There is no internationally agreed methodology for generating an ecological footprint. The method was created by Rees and Wackernagel in the early 1990s and the ecological footprint methodology has matured considerably over the past 20 years. Details of the methodology used by the Global Footprint Network for calculating the ecological footprint is described in http://www.footprintnetwork.org/gfn_sub.php?content=datamethods This is a common methodology that can be applied across many countries and is constrained by the availability of data for less developed economies. However the methodology cannot be used for regions of countries as it relies on the availability of internationally produced trade data The methodology used by Best Foot Forward is described in their report ( http://www.scotlands-footprint.com/download.htm). Full details of the methodology used by SEI and how it differs from the methodology used by Best Foot Forward are described in detail in the SEI report.
The method used by SEI is environmentally extended input-output analysis. Economic input-output tables describe the flow of goods and services between all the individual sectors of an economy over a stated period of time, commonly a year. The sectors of an economy range from agricultural and manufacturing industries (for example meat production and chemical production) to transport, recreational, health and financial services. This standard economic modelling framework is extended to incorporate environmental data which is what the term "environmentally extended" refers to. This part of the modelling assigns supply chain direct land use from the production and use of intermediate outputs by the different sectors of an economy to the point of final demand (final consumption). Framed in a product context, all direct and indirect land use associated with different final product groups within a given reporting period (year) can be assessed.
The main output of this modelling is the land use by product group data, the input-output framework has facilitated the re-allocation of land from the sectors that directly use land to the final products that are produced. Once the impacts per product are known this can be combined with information on how many products are consumed in order to generate a footprint. (This is simplified, describing only the domestic calculations, the full explanation of how imports are included is provided in the report noted above, Annex A paragraph A.31 onwards). Consumption data is gathered from regionally specific expenditure data, derived from national economic accounts and regional expenditure surveys in fine detail (123 economic sectors and over 300 expenditure categories). This is used to calculate the total ecological footprint of Scottish consumption activities. EIO analysis is a comprehensive modelling framework that ensures that all indirect output effects (and with them the land-use impacts) are captured in their entirety. The approach described above does not require the use of secondary or 'one-off' conversion factors as the 'total impact multipliers' (land use per product groups) are intrinsically calculated by the input-output model, using the most up-to-date economic and environmental input data for each year of the time series. |