GHG emissionIf you are among those facility managers that are new to EPA GHG Reporting (for Greenhouse Gases), or are embarking on voluntary GHG reporting for the very first time, one of the first obstacles you might encounter is understanding the specific units used for Greenhouse gas reporting: the Carbon Dioxide Equivalent (CO2e).

    When you measure your GHG emissions during your everyday air emissions management, you’ll likely be generating results measured in tones of emissions. However, one ton of a particular GHG is not the same as one ton of another. You can’t just add up all your tons of GHG emissions and report that as your carbon footprint.

    And there can be a lot of different GHGs to keep track of. For EPA GHG reporting, you’ll need to track the following GHG emissions:

    • Carbon dioxide
    • Methane
    • Nitrous Oxide
    • Hydrofluorocarbon gases
    • Perfluorocarbon gases
    • Sulfur Hexafluoride

    Every greenhouse gas has its own global warming potential (GWP), which is a measurement of how much heat the GHG can trap within the atmosphere and how much of an environmental impact it is expected to have.  Specifically, GWPs determine the ratio of heat trapped by one unit mass of the specific GHG to that of one unit mass of carbon dioxide over a specified time period.

    These GWP factors were developed by the International Panel on Climate Change (IPCC), a United Nations-established scientific organization. And because every GHG has a different GWP, you can’t just rely on the typical air emission report to calculate your total GHG output.

    The solution to this issue is to use each GHG’s individual GWP and use it to translate your air emissions into a common unit that compares and relates all your GHG emissions so you can report them as a single combined quantity. That unit is CO2e.

    CO2e puts all your GHG emissions in relation to carbon dioxide, which is considered to have a GWP of 1. Carbon dioxide is used as the reference GHG that all others gases get compared to.

    Here’s how to convert your GHG emissions into tons CO2e so that you can report them to the EPA, your shareholders, or any other voluntary carbon footprint registry:

    1. Calculate your GHG emissions in tons, by type of GHG. For example, determine how many tons of methane was generated by your processes this year.

      You can do these calculations in a number of ways, depending on your equipment, monitoring practices, and environmental management system.
      The most common method is the Tier 1 Calculation Method: 

      GHG emission
      = 0.001 * Fuel Usage * High heat value *Emission factor.

      You can get these values from the EPA’s GHG Reporting Program (GHGRP) documentation and your own records. This Tier 1 methodology can be used readily for a handful of GHGs, including CO2, CH4, and N2O, but only if the GHGRP ruling documentation allows for it in for your specific operating scenario.
    2. The next step is to do a fairly easy conversion from tons to tons CO2e. To do this, multiply your tons emissions by the GHG type’s GWP:

      CO2 e = GWP*GHG emission (tons)

      The EPA only accepts GWP factors developed by the IPCC’s Second Assessment Report (SAR), so be sure to use the correct values.

      The EPA has developed an easy to use online CO2e calculator that you can use to convert your emissions into CO2e. Even when using an EPA-designed web tool, always double check your results.
    3. Sum up all your tons CO2e. Adding up all your GHG emissions with the shared unit will give you your total GHG emissions for the year (or any reporting period you’ve chosen for internal/voluntary reporting) and is used to determine if you are required to participate in the EPA GHG reporting program.

    And that's the three quick steps for GHG emissions reporting with CO2e.


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    This Blog was Co-Authored By:


    Alex Chamberlain
    Post by Alex Chamberlain
    August 27, 2012
    Alex Chamberlain is a writer for ERA Environmental Management Solutions.