Greenhouse gas (GHG) emissions are: those gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit infrared radiation from the earth, clouds and the atmosphere itself, causing the greenhouse effect. Water vapor (H20), carbon dioxide (CO2), nitrous oxide (N20), methane (CH4), and ozone (O3) are the primary greenhouse gases in the Earth's atmosphere. Moreover, there are a number of entirely human-made greenhouse gases in the atmosphere (IPCC 2013).