**4.1 Greenhouse gases**

To maintain earth's radiation budget, the radiant energy coming from the sun must be in a fair balance with the radiation leaving the earth. If the emission from earth falls short, energy would accumulate and force the earth's temperature to rise. There are gases in the atmosphere that absorb and prevent the radiation emitted by the earth from escaping into outer space. The energy trapped by these gases is radiated back to earth, causing the earth's temperature to warm up. Gases with this ability are called greenhouse gases (GHGs). GHGs include Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O), and Halocarbons. GHGs do occur naturally. But a group of halocarbons that contain fluorine, known as Fluorinated gases (F-gases), are mostly human-generated. F-gases include sulfur hexafluoride (SF6) used as an insulating gas, and for the production of aluminum and magnesium; hydrofluorocarbons (HFCs) used as blowing agents and refrigerants; and perfluorocarbons (PFCs) used in the electronics industry for semiconductor manufacture. F-gases are potent GHGs that contribute significantly to climate change [36, 37]. **Table 1** highlights the characters of some GHGs.

