Greenhouse gas
From Environment & Energy Wiki
This page is incomplete and is still being worked on. If you think there is nothing more to add, please delete this banner, in the edit tab.
Description
A greenhouse gas is one that absorbs little or no short-wave radiant energy from the sun but absorbs some of the long-wave radiant energy from the earth's surface, causing an increase of air temperature.
Detailed description
Carbon dioxide is the most important greenhouse gas. Without the pre-industrial era concentration of about 280 ppm, the average global temperature would be sub-zero. The increase of the concentration to about 390 ppm has created an increase of air temperature over the last 180 years of nearly 1 °C, this being a major contribution to global climate change.
Methane is another important greenhouse gas. Its concentration is much lower than that of carbon dioxide, but its concentration has increased more significantly and it has much higher global warming potential.
Other important greenhouse gases include the man-made sulfur hexafluoride (SF6), perfluorocarbons (PFCs), chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs).
Water vapour is also a greenhouse gas, mainly because of the vast quantities in the lower troposphere. However, its absorption spectrum does not correspond with the major radiation spectrum from the earth's surface, so it traps much less energy than most other greenhouse gases. It should be noted that the water vapour content of the atmosphere changes constantly with the season and weather. However, the average water vapour content in each hemisphere, over the year, is governed by a negative feedback loop, so that the global yearly average quantity of water vapour is fairly constant and water vapour has not contributed substantially to climate change.
