State the utility of carbon dioxide for manufacture of food by plants. State its role in warming the earth's environment and in excess resulting in global warming.

Plants manufacture food by the process of photosynthesis. Carbon dioxide in the atmosphere is absorbed by the plants in the presence of chlorophyll [the green pigment in plants] and sunlight, resulting in the formation of carbohydrates and release of oxygen.

The sun's rays consist of infrared, visible rays and ultra violet rays. Carbon dioxide in the atmosphere allows the reflected ultraviolet rays to pass through but prevents the infrared radiations from being radiated out, resulting in warming of the earth.

Due to pollution, concentration of carbon dioxide in the atmosphere is increasing. This excess carbon dioxide is warming the earth's surface to a harmful extent resulting in global warming.