Located in the atmospheric layer known as the stratosphere is a region of concentration of the ozone (O3) molecule. This “ozone layer” is found at an altitude of about 10 to 50 kilometers (6 to 31 miles), with a maximum concentration in the stratosphere at an altitude of approximately 25 kilometers (16 miles). Starting in the late 1970s, scientists began measuring a seasonal depletion of ozone in the ozone layer mainly at the South Pole. The ozone layer naturally shields Earth's life from the harmful effects of the Sun's ultraviolet (UV) radiation. The nation’s of the world have responded to this global environmental problem by proposing a plan known as the Montreal Protocol, to reduce and eliminate the use of chlorofluorocarbons (CFCs) the human-made chemical primarily responsible for ozone loss.