Models and estimates of Earth’s human carrying capacity vary widely and assume, rather than solve for, binding environmental constraints (the process or resource in shortest supply relative to human biological needs). The binding constraint, and therefore the true upper bound on the number of humans that Earth could sustain indefinitely, remains unknown. We seek to resolve this uncertainty by considering a full range of technological possibilities and incorporating a potential stoichiometric constraint not previously explored. We find that limits to photosynthesis constrain population before micronutrients become limiting unless technological capabilities for utilizing nutrient resources lag far behind other technologies. With ideal technology, human carrying capacity runs into the tens of trillions, while with currently demonstrated technology Earth could support more than 200 billion humans. These numbers reflect neither a desirable nor a natural equilibrium population level, but represent a rough estimate of the maximum number of humans Earth could sustain.
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Data Availability Statement
The datasets generated and analyzed during the current study were derived from publicly available data sources, as cited. The data generated for use as immediate input to our model are available in the figshare repository at doi.org/10.6084/m9.figshare.9983369. Model code can be found at https://github.com/binders1/maxpop.
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We thank Anne Gothmann, Forest Isbell, Paul Jackson, Steve McKelvey, and Charles Umbanhowar for helpful comments. We also thank Mari McClelland and Udeepta Chakravarty for excellent assistance with a literature review. This work benefitted from the support of the Collaborative Undergraduate Research and Inquiry program and the Gery-Kleber Chair of Economics and Management Studies at St Olaf College.
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Binder, S., Holdahl, E., Trinh, L. et al. Humanity’s Fundamental Environmental Limits. Hum Ecol 48, 235–244 (2020). https://doi.org/10.1007/s10745-020-00140-w
- Human carrying capacity
- Maximum population
- Environmental limits
- Resource constraints
- Ecological stoichiometry