Global warming is the increase in the average temperature of the Earth's near-surface air and the oceans since the mid-twentieth century and its projected continuation.Global warming is caused by several factors:carbon dioxide from power plants,carbon dioxide emitted from cars,carbon dioxide from heating systems,and deforestation.
Carbon dioxide is emitted from burning fossil fuels for the purpose of electricity generation.Coal accounts for 93% of the emissions from the electricity utility industry.The released carbon dioxide contributes to the increase of green house gas and causes the temperature raise.Carbon dioxide is also produced from the heating systems in buildings and houses from natural gas furnaces and coal-fired generation.Aside from the burning of gasoline,deforestation also contributes to global warming.Cutting down tropical forests will cause more carbon dioxide in the air because the temperate forests of the world absorbs 2 billion tons of carbon each year.