Green electricity is generated using renewable sources such as wind, solar, small hydroelectric, or biomass power. Unlike traditional electricity sources, these alternative sources reduce or avoid greenhouse emissions, nuclear waste, and other pollution sources. Since conventional electricity generation contributes to air pollution more than any other industry in the United States, switching any percentage of our electricity to renewable sources can make a significant, positive impact on the environment and human health. Each year, for example, the use of a single 750-kilowatt wind turbine in the United States prevents on average as much carbon dioxide as can be absorbed by 500 acres of forest. Purchasing one megawatt of electricity from Pennsylvania's wind farms reduces the same amount of carbon dioxide as planting 81 trees or driving 1,040 fewer miles would in that region.