Carrying out a GHG inventory highly relies on emission factors. These ratios are used to compute GHG emissions from activity or monetary data.
Knowing what an emission factor is, is therefore crucial for understanding the methodology behind a GHG inventory.
What is an emission factor ?
An emission factor is a ratio that converts activity data (km, kWh, L, kg, etc.) or monetary data (€, $, £, etc.) into CO2 emissions equivalent (CO2e).
These emission factors can be expressed in terms of activity units (kgCO2e per km, per kWh, per unit) or in monetary units (kgCO2e per €, $, £ spent).
💡 Carbon dioxide equivalent (CO2e) is a common unit used to describe and compare all GHGs. It quantifies, using the gases’ global warming potential (GWP) for a certain time horizon, the impact of the different GHGs described in the Kyoto Protocol compared to the impact of CO2.
How does Greenly compute its emission factors?
Activity based emission factors are provided by various databases, such as EPA's emission factors database or Ecoinvent database.
Activity emission factors can also directly be provided by a company when it has computed the carbon footprint of one of its products (e.g. Dell).
Monetary emission factors (MEF) are computed in three different ways:
MEF computed using activity data
For expenses linked to direct physical flows (transport, energy consumption, purchase of goods, etc.), Greenly uses emission factors published by accredited authorities such as the EPA, the UK government, the International Energy Agency, and LCA published by manufacturers. These emission factors are then divided by the average price of the product.
Example: according to ADEME (the French Environment Agency), average GHG emissions resulting from using a car are equal to 0.193 kgCO2e/km. In France, the average price of a taxi is €1.45/km. The monetary ratio of a taxi is therefore equal to 0.133 kgCO2e/€. Greenly estimates that a €30 taxi ride will cover 20 kilometres, emitting nearly 4 kgCO2e.
MEF computed using the carbon intensity of a sector
For companies in the service and digital sectors, activity studies cannot be carried out: no physical metrics can be used to compute the company's emissions.
Hence, to estimate the impact resulting from the service, Greenly uses the GHG inventories of the company when quality standards are met (a minimum CDP grade of B), and when the report is thorough and comprehensive enough (complete scopes 1, 2 and 3).
We then compute the carbon intensity of the company by dividing its overall emissions by its revenue. This ratio is then used to compute the emissions of a service based on its price.
Example: physical data required to estimate the impact of using Salesforce are multiple and inaccessible. However, the company publishes a GHG Report graded A by the CDP, disclosing an overall inventory of 1.3 Mt CO2e in 2019. By dividing these emissions by the company's turnover, a monetary ratio of 0.098 kgCO2e/€ is computed. The carbon impact linked to using the platform is computed by multiplying this ratio by the expense amount.
MEF provided by other sources
To compute GHG emissions linked to a service company that doesn't publish a GHG report, average sectoral carbon intensities are used. These monetary ratios are mainly published by public authorities, such as the EPA, the UK Government or ADEME. These ratios can also be computed using input-output models (EXIOBASE, USEEIO).
Some sectoral averages are computed by Greenly using the average carbon intensity of several companies within the sector (as described in the previous section).
👩🏫 The methodological details, descriptions and sources of all emissions factors used by Greenly to compute your GHG inventory are available on the platform.