lobal Warming occurs as a result of increased concentration of greenhouse gases in the atmosphere. The main greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide and ozone. These gases do now allow all the radiations from the Earth to escape back info space. This is known as the Greenhouse Effect. This trapped radiation or heat helps to keep the Earth at a constant temperature. Greenhouse effect is thus very important to main the temperature of the Earth at a habitable level.Over the past few 100 years, human have been burning trees and fissile fuels, thereby releasing millions of tones of carbon dioxide into the atmosphere. The increased level of carbon dioxide in the atmosphere has caused the temperature of the Earth to rise. This, in turn, causes more water to evaporate into the atmosphere. Water vapor is also very good at absorbing heat. This cause the Earth’s atmosphere to become even warmer. Scientist has called this effect ‘Global Warming’. They have warned that Global Warming could shift rainfall patterns, raise the sea level and alter the ecological balance.

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Global Warming is the heating up of the Earth's Surface and the rise in the usual temperature of the Earth.

The main causes for the rise in temperature are :
The smoke from automobiles, 
The green house effect where the clouds hold the heat given by the sun and when Earth radiates it back the cloud cover reflect it back and so the excess heat cannot escape into the atmosphere and 
CFC's (Chlorofluorocarbon) given out by Air Conditioners,Fridges,coolers,etc.

The results of the Global Warming are that 
There is rise in temperature of the Earth's surface, 
The melting of glaciers at the poles causing in floods and depletion of the ozone layer with the effect of CFC and due to this a big hole in the ozone layer which protects us from sun's ultraviolet rays. The hole is over Antarctica whose extent is  as North America.
Ways to prevent Global Warming are:
1. To use CNG (Compressed Natural Gas) Buses.
2. Use of Buses with CNG because people can travel place to place with only the emission of gas from the bus, Suppose 30 people go in bus then it will produces less harm than if 30 people start their own cars.
3. Limited use of AC's.
4. Fridges must be left open for very less time.