Popular usage definition: Warming caused by human activity.
Human Causes: Carbon dioxide (CO2), e.g. exhaust from cars and power plants.
Carbon dioxide + other air pollution • like a thickening blanket, trapping the sun's heat Source: • Coal-burning power plants are the largest U.S. -- they produce 2.5 billion tons CO2 every year. • Automobiles, the second largest source, create nearly 1.5 billion tons of CO2 annually. From household: • Vehicles • Home Heating • Electricity