All About Emissions Factors
A primer on GHG emissions factors and how to use them while calculating your carbon footprint.
Ever wondered how scientists, governments, and companies count their carbon emissions? If so, you’re in luck, because today, we’re going to take a look into the world of emissions factors: an essential, complex, and sometimes controversial element of carbon accounting and emissions measurement.
With many new proposed and mandated global regulations that require organizations to calculate and report their emissions, it’s important to understand what emissions factors are, how they’re calculated, and where you can find them.
What are emissions factors?
An essential component of carbon accounting is the emission or conversion factor.
According to the EPA, an emission factor is:
“a representative value that attempts to relate the quantity of a pollutant released to the atmosphere with an activity associated with the release of that pollutant.”
Essentially, emissions factors are multiplication coefficients in math. These factors are determined by scientific studies, on-site research, and data analysis. Before we dive deeper into emissions factors, let’s review the basics of carbon accounting to help understand emissions factors' role in calculating emissions.
Where (and why) are emissions factors used in carbon accounting?
Carbon accounting is a way to add up, track, and report your organization's greenhouse gas (GHG) emissions. This is also known as your carbon footprint.
The established global accounting unit for carbon is the greenhouse gas carbon dioxide (CO2), and "carbon equivalents" (CO2e), the sum of carbon plus other emissions like methane, nitrous oxide, and others converted into carbon.
Carbon accounting can be compared to financial accounting. Just as a business keeps track of its financial transactions to understand its financial performance, carbon accounting involves monitoring and quantifying the GHG emissions and removals associated with the operations of a company. Think of GHG emissions as expenses and carbon removal activities as income for the business. Just as a business tracks its expenses to control costs and maximize profits, carbon accounting helps track and manage emissions to minimize the environmental impact and maximize sustainability.
Similar to financial accounting, carbon accounting enables a business to assess its carbon footprint, which is the total amount of GHGs emitted directly or indirectly due to business activities. By carefully monitoring emissions from various sources such as energy consumption, transportation, production processes, or supply chain, the business can gain insight into its environmental impact.
Common practice in carbon accounting is to categorize carbon dioxide equivalents (CO2e) as Scope 1, Scope 2, or Scope 3 GHG. Emission "scopes" were developed by the Greenhouse Gas Protocol, one of the international gold standard frameworks for carbon accounting. Feel free to read more on carbon accounting here.
Emission factors convert activity into the equivalent of carbon dioxide (CO2) emissions. This allows companies to convert their business operations, purchases, and investments into terms of carbon dioxide equivalent emissions.
Most commonly, an activity is converted into the measurement units of kilograms or metric tonnes of CO2e. Once the correct emissions factor is selected, all that is needed to be done is to multiply the activity (amount) by the emissions factor.
The higher the emissions factor, the more greenhouse gasses are emitted a given activity. It’s also very important to make sure measurement units of the activity and emissions factors match.
Here are some examples of real emission factors:
The emission factor for coal-fired power generation is about 0.85 kilograms of CO2 per kilowatt-hour of electricity generated
The emission factor for gasoline-powered vehicles is about 200 grams of CO2 per kilometer driven
The emission factor for cattle farming is about 16 kilograms of CO2 per kilogram of beef
For example, if a coal-fired power plant generates 100 megawatt-hours (MWh) of electricity per day, and the emission factor for coal-fired power generation is 0.85 kilograms of CO2 per kilowatt-hour, then the plant will emit 85,000 kilograms of CO2 per day (100 * 1,000 * 0.85).
There are a variety of emission factors available for different countries, activities, processes, transactions, and investments. These factors are typically developed by government agencies, research institutions, scientific studies, or lifecycle assessments (LCAs), and are based on a variety of data sources, such as emissions measurements, fuel consumption data, and engineering models.
Different types of emissions factors
There are different methods for calculating carbon footprint and the most common methods use either activity-based emissions or spend-based emissions or a combination of the two. Each method has its advantages and disadvantages in terms of available data, estimations, and accuracy.
Activity-based emissions factors, also known as process-based or source-based emissions factors, are used to estimate the amount of emissions associated with a specific activity or process.
For example, an activity emission factor could be used to calculate the amount of carbon dioxide emitted per kilowatt-hour of electricity generated from a coal-fired power plant. This emission factor allows us to estimate the CO2e emissions based on the amount of electricity consumed.
Spend-based emissions factors, also known as expenditure-based emissions factors, are used to calculate emissions related to monetary expenditure or economic activity. They provide a way to measure emissions associated with the consumption or spending of goods and services.
For example, a spend-based emission factor might indicate the amount of GHG emissions generated per dollar spent on a specific category, such as transportation, food, or housing.
How are emissions factors calculated?
Activity-based emissions factors are often deemed as the more accurate and precise way of measuring emissions. Since activity-based emission factors are based off of direct measurements and rigorous scientific research, they can provide sector-specific insight on specific activities or processes. One of the downsides of activity-based emissions factors is that they’re a bit more difficult to calculate and require a lot of time and resources to collect accurate underlying data to serve as the activity input. Additionally, activity-based emission factors focus solely on emissions from a specific activity, so associated emissions with other parts of the activity may be over looked.
Spend-based emission factors are often considered the next-best method for calculating carbon emissions. They are estimated using a mixture of economic models and analytical frameworks including Input-Output Models and Environmentally Extended economic models.
Even though many experts recommend using activity-based over spend-based emissions factors, spend-based emission factors can be a great solution for calculating a company’s carbon emissions, especially if activity data is lacking and the underlying accounting inputs have been reviewed and audited. Ultimately, one things most companies (hopefully) are already good at is counting and tracking their expenses.
Financial accounting typically provides the clearest data on emissions from purchased goods and services. Using spend-based emission factors allows a company to convert their financial spend for general items like fuel or more complex items like hired services, into carbon equivalent emissions. These emissions factors can be easier to use than activity-based emissions factors, particularly in many Scope 3 categories.
While spend-based carbon accounting is often more accessible, one of its downsides can be accuracy relative to activity-based calculations. Spend can lack specificity and provide a broad view of the emissions linked to an activity or process instead of a detailed insight of that activity. Spending $10,000 on servers or management consulting can provide an approximate proxy for emissions, but a lot of detail or variability gets left out.
Where to find the right emissions factors
Now that we’ve looked at the basics of carbon accounting and emissions factors’ role in calculating GHG emissions, it’s important to understand how to determine the right emissions factors to use and where to find them.
Emissions factors for different types of activities can vary. Making sure that you have the right emissions factor when calculating emissions will ensure you’re sharing the most accurate emissions data.
Location: emissions factors will vary based on the activity’s geographic location. For example, electricity emissions factors in the United States versus the United Kingdom are different because the underlying energy generation and grids aren’t the same. Make sure the emissions factor you select for your activity align with where that activity takes place.
Type of activity: different activities release different amounts of emissions. For example, a company’s propane consumption should use a different emissions factor than company vehicles because the activities aren’t the same.
Units: units used for emissions factors need to align with the activity and geographic location. You need to determine if you’re calculating emissions in kilograms of carbon equivalents or metric tonnes of carbon equivalents. Let’s say you’re looking for an emissions factor for a car being driven in California. The first step is to find an emissions factor where the unit aligns with car usage, such as emissions per gallon of gasoline, or emissions per passenger mile. An electric vehicle (EV) would need a separate emissions factor, because the fuel is different.
Time Period: many emissions factor databases will update their libraries annually, so it’s best practice to ensure that you’re using the most up to date data available. Things change over time: economies, energy grids, power usage, supply chains, inflation — so emissions factors need to as well.
Credible Data Source(s): many resources are available to find emissions factor data, so it’s important to verify your sources to ensure that they’re reliable and validated by trusted sources.
What are the major emissions factor databases?
Depending on your location and what emissions factors you are looking for here are some reputable sources for finding emissions factors:
United States
Environmental Protection Agency GHG Emissions Hub is updated annually with GHG emissions factors.
United Kingdom
The Department for Business, Energy, & Industrial Strategy publishes emissions factors each year.
European Union (EU)
European Environmental Agency (EEA) published an emissions factor library in 2019.
Other
The Intergovernmental Panel on Climate Change (IPCC) is a UN governing body that’s focused on the science of climate change that manages the Emission Factor Database (EFBD).
The International Energy Agency publishes emissions factors for electricity and heat generation for purchase each year.
Ecoinvent is a database for LCA inventories. Their database helps to understand the environmental impact of various products and services.
Many other databases and sources exist as well, of varying quality and accessibility.
Some final thoughts on emissions factors
Finding the correct emission factors from a reputable source can be challenging and often frustrating. CO2e emissions are the global currency for baselining and benchmarking our progress towards decarbonization and fighting climate change. Yet, emission factors are commonly scattered across different databases, many of which require paid subscriptions for access. There’s often also a lack of consistency for specific activities due to variance in data sources and the assumptions that went into their calculations. It can make calculating emissions into a costly, time-consuming burden instead of a productive, strategic task for organizations.
These issues make it challenging for companies that want to start their carbon accounting journey or that are required to comply with newly proposed and passed ESG regulations. If governing bodies are requiring organizations to disclose their emissions, they should also ensure that companies have the resources to find the right emissions factors to calculate them accurately.
Access to emission factors and other carbon accounting resources shouldn’t be a barrier for organizations wanting to measure their environmental impact. Freely sharing carbon accounting resources, calculations, experiences, successes, and challenges is a win-win solution for all. If organizations don’t have the tools to calculate their environmental footprint, how can we expect them to collect meaningful and accurate data and set realistic carbon reduction strategies?
At Brightest, we’re of the mindset that emission factors should be publicly available. We’ve built our own emissions factors library in response to many of these challenges and needs from our clients (10,000+ factors and counting), and will be taking steps to further expand, update, and open source this library later this year.
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