Gases that help in causing green house effect are called as green house gases (GHGs). These gases either occur naturally or are produced on earth due to human activities of burning fossil fuel and bio-mass.
One of the most abundant naturally occurring green house gases is the water vapour. Other green house gases are carbon dioxide, methane, Nitrous oxide, Trifluoromethyl sulphur pentafluoride and hydrochlorofluorocarbons. It is since 1700s, that a substantial increase in the concentration of green house gases has occurred in the atmosphere.
•Water Vapour: It accounts for about 60 to 70 percent of the natural green house effect. Its level in the atmosphere rises with the increasing global warming adding up further to the green house effect.
•Carbon dioxide: It is released into atmosphere through decay or burning of organic substances and through volcanic eruptions. It circulates in the atmosphere through carbon cycle. A good part of carbon dioxide is utilised through photosynthesis and major part of it is absorbed by oceans, rivers and lakes. But, in the modern age of industrialization and increasing automobile exhausts the concentration of carbon dioxide is increasing faster than the earth’s natural capacity of assimilation. It has been assessed that the level of CO2 in the atmosphere has risen by more than 30 percent since 1750.Currently, the CO2 concentration in the atmosphere is about 370 parts per million (ppm). It accounts for more than 60 percent of the additional green house effect.
•Methane: This gas is produced through various sources like decomposing organic substances, coal mining, production and transport of other fossil fuels etc. Its concentration in the atmosphere has become more than double since 1750. Scientists are of the opinion that it is an extremely effective heat trapping gas. One molecule of methane is 20 times more efficient in terms of trapping infrared radiation than a molecule of carbon dioxide.
•Nitrous Oxide: This gas is released into the atmosphere by burning of fossil fuels, automobile exhaust, decomposition of nitrogenous fertilizers in the soil etc. Its level in the atmosphere has risen by 17 percent since 1750.This gas has a capacity of trapping heat 300 times more effectively than carbon dioxide. It can stay in the atmosphere for about 100 years.
•Fluorinated Compounds: Compounds comprising CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbons) and HFCs (hydrofluorocarbons) are man- made compounds called as fluorinated compounds. These compounds are used in a variety of manufacturing processes. Each molecule of these synthetic compounds is many thousand times more effective in trapping infrared radiations than a single molecule of carbon dioxide.CFCs were first synthesized in 1928. Since then these were widely used in the manufacture of aerosol sprays, blowing agents for foams, packing materials, as solvents and as refrigerants. By 1992 an amendment in the Montreal Protocol was made to ban these compounds worldwide. However, the HFCs compounds do not contain chlorine and stay in the atmosphere only for a short time. Hence, these are regarded as safe for various applications.
•Trifluoromethyl sulphur pentafluoride: This compound was not reported before 2000. Each molecule of this industrially produced compound can trap heat more effectively than all the other gases known to cause green house effect.