In addition to carbon dioxide (CO2), other greenhouse gases are included. These are nitrous oxide (N2O), methane (CH4) and fluorinated gases (F-gases). In order to calculate the combined impact of the different greenhouse gas emissions, emission levels are converted into CO2 equivalents. This conversion is based on the ‘Global Warming Potential’ (GWP), i.e. the measure of warming that is contributed by each gas to the greenhouse effect.
GHG emissions are generally expressed in megatonnes of CO2 equivalents (1 megatonne = 1 million tonnes = 1 billion kilograms). One kg of CO2 equivalents equals the effect of one kg of CO2 being emitted. The emission of 1 kg of nitrous oxide equals 298 kg of CO2 equivalents, and the emission of 1 kg of methane is equal to 25 kg of CO2 equivalents. The GWPs of F-gases vary greatly and levels can be substantial. For example, 1 kg of sulphur hexafluoride equals 22.8 thousand kg of CO2 equivalents.