The Montreal Protocol was a milestone in international cooperation in environmental matters, or environmental diplomacy to use a more recently-coined term. Unlike some treaties and conventions (Kyoto, Camcun, Copenhagen...) we've seen tangible results: Reduction in CFCs. While this was great news for our ozone layer, it has also brought us new worries: HFCs are now the predominant refrigerant, and they have huge global warming potential. They have a GWP of 3922, precisely 3922 times that of carbon dioxide. It is contributing to global warming, and its continued use will likely become more of a headache in the future, perhaps even more than the three most important gases (CO2, methane, N2O).