FAQs

Estimating Emissions and Emissions Reductions/ Emissions Factors and GWPs

• What are Global Warming Potentials (GWPs)?

Global Warming Potentials (GWPs) are used to compare the abilities of different greenhouse gases to trap heat in the atmosphere. GWPs are based on the radiative efficiency (heat-absorbing ability) of each gas relative to that of CO2 as well as the decay rate of each gas (the amount removed from the atmosphere over a given number of years) relative to that of CO2.

• How are GWPs used for emission calculations?

In regard to emission calculations, GWPs provide a construct for converting emissions of various gases into a common measure, which allows climate analysts to aggregate the radiative impacts of various greenhouse gases into a uniform measure denominated in carbon or CO2 equivalents. Reporters to the 1605(b) Program should report total inventory emissions and total reductions in metric tons CO2 equivalents. Reporters should use the respective GWPs for each gas to convert emissions and reductions in native units to metric tons CO2 equivanlents.

General Guidelines, §300.6(j)

• What does carbon dioxide (CO2) equivalent mean?

Carbon dioxide equivalent means the amount of CO2, by weight, emitted into the atmosphere that would produce the same estimated radiative forcing as a given weight of another radiatively active gas. CO2 equivalents are computed by multiplying the weight of the gas being measured by its estimated global warming potential.

General Guidelines, §300.2

• Where can I find a list of GWPs to be used for my 1605(b) report?

EIA uses the GWPs from the Intergovernmental Panel on Climate Change's (IPCC) Fourth Assessment Report (AR4). For a complete listing of IPCC's revised AR4 emission factors, please see Appendix E of the Instructions for Form EIA-1605. For cases where AR4 revisions do not exist, EIA requires reporters to continue to us appropriate GWPs from the IPCC's Third Assessment Report (TAR).

General Guidelines, §300.6(j)

• What is the difference between emission factor and emission coefficient?

For the purposes of the 1605(b) Program, the terms emission factor and emission coefficient are interchangeable. However, please note that the 1605(b) Program uses the term emission factor, since it is the term used by the Intergovernmental Panel on Climate Change (IPCC) in its national greenhouse gas inventory guidance and is generally understood by participants in the 1605(b) Program.

• How do I account for transmission and distribution losses on imported electricity?

EIA has accounted for transmission and distribution (T&D) losses on imported electricity in the regional emission factors used to determine indirect emissions from purchased energy. If using site- or supplier-specific factors, you must account for these losses using a supplier-specific transmission loss adjustment factor.

• Can I use specific emissions factors provided by electricity suppliers instead of regional emissions factors to calculate emissions for purchased electricity?

In almost all circumstances, regional emission factors should be used to calculate emissions for purchased electricty. However, the General Guidelines recognize that if you purchase your electricity from a specific generating plant, you may obtain source-specific emissions information directly from your electric supplier.