In general, the Ecological Footprint measures resource consumption of human activities across the whole lifecycle of a product or service and converts this to the amount of land needed to supply the resources consumed and assimilate the waste generated. Ecological Footprint accounts for our global nature of our economy by capturing the impact of imports and exports.
The Ecological Footprint does not account for hazardous impacts of products such as the impact of dioxins released in the atmosphere, nor does it measure water usage against water availability. The Footprint tool does, however, measure the land required to eliminate Carbon dioxide (CO2) emissions and the impact of the energy required to provide the water we consume.
Ecological Footprint accounts calculate humanity's demand on nature in specific, understandable terms, using official government statistics. The accounts are helping hundreds of individuals, businesses, governments and sustainability practitioners around the world to more effectively manage the earth's ecological assets and move society toward a sustainable way of living.
There are two recognised approaches to accounting flows, be they economic or environmental. Bottom up approaches (or 'process analysis', as known in life cycle assessment) build up a system from discrete identifiable 'unit processes' which are then assembled into an overall model of an industrial/commercial activity.
Alternatively, the top-down approach examines overall exchanges between sectors of the economy (through input-output analysis) and, by understanding the direct impacts of a single sector, indirect emissions resulting from interactions with other sectors can be estimated.
Both forms of analysis have their pros and cons. While the process analysis provides detailed feedback on actual processes or activities that lead to specific impacts, it is limited due to the model of the industrial/commercial system being to some extent simplified. On the other hand, input-output analysis generally captures most activities (all those which result from economic exchanges), but may lack definition within some sectors and is reliant on economic/environmental flow factors.
In the EPA Ecological Footprint Calculators, both process analysis data and input-output data have been used for different consumption items, depending on the specificity required in the consumption item and the availability of data. For example, consumption items such as food and computers are modelled using an input-output framework, while office consumables such as paper and toner cartridges are modelled from a process analysis framework, where recycled content (or recycling behaviour) can be taken into account.
The Ecological Footprints calculated through EPA's Calculators are based around consumption of items, and in terms of the Home Calculator, total consumption by household members. Land use values in the input-output model are initially modelled around production impacts, which include local consumption and exports. When the consumption categories are calculated from the output of input models, they are based on local consumption of both domestic production and imported products. All imports are modelled in the input-output model as if they have the same impact as local production
For further information on the assumptions, methodology and data sources behind our Footprint calculations, you can download EPA Publication 972 - The Ecological Footprint Calculators: Technical Background Paper (Adobe PDF file, 260KB).