City systems theory
Urban areas can be seen as a type of system, with inputs, throughputs and outputs – just as in the human system.
© Brent Council Archives
The inputs may be made up of people, whether daily commuters or more permanent migrants and immigrants, goods such as bricks, bread, furniture and computer microchips and services such as water and electricity.
Outputs may appear to be more obvious – like waste water and refuse, outgoing commuters and migrants but there are also ‘unseen' exports, the main being air pollution. Where great amounts of products are exported without much recycling, this type of system is called an open system. Such a system may be thought of as unsustainable in the long term because of the escalating demands for resources from an ever-widening area, creating a widening ecological footprint. This is a linear type of system as suggested in the diagram below.
Case study: London
The Canadian economist William Rees started a debate about the footprint of cities which he defined as ‘the land required to supply them with food and timber products and to absorb their CO2 output'.
Herbert Girardet is a consultant to Habitat II, the UN agency concerned with sustainability in cities. He has researched the amount of land required by a city to sustain its metabolism, that is to provide the raw materials on which it feeds and process the waste products that it excretes.
London's total footprint, following Rees's definition, extends to 20 million hectares: around 125 times its surface area of 159,000 hectares.
With approximately 12% of the UKs population, 7,000,000 people live in London, occupying a surface area of 158,000 hectares.
The area required for food production at 0.2 hectares per person is 8,400,000 hectares. The forest area required by London for wood products is 768,000 hectares. The land area that would be required for carbon sequestration (fuel production) at 1.5 hectares per person is 10,500,000 hectares.
The total London footprint is 19,700,000 hectares: 125 times London's surface area. London therefore requires the equivalent of Britain's entire productive land.
In reality, with our increasingly sophisticated consumer tastes aided by rapid transport technology, this means increasing impact on remoter areas: such as obtaining mangoes from Brazil, teak furniture from Malaysia, copper from Zambia … not to mention our appetite for increasingly far flung holiday destinations…
Herbert Girardet, OneWorld website
How does this system work?
One problem is obtaining reliable accurate statistics. However since the growth of the concept of sustainability many organisations (ranging from the UK Government Department of Environment, Farming, and the Regions (DEFRA) to private companies such as ‘Best Foot Forward', consultants for London's Mayor) have been attempting to quantify the inputs and outputs and the impact or footprint of cities. The aim is to be able to manage them more effectively.
Surburban London: Wembley High Road, Brent. c.2003.