Global warming is a serious threat to earth. The continuous increase in the average  temperature of the earth is called global warming. It is caused by the excessive heat trapped by the green house gases. The increase in the green house gases due to the human activities and the cutting down of trees which utilize carbon dioxide a major green house gas is paving way for global warming.  
Global warming could result in wide ranging effects like rise in the sea level, submergence of the coastal area, change in rainfal, agriculture pattern etc. Research has shoen that if we do not keep the greenhouse gases at the present level, then, the temperature may rise by more than 2 degrees Celsius by the end of the century, which can be very dangerous for all the life forms. Therfore, we need to control global warming.