Greenhouse effect is one of the phenomena caused by industrial pollution. From the data taken by scientists, our earth has been warming up since the Industrial Revolution. Why does it happen? The factories' emissions have created smog on the atmosphere. The earth's atmosphere becomes like a greenhouse, and the earth and everything inside of it have become like the plants in the green house. The sunlight can pass through the ozone layer but the heat transferred by the sunlight can not escape easily from the layer of smog and is deflected to earth's surface again.