Disaggregating the National Footprint Accounts : Stepwise™
Best Foot Forward Ltd. use a component-based methodology called Stepwise™ to re-analyse the National Footprint Accounts. See Barrett & Simmons (2003) for a comprehensive account of the general approach. The results derived using the Stepwise™ methodology are wholly compatible with the National Footprint Accounts, and with the methodology used by the European Common Indicators Programme (ECIP), which allows for benchmarking of cities and regions across Europe. For further information on the ECIP methodology see Appendix 1 and Lewan & Simmons, 2001.
The Stepwise™ methodology combines resource consumption, life cycle, and trade data to calculate a range of smaller, more detailed ecological footprint components.
This is a two-step process:
Step 1
The national footprint account for the UK is disaggregated into Stepwise™ components: direct energy, materials and waste, food, personal transport, water and built land. For a detailed description of the disaggregation process, see Barrett & Simmons (2003). In essence it involves factoring consumption data with the ecological footprint conversion factors used in the National Footprint Accounts (Redefining Progress, 2003), supplemented by life cycle data when required, to derive ecological footprint results for each component. This is more complex for some components than others. For example, deriving a component ecological footprint for a car passenger travelling one kilometre (1 pass-km), requires analysis of data on fuel use, materials and energy for manufacture and maintenance of the vehicle, and the share of UK roadspace appropriated by the car (Table 2). The associated conversion factors are then applied to the number of passenger-kilometres (pass-km) travelled, and used as a breakdown of the energy and built land categories of the National Footprint Accounts.
| Energy land | Built land | |
| Carbon per pass-km (kg) | 0.031 | |
| Uplift factor* | 145% | |
| Carbon responsibility** | 69% | |
| World carbon absorption (tonnes C/ha/yr)** | 0.95 | |
| Direct land (total ha) | 258,175 | |
| Land use (ha/car km) | 6 x 10-7 | |
| Equivalence factor | 1.35 | 2.18 |
| Yield factor | 2.44 | |
| Average occupancy (persons/car) | 1.6 | |
| Total ecological footprint (gha/pass-km) | 4.3 x 10-6 | 2 x 10-6 |
| * The uplift factor represents the fuel equivalent used for manufacturing and maintenance, and comes from Wackernagel & Rees (1996). Other sources suggest the uplift factor can range between 11% (derived from Hill et al., 1995 and Teufel et al., 1993) and 93% (derived from Teufel et al., 1993). ** See glossary. |
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| Sources: British Road Federation, 1998; DETR, 1997 and 1999; Loh, 2002 and Wackernagel & Rees, 1996 | ||
To derive a similar conversion factor for a material is considerably more complex, particularly where imports and exports, and differing national production efficiencies are taken into account.
For example, to calculate the ecological footprint of ' SIC 20101010: railway or tramway sleepers (cross-ties) of wood, not impregnated' the equations below are used. Separate equations are required for energy use and forest use, as well as for the production, imports and exports of the wood.
Energy footprint
Production & Exports:
( ( C x E x Nc ) + ( C x E x Wni x Wc ) ) / WCA x CR x EQ
Imports:
( ( C x E x Wc ) + ( C x E x Wni x Wc ) ) / WCA x CR x EQ
Where:
C = Consumption (tonnes)
E = Embodied energy (GJ/tonne)
Nc = National carbon content of energy (tC/GJ)
Wni = World nuclear intensity (nuclear GJ/GJ)
Wc = World carbon content of energy (tC/GJ)
WCA = World average carbon absorption (tC/ha/yr)
CR = Carbon responsibility (69%)
EQ = Equivalence factor (1.35 for energy land)
Forest footprint
Production:
( C / Cv x EQ ) / ( NY x ( NHLF / NNLF ) / YF ) / Rr
Imports:
( C / Cv x EQ ) / ( WY x ( WHLF / WNLF ) )
Exports:
C x ( ( EFi + EFp ) / ( I + P ) )
Where:
C = Consumption (tonnes)
Cv = Conversion (tonnes to WRME tonnes underbark)
Efi = Ecological footprint of imports
EFp = Ecological footprint of production
EQ = Equivalence factor (1.35 for forest)
I = Import (tonnes)
NY = National yield (m3 underbark/ha/yr)
NHLF = National harvest loss factor (%)
NNLF = National natural loss factor (%)
P = Production (tonnes)
Rr = Roundwood ratio (converts tonnes underbark to m3 underbark)
WY = World yield (m3 underbark/ha/yr)
WHLF = World harvest loss factor (%)
WNLF = World natural loss factor (%)
YF = Yield factor (2.63 for UK forest)
Additional equations are required whenever another area type is involved, for example cropland and pasture for animal-based food products, or the sea for fish and other sea-based products.
A similar approach is used to derive ecological footprint results for
- direct energy (domestic and services)
- materials and waste
- food and drink
- personal transport
- water
- built land.
Details of how ecological footprints were derived for these components is shown in Deriving the ecological footprint results: Component by component.
The components represent the main categories of impact, and each key component can be sub-divided into smaller categories. For example direct energy splits into fuel types such as electricity, gas and domestic heating oil. Each of these sub-categories can be broken down further, for example into domestic and commercial sectors. The availability and reliability of data is the key limiting factor in determining the number and coverage of components. Stepwise™ components are chosen to reflect data availability at the European level, to maintain consistency and compatibility. The key component ecological footprints are added together to obtain a total ecological footprint, which is then calibrated to the National Footprint Accounts.
Step 2
Once the National Footprint Accounts have been disaggregated into the Stepwise™ components, consumption data is assessed. Consumption data used in the ecological footprint analysis is taken from the resource flow analysis. The consumption data used for the ecological footprint is presented in component-specific units alongside the ecological footprint results. For a methodological description of data quality and availability for these components see the Resource Flow Analysis Methodology section.