Previously all climate changes occurred naturally. However, during the Industrial Revolution, we began destroying our environment through changing agricultural and industrial practices. Global warming is the gradual increase in global temperatures caused by the emission of gases that trap the sun¿s heat in the Earth¿s atmosphere. Most of the sun's energy that reaches the earth is absorbed by the oceans and land. Some of the energy is radiated back into the atmosphere in the form of heat by atmospheric gases. This process is called greenhouse effect. Without the greenhouse gases the surface of the Earth would be as cold as the surface of the Moon (about -18 °C).