Emission factors are an essential part of the calculation to measure your greenhouse gas emissions, measuring is essential to help you determine how to reduce your emissions. But what exactly does it mean, and how is an emission factor determined?
What is an Emission Factor?
An emission factor (also called a carbon emission factor) is a coefficient that attempts to quantify how much of a greenhouse gas is released into the atmosphere by an activity or process that releases that gas.
Although CO2 is the primary greenhouse gas produced by human activity, it is not the only one we need to worry about concerning climate change. Other greenhouse gases, such as methane and nitrous oxide, also contribute to global warming at different rates.
These other greenhouse gases are measured in terms of their global warming potentials or the amount of warming they will cause over a specified timeframe. To make calculating emissions easier, other GHGs are converted into units of carbon dioxide equivalent (CO2e), typically expressed in weight.
The calculation to measure the emissions from an activity is as follows:
Emission factor x activity rate = emissions
The emissions factor quantifies the amount of CO2e produced by an activity. It is usually expressed in weight per unit of activity but may also be measured in time or distance. For example, the emission factor for burning natural gas might be expressed in kg of CO2e/kWh of natural gas.
To work out the overall emissions from burning natural gas, you would take the emission factor of natural gas and multiply it by the ‘activity rate’ – in this case, the quantity of natural gas burned over a specific timeframe. In 2021, the Australian government estimated the emission factor for CO2 produced by burning natural gas to be 51.4 kg CO2-e/GJ.
This means that if a business was consuming 100,000 gigajoules of natural gas per year, according to the emission factors Australia provides, you could calculate the CO2 emissions from that activity as:
(100,000 × 1 × 51.4)/1,000 = 5,140 t CO2-e
This process must be repeated for all the business’s activities to measure its total carbon footprint.
Why Emissions Factors are Necessary
When you consider all three emissions scopes, measuring your total carbon footprint is complex. Without emission factors to quantify emissions from each activity/process, it would be impossible.
Businesses and governments use emissions factors to accurately estimate the GHG emissions released by each of their activities. Calculating emissions is a necessary first step in any attempt to reduce carbon footprint. You can only set accurate targets for the future when you have full knowledge of your current state.
Emission factors for greenhouse gas inventories are integral to deciding everything from a country’s environmental policies and its granting of operating permits to the emission-reduction strategies of SMEs.
Policies and activities to become carbon neutral and achieve net zero are essential if we hope to limit global warming to below the 1.5°C set out in the Paris Agreement and avoid the worst effects of climate change.
Determining Emission Factors
Emission factors are usually determined by amalgamating extensive scientific research into greenhouse gas emissions from a specific activity to come up with an accurate estimation of the emissions produced by that activity.
The data used to determine the emission factor should be of sufficient quality and the result must represent a long-term average. Emission factors for various activities are often expressed in an emission factor table or emission factor database from governing bodies. For example, in the UK, the Department for Business, Energy and Industrial Strategy tables its BEIS emission factors.
Emission Factor Uncertainty
As emission factors are estimations, they are subject to a percentage uncertainty. The uncertainty of emissions factors depends on several variables, including the type of emissions released and how many tests were conducted to determine the emission factor.
Uncertainty may be exceptionally high in localisations with a more considerable variation between national and local values. This can mean carbon footprints are calculated based on generic data that may not be relevant to the specific situation, making them less credible.