Carbon dioxide present in normal concentration in the air is not an air pollutant. Rather it helps to maintain the temperature on the earth required for the existence of living organisms. However, due to human activities such as burning of fossil fuel like coal, natural gas, petroleum etc. The amount of carbon dioxide in the air is increasing. This result in warming of the earth surface and thus bring about drastic changes in the climate as explained below :-
Out of sun's energy entering the atmosphere about 34% is scattered and reflected back by the particulates and the remaining 66% is absorbed by the earth. The reason for this energy reaching the earth is that visible and ultraviolet radiation can pass through carbon dioxide and water vapour present in the atmosphere. Ultraviolet radiation are absorbed by ozone layer but visible light reaches the earth and heats it up. However, when the earth cools, the energy is 're-emitted from the earth surface in the form of infrared radiations. These radiation can be absorbed by carbon dioxide and water vapours but cannot pass through them. The heats thus absorbed by carbon dioxide and water vapours cannot go to the upper atmosphere and is radiated back to the surface of the earth. In this way, additional heat is kept with in the lower atmosphere and warming of the earth occurs.
The phenomenon has been named as green house effect because it is similar to a green house for plants. A green house is a place where plants are grown on the soil but there are walls and roof made of glass. The sun's energy can enter through the glass but cannot go out of it. The energy is thus absorbed by the soil and the structure of green house. The energy thus absorbed is 're-emitted back into the green house. The same situation is observed inside a car which becomes very hot inside when it is parked in the sun for some time with its glass windows closed. In the atmosphere, carbon dioxide is playing the role of a glass of a green house. Hence it is called green house effect.
Greenhouse Effects :-
* If the rate at which solar radiation are arriving the earth remains constant but the amount of carbon dioxide in the air increases, the heat radiated back to the earth will increase. Consequently, the temperature of the earth surface will increase. As a result, evaporation of surface water will increase which will further helps in the rise of temperature. This increase in temperature will have a drastic effect on the climate and may prove even disastrous.
* Due to higher concentration of carbon dioxide in atmosphere, the plants undergoing photosynthesis will take up the gases at a faster speed. As a result, the plants in warmer climates and adequate rainfall would grow faster.
* Higher global temperature is likely to increase the incidence of infectious disease like malaria, dengue, yellow fever and sleeping sickness.
It is important to mention that earth is being saved from excessive heating due to certain opposing factors taking place simultaneously.
How to reduce rate of global warming :- As green house gases are added into the atmosphere due to burning of fossil fuel and cutting down of forest and trees , we can follow some simple method so that the green house gases are added into the atmosphere as minimum as possible. A few of these can follow s :-
* By preferring walking or using bicycles or going for car pools or taking public transport.
* By planting a new trees every month and increasing green cover.
* By avoiding burning of dry leaves etc.
* By not smoking and persuading others also not to smoke in public places.
* By importanting knowledge to those who do not know about the greenhouse effect.
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