Greenhouse Gases
Most sunlight is visible wavelength light that passes through the Earth’s atmosphere and heats up the Earth’s surface. Heat from the Earth’s surface then attempts to escape into the coldness of outer space.
Greenhouse gasses (GHGs) are constituents of the Earth's atmosphere that prevent heat from escaping the atmosphere into outer space. Specifically, (GHGs) absorb heat energy (infrared radiation) emitted from the Earth’s surface and re-emit it back towards the Earth’s surface, resulting in a build-up of thermal energy and therefore temperature increase at the Earth’s surface and lower atmosphere layers. Examples of greenhouse gasses are carbon dioxide and methane. Both of these are dominated in terms of mass by the element carbon.
Use of The Term Carbon
The term carbon is used in this context to refer to all gasses that contribute to the retention of thermal energy by the Earth’s atmosphere. Such gasses are known as greenhouse gasses, and typically include carbon-containing compounds such as CO2 (carbon dioxide) or CH4 (methane) but may also include gasses that lack carbon such as N2O.
The six “standard” GHGs frequently reported are:
- CO2
- CH4 (= 25 x global warming potential of CO2)
- N2O (= 298 x global warming potential of CO2)
- HFCs (= up to 14,800 x global warming potential of CO2)
- PFCs (= up to 12,200 x global warming potential of CO2)
- SF6 (= up to 22,800 x global warming potential of CO2)
(NOTE: the terms “carbon”, “greenhouse gasses” and “GHGs” are used interchangeably)
[Source: e.g. see 2004 GHG Protocols from WRI]
Water vapor (H2O) is also a GHG, but its emissions often do not get reported.