A carbon dioxide equivalent (CO2-eq) is a way of expressing all the different greenhouse gases (GHG) as a single number. For any quantity and type of greenhouse gas, CO2-eq shows the amount of CO2, which would have the equivalent global warming impact. A quantity of GHG can be expressed as CO2-eq by multiplying the amount of a given GHG by its global warming potential (GWP). According to IPCC’s Fifth Assessment Report, the GWP of methane is 28 (i.e. 1 kg of methane equals 25kg of CO2e) and the GWP of Nitrous oxide is 265 (see IPPC’s report attached below, page 87, for the GWP of these and other gases).
In order to measure emissions of CO2-eq, there are three steps you need to take:
1) Quantify how much of the emission-releasing activity was reduced or avoided: Burning firewood or petrol, applying chemical fertilizers, using electricity, and raising animals are some of the many activities that release GHG. Your task is to quantify the amount of these activities (e.g. tonnes of wood, kWh of electricity) that was reduced or avoided as a result of your project’s support. This site provides some basic guidance on measuring the amount of resources saved. Keep in mind that the amount must be for the entire period stated in your indicator.
2) Determine the GHG emission factor for the given activity: GHG emission factor is a coefficient that allows you to convert activity data into GHG emissions. It is the average emission rate of a given activity. For example, an emission factor for electricity can be expressed as X kg of CO2-eq per kWh. The emission factor for concrete can be expressed as X kg of CO2-eq per ton.
Unfortunately, there is not a comprehensive overview of emission factors that could easily be used in the context of international development projects. Among the most recommended sources are:
- GHG Protocol’s Emission Factors from Cross-Sector Tools (download worksheet)
- IPCC’s Emission Factor Database
- high-quality studies that measured GHG emissions from the activity you are interested in, ideally in the same country or at least in the same region (always verify through an online search whether the emission factor the study used is reliable)
Be aware that emission factors for the same activity (e.g. electricity) can differ depending on the nature of the activity (e.g. how electricity is produced in a given country). As much as possible, use country- or region-specific emission factors.
Determining the emission factor on your own is discouraged, as it requires a higher level of expertise and equipment.
3) To calculate the emissions of CO2-eq reduced / avoided, multiply the total amount of the reduced / avoided emission-releasing activity by the relevant emission factor. If your intervention replaced one activity with another activity that releases fewer emissions (e.g. replacing cooking on charcoal with cooking on biogas), you must deduct from this amount the CO2-eq that is (within the same measured period) emitted by the new activity.