Nowadays, because of the greenhouse effect, the Earth becomes warmer markedly. Viet Nam is a tropical country which has extremely hot summer. So in this season, the demand for air conditioning is extremely numerous and it leads to overloading national power grid, especially, in the big cities. What are the reasons of this problems? And how does this affect on our lives? It is true that nobody want to work, study or sleep in a flaming environment. It makes us feel uneasy. So it's difficult to do everything effectively when we are drenched in sweat. However, in now modern life, people use air-conditioners as a best way to reduce the heat of the summer. We can see the air-conditioners everywhere: at the offices, at the cafes or the restaurants , at large shopping malls or supermarkets, at the companies or at bedrooms. In some places, they are used in a whole day, and of course, they can't have a rest! In my point of view, this is a main reason that makes a huge strain on the citywide electricity grid. There are also some causes of this problems, such as the demand for using electricity is increasing day by day, yet, the electricity is drying up step by step. I strongly believe that there are many negative consequences in using air-conditioner excessively. Firstly, it costs too much money to pay the electric bill instead of investing in public services like health care service, education or transport. Moreover, I am convinced that air-conditioners are not good for our health. This easily leads to the skin and respiratory diseases. Last but not least, this is also one of the reasons causing greenhouse effect. In conclusion, there are many causes and bad problems of using air-conditioner excessively in our life. This led to a most worrying issue at present, it is global warming.