Carbon dioxide gas present in atmosphere performs an important function in the atmosphere and produces the green-house effect, leading to the heating up of earth and its atmosphere. Let us discuss it in detail. There is a protective layer of ozone gas, high up in the atmosphere and then a blanket of carbon dioxide gas in the lower atmosphere. Now, when sun-light consisting of ultra-violet rays, visible light and infra-red rays, falls on the top of the atmosphere, then first of all the harmful ultra-violet radiation is absorbed by the ozone layer. The visible light and infra-red rays then pass through the carbon dioxide layer and fall on the surface of earth.
The infra-red rays which come down from the sun are of short wavelength and pass through the carbon dioxide layer easily. Since the infra-red radiation has heating effect, so it heats the earth and the various objects on the earth. Now, since the earth and its objects become hot, so they also start emitting heat rays or infra-red rays. But since the earth’s surface and the objects on it are less hot so the infra-red rays emitted by them are of long wavelength. In other words, the infra-red rays which fall on the earth from sun are of short wavelength but the infra-red rays reflected from the earth and its objects are of long wavelength.
Now, this long wavelength infra-red radiation reflected from the earth and its objects cannot escape out from the carbon dioxide layer in the atmosphere. Since the carbon dioxide molecules have the ability to absorb the long wavelength infra-red radiation reflected from the earth, so a blanket of carbon dioxide gas in the atmosphere traps all the infra-red rays or heat rays in the atmosphere. And these trapped infra-red rays or heat rays heat the earth’s atmosphere. The heating up of earth’s atmosphere due to the trapping of infra-red rays (reflected from the earth’s surface) by the carbon dioxide layer in the atmosphere is called green-house effect.
The green-house effect in the atmosphere occurs due to the presence of a blanket of carbon dioxide gas in the atmosphere. This blanket of carbon dioxide gas in the atmosphere allows the sunlight to come in freely but does not allow the infra-red radiation reflected by the earth’s surface to go out. It is just because the sun-light can come in freely but the infra-red rays cannot go out freely that the temperature of earth’s atmosphere is raised. It should be noted that the rise in temperature produced by green-house effect in earth’s atmosphere depends on the amount (proportion) of carbon dioxide gas in the atmosphere.
In other words, the proportion of carbon dioxide in atmosphere affects the temperature of atmosphere. So, if the proportion of carbon dioxide gas in the atmosphere increases, then the temperature of earth’s atmosphere will also rise further. The name ‘green-house effect’ comes from the fact that this effect is used in horticulture for the upbringing of green plants in small houses made of glass walls and glass roof. The glass walls and roof of a green-house allow the sun-light (including short wavelength infra-red rays) to come in freely but it does not allow the long wavelength infra-red radiations reflected by the soil, plants and other contents of green-house to go out. These trapped infra-red rays show their heating effect due to which the temperature is raised inside the green-house.
Thus, even without an external supply of heat, the temperature inside a green-house is found to be higher than it is outside. Thus, green-house acts as a heat trap. Due to the presence of carbon dioxide, our atmosphere acts like the glass roof of an ordinary horticultural green-house.