Ecological Overshoot:
Our Gift to Posterity

A sermon delivered at the Unitarian Universalist Congregation (Blacksburg Virginia), July 31, 2005, by John Cairns, Jr., a long-time UUC member and Virginia Tech University Distinguished Professor of Environmental Biology Emeritus.

Shakespeare is rumored to have said that all literature is about loss—a concept I struggle with and wanted to reject upon first hearing—preferring to write out of joy—indeed ideally out of exaltation bearing witness to the things I love during this brief life—it took me a while to realize that even the act of celebrating is an acknowledgment of loss for it is the temporal nature of celebration—the awareness that a thing has not always been one certain way before, and may not always be thereafter—which most sharpens the poet’s and the reader’s senses. Celebration and loss are shadows of one another in literature.

Rich Bass, The Space Between

One lesson from the five great global extinctions is that species and ecosystems come and go, but the evolutionary process continues. In short, life forms have a future on Earth, but humankind’s future depends on its stewardship of ecosystems that favor Homo sapiens

John Cairns, Jr., Future of Life on Earth

My purpose this morning is to persuade you that global environmental catastrophes are the result of the cumulative impact of small, individual decisions, which are threatening the future of our children, grandchildren, and posterity globally.

In 1948, my mentor Ruth Patrick selected the concept of “use without abuse of the planet” as a major goal of her work. Currently, this goal is described by the word sustainability. Eco-ethics is the essential foundation for sustainable use of the planet. E. O. Wilson remarks: “in the end, however, success or failure will come down to an ethical decision, one on which those now living will be defined and judged for all generations to come.” Sustainability is a utopian vision that requires living harmoniously with nature, which will exact harsh penalties on species that exceed Earth’s capacity and violate nature’s laws. Sustainability attempts to combine a homocentric with an ecocentric view.

Temporal and Spatial Scales

Earth has existed for about 4½ billion years and has an estimated 15 billion years left. Humans have existed for a mere 160,000. Species survival spans vary from a few years to 40 million years (for one species of marine ostracod). Collapses of the civilizations in the past have been regional and, with humans low in numbers and spread thinly over the planet, the effects did not spread widely. Globalization has made societal collapse likely to have global effects. Exponential growth of the human population and continued excess resource consumption increases the probability of a global collapse.

The Biospheric Life Support System

The biospheric life support system consists of natural capital and the ecosystem services it provides. Natural capital consists of natural resources, including living organisms. Ecosystem services include:

  1. maintenance of breathable air

  2. capture of solar energy and conversion into biomass

  3. control of both microclimate and macroclimate

  4. generation and maintenance of soils

  5. decomposition of wastes

  6. regeneration of nutrients.

An economy needs four types of capital to function properly:

  1. human capital—labor, intelligence, culture, organization

  2. financial capital—cash, investments and monetary instruments

  3. manufactured capital

  4. natural capital

Ecological Footprint

The ecological footprint is a measure of the “load” imposed by a given population on nature. The best way to approach the ethical issues involving humankind and Earth’s resources is the calculation of an individual ecological footprint. My favorite calculation can be found on line at The global average of an individual ecological footprint is 1.7 biologically productive hectares per human. (See this Web site) If present growth rates continue, the biologically productive space will drop to 1.0 hectares per person once the population reaches its predicted 10 billion in just over 30 years. The United States now has an ecological overshoot of 3.6 hectares per capita.

Only 12% of Earth’s ecological capacity is set aside as preserved for the over 30 million species that constitute the biospheric life support system. This area is almost certainly not enough. Global warming and the acidification of the planet’s oceans will probably have major deleterious impacts upon the biospheric life support system.

Ecological Overshoot

In 1960, the ecological footprint of humankind required only 0.7 planet Earths. In 1980, it required only 1.0 planet Earth. In 2000, it required 1.2 Earths and continues to rise. If global warming and acidification of the world’s oceans place the biospheric life support system in disequilibrium, the planet’s carrying capacity will be dramatically reduced. This situation would not be good for either posterity or us.

The Case for Optimism

Kerala, a southern state in India, has a per capita income of US$1.00/day (about one sixtieth of North American incomes). However, the life expectancy, infant mortality, and literacy rates there are similar to those of industrialized countries. A major difference is that Kerala emphasizes social capital while the United States emphasizes manufactured capital.

Choosing Success or Failure

One can get insights into the fate of humankind from small island biogeography. Tikopia Island inhabitants lived sustainably for over 3,000 years. A translation of a native expression shows that a community of interest and kinship is important. The Tikopia are “primitive” Polynesians without much interest in present day technology (Firth, 1983). Firth’s sociological study describes in detail some of the measures they used, even though the methods will be repugnant to many persons now alive. However, when compared to the fate of the people of Easter Island (Rapa Nui), the consequences were less catastrophic. Rapa Nui provides a classic study of societal collapse caused by excessive anthropogenic transformation of the island’s ecological life support system. The population of Rapa Nui went from under an estimated 2,000 in 400 AD to approximately 10,000 around 1600 AD (Kirch, 2000). The numbers then plunged precipitously to well under 2,000 and returned to 2,000 about 2000 AD, but carrying capacity of the island had been severely reduced (on-line literature on this contrast is available: “Sustainability Ethics: Tales of Two Cultures”; “Ecological Overshoot and Ecological Restoration”; “You and the Earth’s Resources”). Diamond (2005) lists five causes for failure of civilizations: deeply held religious beliefs, failure to anticipate, failure to perceive a problem, rational bad behavior, disastrous values.

The danger to humankind from the worsening ecological overshoot makes the reevaluation of our values mandatory. Many people are repelled by the means taken to stabilize the human population on a finite space with finite resources (Tikopia). However, does the precipitous loss of 8,000 people out of 10,000 (disease, famine, cannibalism, and homicide) on Easter Island disturb you even more? A few illustrative issues follow.

  1. Is respect for the interdependent web of life (the biospheric life support system) adequate?

  2. Do we have sustainable balance of homocentric views with ecocentric views?

  3. What percentage of Earth should be primarily reserved for naturalistic, self-maintaining ecosystems? At present, it is 12% globally, and the percentage continues to fall. The addition of 3-4 billion people in the next 30 years will make the decision even more difficult. Do you favor more or less than 12%? Try to pick your percentage allocation.

  4. What changes in behavior are you prepared to initiate to make sustainable use of the plant more probable?

  5. If you had to choose between living on Tikopia any time in the last 3000+ years or Easter Island during the ecological overshoot period, which one would you choose? Why?

  6. On a highly urbanized planet, how might humankind develop a mutualistic relationship with natural systems?

Remember, if humankind fails to address the ecological overshoot issue effectively, nature will resolve the issue as many societies suffering ecological collapse have discovered.

Literature Cited

Diamond, J. 2005. Collapse: How Societies Choose to Fail or Succeed. Penguin Group, New York.

Firth, R. 1983. We, The Tikopia. Stanford University Press, Stanford, California.

Kirch, P. V. 2000. On the Road of the Winds. University of California Press, Berkeley, California.

Copyright 2005, John Cairns, Jr.; Commercial Duplication Prohibited
UUC Home Page