Appendix Procurement and Supply Chain Full Methodology

Methodology basis

Scope 3 emissions encompass all indirect greenhouse gas emissions associated with activities outside the direct control and ownership of Imperial. Scope 3 emissions of goods and services were calculated based on the approach used in the Higher Education Supply Chain Emissions Tool (HESCET). Modifications have been implemented to the tool to make it more specific to Imperial as an academic institution and aid in categorising scope 3 emissions.

In general, the HESCET approach entails classifying procurement spent by Procurement Higher Education (ProcHE) coding. This coding is then mapped to 311 standard categories set by the Department of Environment Food and Rural Affairs (DEFRA) with known spend-based emission factors. Once mapped, an aggregated spend for each DEFRA category is calculated and multiplied by the respective emission factor to derive the carbon dioxide equivalent emission (CO₂e).

The 311 DEFRA categories could be grouped into 12 high-level sectors representing different areas of spend. A detailed breakdown of the sectors and their representation are summarised in Table 1.

Table 1: List of high-level grouping of DEFRA categories and a description of each.

Note, HESCET utilises DEFRA emissions categories designed for households, rather than large organisations so we have restructred some of the emission categories to align better with our purchasing to give a better assessment of these emissions.

Changes implemented to the HESCET Tool

To ensure an accurate reporting of scope 3 emissions, the HESCET tool mapping and categorisation was revised:

• Emission factors for all categories were revisited and updated (where needed).
• The mapping of ProcHE codes to the 311 DEFRA categories was revised.
• New categories were created (21 in total) based on the mapping revision and divided into two high-level emission sectors:
  • Laboratory and research: includes all purchase of lab materials, equipment, and supplies as well as scientific research and development services and chemical waste disposal.
  • Professional and bought-in services: Includes all technical, computer, insurance, financial, and educational services purchased externally.

The 21 new categories were adding on to the original HESCET tool and mapped accordingly with the relevant ProcHE codes. Mapping for these categories was internally revised to ensure the validity of the proposed changes. Emission factors for the new categories were gathered from different databases.

• Where possible, a mass-based calculation approach was used and integrated into the HESCET tool. For example, to calculate transmission and distribution (T&D) emissions for electricity, the kWh spend of electricity was multiplied by the mass-based emission factor for T&D. A similar approach was used for water and gas emissions. The final utility emissions were added into the respective category in the results table.
• A recategorisation of the emission sectors was implemented in such a way that the different categories matched with Imperials’s procurement department category managers.

Emissions recategorisation

Spend items were re-grouped according to the existing university structure for ease of data analysis, future monitoring of emissions and decision making (Table 2).

Table 2: List of categories used for emission grouping and a description of each.

To perform the calculations for the different categories in this methodology, reverse engineering of the HESCET mapping were implemented:

• New emission factors were calculated for each ProcHE code derived from the existing DEFRA emission factors. The new factor was assumed to be a weighted average of the factors used for the categories considered for each ProcHE code based on the mapping.
• The new factor was multiplied by its relevant ProcHE code to calculated emissions.
• Each ProcHe code was categorised based on the groups presented in Table 2.

The new system was referred to as “Emissions per actionable group”.

Emission factors

Two main methodologies were implemented to calculate scope 3 emissions of goods and services based on the type of available data.

• A mass-based methodology was implemented for emissions from transmission and distribution of electricity and gas due to the availability of energy data per hour. Updated emission factors were found in the most recent greenhouse gas reporting publication released by the Department of Energy Security and Net Zero as well as the Department of Business, Energy, and Industrial Strategy (BEIS). [1]
• A spend-based methodology was used to assess emissions from all remaining purchased goods and services since the data was provided by the procurement department in amount spent. Spend-based emission factors were gathered from a variety of sources. Priority was given to factors provided by BEIS. Where not found, emission factors from the United States Environmental Protection Agency (EPA)[2] or the European environmental Agency (EXIOBASE) [3].

Last updated: October 2024

Sources

Student and staff statistics: College overview | About | Imperial College London

2023: Greenhouse gas reporting: conversion factors 2023 - GOV.UK (www.gov.uk)

2022: Greenhouse gas reporting: conversion factors 2022 - GOV.UK (www.gov.uk)