The emissions methodology is based upon emissions factors which describe the rate at which greenhouse gas emissions are produced during the freighting of goods in relation to distance travelled and the quantity of goods freighted. These emissions factors represent emissions associated with individual units of freight, which can be contrasted with similar transport-related emissions factors which describe emissions on the basis of entire vehicles (e.g. entire ship or lorry).
Emissions - expressed in terms of mass (e.g. kg) - are calculated by multiplying these rates (mass emitted per mass per distance; e.g. kg CO2 per tonne km) by a distance (e.g km) and quantity (e.g. tonne) freighted.
The rate at which freight transportation produces greenhouse gas emissions varies with the mode of transport, depending on factors such as the fuel efficiency (i.e. the distance acheived per unit of fuel consumed) of the particular type of vehicle (e.g. lorry, plane, train, ship) as well as the typical freight loading. Fuel efficiency may be related factors such as the type of fuel used (e.g. petrol, diesel, biofuel, electricity) and the physical dynamics of the transportation context (i.e. road, rail, water, air). The loading of freight indicates the extent to which the emissions of the entire vehicle can be 'shared' between units of freight. Therefore, emissions factors for a broad range of generalised freight transport scenarios are provided.
A total of 75 specific types of freight transport scenarios are represented and are differentiated by transport type (i.e. ship, plane, rail, van, heavy goods vehicle), subtype (e.g. 'petrol' versus 'diesel' vans, 'crude tanker' versus 'general cargo' in shipping) and vehicle size (e.g. gross vehicle weight, deadweight tonnes, TEU, CEU).
Each freight transport type is represented by six distinct emissions factors which differentiate greenhouse gas emissions into the following types:
- direct CO2 emissions: carbon dioxide emissions produced during freighting, i.e. fuel combustion
- direct CH4 emissions: methane emissions produced during freighting, i.e. fuel combustion
- direct N2O emissions: nitrous oxide emissions produced during freighting, i.e. fuel combustion
- total direct emissions: all direct emissions, i.e. CO2 + CH4 + N2O
- indirect emissions: emissions associated with stages in the fuel production chain such as raw material extraction and fuel delivery
- total or 'life cycle': the total of direct and indirect emissions
Activity data required
According to this methodology, greenhouse gas emissions are directly proportionate to distance and quantity (mass) of goods freighted, both of which therefore must be specified in order to make an emissions calculation.
Calculation and results
This emissions calculated by this methodology represent those per unit of freight and therefore should be considered attributable to the freighting of the specified quantity of freight only (rather than, say, the emissions attributable to the entire vehicle(s) on which it was transported).
The methodology calculates several emissions quantities including direct CO2, CH4, N2O as well as indirect and total life cycle emissions. All quantities in this methodology are expressed in terms of CO2e - the quantity of CO2 which would exert the same atmospheric warming effect and the emissions quantity.
Great circle distance 'uplift' factors
Following IPCC advice, the DEFRA methodology stipulates that flight distances which are defined as direct 'great circle' distances between two locations should be inflated by 9% in order to account for the typical indirect routing of actual flights and deviations related to congestion. The calculations for air travel made herein assume that the distance specifed is known to be the actual distance flown - rather than the distance estimated on the basis of the Great Circle - and therefore this adjustment factor is not applied. In order to make calculations based on Great Circle estimates between two locations (airports or specifed by latitiude/longitude) see the Great Circle route methodology.
- DEFRA / DECC's Greenhouse Gas Conversion Factors for Company Reporting homepage