Greenhouse gases (GHGs) trap heat in the Earth's atmosphere significantly affecting the Earth's temperature and climate.
The most well-known greenhouse gas is carbon dioxide (CO2) which is vitally essential for all plant life, and also animals that need the plants for food. Without atmospheric CO2, virtually all life on Earth would end.
Most CO2 is emitted by natural causes such as breath exhalations from oxygen using animals and other organisms, the decay of dead organisms, volcanic activity and wild fires. But some is emitted from automobile tail-pipes and the burning of fossil fuels (coal, oil, and natural gas) for transport, electricity generation, residential and commercial heating. It is also produced by deforestation, many industrial processes like cement production, agriculture and the incineration of waste, or natural decomposition of organic waste in landfills. Also converting forests to agricultural land contributes to CO2 emissions.
Most CO2 is recycled by growing plants that use the carbon and emit oxygen to the atmosphere. The amount of CO2 in the atmosphere has remained fairly stable for the past 800,000 years ranging from about 170 ppm (parts per million) during cooler periods to about 290 ppm during warmer periods. But in the past 200 years it has increase to 410 ppm probably as a result of our use of coal, oil and natural gas as energy sources.
Water vapour is the most abundant greenhouse gas, but while clouds reflect the lower frequencies of heat radiating from the Earth's surface back down, they also reflect solar radiation back into space thus acting as a sun shield as well as a greenhouse gas. The amount of water vapour in the atmosphere varies from 4% to 1% and this is influenced mainly by temperature changes rather than human activities.
Water vapour represents up to 90 % of greenhouse gas volume in the atmosphere compared to a volume of 9 to 26 % for carbon dioxide.
Methane (CH4) is a greenhouse gas that makes up about 1,800 parts per billion (just 0.00018% of the atmosphere, compared to 0.041% for carbon dioxide but it has a much stronger warming potential than CO2.However, it has a shorter lifespan in the atmosphere as it burns with atmospheric oxygen to produce CO2 and water. Methane is emitted by the digestive process of some livestock such as cattle and other agricultural practices, as well as the decay of organic waste in landfills and wetland where it is produced by anaerobic bacteria. It is also release by leakage of fossil natural gas which is mostly methane.
Agriculture also produces nitrous oxide (N2O), a potent greenhouse gas, from animal excrement, nitrogen-based fertilizer use and the burning of biomass. Nitrous oxide has a warming potential several hundred times greater than CO2 and can stay in the atmosphere for over a century.
Synthetic gases used by industrial processes, refrigeration, air conditioning and electronics, including hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) while present in much smaller quantities than CO2, have extremely high global warming potentials and can remain in the atmosphere for long periods.
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