Halocarbons

Halocarbons are carbon compounds containing halogens such as chlorine, fluorine, and bromine. Unlike the preceding greenhouse gases, these are almost entirely anthropogenic (produced by human activities). These gases not only have radiative forcing capabilities but are also ozone destroyers. For this reason, their emissions have been controlled under the Montreal Protocol (1987) and their increase in concentration since then has steadily declined. However, they are long-lived and they will continue with their radiative forcing and ozone depletion for at least the next century.

The following are sources of halocarbons:

• Chlorofluorocarbons (CFCs): Refrigerants (Freon) used in air conditioners and refrigerators, propellants in aerosol spray cans, and industrial solvents.
• Other halocarbons: Insulation and foam used in fire extinguishers.

Per molecule halocarbons have a much greater capacity to trap heat than carbon dioxide, but due to their concentration, their radiative forcing is just 0.25Wm-2. They also have an indirect negative radiative forcing (-0.1Wm-2) because of their destruction of ozone, which is another greenhouse gas.

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