Measures of Sustainability
Overview / Embodied Energy / Operating Energy / Exergy / Durability / Externalities / Ecological Footprint / Eco-Labeling / Life Cycle Assessment

Ecological Footprint
The idea of ecological footprint is a composite measure which informs sustainable development, ecological economics and urban studies. It is quickly becoming a very practical tool for measuring human impact on the Earth's resource base. The concept of ecological footprint has been advanced for nearly three decades by Canadian researcher Dr. William Rees at the University of British Columbia. His ongoing work attempts to take a much larger view on the impacts of human activities and interventions. The relationship between the capacity of the ecosystem to support or absorb human activities, and the intensity of those activities, was not only revealing, but also disturbing.

Ecological footprint may be simply defined as:

A measure of a community's demand on the global carrying capacity, which compares this with nature's available long-term carrying capacity.

At present, 1.7 hectares per person is the accepted ecological benchmark for global sustainability, after taking biodiversity into account. With the anticipated global population of 10 billion for the year 2050 or before, the available space will be reduced to 1.2 hectares, including the sea space. This trend takes on important meaning for urban planners as the trend toward urbanization advances.


Toronto: An Urban Perspective
The Environmental Impact Assessment & Policy Development Office of the City of Toronto has maintained an ongoing survey of Toronto's ecological footprint since 1996. The results are periodically processed according to the same categories of inputs and outputs employed in consensus international studies, and summary statistics updated and posted on the Web.

To date, the ecological footprint of the "average" respondent was 5.30 ± 1.70 hectares, which is 26 per cent smaller than the Canadian average of 7.7 hectares. Extrapolating the data obtained from survey respondents (assuming the "average" participant from this pilot study sample is the "average" Torontonian), the amount of land needed for all of Toronto's residents is 12,642,734 hectares or 126,427 km2. In other words, given Toronto's current area of 630 km2, the amount of land that its residents appropriate is approximately 201 times larger than its geographic size. The allocation of consumption patterns among housing, transportation, food, purchases of products and services, and waste are depicted in the figure below.

It is interesting to note that almost twice as much carrying capacity is allocated to waste (5.6%) when compared to the minimum amount recommended by environmentalists for wildlife reserves, approximately 3%.

Average Ecological Footprint for City of Toronto
[Source: The Environmental Impact Assessment & Policy Development Office, City of Toronto.]

Global Perspective on Ecological Footprint
Data gathered for the United Nations using 1997 data produced interesting insights into the global ecological footprint. Selected data excerpted from the main study have been reproduced in the table to the right.

Many countries are operating at a capacity deficit suggesting that their populations exceed the sustainable yield of their natural resources. Others, like Peru, have a significant surplus indicating they are under-populated relative to their way of life. Among industrialized countries, both deficits and surpluses exist - it appears there is no positive correlation between technological advancement and sustainability based on these data. Globally, humankind is existing at a net deficit, and according to researchers the trend is not encouraging.

Ecological Footprints for Selected Countries
[Source: Wackernagel, Mathis, Larry Onisto, et. al. Ecological Footprints of Nations: How Much Nature Do They Use? - How Much Nature Do They Have? Rio+5 Forum Study, March 10, 1997.]

Architectural Science Perspective on Ecological Footprint
Unlike the previous measures of sustainability, ecological footprint is not confined to buildings and architecture, but holistically regards all human activities. Viewed from an architectural perspective, it would be interesting to selectively extract from the ecological footprint of a building to obtain its attached energy and resource dependency, representing the numerous environmental relationships associated with building development. The energy component is largely related to the urban form, amenities and resources comprising and sustaining the building entity. Infrastructure, transportation, communications and services (health care, education, etc.) are indirectly attached to every building, to some degree. The characteristics of buildings, their usage, and their grouping as part of an urban, suburban or rural fabric define to a large extent this attached energy. A single family dwelling in a typical suburban setting may have a different attached energy component than a similar dwelling unit in a multi-family, mixed-use occupancy in an urban setting.

To date, the research does not appear to have been extended to assess building projects. It would be interesting to estimate the ecological footprint of buildings to see if architects actually use more or less than one square metre of available ecological carrying capacity to deliver one square metre of building area, thereby demonstrating that less is more. This is not beyond the realm of possibility if buildings become net producers of energy, water and food. Refer to the Related Resources + References page for further information on ecological footprint.


The next section deals with the multi-dimensional measure of Eco-Labeling.


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