The best known halocarbons are CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbons) and the newer substitutes, HFCs (hydroflurocarbons). Halocarbons are used for, for example, for propellants, refrigeration devices, air conditioning, for certain types of heat pumps, and for foam plastic.
Halocarbons are long lasting and powerful greenhouse gases. For example, CFC12 can remain in the atmosphere for over 102 years and has 3800 times more powerful warming effect that CO2 molecule. However, international regulation, such as the Montreal Protocol, has effectively limited the emissions these gases, and the concentrations of most of these gases are now declining or at least levelling off.