Carbon dioxide equivalent defined – 1 Best read

Carbon dioxide equivalent defined

In study material each GHG described has a different global warming potential (GWP). The GWP of a given GHG indicates how much energy one unit of the GHG absorbs (i.e., the ability of that gas to trap heat in the atmosphere) compared to one unit of carbon dioxide, generally over a 100-year period.

The larger the GWP, the more that the GHG warms the earth compared to carbon dioxide over the stated time period. For example, PFCs and HFCs often absorb thousands of times more energy than carbon dioxide. The GWP of each GHG is published as a factor and used to translate GHGs, other than carbon dioxide, into carbon dioxide equivalent (C02e) units.

The GHG Protocol considers C02e to be the universal unit of measurement for GHGs since it expresses the GWP of each GHG in terms of the GWP of one unit of carbon dioxide. C02e and individual GHGs are often expressed in metric tons, which is the equivalent of 1,000 kilograms (or approximately 2,204 pounds).

The purpose of this measure is to enable a reporting entity, users and other stakeholders to compare the potency of the overall emissions from a reporting entity, both across entities and over time, even when the composition of the GHG emissions changes.

Carbon dioxide equivalent defined – GWP factors

Excerpts from GHG Protocol

Scope 3 Standard

Chapter 7

Global warming potential (GWP) values

Global warming potential (GWP) values describe the radiative forcing impact (or degree of harm to the atmosphere) of one unit of a given GHG relative to one unit of carbon dioxide. GWP values convert GHG emissions data for non-C02 gases into units of carbon dioxide equivalent (C02e).

Companies should use GWP values provided by the Intergovernmental Panel on Climate Change (IPCC) based on a 100-year time horizon. Companies may either use the IPCC GWP values agreed to by United Nations Framework Convention on Climate Change (UNFCCC) or the most recent GWP values published by the IPCC.

Companies should use consistent GWP values across their scope 1, scope 2, and scope 3 inventory and should maintain consistency in the source of GWP values used over time (by consistently following guidance provided by either the UNFCCC or IPCC, once selected).

Companies that have already developed scope 1 and scope 2 GHG inventories should use the same GWP values for scope 3 to maintain consistency across the scopes. Companies that have not previously developed a corporate GHG inventory should use the most recent GWP values.

Companies are required to disclose the source of GWP values used to calculate the inventory.

Accounting and Reporting Standard Amendment

Companies:

  • Shall use 100-year GWP values from the IPCC.
  • Should use GWP values from the most recent Assessment Report, but may choose to use other IPCC Assessment Reports.
  • Shall use GWPs from a single Assessment Report for any one inventory, where possible. If GWPs for a particular gas are not provided in the chosen Assessment Report. companies shall select the most recent GWPs for that gas.
  • Should use the same GWPs for the current inventory period and the base year, as well as for inventories prepared according to the Scope 3 Standard, to maintain consistency across time and scopes.

Accounting and Reporting Standard Amendment

Required information:

  • Source of the GWP values and indicate if multiple Assessment Reports have been used.
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The GHG Protocol recommends that a reporting entity use GWP factors published by the Intergovernmental Panel on Climate Change (IPCC), which are calculated based on a 100-year time horizon.

If a reporting entity reports a GHG inventory for the first time, it should use the most recent values published by the IPCC. A reporting entity that has already developed a GHG inventory may use either the:

The source of the GWP values that are used should be, where possible, consistent across all scopes and must clearly be disclosed, including indicating whether multiple assessment reports have been used.

Additionally, once a selection has been made (i.e., either the most recent GWP values or values agreed to by UNFCCC), a reporting entity should consistently apply this selection over time. See ‘Updating base year and prior-year (if reported and recalculated) emissions of this website for a discussion of how a reporting entity should update previously reported emissions if it elects to use the most recent GWP value issued by the IPCC and the IPCC issues new GWP values.

The GHG Protocol website (https://ghgprotocol.org/sites/default/files/Global-Warming-Potential-Values%20%28Feb%2016%202016%29_0.pdf) has not been updated for the GWP values published by the IPCC in AR6 but includes the values published within AR4 and the Fifth Assessment Report (AR5). Many of the tools published by the GHG Protocol also currently use GWP values from AR5. The following chart lists the IPCC GWP values for certain GHGs published in AR4, AR5 and AR6 using a 100-year time horizon:

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Carbon dioxide equivalent defined

See the GHG Protocol website (https://ghgprotocol.org/sites/default/files/Global-Warming-Potential-Values%20%28Feb%2016%202016%29_0.pdf) for the GWP values for the various HFCs and PFCs. As discussed in ‘Circumstances that require recalculation, when a new or updated emissions factor or GWP value is used, a reporting entity should recalculate base year emissions (and prior year emissions if recalculated) using the new emissions factor or GWP value if the impact is material.

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