“…development that meets the needs of current generations without compromising the ability of future generations to meet their needs and aspirations” (World Commission on the Environment and Development 1987).
However this definition, and similar ones, may have inadvertently been a stumbling block to the implementation of sustainability in built environment as the definition could not be readily translated into action. Button (2002), for instance, suggests that this definition has a biblical vagueness. He argues that this definition is very difficult to apply to urban areas as it only refers to temporal and generational effects of sustainability, without addressing key geographical aspects and the inherent dynamism of cities.
Newer definitions of sustainability are more relevant to the built environment. A number include resilience as a preferred, or essential, characteristic of sustainability. López-Ridaura et al (2005), for instance includes resilience as a key attribute of sustainable systems:
“..the degree to which a system is sustainable will depend on its capabilities to produce, in a state of stable equilibrium, a specific combination of goods and services that satisfies a set of goals (the system is productive), without degrading its resource base (the system is stable)
even when facing ‘normal’ (the systems is reliable), ‘extreme’ and ‘abrupt’ (the system is resilient) or ‘permanent’ (the system is adaptable) variations in its own functioning, its environment or co-existing systems”.
One of the most relevant definitions of sustainability for the built environment has been developed by the World Wildlife Fund (WWF). This describes sustainability as being the achievement of above 0.8 on the Human Development Index (HDI) and the achievement of an Ecological Footprint (EF) below 1.8 global hectares per person (World Wild Life Fund, 2006).
The Human Development Index was developed by the United Nations as an alternative to economic progress indicators and aimed to provide a broader measure that defined human development as a process of enlarging people’s choices and enhancing human capabilities (United Nations Development Programme, 2007). The measure is based on:
- A long healthy life, measured by life expectancy at birth
- Knowledge, measured by the adult literacy rate and combined primary, secondary, and tertiary gross enrolment ratio
- A decent standard of living, as measure by the GDP per capital in purchasing power parity (PPP) in terms of US dollars
An Ecological Footprint is an estimate of the amount of biologically productive land and sea required to provide the resources a human population consumes and absorb the corresponding waste. These estimates are based on consumption of resources and production of waste and emissions in the following areas:
- Food, measured in type and amount of food consumed
- Shelter, measured in size, utilization and energy consumption
- Mobility, measured in type of transport used and distances travelled
- Goods, measured in type and quantity consumed
- Services, measured in type and quantity consumed
- Waste, measured in type and quantity produced
The area of biologically productive land and sea for each of these areas is calculated in global hectares (gha) and then added together to provide an overall ecological footprint(Wackernagel and Yount, 2000). This measure is particularly useful as it enables the impact of infrastructure and lifestyles to be measured in relation to the earth’s carrying capacity of 1.8 global hectares (gha) per person.