Types of Greenhouse Gases :-
In the environment, greenhouse gases occur (i) naturally or (ii) from human activities.
The most abundant greenhouse gas is carbon dioxide. It reaches the atmosphere due to volcanic eruptions, respiration of animals, burning and decay of organic matter such as plants. Normally carbon-dioxide is removed by the plants by photosynthesis. Carbon-dioxide is also absorbed into ocean water. But humans by their activities increase the release of carbon dioxide into the atmosphere . Such activities include burning of fossil fuels, solid wastes, wood and wood products to drive vehicles, generate electricity etc. At the same time due to deforestation, the number of trees available to absorb carbon-dioxide through photosynthesis has been greatly reduced.
Human activities have caused carbon - dioxide to be released to the atmosphere at rates much faster than that at which earth's natural processes can recycle this gas. There were about 281 molecules of carbon-dioxide per million molecules of air (i.e., parts per million or ppm) in 1750. Today atmospheric carbon-dioxide concentrations are 368 ppm, a 31% increase.
Methane traps 20 times more heat than carbon-dioxide. It is emitted during the production and transport of coal, natural gas and oil. It is also emitted from rotting organic waste in sand fills, by the cows as a by product of digestion. Since 1750, the amount of methane in the atmosphere has more than doubled.
Nitrous Oxide traps 300 times more heat than carbon-dioxide. burning fossil fuels and ploughing farm soils releases nitrous oxide. Since 1750 its level increased by 17%. Hydrocarbons formed from the manufac-ture of foams, coolants such as chlorofluorocarbons used in refrigerators are the other gases responsible for global warming.In 2000, scientists discovered an alarming increase in the level of a new gas called trifluoromethyl sulphur penta fluoride. Eventhough the gas is rare, it traps more effectively than all other greenhouse gases. The saddest part of it is that the industrial source of the gas is not yet identified.