ECOLOGICAL FOOTPRINT

In the early 1990s, Dr. William Rees and a graduate student, Mathis Wackernagel, developed and quantified the first "ecological footprint" for the city of Vancouver, Canada. Fundamental to this research was answering the question, "how large an area of productive land is needed to sustain a defined population indefinitely, wherever on earth that land is located?" Ecological footprints build on earlier studies, all designed to quantify the natural resources used by humans and compare that to those that are available. However, footprints are distinguished, according to leading practitioners, by the many categories of human activity included in the analysis,

and by the measure's ability to compare current demand with current ecological limits (biocapacity).

The ecological footprint is an environmental accounting tool that measures human impact on nature, based on the ability of nature to renewably produce the resources that humans use and absorb the ensuing waste. Footprinting provides a way to aggregate into a single composite measure many of the ecological impacts associated with built-up land (i.e., roads and buildings), food, energy, solid waste, and other forms of waste or consumption. The result represents the impact or footprint. Using an area-based measure, such as hectares or acres, the size of a footprint can be compared to the renewable services the Earth's biocapacity can produce in a given year. The footprint methodology can be used to evaluate a population's progress toward ecological sustainability.

The footprint has been criticized on a variety of fronts, primarily related to the complex methodology that underlies the measure, as well as the applications for which it is appropriate. Along with other aggregate indicators, the footprint has been criticized for obscuring the components and assumptions that comprise the measure. While the methodology behind the measure is readily available, it is complicated and therefore not approachable without some technical background. Other critics argue that the premise of living within resource limitations can be overcome with technological innovation. It is true that in many ways the footprint is a worst-case scenario because it describes the situation if there are no technological improvements; but the converse, counting on improvements, could be risky in the long run as well.

When a country or community uses more renewable resources than are available, it has exceeded ecological limits. It will not be sustainable over an indefinite period of time. Such a situation can occur over a relatively short time-span because natural capital can be depleted to fill the renewable resource gap. Imports can also meet society's needs, but may simply shift depletion of natural capital around the globe. Over time, global stocks may be depleted to the point where they cannot regenerate or require significant human intervention to do so.

The Living Planet Report 2002 contains footprints of countries with populations greater than one million. Estimates for the year 1999 show that the average American required approximately 9.6 hectares (24 acres) of ecologically productive land to sustain his or her lifestyle. In comparison, the average Canadian lived on a footprint that was nearly one-third smaller (6.9 global hectares or 17 acres), while the average Italian lived on an ecological footprint that was less than half the size (3.8 global hectares or 9 acres) of the American's. Each of these footprints can be compared to the amount of ecologically productive land area available locally or to the amount available globally on per person basis (1.9 hectares or 4.7 acres). See Table 1.

Footprint Methodology

The basic procedure for the footprint methodology is to determine annual global productivity and assimilation capacity (biocapacity) of major land areas. Then, this biocapacity is compared to the demands placed on it by human consumption and waste production. Productive lands are aggregated as cropland, pasture, forest, fisheries, and built-up land. Built-up land is generally assumed to occupy former cropland, as this is the predominant settlement pattern in human history. The present footprint methodology holds that less than one quarter of the Earth's surface provides sufficiently concentrated biomass to be considered biologically productive—leaving out deep ocean areas, deserts, frozen tundra, and other less productive parts of nature. Biocapacity can change: both negatively, due to land alterations such as desertification; and positively, due to improvements in technology that result in higher yields.

Ecological footprints can be calculated using two basic approaches: component and compound. Component footprinting is a bottom-up approach consisting of calculating the ecological footprints of individual parts of a system and then adding them up. Compound footprinting, on the other hand, is a top-down approach using aggregate figures such as production, imports, and exports of agriculture, energy, and other commodities, usually for nations.

Using either methodology, human consumption and waste components of a footprint are attributed to the final point of utilization (where a product is used up and enters the waste stream), regardless of where the output is actually assimilated. For example, some waste products, such as carbon dioxide, may be assimilated well outside the boundaries of the place where they are actually emitted, either because the wastes are carried away from the point of use or because the wastes are generated at a remote production site.

The final footprint results from the comparison of global biocapacity to consumption and waste. High available biocapacity allows for more or larger footprints, and higher levels of consumption require more biologically productive land. Consumption beyond renewable levels of biocapacity requires the depletion of natural capital and is considered unsustainable if it draws resources down to the point at which they cannot regenerate.

Measuring the ecological footprint of energy is a particularly significant and complex challenge that can be addressed in a variety of ways. A primary question that arises concerns the type of energy that is being used. Highly renewable forms of energy production, such as wind and solar power, typically have footprints equivalent to the land area they occupy plus the materials embodied in the collection mechanism. At the other extreme, nuclear energy is inherently unsustainable both because the resources it utilizes are non-renewable and extremely toxic, and because the potential destruction from nuclear accidents produces a dramatic increase in footprint area. The current approach is to convert nuclear energy to the equivalent fossil fuel impact. The footprint of fossil fuels can be calculated as either the amount of land area that would be required to grow and harvest an equivalent amount of fuelwood, or as the amount of land area required to assimilate associated carbon dioxide emissions. The latter approach is the most typically used in footprint accounts.

Footprint calculations through the beginning of the twenty-first century have assumed optimistic yield factors for foods and forests (making them conservative) and have left unmeasured many of the impacts associated with pollution, water use, and habitat and species decline. Though improvements are being made in the methodology, the ecological footprint cannot be considered a definitive measurement of humanity's ecological impact without significant additions.

Applications

Footprinting provides a methodology to evaluate potential tradeoffs among alternative actions, designs, energy sources, policies and products. It can be used as a yardstick for measuring humanity's impact on the earth in terms of ecological sustainability. Research in the field has provided the stimulus and foundation for academics at universities throughout the world. The ecological footprint has informed discussions and debates from the global to local level in national governments, meetings of the United Nations, research institutes, and municipal sustainability initiatives.

Footprints change over time, as populations change, consumption patterns shift, and biocapacity increases or decreases. The changes allow humanity to see its progress toward sustainability, at a global, national, state, and local level.

DAHLIA CHAZAN
JASON VENETOULIS

SEE ALSO Ecology;Ecological Economics;Ecological Restoration;Sustainability and Sustainable Development.

BIBLIOGRAPHY

Chambers, Nicky; Craig Simmons; and Mathis Wackernagel. (2000). Sharing Nature's Interest: Ecological Footprints as an Indicator for Sustainability. London: Earthscan.

Costanza, Robert. (2000). "Commentary Forum: The Ecological Footprint. The Dynamics of the Ecological Footprint Concept." Ecological Economics, 32: 341–345.

Rees, William. (1992). "Ecological Footprints and Appropriated Carrying Capacity: What Urban Economics Leaves Out." Environment and Urbanization 4(2): 121–130.

Rees, William, and Mathis Wackernagel. (1994). "Ecological Footprints and Appropriated Carrying Capacity: Measuring the Natural Capital Requirements of the Human Economy." In Investing in Natural Capital: The Ecological Economics Approach to Sustainability, ed. AnnMari Jansson et al. Washington, DC: Island Press.

Venetoulis, Jason. (2001). "Assessing the Ecological Impact of a University: The Ecological Footprint for the University of Redlands." International Journal of Sustainability in Higher Education 2(2): 180–196.

Wackernagel, Mathis, and William E. Rees. (1996). Our Ecological Footprint: Reducing Human Impact on the Earth. Gabriola Island, BC: New Society Publishers.

Wackernagel, Mathis et al. (2002). "Tracking the Ecological Overshoot of the Human Economy." Proceedings of the National Academy of Sciences of the United States of America 99(14): 9266–9271.

INTERNET RESOURCES

"The Ecological Footprint Project." Sustainable Sonoma County. Available from http://www.sustainablesonoma.org/projects/scefootprint.html.

"Living Planet Report 2002." World Wildlife Fund. Available from http://www.panda.org/news_facts/publications/general/livingplanet/index.cfm.