Greenhouse gases are those gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of infrared radiation emitted by the Earth’s surface, the atmosphere and clouds. Human-made greenhouse gases in the atmosphere such as halocarbons and other chlorine- and bromine containing substances are dealt with under the Montreal Protocol. Beside carbon dioxide, nitrous oxide and methane, the Kyoto Protocol deals with the greenhouse gases sulphur hexafluoride, hydrofluorocarbons and perfluorocarbons.