NOTE: CF₄ = perfluoromethane; CFC-11 = chlorofluorocarbon-11; HFC-23 = hydrofluorocarbon-23; ppm = parts per million; ppb = parts per billion; ppt = parts per trillion.

^a Rate is calculated over the period 1990 to 1999.

^b Rate fluctuated between 0.9 and 2.8 ppm yr^-1 for CO₂ and between 0 and 13 ppb yr^-1 for CH₄ over the period 1990 to 1999.

^c No single lifetime can be defined for CO₂ because of coupling with surface reservoirs.

^d This lifetime has been defined as an “adjustment time” that takes into account the indirect effect of the gas on its own residence time.

SOURCE: IPCC (2001).