The heat caused by infrared radiation from the sun which escapes from the Earth’s outer surface, is absorbed by “greenhouse gases” which trap the heat forming a kind of blanket of warm air that surround the planet. This occurrence is called the “green house effect”. It is suggested that the temperature on average would have been much lower compared to what is now. Survival of the ecosystem would have been difficult in such extreme condition.

UNDERSTANDING THE GREENHOUSE EFFECT

In the natural greenhouse effect, the type of topograpyh the sunlight falls plays a key role. Different types of surfaces absorb or radiate heat differently. For example, white glaciers reflect maximum sunlight resulting in minimum heating of the surface and the lower atmosphere. On the other hand, sunlight is absorbed the maximum by dark desert soil causing more heating of the surface and the lower atmosphere. Clouds that cover the sky reduce the amount of solar radiation penetrating onto the earth’s surface and also reduce the amount of radiation emitted into space.

BASIC MECHANISM

About 50% of the solar radiation is absorbed by the earth’s surface and the rest is emitted as infrared radiation by the surface of earth. Green house gases absorb most of the infrared radiation and pass on to the other atmospheric gases by molecular interaction. The greenhouse gases too radiate some heat. Heat is radiated both upwards and downwards with some escaping into the space and some getting back to the earth surface. The earth surface and the lower atmosphere is thus aiding to the survival of life on earth.

Greenhouse gases such as carbon dioxide, methane, water vapor, nitrous oxide etc. are molecules formed by two atoms which are loosely bound and are thereby easily excited by solar radiation. The loose atoms then pass on the heat to other gases by molecular interaction. Major components of the atmosphere such as oxygen and nitrogen are formed my tightly bound atoms which are not easily excited and thus do not absorb heat.

EFFECTS ON GLOBAL WARMING

Though greenhouse effect is an essential environmental phenomenon, the trouble begins when human activities disturb or accelerate the natural process by creating more of the green house gases necessary for the optimum warming of the earth surface and thus raising the surface temperature above ideal one.

Higher the concentration of the green house gases more is the heat radiation towards the earth. The emission of green house gas such as carbon dioxide is mainly due to burning of fossil fuels such as oil, gas, petrol, kerosene etc.
Higher concentration of such man-made greenhouse gas causes considerable warming of the earth and the sea resulting in Global Warming.

HUMAN CONTRIBUTION

• Level of carbon dioxide is increased by burning of natural gas, coal, oil, petrol etc.
• Some agricultural and land-use methods increase the level of methane and nitrous oxide in atmosphere.
• Industrial wastes and gases contribute substantially to the green house effect and thus adding to global warming.
• Deforestation is one of the major causes of global warming today.
• Population explosion is another prime factor contributing towards global warming.