The main way of measuring carbon is Co2e, or carbon dioxide equivalent. It allows for the capture of several different greenhouse gases into a common unit.
Co2e captures the following seven greenhouse gases:
Taken after the city in Japan where the protocol was adopted in December 1997, it provides measurements against seven greenhouses gases responsible for climate change.
The Intergovernmental Panel on Climate Change (IPCC) reports on the assessable values under the Kyoto Protocol. It is updated every 5 to 7 years and the assessment of the seventh cycle began in July 2023. The current version is the sixth assessment cycle finalised in March 2023. This current version will likely be the core version used by companies in the lead up to the first milestone in 2030.
The protocol allows for conversion of each of the seven gases to be convertible into a common Co2e value. This conversation factor is called Global Warming Potential (GWP).
The current values are:
| Greenhouse Gas | Global Warming Potential (GWP) |
|---|---|
| Carbon Dioxide (Co2) | 1 |
| Methane (Ch4) | 29.8 |
| Nitrous Oxide (N2o) | 273 |
| Hydrofluorocarbons (HFCs) | 5 - 14,600 |
| Perfluorocarbons (PFCs) | 78 - 12,400 |
| Sulphur Hexafluoride (Sf6) | 25,200 |
| Nitrogen Trifluoride (Nf3) | 17,400 |
The Global Warming Potential (GWP) of a greenhouse gas is an index, with Co2 having the index value of 1, and the GWP for all other greenhouse gases is the number of times more warming they cause compared to Co2.
For example, 1kg of methane causes 29.8 time more warming over 100 year period compared to 1kg of Co2, and so methane has a GWP of 29.8. This GWP calculation can be used to directly express methane (or another of the other six gases in the above table) in terms of Co2e. Therefore the amount of Co2e produced by 1kg of methane is 29.8kg of Co2e.