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Stories about the lives we've made

module:Urban sustainability

Cities and the role of technology

page:Cities as systems: Circular metabolism

Achieving more sustainable cities

Traditional settlements were delineated and structured by transport and production systems based on human or animal power.

A pollution-monitoring unit, southern England, 2003. picture zoom © Kim Adams

A major effect of fossil fuel-based technology has been that the high density of traditional cities has given way to urban sprawl. Fossil fuel-powered transport, starting with railways, steam ships and more latterly cars and aircraft, has also caused many cities to stop relying on resources from their local regions and to become dependent on an ever-widening area, creating an ecological footprint.

As cities draw resources from increasing distances, they also accumulate large amounts of inert and toxic materials within themselves – that is to say, pollution. Waste gases and water expand the negative impact of cities at a regional and increasingly global scales.

An attempt at reducing fuel emissions: The Co-Cat catalytic converter, 1992 picture zoom © Science Museum/Science and Society Picture Library

A large part of the increasing amount of carbon dioxide in the atmosphere is attributable to combustion in the world's cities. In addition, most rail, road and aircraft traffic occurs between cities. Virtually all the world's climatologists agree on their concern about climate change, resulting mainly from fossil fuel burning enhancing the natural greenhouse effect.

In nature, a circular metabolism is developed whereby every input is also able to renew and sustain the living environment by recycling the outputs. In the past medieval cities had something approaching this relationship, with the following closely linked nearby: market gardens, orchards, arable and grazing land, local water supply, forest products and so on.

Circular city metabolism

Indeed, until the recent and rapid industrially led growth of the late twentieth century, many Chinese cities were largely self-sufficient in food. They were unique among the world in having highly developed low technology systems of using human waste as fertiliser for local farms. It must be stressed that any city has an ecological footprint – the question is to what degree?

Cities in less economically developed countries such as India often have a higher ‘re-use' system than do those in more economically developed countries. In the USA and UK, ‘disposable culture' and ‘built-in obsolescence' permeate society. Modern cities have broken the close links with the local biosphere.

In order for cities to become more sustainable they must change the linear metabolism (shown in the last section) to a more circular metabolism, creating a self-regulating sustainable relationship with the biosphere. Later in this module we look at a case study on Curitiba in Brazil, one of the most famous examples of a city's attempts to adopt sustainability measures.



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A pollution-monitoring unit, southern England, 2003.
An attempt at reducing fuel emissions: The Co-Cat catalytic converter, 1992
Learning Module
Learning Module