CO2 is released into the air by the combustion of fuels. It is estimated that CO2 content of the air is increasing at the rate of 0.4% per annum. This will result in an appreciable warming up of the earth. This is called green house effect. It is very likely that this will cause the melting of polar ice caps resulting in a rise of nearly 60 feet on the sea level. Coastal regions and low lying areas all over the world will be go under water.
 Not only CO2 but CFC and to some extent methane and oxides of nitrogen disturb the temperature of earth hence they all are described as green houses gases.
 3.0 pH has been recorded in acid rain.