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Study shows that the ozone hole over Antarctica is beginning to heal, thanks in part to a global treaty

Amar Toor, THE VERGE
The ozone hole over the Antarctic has begun to heal, according to a new study, more than 30 years after its discovery. The findings suggest that global efforts to phase out ozone-depleting chemicals have been effective, though scientists still aren’t entirely sure about what’s driving the ozone hole’s recovery.
The study, published in the journal Science, combines data gathered from balloons and satellites to measure the area of the ozone layer over Antarctica from 2000 to 2015. Since 2000, the paper reports, the size of the ozone hole over Antarctica shrank by about 4 million square kilometers — an area equivalent to about half of the contiguous United States. Using computer simulations to account for changes in wind and temperature, the study’s authors estimate that about half of its reduction can be attributed to a decline in levels of the ozone-depleting gases chlorine and bromine.
The stratospheric ozone layer protects Earth from the sun’s harmful ultraviolet (UV-B) rays, which can cause skin cancer and cataracts in humans, and physiological damage in animals and plants.
Faced with growing evidence of ozone depletion, governments in 1987 ratified the Montreal Protocol, a global treaty that aimed to phase out the production of harmful chemicals known as chlorofluorocarbons (CFCs). At the time, CFCs were used in hairspray, aerosol cans, and refrigerators. A single CFC molecule can last for between 20 and 100 years in the atmosphere, and can destroy100,000 ozone molecules.
Previous studies have shown that the rate of ozone depletion has declined since the Montreal Protocol went into effect, and a 2014 United Nations report showed that Earth’s ozone layer has begun to heal. But the ozone hole over the Antarctic reached a record size in 2015, casting some doubt over claims of a recovery, and the UN report said it was still unclear whether healing in the Antarctic could be attributed to a decline in ozone-depleting gases.
Susan Solomon, professor of atmospheric chemistry and climate science at MIT and lead author of the study published this week, says her findings suggest that the Montreal Protocol has in fact worked.
“We are beginning to see clear signs that actions that society took to phase out chlorofluorocarbons are actually having the intended effect of beginning to heal the Antarctic ozone layer,” Solomon says, stressing that the recovery is still in its early phases. “It’s really a remarkable achievement for society,” she adds. “It’s a global environmental problem, and we have put ourselves on a good trajectory.”
Read more at: The world’s decision to fix the ozone hole is paying off 30 years later | The Verge