Urban Ecological Footprints

In an effort to quantify this dilemma, the author and his students have developed a method to estimate the spatial dimensions of the human ecological niche. Our approach, called ‘ecological footprint analysis,’ starts from the premise outlined earlier, that human beings remain integral components of the ecosystems that support them (Rees and Wackernagel 1994; Rees 1996; Wackernagel and Rees 1996). Ecological footprinting therefore explicitly builds on traditional trophic ecology. We begin by constructing what is, in effect, an elaborate ‘food-web’ connecting any specified human population to the rest of the ecosphere. This niche analysis involves quantifying the material and energy flows required to support that population and identifying significant sources and sinks. However, the human food-web differs significantly from those of other species. In addition to the material and energy required to satisfy the metabolic requirements of our bodies, the human food-web must also account for our industrial metabolism – the material demands of the economic process and the built environment. Ecological footprinting is further based on the fact that many material and energy flows (resource consumption and waste production) can be converted into land- and water-area equivalents. Thus, the ecological footprint of a specified population is the area of land/water required to produce the resources consumed, and to assimilate the wastes generated, by that population on a continuous basis, wherever on Earth that land may be located. It therefore includes the area appropriated through commodity trade and the area needed for the referent population’s share of certain free land- and water-based services of nature (e.g., waste assimilation and nutrient recycling). In other words, ecological footprinting estimates the area of productive ecosystems all over the world whose biophysical output is appropriated for the exclusive use of a defined human population. How Big is our Ecological Footprint? Our early estimates, accounting for just food, fibre, and fossil energy consumption, show that the ecological footprints of typical residents of high-income countries, ranges as high as five or six hectares per capita (Rees and Wackernagel 1996; Wackernagel and Rees 1996). More recent analyses push the upper estimate to nine or 10 hectares per capita (Wackernagel et al. 1997). By extrapolation, the ecological footprints of high-income cities is typically two to three orders of magnitude larger than geographic areas they physically occupy. For example, assuming Vancouverites are average Canadians, the 472,000 residents of the author’s home city generate an average ecological footprint of about seven hectares per capita to support their consumer lifestyles (Wackernagel et al. 1997). This means that the aggregate eco-footprint of the city proper is 3,304,000 ha, or 290 times its political-geographical area (11,400 ha). Similarly, in a more comprehensive study, Folke et al.(1997) estimate that the 29 largest cities of Baltic Europe appropriate for their resource consumption and waste assimilation, an area of forest, agricultural, marine, and wetland ecosystems 565-1130 times larger than the area of the cities themselves. These data emphasize what should be obvious but which is often forgotten in a rapidly urbanizing world – that no city as presently defined can be sustainable. In ecological terms, cities and urbanized regions are intensive nodes of consumption sustained almost entirely by biophysical production and life-support processes occurring outside their political and geographic boundaries (Rees 1997; Rees and Wackernagel 1996). The resultant separation of production from consumption renders urbanites blind to the degradation that results from their consumer lifestyles and unconscious of their increasing dependence on a deteriorating resource base. Far from reflecting our assumed increasing independence from nature, the modern high-income city resembles a parasite on an increasingly global hinterland. Ecological footprinting also reveals that in some dimensions, consumption by the present human population already exceeds the long-term productivity of the ecosphere. According to Folke et al. (1997), the carbon dioxide emissions of just 1.1 billion people (19% of humanity) living in 744 large cities exceed the entire sink capacity of the world’s forests by 10%. Similarly, Wackernagel and Rees (1996) and Wackernagel et al. (1997) estimate that with prevailing technologies and average consumption levels, the present world population exceeds long-term global carrying capacity by up to one third. Contrary to prevailing international development models, so-called “first world” material lifestyles are not extendible to the entire world population along the present development path. More Bad News About Cities Urban regions not only appropriate an increasing share of global production but they also destroy the structure of the ecosystems that support them. Most important, cities significantly alter natural biogeochemical cycles of vital nutrients and other chemical resources. Removing people and livestock far from the land, prevents the natural recycling of phosphorus, nitrogen, other nutrients and organic matter back onto farm- and forest-land. As a consequence of urbanization, local, cyclically integrated ecological production systems have become global, horizontally disintegrated, throughput systems. For example, instead of being returned to its source, Vancouver’s daily appropriation of Saskatchewan mineral nutrients goes straight out to sea. Similarly, in their classic 1978 analysis of The Metabolism of Hong Kong, Newcombe et al. found that 2.4 million tonnes of plant nutrients passed through the city’s human food supply system annually (cited in Girardet 1992). This is half a tonne of vital nutrients per capita, most of it discharged into Hong Kong’s Victoria Harbour. As a result, agricultural soils are degraded – half the natural nutrients and organic matter from much of Canada’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 thing. This results in ground and surface-water pollution and consequent additional ecological damage. Clearly, there is need for much improved accounting for the hidden costs of cities and their supportive infrastructure and for a redefinition of economic efficiency to include biophysical factors.
source: The Built Environment See also XlnkS43D

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