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Ecological footprints:
Making tracks toward sustainable cities
William E. Rees,
University of British Columbia
School of Community and Regional Planning
Have you ever asked yourself: How much of the Earth is dedicated to sustaining just me? Not many of us have urbanization, trade, and technology have alienated modern urbanites from the land. The fact is, however, that the ties that bind have never bee n stronger. High income urban societies require a constant input of material and energy from nature not only to feed themselves, but also to build and maintain the consumer and capital goods, the factories, the service infra-structure all the accoutreme nts of modern life. The waste burden has, of course, increased proportionately. In fact, since the beginning of the industrial revolution, our industrial metabolism has grown to far exceed our biological demands on the ecosphere. As a result, popular illu sions notwithstanding, people today are more dependent on nature s services than at any previous time in history. The material flows necessary to sustain our consumer lifestyles and our cities make direct and indirect claims on land and ecosystems all over the Earth. By estimating these physical appropriations, my students and I have shown that the citizens of high income countries typically use the output of between three and five hectares of ecologically productive land per capita. It is a simple step from there to estimate the true ecological footprint (EF) of a whole city, region, or country. We define the ec ological footprint of any specified population as the total area of productive land and water required on a continuous basis to produce all the resources consumed, and to assimilate all the wastes produced, by that population, wherever on Earth that land is located.
Why cities aren t where they areshown on the map!
Wealthy cities and countries prosper by appropriating the carrying capacity of an area vastly larger than the spaces they physically occupy. For example, the Canadian city of Vancouver had a 1991 population of 472,000 and an area of 114 km2 (11,400 hecta
res). With a per capita land consumption rate of 4.3 hectares, Vancouver s residents require (conservatively) two million hectares of land to support current consumption levels. However, the area of the city is only 11,400 ha. This means that the city s p
opulation uses the productive output of a land area nearly 180 times larger than its political area to maintain its consumer lifestyle. If we add the aggregate marine footprint (.7 ha/capita), the total becomes 2.4 million hectares or over 200 times the s
ize of the city.
These results are fairly typical. The UK s International Institute of Environment and Development estimates that London s ecological footprint for food, forest products, and carbon assimilation to be 120 times the surface area of the city proper. Research
ers at Stockholm University report that the aggregate consumption of wood, paper, fibre, and food (including seafood) by the inhabitants of 29 cities in the Baltic Sea drainage basin appropriates an ecosystem area 200 times larger that the cities themsel
ves (the later study does not include an energy component.)
These data show that as a result of enormous increases in per capita energy and material consumption, and growing dependencies on trade, the ecological locations of cities no longer coincide with their geographic locations. Modern high-density settlements necessarily appropriate the ecological output and life support functions of distant regions all over the world through both commercial trade and natural biogeochemical cycles. Cities may be the engines of economic growth and the brightest stars in the in the constellation of human achievement. However, they also resemble entropic black holes, sweeping up the output of whole regions of the ecosphere vastly larger than themselves. Perhaps the most important insight from this result is that no city or urban region can be sustainable on its own. Regardless of local land use and environmental policies, a prerequisite for sustainable cities is sustainability of the global hinterland.
Toward Urban Sustainability
For deep structural and ideological reasons, continued GDP growth in both the North and South remains virtually unchallenged as a goal of global sustainable development. Meanwhile, various studies suggest that even the present level of aggregate consum
ption exceeds the long-term human carrying capacity of the Earth. Let s assume a near-doubling of population and a quadrupling of world output over the next 50 years (only 2-3% growth per year). Scientists agree that in these circumstances, resource use a
nd environmental impact per unit consumption in high income countries must be reduced by up to 90% if we are to achieve sustainability fairly within the planet s ecological means.
Cities present both unique problems and opportunities in closing this sustainability gap. Perhaps the most significant problem is that cities typically disrupt the biogeochemical cycles of vital nutrients and other chemical resources. Removing people and
livestock far from the land that supports them prevents the economic recycling of phosphorus, nitrogen, other nutrients and organic matter back onto farm- and forest land. As a consequence, local, cyclically integrated ecological production systems have b
ecome global, horizontally disintegrated, throughput systems. For example, instead of being returned to the land, Vancouver s daily appropriation of Saskatchewan mineral nutrients goes straight out to sea. Agricultural soils are therefore degraded (half t
he natural nutrients and organic matter from much of North America s once rich-prairie soils have been lost in a century of mechanized export agriculture) and we are forced to substitute non-renewable artificial fertilizer for the once renewable real thin
g. This further damages the soil and contaminates water supplies. All this calls for much improved accounting for the hidden ecological costs of urbanization and a redefinition of economic efficiency.
On the plus side, the sheer concentration of population and consumption gives cities considerable leverage in reducing their ecological footprints. Properly planned, urbanization can mean: lower costs per capita of providing piped treated water, sewer sys
tems, waste collection, and most other forms of infrastructure and public amenities;
greater possibilities, and a greater range of options, for material recycling, re-use, re-manufacturing, and the specialized skills and enterprises needed to make these things happen; high population densities which reduce the direct per capita demand for
land;
more opportunities through economies of scale, co-generation, and the use of waste process heat from industry or power plants, to reduce the per capita use of fossil fuel for space-heating; great potential to reduce (mostly fossil) energy consumption by m
otor vehicles through walking, cycling, and public transit.
For a fuller appreciation of urban leverage, particularly in auto-dependent cities, lets examine this last option in more detail. Various estimates place suggest that the direct and indirect public subsidy to private cars is as much as $US 2500 per year. Suppose we gradually move toward full cost pricing of urban auto use and reallocate a significant proportion of this subsidy to public transit. This would make public transportation faster, more convenient, and more comfortable than at present, and vastly cheaper than private autos. City residents would demand improved public transit with the same passion they presently reserve for expanded roadways.The resultant shift in modal split would not only be ecologically more sustainable but also both economical ly more efficient and socially more equitable. (It should therefore appeal to both the political right and left.) Over time, it would also contribute to better air quality, improved public health, greater access to the city, more affordable housing, more efficient land use, the hardening of the urban fringe, the conservation of food lands, and levels of urban density at which at least direct subsidies to transit become unnecessary. In short, because of complex systems linkages, seriously addressing even a single issue can affect many factors contributing to urban sustainability and livability. I call this positive feedback effect the urban sustainability multiplier.
Finally, we should recognize here that many of the environmental demands and impacts that can be traced to cities have nothing to do with the structure, form, or other inherent properties of cities per se. Rather, they are a reflection of societal and ind ividual values and behaviour. These impacts would occur regardless of settlement pattern. For example, if an individual s personal consumption demands the continuous output of four hectares of land scattered about the globe it doesn t much matter where th at individual resides. Thus, the issue here is whether the unique properties of cities make them inherently more or less sustainable than alternative settlement patterns. Until we know the answer to this question, we cannot know whether further urbanizati on should be encouraged or resisted. In the meantime, we clearly must liberate ecological space for the world s poor. It seems that the wealthy have a moral obligation both to make their cities more ecologically benign and to reassess their private consum ption patterns.
Details of methods and examples can be found in:
William Rees 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 (A-M
. Jansson, M. Hammer, C.Folke, and R. Costanza, eds.) Washington: Island Press, and
Mathis Wackernagel and William Rees. 1995. Our Ecological Footprint: Reducing Human Impact on the Earth. Gabriola Island, BC and Philadelphia, PA: New Society Publishers.
For elaboration see Diana Mitlin and David Satterthwaite. Cities and Sustainable Development. Background Paper prepared for Global forum 94 , Manchester, 24-28 June 1994. London: International Institute for Environment and Development.
-From People and Planet Magazine