The atmosphere is trapping too much heat and causing the earth to heat up. This is known as GLOBAL WARMING.
GREEN HOUSE GASES
Carbon dioxide , Methane ,Nitrous oxide ,CFCs etc are called ‘green house gases’. These gases form a layer in the atmosphere and this layer acts like glass in the ‘green house’. Most of the light energy from the sun is emitted in short wave lengths, and it can pass through the layer of green house gases. The sun light warms the ground and the warm ground sends out radiation with longer wave lengths which cannot pass out through the layer of Carbon dioxide .So in effect, Carbon dioxide lets the light energy in, but doesn’t let all the heat energy out. So heat is trapped in the atmosphere as in a green house.