Without it, carbon accounting wouldn’t exist. Yet it is data that vary form a region of the globe to another, that need regular update to be relevant, and is compatible with a lot of different units.

 

 

We are talking here about the emissions factor (also called Carbon Intensity, or emission intensity), the factor of multiplication that converts quantified data into a kg or a ton of equivalent CO2 (CO2e), allowing to estimate the carbon impact of a complex organisation by a simple sum of the different emission activities.

 

 

We will see, what’s an equivalent CO2, the definition of the emission factor, the way of calculation, and which one are the main European databases.

 

 

What is equivalent CO2

 

 

There are several greenhouse gases (GHGs) that contribute to climate change. The mains one are: CO2, CH4, N20 and the fluorinated gases. In the graph below you can see in which proportion these gases are presented in the atmosphere.

 

 

 

 

All these gases have various lifetime and different impact on the global warming, nevertheless CO2 represents the majority of the gases, moreover CO2 is a very stable gas, staying without degrading for centuries in the upper atmosphere. Hence it was chosen as the etalon. The global warming potential (GWP) of other gases is converted into an equivalent of CO2 by a GWP factor.

 

 

For example, methane (CH4) has a GWP of 28, meaning that methane is 28 times more potent in global warming than CO2. In other word that 1 ton of CH4 is the equivalent of 28 tons of CO2.

 

 

As a comparison nitrous oxide (N20) – which is mainly generated through agriculture activities – , is 273 kg of CO2e/kg.

 

 

The definition of the emission factor

 

 

An emission factor is a coefficient which allows to convert data of the activities into GHG emissions. It is the average emission rate of a given source, relative to units of activity or process(es).[1]

 

 

For example: the natural gas emits 0.244 kg CO2e / kWh (European mean) with 5% uncertainty.

 

 

Thus, the emission factor is the sum of emissions of CO2eq of the human activity described as mass unit of CO2e / reference flows. For example: emission Factor for the natural gas is the sum of the combustion (0.205 kg CO2e / kWh ) and the upstream (i.e. the production and transport of the gas) (0.0389 kg CO2e / kWh). [2]

 

 

How emission factor is being calculated?

 

 

The emission factor is calculated by the average sum of the different GHG generating during the process of the activity. There are two approaches, depending on when relevant from “cradle to grave” or “cradle to gate”. Cradle to grave means a calculation of the emissions of the overall process of creating a product/service, including the period the consumer starts to use it; contrary at the cradle to gate approach which only calculates the emissions till the product/service is being sold to the consumer. The emission factor represents an average value for a given activity in a given area of the world. Therefore, it contains a level of uncertainty that indicates the variation of the emission (toward the value). For example for the calculation of the emission generated by employee commuting, the emission would be in function of the type of car used, the type of driving, the load of the car etc.. Therefore, variation of emission for the same vehicle expressed in the km.vehicle unit can be significant, the level of uncertainty will therefore be high (up to 50%). Mapping the exact vehicle with the exact consumption of fuel used for this purpose would result in a way more precise result with lower uncertainty level.

 

 

It is also important to notice that during the accounting, we will also add an uncertainty value, this time related to the precision of the data itself, high in case of an estimation, low when verifiable (for example: ex-quantity of KWh consumed, taken form an invoice).

 

 

In carbon accounting the results are always estimative, what is important is to get the magnitude of the T CO2e (ton CO2e) with the lowest possible uncertainty level. To ensure the best level of uncertainty it is recommended to use a physical approach rather than a monetary approach (where CO2 level is converted form monetary expenses) as the physical emission factors are far more precise.

 

 

Main European database

 

 

The research of the most relevant emission factor plays a key role on a carbon accounting project.

 

 

To help them carbon accountants can rely on several online database such as:

 

 

Clim’foot project:  European initiative to develop national emission factor database in Europe. This initiative allows the construction of 5 national databases free of access for Hungary, Italy, Greece, Croatia and France.

 

 

Base empreinte is a free access French database that contains more than 10 000 emission factor, continuously.

 

 

DEFRA: Free access database of the UK that contain more than 5000 emission factors.

 

 

Ecoinvent: this database needs subscription and contain more than 21000 emission factor over the world

 

 

PCAF (Partnership for Carbon Accounting Financials): a database that contains more than 23000 financial emission factor (real estate assets)

 

 

Negaoctet: a database for digital technology emission factor

 

 

EEA Passenger car: a database that contains the factor of emission of passenger cars sold in European Union.

 

 

To sum up, we saw is that the emission factor is a key data into the evolution of a carbon footprint assessment. The precision of the result will depend significantly of the emission factor chosen and the related precision of the physical data. Consequently, carbon accounting gives an indication of magnitude and is always estimative yet it gives precious information about the reliance of an organisation on fossil fuels and constitutes the first step towards a low carbon, more resilient business model.

 

 

[1]http://unfccc.int/ghg_data/online_help/definitions/items/3817.php

 

 

[2] https://www.climfoot-project.eu/en/what-emission-factor