Thirty years after a treaty was signed to phase out production of ozone-depleting substances, scientists have found that the gaping hole in the Antarctic ozone is showing signs of shrinking.

Known as the 1987 Montreal Protocol, the treaty was signed by virtually every country across the world to protect the damaged ozone layer from further deterioration. Now, a new study shows that the treaty's prohibition of chemicals including chlorofluorocarbons (CFC) is finally paying off.

Signs Of Healing

In October 2015, NASA and the United Nations World Meteorological Organization announced that the Antarctic ozone layer expanded to about 10.9 million square miles. Back then, experts affirmed that this was no cause for undue alarm.

In the new study, researchers found that the September ozone hole has lessened by more than 4 million square meters since 2000. For comparison, this area is equivalent to half the contiguous United States.

Scientists also demonstrated for the first time that the ozone's recovery has slowed somewhat at certain times because of the effects of volcanic eruptions every year. Still, overall, the ozone layer appears to be on a path to healing, they said.

Susan Solomon, an expert from the Massachusetts Institute of Technology and lead author of the study, says scientists can now be confident that efforts in the past have put the ozone on a path to heal.

"[N]ow we've actually seen the planet starting to get better," says Solomon.

Solomon and her colleagues tracked "fingerprints" of ozone changes with altitude and season in order to attribute its recovery to the ongoing atmospheric chlorine decline — a compound that usually comes from CFCs. These were also once generated by aerosols such as hairspray, dry cleaning processes and old refrigerators.

Expanding Hole

The Antarctic ozone hole was first detected through ground-based data in the 1950s. By the mid-1980s, experts from the British Antarctic Survey found that the October total ozone was plummeting. From then on, scientists all over the world have used October measurements of the Antarctic zone for monitoring.

Ozone layer, the shield of region of the planet's stratosphere that absorbs the ultraviolet radiation from the sun, contains ozone that is sensitive to chlorine, sunlight and temperature.

Scientists say that chlorine slowly destroys ozone, but only if the atmosphere is cold enough and only if light is present. If such conditions are present, it will be enough to create polar stratospheric clouds on which chlorine could occur.

Solomon says that it has been customary for scientists to track the ozone during October, but she says they have found that tracking ozone levels during September would give them a clearer picture of the effects of chlorine.

Details of the study are published in the journal Science.