It also suggests the amount of aerosols that humans emitinto the atmosphere could impact tree growth, as high levels of aerosols cause "global dimming", an effect that occurs when the levels of light reaching the Earth's surface fall.
However, to build the dams often cause irreversible environmental damage despite the fact that the mills do not emit harmful CO2 emissions into the atmosphere.
Approximately 1, 100 such units at more than 450 existing power plants emit 48 tons of mercury into the air each year, with 11 tons of that deposited on to U.S. soil and waters, says EPA. Those plants also release arsenic, lead and other heavy metals, all of which are considered hazardous and are therefore subject to clean air laws that require those facilities to use modern pollution controls.