You know what is green house, cold countries plants are grown in a green house to protect them from external cold. Usually this house is made of glasses. As a result sunlight can enter inside. Inside the room plants live on carbohydrates manufacture through photosynthesis by the help of sunlight. With the help of sunlight the internal environment of the house remain warm. As glass is bad conductor of heat so external cold cannot reach inside nor internal heat can go out. Carbon dioxide in the atmosphere acts almost like the glass of the green house.
The earth is heated by sunlight. Much of this heat is lost to the space-by radiation through the atmosphere. As a result the temperature of the atmosphere remains more or less same. But if the amount of CO2 is increased in the atmosphere, the condition becomes different.
Some of the radiated heat is absorbed and retained by carbon dioxide; this results in the increase of atmospheric temperature. Scientists have calculated and found that the amount of CO2 in the atmosphere has been increasing day by day. You must know why the amount of carbon dioxide is increasing. Large-scale deforestation is one of the main reasons. Another reason is the use of fossil fuel. Petrol, diesel, kerosene, coal etc. are mineral fuel. Its uses are increasing in factories, vehicles, and household purposes. As a result the amount of carbon dioxide in the atmosphere is increasing day by day.