Short for chlorofluorocarbons, CFCs are nasty chemical compounds that wreak havoc on the environment. Used in refrigeration units and aerosol cans, CFCs combine with atmospheric ozone, neutralizing the molecular compound and weakening the ozone layer, an important environmental barrier that protects the earth's surface from ultraviolet radiation from the sun. While increased regulation since the 1970s has diminished their use, CFCs can endure in the atmosphere for nearly a century, making this a very long-lived mistake.