Changes in population can have a variety of economic, ecological, and social implications. One population concern is that of carrying capacity?the number of individuals an ecosystem can support without having any negative effects. It also includes a limit of resources and pollution levels that can be maintained without experiencing high levels of change. If carrying capacity is exceeded, living organisms must adapt to new levels of consumption or find alternative resources. Carrying capacity can be affected by the size of the human population, consumption of resources, and the level of pollution and environmental degradation that results. Carrying capacity, however, need not be fixed and can be expanded through good management and the development of new resource-saving technologies.

Throughout the late 1960s and 1970s, Garrett Hardin and Paul Ehrlich, both authors on overpopulation, contended that the human population had already exceeded the carrying capacity. Hardin is best known for his paper The Tragedy of the Commons, in which he argues that overpopulation of any species will deplete shared natural resources. Ehrlich, who wrote The Population Bomb in 1968, predicted a population explosion accompanied by increasing famine and starvation. Although his prediction did not come true?in fact, in 1970 there was a slight decline in the population growth rate?Erlich was correct in pointing out that, with the exception of solar energy, the Earth is a closed system with limited natural resources.

The standard of living in a region can also help to alter an area’s carrying capacity. Compared to areas with a lower standard of living, areas with a higher standard of living tend to have a reduced carrying capacity due to greater access to and demand for more resources. Nevertheless, there is the suggestion that beyond some point, increased income and environmental improvement often goes hand-in-hand. The effect of an individual or a population on an ecosystem is called an ?ecological footprint,? which can be used to measure and manage the use of resources throughout an economy. It is also widely used as an indicator of environmental sustainability.

Carrying capacity often serves as the basis for sustainable development policies that attempt to balance the needs of today against the resources that will be needed in the future. The 1995 World Summit on Social Development defined sustainability as ‘the framework to achieve a higher quality of life for all people in which economic development, social development, and environmental protection are interdependent and mutually beneficial components’. The 2002 World Summit furthered the process by identifying three key objectives of sustainable development: eradicating poverty, protecting natural resources, and changing unsustainable production and consumption patterns.

While the exact value of the human carrying capacity is uncertain and continues to be under debate, there is a question as to the strain that population and consumption has placed on some societies and the environment. Economists, ecologists, and policy analysts continue to study global consumption patterns to determine what the human carrying capacity is and what steps can be taken to ensure it is not exceeded. In the meantime, actions to ensure natural resource recovery for the future will depend on an increase of sustainable development policies worldwide.

Recommended Resources

Ethical Implications of Carrying Capacity
Garrett Hardin’s 1977 essay on the importance of carrying capacity is closely related to his famous concept of the tragedy of the commons that became well-known in 1968.


Population, Sustainability, and Earth’s Carrying Capacity
In 1992, Paul Ehrlich and Gretchen Daily published this article addressing population patterns at the time and what could be done to create more sustainable patterns.

Nicholas Eberstadt: Population Sense and Nonsense
Population scholar Nicholas Eberstadt reviews changing trends in population and argues that there is considerable evidence for optimism.

For the Classroom

Something for Everyone
In this simulation from the Population Connection, students compete for natural resources in a commons and discuss the social dilemmas that arise. Students will also devise short-term consumption strategies to preserve a long-term supply of the resource. [Grades 9-12]