Deriving the ecological footprint results: Component by component

Deriving ecological footprint conversions is different for each component. The following sections illustrate the key data and methodology issues involved.

The direct energy footprint

The National Footprint Accounts present energy consumption data for a nation, and per person. The Stepwise™ methodology enables this total to be broken down into direct and indirect energy.

Direct energy includes domestic energy, and energy for the provision of services, for example hotels and schools.

Indirect energy use is accounted for in other component ecological footprints. For example, energy used to produce materials and products (known as embodied energy) is accounted for in the materials and waste ecological footprint, and energy for transport is accounted for in the personal transport component.

CO 2 emissions associated with direct energy usage are calculated according to energy source (see Table 3), and the ecological footprint derived by calculating the global hectares of new forest required to assimilate these emissions* (see formulae in Stepwise™ Step 1). The conversion factor used for brown grid electricity is given in Table 4.

* The default method for accounting CO 2 (using new forest area to assimilate emissions) assumes that 31% of CO 2 emissions are assimilated by the sea (these emissions are excluded (Wackernagel et al., 2002)). This is used as the default as it indicates the implications of current climate change abatement policies adopted in many countries.

Table 3
CO2 emissions from the use of different energy sources
Energy source Kg CO 2 per kWh
Coal 0.30
Oil 0.25
Gas 0.19
Renewables 0.00
Source: DETR, 1999
Table 4
Calculating the brown grid electricity conversion factor
Brown grid electricity (per GWh) Energy land
A Carbon per GWh (tonnes) 131.47
B Carbon responsibility* 69%
C World carbon absorption (tonnes C/ha/yr)** 0.95
D Equivalence factor 1.35
( A x B x D ) / C Ecological footprint (gha/GWh) 128.89
* CO2 emissions assimilated by the sea are excluded from the ecological footprint, which leaves approximately 69% of emissions to be accounted.
** See glossary.

The materials and waste footprint

The National Footprint Accounts assess the bioproductive land and energy land requirements of materials and products separately. The bioproductive land requirements are all accounted for in the raw materials production, import and export data. Additional embodied energy impacts, which occur during the manufacture and production of materials and products are not identified separately, but aggregated as part of a national energy consumption figure adjusted for imports and exports.

The Stepwise™ methodology uses the same approach, but disaggregates energy and materials into more detailed components. Consumption data is taken from the resource flow analysis, where double counting between materials and products has been removed (see Resource Flow Analysis Methodology).

Unlike the other components, official data on consumption of materials and products was not available for the South West and was therefore based on UK data. In the resource flow analysis UK ProdCom data was proxied to reflect the economic activity of the South West (geographical principle). For the ecological footprint analysis the UK data was proxied using domestic waste as a proxy to reflect South West residents' consumption (responsibility principle).

Consumption by area type (energy land, crop land, pasture, forest and sea) is first calculated from the National Footprint Accounts for the UK and then disaggregated into Stepwise TM components (see Barrett & Simmons (2003) for further details). Built land is not included in the 'materials and waste' component but is presented as a separate component.

To adjust the UK material and products data to estimate South West consumption, household waste was used as a proxy. This proxy is a comparison between household waste arisings in the UK for 1999 (Barrett & Simmons, 2003)) and the South West for 2001:

UK household waste arisings = 480 kg per person
South West household waste arisings = 504 kg per person


Proxy = South West waste / UK waste
  = 504 / 480
  = 105%

The South West per person footprint for materials and waste in 2001 will be 5% more than the UK footprint for materials and waste in 1999.

Materials and products

Energy ecological footprints are captured separately from other area types for materials and products, driven by data availability and the necessity to discount double counting between material and product consumption data.

Energy land ecological footprints for materials and products are captured from the embodied energy associated with final products, which includes energy inputs throughout the lifecycle of the product, including extraction and harvesting of the raw materials. Embodied energy figures used in the National Footprint Accounts were applied to the 4,800 products outlined in ProdCom (ONS, 2001) to ensure consistency. See Appendix 5 for a detailed discussion of ProdCom data.

The energy ecological footprint calculations do not capture data for materials consumed as raw materials. This was the case for SIC 13: 'metal ores' and SIC 14: 'other quarrying and mining' and part of SIC 2: 'timber'. These categories were analysed further to incorporate associated energy land requirements not elsewhere captured.

Ecological footprints for the other bioproductive area types (arable, pasture, forest and sea) are captured from raw materials consumption data, which includes all the materials used in the production of final products. Examples of the algorithms used to derive the bioproductive ecological footprints are shown earlier (see formulae in Stepwiseâ„¢ Step 1) and are compatible with those used for the National Footprint Accounts .

Once the separate ecological footprints were calculated for materials and products, they were combined to give a total ecological footprint for materials and products in the South West.

This approach is summarised in Figure 4.

Figure 4
The boundaries considered for calculating the ecological footprint of materials and products

fig 4

Waste management

Where waste was sent to landfill for disposal, no embodied energy savings were assumed. Where waste was sent for incineration, the energy reclaimed from the incineration of waste was accounted for in the energy data. Where waste was recycled or composted, it was assumed to reduce the need for virgin resource consumption: embodied energy savings of 51% were assumed (Barrett & Simmons, 2003) for recycled and composted materials. Waste sent for recycling or composting resulted in a net deduction from the materials ecological footprint.

The food footprint

The National Footprint Accounts (Redefining Progress, 2002) identify food materials and products only at the raw material stage, for example wheat, potatoes, bovine meat. Food products such as ice cream or soup are not identified. For this study, food was disaggregated into categories listed in the National Food Survey (DEFRA, 2000). The embodied energy associated with food production was also identified and accounted. The methodology for calculating the ecological footprint of fish and seafood in the National Footprint Accounts is based on the bioproductivity of the continental shelves, the trophic level of the fish catch, normalisation of ocean and land bioproductivity, and also includes freshwater fish and aquaculture (Wackernagel et al., 2002).

The consumption of food products in the South West (net consumption) (taken from DEFRA, 2000) was converted into the raw materials required to produce them. Thus the energy used, and biodegradable waste produced, during the production and manufacturing of food products (not post-consumer food waste, which was included in the 'materials and waste component'), were included in the ecological footprint of food consumed by South West residents.

The area required for growing crops and rearing animals to supply the South West population with food, was calculated using global yield factors from the National Footprint Accounts, and converted to global hectares following methodology set out there. Embodied energy of food products was derived from South West consumption data, and embodied energy estimates are shown in Table 5. An example of calculating a food ecological footprint is shown in Table 6.

Table 5
Estimates for embodied energy in food
Food type MJ per kg
Confectionery 43
Fish & seafood 40
Other aquatic products 40
Meat 37
Edible offal 37
Animal fats 37
Stimulants 30
Spices 30
Vegetable oils 21
Treenuts 20
Soft drinks 18
Miscellaneous 17
Sugar & sweeteners 15
Alcoholic beverages 15
Oil crops 7
Pulses 5
Milk 5
Cereals 4
Starchy root 2
Vegetables 1
Fruits 1
Eggs 1
Sources: Based on Redefining Progress, 2002 and Coley et al., 1998
Table 6
Calculation of beef and veal import conversion factors
Beef & veal* (1 tonne) Energy land
A Carbon per tonne 0.681
B Carbon responsibility** 69%
C World carbon absorption (tC/ha/yr)** 0.95
D Equivalence factor 1.35
( A x B x D ) / C Ecological footprint (gha/tonne) 0.668
Beef & veal* (1 tonne) Pasture
A World yield (tonnes/ha/yr) 0.032
B World waste factor 1
C Equivalence factor 0.47
( 1 / ( A x B ) ) x C Ecological footprint (gha/tonne) 14.92
Beef & veal* (1 tonne) Crop area
  UK imports as % of world production 0.10%
A Feed (gha/tonne) 1.08
B Fodder (gha/tonne) 1.95
A + B Ecological footprint (gha/tonne) 3.03
* Tables relate to imports only. Separate calculations are undertaken for home production and exports.
** See glossary.
Note: National Footprint Accounts (Redefining Progress, 2002) conversion factors are used.

The personal transport footprint

The National Footprint Accounts do not identify transport impacts separately; instead the energy and built land impacts are aggregated within the total ecological footprint calculations. Freight transport was accounted for in the 'food' and 'materials and waste' ecological footprints, with only passenger transport data accounted for in the personal transport component.

In this study , personal transport impacts were disaggregated by mode. A range of personal transport modes was considered. Carbon emissions associated with each mode are given in Table 7. An example calculation for the ecological footprint of air transport is shown in Table 8.

Table 7
Carbon dioxide emissions per passenger-kilometre, by mode
Transport mode CO 2 /pass-km (kg)
Car 0.11
Motorbike & scooters 0.10
Rail 0.06
Bus & coach 0.05
Waterborne 0.28
Tram & metro 0.03
Air intra-EU (short haul) 0.25
Air extra-EU (long haul) 0.16
Sources: CAA, 2002; DfT, 2002 & 2002a and Scottish Executive, 2002a
Table 8
Calculation of the air transport conversion factor
Air intra-EU (1 pass-km) Energy land
A Carbon per pass-km (kg) 0.067
B Uplift1 factor 145%
C Air uplift2 factor 168%
D Carbon responsibility* 69%
E World carbon absorption (tonnes C/ha/yr)* 0.95
F Equivalence factor 1.35
( ( A / 1000 ) x B x C x D x F ) / E Ecological footprint (gha/pass-km) 1.6 x 10-6
1: 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).
2: The air uplift factor is an additional adjustment used to account for international air travel.
* See glossary.

The water footprint

The supply and consumption of water is not identified in the National Footprint Accounts (Redefining Progress, 2002). For this study, the ecological footprint of water was calculated by measuring the energy used to supply, collect and treat water, as well as treatment of wastewater and release back into the environment. Table 9 shows the ecological footprint calculations for the supply of water.

Table 9
Calculation of the water supply conversion factor
Water supply (1 Megalitre) Energy land
A Carbon per megalitre (tonnes) 0.1
B Carbon responsibility* 69%
C World carbon absorption (tonnes C/ha/yr)* 0.95
D Equivalence factor 1.35
( A x B x D ) / C Ecological footprint (gha/megalitre) 0.099
* See glossary.

It has been argued (see Chambers et al., 2000) that water catchment area should also be included in water ecological footprints. However, including the catchment area would incur a double counting of existing areas of demand (arable, energy, pasture, forest and sea areas), because most land types also serve a water catchment function.

The built land footprint

The National Footprint Accounts include built land as a separate component, but do not distinguish different uses. Built land includes all areas that are built on, contaminated or degraded to the degree that they are rendered biologically unproductive. This study used South West-specific data to identify land uses within the region. To calculate each built land ecological footprint, a yield factor was applied to the raw data to convert it into hectares of global average crop area (National Footprint Accounts assume that most built land was once productive). A crop area equivalence factor was then applied to convert the data into global hectares. Table 10 shows the ecological footprint calculation for built land.

Table 10
Calculation of the built land conversion factor
Built land (per hectare) Built land
A Built land (ha) 1
B Crop yield factor 2.44
C Equivalence factor 2.18
A x B x C Ecological footprint (gha/hectare) 5.32
* See glossary.