The Antarctic ozone hole is healing, study finds

The hole in the Antarctic ozone layer is slowing beginning to heal, mostly thanks to an international treaty signed in 1987 banning the use of chlorofluorocarbons (CFCs), according to new research published in this week’s edition of the peer-reviewed journal Science.

In the study, Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT, and her colleagues reported that in September 2015, the hole had shrunk by more than four million square kilometers (almost 2.5 million square miles), or about half the area of the continental US, since reaching its largest point 16 years ago.

While that recovery varies from time to time due to volcanic eruptions, the overall trend is that the Antarctic ozone layer is on the road to recovery, and much of the credit is being given to the passage of the Montreal Protocol, the agreement that looked to ban CFC use globally. As a result the amount of atmospheric chlorine originating from CFCs, chemical compounds that previously had been used in old refrigerators and aerosol cans, has been on an overall decline.

“We can now be confident that the things we’ve done have put the planet on a path to heal.” Solomon said Thursday in a press release. “We did something that created a situation that we decided collectively, as a world, ‘Let’s get rid of these molecules’?” “We got rid of them, and now we’re seeing the planet respond.”

If trends continue, hole could close completely by mid-century

Scientists first discovered the ozone hole in the 1950s, and about three decades later, they first noticed that the October total ozone was decreasing. As a result, they began to measure October levels of Antarctic ozone, which can be destroyed by chlorine provided that there is enough light and the atmosphere is cold enough to produce polar stratospheric clouds.

Previous data has demonstrated that ozone depletion typically starts in late August, just after the region’s winter comes to an end, and that the hole is completely formed by early October. Since this is the case, Solomon’s team decided to observe the hole in September, when the ozone hole was still forming during the winter. They discovered that the rate at which the hole opens during the month of September has decreased along with chlorine levels.

They tracked the ozone hole in September every year from 2000 through 2015, analyzing the ozone data collected by satellites and weather balloons as well as satellite measurements of the sulfur dioxide emitted by volcanoes (which can also result in ozone depletion). The researchers also tracked wind, temperature and other meteorological data.

Their analysis revealed that, as of September 2015, the ozone hole was more than four million square kilometers smaller than it was at its 2000 peak, and that at least half of this shrinkage was due directly to reduced levels of atmospheric chlorine. Furthermore, Solomon said that she sees no reason why the trend should not continue, and that if chlorine continued to dissipate from the atmosphere, the Antarctic ozone hole could permanently close by mid-century – provided no unexpected volcanic eruptions cause it to temporarily expand.

“What’s exciting for me personally is, this brings so much of my own work over 30 years full circle,” said the professor, whose research into chlorine and ozone played a key role in bringing about the Montreal Protocol. “Science was helpful in showing the path, diplomats, countries, and industry were incredibly able in charting a pathway out of these molecules, and now we’ve actually seen the planet starting to get better. It’s a wonderful thing.”

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Image credit: MIT

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