GWP (Global Warming Potential)
Global Warming Potential (GWP) is a metric used to compare the relative impact of different greenhouse gases (GHGs) on global warming. It measures how much energy the emissions of 1 ton of a gas will absorb over a given period of time, compared to the emissions of 1 ton of carbon dioxide (CO2). The larger the GWP, the more that a given gas warms the Earth compared to CO2 over that time period.
Time Horizons for GWP
The GWP values are typically calculated over specific time horizons, most commonly 20 years and 100 years, due to the differing lifetimes of GHGs in the atmosphere. This provides a measure of the immediate and long-term impacts of these gases on the atmosphere:
- 20-Year Time Horizon: Highlights the short-term impacts of GHGs. It's particularly useful for gases like methane (CH4), which have a shorter atmospheric lifetime but a high short-term impact on global warming.
- 100-Year Time Horizon: Provides a measure of the long-term impact of GHGs. This is the more commonly used time frame, especially in global climate agreements and policies.
GWP Values for Common GHGs
Below is a table showcasing the GWP values for some common greenhouse gases over both 20-year and 100-year time horizons:
| Greenhouse Gas | Chemical Formula | GWP (20 years | GWP (100 years) |
|---|---|---|---|
| Carbon Dioxide | CO2 | 1 | 1 |
| Methane | CH4 | 84-87 | 28-36 |
| Nitrous Oxide | N2O | 264-268 | 265-298 |
| HFC-134a (1,1,1,2-Tetrafluoroethane) | C2H2F4 | 3830 | 1430 |
| Sulfur Hexafluorid | SF6 | 17300 | 23500 |
IMDE Framework Table to be used
Within the IMDE framework when combining all GHG gas emissions into the total GHG Emission value the conversion is based on a 100 year time horizion, using the conversion factors from the IPCC Fifth Assessment Report, 2014 (AR5).
The full list can be downloaded here.
The six Kyoto Protocol greenhouse gases covered in the Corporate Value Chain Standard of the GHG Protocol (Greenhouse Gas Protocol: Corporate Value Chain (Scope 3) Accounting and Reporting Standard are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), sulfur hexafluoride (SF6), perfluorocarbons (PFCs), and hydrofluorocarbons (HFCs).
Table with the most used GWPs:
| Greenhouse Gas | Chemical Formula | GWP 100y |
|---|---|---|
| Carbon Dioxide | CO2 | 1 |
| Methane | CH4 | 28 |
| Nitrous Oxide | N2O | 265 |
| HFC-134a | C2H2F4 | 1300 |
| SF6 | Sulfur Hexafluorid | 17300 |
Standardizing on one time period and one GWP value will make Carbon FootPrint values comparable and will support consolidation for example in ESG reporting.
