Heating up of the earth’s atmosphere due to infra-red radiation re-radiated from the earth’s surface and absorbed by the greenhouse gases present in the atmosphere is called greenhouse effect.
Glass allows visible light to pass through but not infra-red rays. During the day, sunlight passes into the greenhouse. Greenhouse is a building constructed mainly of glass to grow and protect plants. During the daytime the sun light passes into the green house and is absorbed by the walls, earth, plants and so on. This absorbed visible light is re-radiated as infra-red radiation, which cannot escape the enclosure. The trapped infra-red radiation causes the temperature of the interior to rise. As a result, the greenhouse is warm inside.
Carbon-dioxide, methane, nitrous oxide and ozone in the earth’s atmosphere act like the glass in the greenhouse. These gases are called green house gases. They allow the visible light from the sun to pass through but not much of the infra-red rays. The visible light that reaches the earth’s surface is absorbed and re-radiated as infra-red radiation. This IR radiation is trapped and absorbed by the earth’s atmosphere. This results in warming up of the earth’s atmosphere.
As fossil fuels are burnt, a large amount of carbon-dioxide is released into the atmosphere, which absorbs Infra-red radiations from the surface of the earth. This raises the temperature of the earth. Consequently the polar ice-caps would melt raising the sea level. This is of great concern to the whole world, as the coastal areas are likely to be submerged.