Carrying Capacity

Carrying capacity refers to how many organisms can live sustainably in a particular environment without destroying its resources. Many things can be limiting factors, such as food or water supply, amount of shelter, capacity to absorb wastes, or predation, and different factors can be the limit that determines carrying capacity at different times and places.

The planet's carrying capacity is the number of people that can live on it without dangerously threatening its future. Given rapid population growth on a planet that is ultimately finite, and our present inability to meet even the basic needs of much of the world's population, the human carrying capacity of the Earth has become a significant issue. The planet could support many more people living a simple rural village life than an American suburban lifestyle. One measure that has been developed to estimate carrying capacity and the share of each person is the ecological footprint.

The idea of carrying capacity relates closely to that of sustainable development, because both refer to the need to live off of interest rather than capital. If we cut down forests faster than they can grow back, intensify agriculture until it robs the soil of its fertility, and make profligate use of non-renewable resources such as minerals and fossil fuels, we can increase our standard of living and/or the number of people living on the planet, but we reduce its capacity to support people in the future. The success of development in the West has come partly from diminishing stocks of non-renewable resources, and partly from the import of cheap primary commodities often produced by over-exploitation in developing countries, just as the empires of earlier times flourished through colonial exploitation.

It is difficult to estimate the carrying capacity of the planet, since this depends on the technologies available, our efficiency in the use of resources, and the acceptable standard of living. Since the richest one-fifth of the population today uses about four-fifths of the world's resources, the existing world population could not be brought up to European living standards using present technologies and consumption levels. Pessimists will say that the world is already over-populated, and that the future population must be reduced to achieve sustainability. Optimists assume that science and technology will find solutions to all our problems so that growth can go on for ever. Earlier predictions of limits to growth and a decline in civilization have not yet been realized, but we may already be beyond the limits, cushioned only by the time lags between cause and effect (Meadows et al. 2004). Common sense shows that the present situation of rapid population growth in some regions, massive overexploitation of resources and steady accumulation of pollution and wastes cannot continue. The question is how and by what means change will come, and how much damage to the natural capital and carrying capacity of the planet we shall do in the process (Dahl, 1996).

There are already signs that we are exceeding the carrying capacity of many parts of the planet. Some of the worst humanitarian crises since the 1992 Rio Earth Summit, in countries like Haiti, Rwanda and Somalia, share as underlying causes, behind obvious political and ethnic divisions, a high and rapidly increasing density of population, extreme poverty, and a shortage of essential environmental resources, in particular a drop in per capita food production. These may be some of the first illustrations of the consequences of exceeding the environmental capacity of a country or region (Mathews, 1994; Atwood, 1994). The increase in environmental refugees who leave their homes because local resources can no longer support them is another symptom of this problem. The International Conference on Population and Development in Cairo in 1994 recognized the need to integrate population, environmental and poverty eradication factors in sustainable development policies, plans and programmes (UN, 1994).

Atwood, Brian. 1994. Atwood, Brian, head of USAID, at Nairobi news conference, quoted in Hartley, Aidan. "U.S. official says overpopulation partly caused Rwanda war". Reuter, 31 May 1994.

Dahl, Arthur Lyon. 1996. The Eco Principle: Ecology and Economics in Symbiosis. Zed Books, London.

Mathews, Jessica. 1994. "Slow-motion security threats". Washington Post, 25 July 1994.

Meadows, Donella, et al. 2004. Limits to Growth: The 30-year Update. Chelsea Green Publishing Co., White River Junction, Vermont.

UN. 1994.  Report of the International Conference on Population and Development, Cairo, 1994. A/CONF.171/13, paragraph 3.28.