In the next century, chlorine-induced ozone losses will be reduced as chlorine amounts throughout the stratosphere decline, and ozone levels will begin to recover. The actual rate of recovery will likely be affected by the increasing abundance of greenhouse gases in the atmosphere. Detecting the recovery of the ozone hole will require a number of years of measurements. Ozone molecules, made up of three atoms of oxygen, comprise a thin layer of the atmosphere that absorbs harmful ultraviolet radiation from the Sun. Most atmospheric ozone is found between 6 and 18 miles above the Earth's surface.
Ozone shields life on Earth from the harmful effects of the Sun's ultraviolet radiation.
Scientists and others have a keen interest in ozone depletion. Increased amounts of ultraviolet radiation that reach the Earth's surface due to ozone loss might increase the incidence of skin cancer and cataracts in humans, depress the human immune system, harm some crops and interfere with marine life. NASA instruments have been measuring Antarctic ozone levels since the early 1970s. The previous record of 10.0 million square miles was set on Sept. 7, 1996. The ozone level fell to 90 Dobson units on Sept. 30, 1998.