Supply Chain (Scope 3) Greenhouse Gas Emission Factors

CenSA calculates and supplies supply chain (scope 3) GHG emission factors to the UK Department for Environment, Food and Rural Affairs (Defra). Factors for the year 2006 are published by Defra as part of its "Guidance on how to measure and report your greenhouse gas emissions". The factors can be used in an 'Optimum Hybrid Analysis' for scope 3 accounting.


What do these factors mean?
The supply chain emission factors express the total amount of GHG emissions associated with one £ of expenditure on a particular good or service. They are based on a "cradle-to-shelf" life-cycle approach, taking into account emissions along all stages of the production chain. This does not only include material extraction, manufacturing, and distribution but also more indirect processes and activities that take place further up in the supply chain, such as infrastructure provision, machinery, banking and financing, advertising etc. The factors encompass the 'upstream' part of scope 3 emissions as defined by the GHG Protocol Standards. They do not account for emissions from the use of products and from end-of-life processes.

How can these factors be used?
The supply chain factors published by Defra can be used to obtain a broad estimate of the total GHG emissions embodied in goods or services bought by an entity (companies, organisations, households, etc.). The analysis requires two main steps: Expenditure (procurement data) on goods and services are allocated to the 75 economic sectors for which the factors are provided and then multiplied with the factor of the matching sector. The result is the sector-average carbon footprint of the production of products bought by the entity.
The accuracy of the analysis can be enhanced by using more up-to-date factors and a higher resolution of economic sectors, see below.

How were the supply chain factors calculated?
At CenSA, we employ environmentally extended input-output analysis for these calculations, using official data from the ONS National (economic) Accounts and ONS Environmental Accounts. The supply chain factors supplied to Defra are based on a model of the UK economy using own updates of published input-output tables. More details on the methodology have been published in this journal article:
Wiedmann, T. and Barrett, J. (2011) A Greenhouse Gas Footprint Analysis of UK Central Government, 1990-2008. Environmental Science & Policy In Press, Corrected Proof > http://dx.doi.org/10.1016/j.envsci.2011.07.005

Do the factors take into account imports to the UK?
Yes. Imports to intermediate and final demand to the UK from the rest of the world are considered in our model, using world-average GHG emission intensity factors for foreign production.

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