Ecological Footprint -
calculated with the Sustainable Process Index (SPI ®)

The idea of the ecological footprint is - among many others - one kind of ecological assessment.
It is a measure of how much human activity changes and stresses nature. The more raw materials are consumed and the more pollutants are produced, the greater the ecological pressure.

A basic principle of the Ecological Footprint is that sustainable development is based on the income of sunlight. Solar energy drives all natural material cycles, it is the basis of life and it provides all renewable resources for sustainable economy. Starting point for footprint calculations therefore is the assumption that the sole natural income of nature is solar energy. All natural and anthropogenic processes in a sustainable system must live on that income. Solar energy however needs area for its utilisation: direct utilisation pathways like photovoltaic or indirect utilisation via biomass, all are dependent on area as the primary resource. Technical and natural processes therefore compete for area to utilise solar energy. This is the reason that area is the basic dimension of ecological footprints: the larger the area (and hence the ecological footprint) required by a certain human activity, the less competitive and the less sustainable it is.

There are different ways of calculating the ecological footprint and all have different relationships between area and human activity. One type of calculation is the Sustainable Process Index (SPI ®). It aggregates different ecological pressures from the given anthropogenic material and energy flows to one number; this single number is the area necessary to embed a process or service sustainable into the ecosphere, in accordance with the tenets of the concept of “strong sustainability” that requires sustainable development to be based on the natural income rather than allowing for unrestricted substitution of different kinds of natural and human capital.
The conversion of the material and energy flows is done according to the following two principles:

  1. Anthropogenic mass flows must not alter global material cycles. This principle refers to circuits, such as the carbon cycle, meaning that not more fossil carbon (coal, oil, gas, ...) may be put into circulation, as the seas again can sediment. If more is brought into circulation (which actually is the case), a larger area is required.

  2. Anthropogenic mass flows must not alter the quality of local environmental compartments. This means that pollutants into the ground, in the air and into the water must not exceed the capacity of the local environment. If more is applied, again a larger area is neccessary in order not to exceed the natural capacity.

The overall footprint area consists of the following partial areas:
  • Direct area for infrastructure

  • Area for non-renewable resources

  • Area for renewable resources

  • Area for the uptake of (fossil) carbon

  • Area for the dissipation of emissions in the water

  • Area for the dissipation of emissions in the soil

  • Area for the dissipation of emissions in the air

In the assessment of specific products or services the whole life cycle is considered (from the “cradle” of the raw material production to the “grave” of all emissions). The definition of the system boundaries and the distribution of the footprint between products and by-products for the evaluation follow the rules of the ISO 14040 standards on Life Cycle Analysis.

The Sustainable Process Index ® is a registered trade mark. It is used here with the kind permission of Dr. Christian Krotscheck, Ingenieurbüro NATAN, 8330 Auersbach/A.

Ecological Footprint and CO2
Excess carbon dioxide (CO2) has been locked away millions of years ago under the earth's surface, and so suitable conditions for life on Earth were created. Through the use of coal, oil and natural gas, we bring this CO2 back into the atmosphere and change its composition - keyword (man-made) greenhouse effect.

A small portion is locked away again.
CO2 is in a global circuit. Part of it is absorbed by the oceans and a small part of it in turn is bound by marine life. When this marine life dies and sinks to the ground, this carbon is locked away again in the long term. As we bring in far more carbon into the atmosphere than can be locked away again, we change the composition of the atmosphere and therefore do not act in a sustainable way.

What does that mean in numbers?
Within the SPI-calculation this ability of the oceans to lock away the carbon is represented in the partial area “for the uptake of (fossil) carbon”. In the calculator this natural uptake flow is set to 73 kg CO2 per hectare and year. A car that runs 10,000 km per year and emits 2,800 kg CO2 (whole life cycle cosidered, also things like road infrastructure) has an ecological footprint of 38 ha (equal to 35 soccer fields). The statistical area that an Austrian person may use as ecological footprint is 6.6 ha (including the aliquot ocean area) for comparison.