The chemical refrigerants used for air conditioning and refrigeration systems have played a major part in the increased CO2 levels in the atmosphere since the 1930's, and has been regulated more strictly throughout the years. CFC, HFC and HCFC, are already or on its way of being phased out.
This phase out started with CFC, a very strong Ozone layer depletion chemical decided phased out in the Montreal Protocol in 1987. 10 years later the New CFC replacement chemicals, the HFC turns out to be a major contributor to the green house effect due to its properties equivalent of up to 14.800 kg (R-23) of CO2 pr kg HFC. In the Kyoto agreement of 1997 it was then decided also to phase out the HFC chemicals.
For replacing the HFC, yet another chemical cocktail was introduced, the HFO*, that is in basic design a HFC with at least one double binding of the Carbon atoms. Later science reports suggests that some of these new HFO* chemicals like the R1234yz are a potent source of spreading the extremely acidic TFA (Trifluoroacetic acid) as it degenerates in the atmosphere. Others, like the R1234ze seems to be forming a large portion of R23 (GWP of 14.800) in the degeneration process.
Latest findings suggests a future HFO* ban may come faster than we think, as 5 European countries now have suggested restrictions in use of a major chemical component found in HFOs*.