Ozone Layer Recovery Continues under Montreal Protocol

The Ozone Hole Is Steadily Shrinking because of Global Efforts

By Meghan Bartels edited by Andrea Thompson

Forty years after global policymakers began grappling with the crisis posed by a gaping hole in Earth’s protective ozone layer over Antarctica, the damage is continuing to heal, according to a new report from the World Meteorological Organization.

Found between about nine and 19 miles above Earth’s surface, the ozone layer is a broad region of the stratosphere where the molecule, which contains three oxygen atoms, is particularly concentrated. Here, ozone plays a vital role in blocking the sun’s ultraviolet radiation—essentially acting as a planetary sunscreen of a sort.

In the 1980s, scientists realized that a massive hole was developing in the ozone layer over Antarctica every southern spring and then tied the observation back to earlier research that discovered that a group of chemicals called chlorofluorocarbons (CFCs) were able to eat away at atmospheric ozone. Nations came together to develop an agreement called the Montreal Protocol on Substances That Deplete the Ozone Layer, adopted in 1987, to stop the production of these chemicals.

On supporting science journalism

If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

“The Montreal Protocol is the best environmental agreement we’ve ever created,” says Durwood Zaelke, an environmental policy expert at the University of California, Santa Barbara, and founder and president of the Institute of Governance & Sustainable Development, an organization that is focused on addressing short-lived but high-powered climate pollutants. These include hydrofluorocarbons (HFCs), which do not harm the ozone layer and replaced many CFCs as they were phased out. The agreement has garnered global signatories, several rounds of successful amendments and the near-total elimination of the chemicals that break down ozone. “This is a hell of an agreement,” Zaelke says.

The result is an ozone layer that scientists predict will recover the health it had in 1980 over the tropics and midlatitudes by 2040, over the Arctic by 2045 and over the Antarctica by around 2066. “It takes a long time to heal stratospheric ozone,” Zaelke says.

The new 2024 report from the World Meteorological Organization proves that slow process is continuing as scientists have expected, says A. R. Ravishankara, an atmospheric chemist at Colorado State University. The report shows that, over 2024, total levels of ozone in the atmosphere were above the 2003–2022 average for most of the planet—just a strip near the equator and a small patch of the Antarctic coastline south of Africa were below that marker.

A particularly notable change came over Antarctica, where ozone depletion was notably lower than those from the years between 2020 and 2023. The 2024 ozone hole also formed relatively slowly and recovered relatively quickly—a good sign for the future of the ozone layer, according to the report.

Ravishankara notes that on the long road to recovery, scientists expect to see some better years and some worse years. “One year does not make a trend,” he says. Ravishankara adds that the new report and other observations of ozone in the atmosphere do show slow but steady ozone replenishment.

Ozone is produced primarily at latitudes nearer the equator. And from there, it must disperse out toward the poles, where production is much slower because of reduced sunlight, Ravishankara says. The production and transportation of ozone can be influenced by larger happenings in atmospheric phenomena, including the natural climate phenomenon called El Niño, the sun’s level of activity, the large-scale movement of the atmosphere and of course climate change.

An additional complication is that ozone in the lowest part of the atmosphere, called the troposphere, still blocks sunlight but also acts as a pollutant that is harmful to human health. “You need to know not only the total amount of ozone above your head but also where it is and how it is changing in different parts of the atmosphere,” Ravishankara says.

That’s why different forms of monitoring—both by satellites and from the ground—are so vital to understanding the status of the ozone layer. “This is what I call the accountability phase of the Montreal Protocol, where you want to make sure the results you want are being achieved,” Ravishankara says. “It is going to get better unless we screw up something else.”

Zaelke worries that the Montreal Protocol, like international agreements generally, won’t fare well under President Donald Trump—even though, at the request of industry groups, he signed U.S. legislation that joined the nation to the latest amendment of the protocol, Zaelke says. Still, he thinks that the global infrastructure dedicated to ozone recovery should be sufficient to withstand the administration’s tendency away from global partnerships. “While the world will miss the U.S. leadership,” Zaelke says, “it will survive.”

It’s Time to Stand Up for Science

If you enjoyed this article, I’d like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in that two-century history.

I’ve been a Scientific American subscriber since I was 12 years old, and it helped shape the way I look at the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does that for you, too.

If you subscribe to Scientific American, you help ensure that our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten labs across the U.S.; and that we support both budding and working scientists at a time when the value of science itself too often goes unrecognized.

In return, you get essential news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-watch videos, challenging games, and the science world’s best writing and reporting. You can even gift someone a subscription.

There has never been a more important time for us to stand up and show why science matters. I hope you’ll support us in that mission.