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).