There are three major gases that are influenced by human activities and that are of interest with respect to greenhouse gas emissions, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The concept of “global warming potential” (GWP or CO2e) has been developed to enable comparison of the ability of different GHGs to trap heat in the atmosphere (radiative forcing)
GHG emissions are typically estimated using emission factors, metrics that relate the number of emissions released to unit levels of activity data. Emission factors, also known as conversion factors, are generally expressed in kilograms of carbon dioxide equivalent (Kg CO2 e). Carbon dioxide equivalent (CO2 e) is used since most forms of energy emit more than one GHG. To calculate the CO2 e the amount of the various GHGs is multiplied by their Global Warming Potential relative to carbon dioxide and then summed. Emission factors are determined using mass balance, fixed chemical equations, or other relationships under average conditions. The factors can be averaged across various geographical ranges – nationally, provincially or even at a facility-specific level.