Project

Over the past two centuries Earth’s human population has doubled, and doubled again, and doubled yet again, increasing from 1 billion to 8 billion people. This huge increase is the root of grave global environmental problems, from climate change to mass species extinction. Yet in recent years, discussing population issues has become taboo among many environmentalists and policymakers. The Overpopulation Project aims to end the silence, by researching the environmental impacts of overpopulation, exploring humane policies to end population growth around the world, and fostering public and scholarly discussion of these issues.

For the past seven years, Swedish ecologist Frank Götmark, Australian agronomist Jane O'Sullivan and I have been co-principle investigators for The Overpopulation Project, headquartered at the University of Gothenburg, Sweden. With help from our research assistant Pernilla Hansson, we study the environmental impacts of overpopulation and advocate humane policies to reduce human numbers and preserve biodiversity. Our recent publications include:

The Impact of Immigration Policy on Future US Population Size. P. Cafaro. The Journal of Population and Sustainability 9 (2025): 61-84.
Big Thirsty Australia: How Population Growth Threatens Our Water Security and Sustainability. J. Sobels, P. Cook, S. Kanck and J. O’Sullivan. Sustainable Population Australia (2024).
Public Opinions about Causes of Declining Fertility in Developing Countries: Differences among Citizens in Sweden and Nigeria. F. Götmark and N. Wetzler. The Journal of Population and Sustainability 8 (2024): 13-34.

* Population Effects on Biodiversity and Climate Change: Evidence from Recent Scientific Literature, 2010-2022. P. Cafaro, P. Hansson and F. Götmark. Indian Journal of Population and Development 3 (2023): 149-206.

* Procreation and Consumption in the Real World. P. Cafaro. Environmental Ethics 45 (2023): 295-306.

* An analysis of three decades of increasing carbon emissions: The weight of the P factor. L. Tamburino, P. Cafaro and G. Bravo. Sustainability (2023) 15: 3245.

* Overpopulation is a major cause of biodiversity loss and smaller human populations are necessary to preserve what is left. P. Cafaro, P. Hansson and F. Götmark. Biological Conservation 272 (2022): 109646.

* Reducing human numbers and the size of our economies is necessary to avoid a mass extinction and share Earth justly with other species. P. Cafaro. Philosophia 50 (2022): in press.

* Climate change and world population. J. O'Sullivan. In T. Letcher (ed.), The Impacts of Climate Change: A Comprehensive Study of Physical, Biophysical, Social, and Political Issues (Elsevier, 2021): 313-350.

* Discussing Population Concepts: Overpopulation is a Necessary Word and an Inconvenient Truth. F. Götmark, J. O’Sullivan and P. Cafaro. Indian Journal of Population and Development 1 (2021): 51-60.

* Climate Ethics and Population Policy: A Review of Recent Philosophical Work. P. Cafaro. WIRES: Climate Change 12 (2021): e748 (1-17).

* Just Population Policies for an Overpopulated World. P. Cafaro. Ecological Citizen 5 (2021): epub-046-1 (1-10).

Here are some of our most popular recent blog posts:

* Human population reduction is not a quick fix for environmental problems. August 15, 2023.

* Walk the talk: the world needs more Gretas and fewer Leonardos. August 8, 2023.

* Why Overpopulation Should Be a Women’s Issue. June 13, 2023.

And here are some old favorites:

* Eight Billion – Our Greatest Mistake. January 3, 2023.

* Conserving biodiversity means limiting human numbers. October 2, 2022.

* The United Nations celebrates World Population Day by shaming population ‘alarmists’. July 11, 2022.

* Population in the IPCC’s new mitigation report. April 12, 2022.