We are what we measure.   It's time to measure what we want to be.

Key term: Carrying Capacity


Carrying Capacity: the population that can be supported indefinitely by its supporting systems.

In ecological terms, the carrying capacity of an ecosystem is the size of the population that can be supported indefinitely upon the available resources and services of that ecosystem. Living within the limits of an ecosystem depends on three factors:

  • the amount of resources available in the ecosystem,
  • the size of the population, and
  • the amount of resources each individual is consuming.

A simple example of carrying capacity is the number of people who could survive in a lifeboat after a shipwreck. Their survival depends on how much food and water they have, how much each person eats and drinks each day, and how many days they are afloat. If the lifeboat made it to an island, how long the people survived would depend upon the food and water supply on the island and how wisely they used it. A small desert island will support far fewer people than a large continent with abundant water and good soil for growing crops.

In this example, food and water are the natural capital of the island. Living within the carrying capacity means using those supplies no faster than they are replenished by the island's environment: using the 'interest' income of the natural capital. A community that is living off the interest of its community capital is living within the carrying capacity. A community that is degrading or destroying the ecosystem on which it depends is using up its community capital and is living unsustainably.

Equally important to community sustainability is living within the carrying capacity of the community's human, social and built capital. Carrying capacity is much harder to measure for these types of capital, but the basic concept is the same -- are the different types of capital being used up faster than they are being replenished? For example:

  • A community that allows its children to be poorly educated, undernourished, and poorly housed is eroding its human capital.
  • A community that allows the quality of its social interactions to decline through lack of trust, respect, and tolerance is eroding its social capital.
  • A community that allows its buildings, roads, parks, power facilities, water facilities, and waste processing capability to decay is eroding its built capital. Additionally, a community that is creating built capital without considering the future maintenance of that capital is setting itself up for eventual decay.

So, in the context of sustainability, carrying capacity is the size of the population that can be supported indefinitely upon the available resources and services of supporting natural, social, human, and built capital.