More than 30 years after scientists first found a hole in the Earth's protective ozone layer, they are seeing signs that it is beginning to heal.
A study released Thursday in the journal Science says the hole is getting smaller. Researchers attribute the good news to the declining release of chlorofluorocarbons into the air.
"It isn't just that the patient is in remission,'' said the study's lead author, Susan Solomon of MIT. "He's actually starting to get better. The patient got very sick in the ‘80s when we were pumping all that chlorine'' into the atmosphere.
The chemical compounds, once commonly used in aerosols, dry cleaning and refrigerators, were banned when nations around the world signed the Montreal Protocol in 1987 in an effort to repair the ozone hole.
Measurements taken in September revealed the hole has shrunk by about 4.5 million square kilometers — about half the area of the contiguous United States — since 2000.
The hole won't be completely closed until mid-century, but the healing is appearing earlier than scientists expected.
"We can now be confident that the things we've done have put the planet on a path to heal," Solomon said.
Ozone is a natural gas made up of three oxygen atoms. About 10 to 50 kilometers high in the stratosphere, the ozone layer shields Earth from the sun's harmful ultraviolet rays.
"There is a sense of ‘mission accomplished,''' emailed University of California San Diego's Mario Molina, who shared the 1995 Nobel Prize for chemistry for his characterization of the ozone problem. He praised the study, in which he played no part.