Compounds that contain chlorine, fluorine and carbon only. Once commonly used as coolants in fridges and in products such as hairspray, they would travel high up into the stratosphere and were a significant contributor to the hole in the ozone layer. At lower altitudes in the atmosphere they are a powerful greenhouse gas, 10,600 times more effective at warming the climate than CO2, but their overall warming effect is low. Their use has been largely phased out over the last 20 years, though some of their replacements have also been implicated in global warming.