An entity that compares emissions of different greenhouse gases to the global warming effect that the emission of one tonne of CO₂ will have over 100 years. Other greenhouse gases sometimes have a much stronger warming effect than CO₂. For example, one tonne of methane has the same greenhouse effect as 21 tonnes of CO₂, while one tonne of fluorinated gas SF₆ is equivalent to 23,900 tonnes of CO₂.