The following picture shows the observed evolution of the atmospheric CFC-11 and CFC-12 concentration for the Northern and Southern hemispheres (Walker et al., JGR, 2000). CFCs are gases of purely anthropogenic origin without natural background with an atmospheric lifetime of approximately 45 (CFC-11) and 100 (CFC-12) years. Their atmospheric concentrations began to increase in the early 1930s an started to stabilize only in the early 1990s, as a consequence of the Montreal Protocol. CFCs are very powerful greenhouse gases, with a much larger global warming potential than CO₂. More importantly, CFCs are involved in the destruction of stratospheric O₃. The CFC concentrations in the Northern hemisphere are slightly higher than in Southern hemisphere, as CFC emissions occur predominatly in the (industrialized) Northern hemisphere.

Picture by Gian-Kasper Plattner, in the framework of the EU-Project GOSAC/OCMIP.