A Global Warming Potential (GWP) is an index of the warming potency of different gases, and can also be thought of as an estimate of how much a given mass of a specific greenhouse gas will contribute to climate change. Carbon dioxide has a GWP of 1, and all other gases are indexed relative to CO2. For example, methane has a GWP of 25 as it causes 25 times more warming than CO2 over a 100 year time period. A quantity of greenhouse gas is converted into carbon dioxide equivalent (CO2e) by multiplying the mass of gas by its GWP.