Greenhouse Gases (GHGs)
Greenhouse gases are 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. This property causes the greenhouse effect.
Primary greenhouse gases
The primary greenhouse gases in the Earth’s atmosphere are:
- Water vapor (H2O)
- Carbon dioxide (CO2)
- Nitrous oxide (N2O)
- Methane (CH4)
- Ozone (O3)
Water vapor is the most abundant and dominant greenhouse gas, but it has a short atmospheric lifetime of approximately 10 days. Although water vapor has a saturation point that limits additional warming, it is still considered a forcing gas in the context of climate change.
Anthropogenic Greenhouse Gases
In addition to the natural greenhouse gases, human activity has added a number of artificial greenhouse gases into the atmosphere. These include:
- Halocarbons
- Chlorine and bromine containing substances
- Sulphur hexafluoride (SF6)
- Hydrofluorocarbons (HFCs)
- Perfluorocarbons (PFCs)
The gases above are addressed in the Montreal Protocol and Kyoto Protocol international treaties due to their heat-trapping properties.
Forcing greenhouse gases
While water vapor is the most abundant greenhouse gas, carbon dioxide (CO2) is considered the dominant forcing greenhouse gas linked to global warming and climate change. Methane and nitrous oxide are also major forcing contributors enhancing the greenhouse effect.
Concentrations of CO2 in the atmosphere have increased by over 40% since pre-industrial times, with over half of that increase occurring since 1980 alone. This dramatic rise is attributed to human activity including burning fossil fuels and deforestation. Methane concentrations have also risen due to human-caused emissions from agriculture, landfills and natural gas infrastructure.
Greenhouse gas emissions by sector
The sectors responsible for the maximum anthropogenic greenhouse gas emissions globally are:
- Power stations – over 21%
- Industrial processes – around 17%
- Agriculture and land use changes – nearly 13%
- Transportation including planes, ships, cars etc. – about 14%
- Buildings including residential and commercial – 17%
- Other fuel combustion – around 11%
Power stations including coal, gas and oil emit large volumes of CO2 through burning fossil fuels to generate electricity. Clearing of forests for palm oil plantations, cattle ranching and other uses also releases stored carbon dioxide and reduces the earth’s capacity to remove CO2 from the air.
