Definition
Greenhouse gases (GHG) are those gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and emit radiation at specific wavelengths within the spectrum of thermal infrared radiation emitted by the Earth’s surface, the atmosphere itself, and by clouds, [IPCC, p. 550, link]
Emissions are the release of GHGs and/or their precursors into the atmosphere over a specified area and period of time. Removals conversely are the absorption of atmospheric GHGs by a sink. CO2 is the only gas for which removals are estimated in the national GHG inventory.
[FDES BSES 1.3.1 and 3.1.1, p.8, link]
Relevance
Causes of climate change: Greenhouse gases cause the greenhouse gas effect which leads to global warming, as a result of long-wave (infrared) energy capture by the GHGs in the atmosphere and its downward re-emitting which causes warming at the lower atmosphere and land/ocean surface. [IPCC, link]
Total annual anthropogenic GHG emissions have increased by about 10 Gt CO2-eq between 2000 and 2010. This increase directly came from the energy (47%), industry (30%), transport (11%) and building (3%) sectors. [IPCC AR5 SYR, Past and recent drivers of climate change, 1.2.2 Human activities affecting emission drivers, link]
