On May 16, 1985, the team published a paper in the journal Nature clearly showing there was a hole in the ozone layer of the atmosphere above Antarctica. It was the culmination of years of work by three researchers from the British Antarctic Survey - Joe Farman, Brian Gardiner, and Jonathan Shanklin - who had quietly been collecting and analyzing data gathered by a Dobson ozone spectrophotometer, a creaky-looking device developed in the 1920s that could measure atmospheric ozone. It would result in the first-ever global treaty to address environmental concerns, the Montreal Protocol, to which every single country on Earth signed up.
At first, they weren't looking for anything extraordinary. They were simply trying to better understand the atmosphere over Antarctica. But in 1981, their data began to show some troubling, unexplained patterns.
"I went for the summer with a brand new Dobson because the idea was that possibly some of these readings were because the instrument was malfunctioning," Shanklin told IFLScience.
"I had some feedback from people saying that the data is falling off the graph [...] It was starting to look as if something was amiss. But equally, people weren't sure because it might just be a one-off," he added.
It wasn't until Shanklin compiled data from the previous decade, collected by Joe Farman, that the unexpected readings took on new meaning. Shanklin explained: "I went back through the 10 years since he [Farman] had written his major report and was able to show that this was systematic. Each year in the springtime, the ozone was a little bit less than the previous year."
"I put a draft paper together and plonked it on his desk, Brian Garner's desk, and their boss's desk - and watched the sparks fly."
The ozone layer, located 15 to 30 kilometers (9.3 to 18.6 miles) above Earth's surface, is a band in the atmosphere with a high concentration of ozone gas. This gas helps absorb harmful UV rays from the Sun, acting as an invisible shield for life on Earth. Without it, or with a large hole in it, we would be bombarded with far more radiation, leading to higher rates of skin cancer, cataracts, and immune system damage, while also disrupting ecosystems, particularly plankton at the base of the ocean food chain.
Ozone levels over Antarctica fluctuate with the seasons. The ozone hole typically reaches its largest size during the Antarctic spring (August to October), before gradually shrinking and ultimately disappearing by the start of summer (December).
Since the 1970s, scientists had worried that CFCs - human-made gases used in aerosol sprays and refrigeration - might be harming the ozone layer. The leading theory at the time suggested that any damage would likely occur high above the tropics, at altitudes over 40 kilometers (24 miles), where intense ultraviolet radiation is most abundant. This UV radiation would break down the CFC molecules, releasing chlorine atoms that could then catalytically destroy ozone.
However, the 1985 study had almost found the opposite: ozone depletion was occurring in Antarctica - and occurring at a dizzying rate.
This was because extremely cold atmospheric conditions and the formation of polar stratospheric clouds created an environment where chlorine compounds from CFCs could become highly reactive. When sunlight returned to the region in early spring, these reactive chlorine molecules rapidly broke down ozone, leading to the dramatic thinning now known as the ozone hole.
"There were lots of other proposals as to what might be going on. Initially, the satellite people thought 'Well, it's clearly solar activity that's driving this.' They had six years' worth of data, half a solar cycle, so you could get a very good correlation between the two on the basis of that data. But correlation is not the same as causation," Shankin noted.
A paper in 1986 by scientists in the US confirmed the complex chemistry and affirmed that CFCs were directly responsible for ozone depletion in Antarctica. It became clear that the world needed to come together, form a plan, and phase out the use of these chemicals ASAP.
Remarkably, that's exactly what happened. In 1987, just two years after the publication of the ozone hole discovery, 197 countries and the European Union signed the Montreal Protocol, which saw the phase-out of CFCs and - crucially - made precautions that would allow the protocol to later ban ozone-depleting chemicals that were yet to be invented.
To date, it is the only UN treaty that has been ratified by all countries of the world and was described by former UN Secretary-General Kofi Annan as "perhaps the single most successful international agreement to date".
Compared to the painfully slow progress in tackling the climate crisis, the success of the Montreal Protocol is striking. So, how did taking this serious action happen so fast? It had a clear message and a straightforward solution, but perhaps most importantly, it didn't require people to make radical lifestyle changes, and the status quo was relatively undisturbed, Shanklin told us. Politically and economically, there was plenty to gain, too.
"The thinning of the ozone allows more UV to the surface, and more UV for skin cancers and cataracts, so there's a public health issue. Cancer has been a big issue for a long time, politically," Shanklin explained.
"The manufacturers were quite happy to move to an alternative. Because the patents on the CFCs were coming to the end of the 50-year span, they could make more money by producing alternatives," he added.
All in all, the quick action taken because of the scientific evidence presented has resulted in the steady shrinking in size of the ozone hole over the last 40 years, with complete recovery in sight (as long as any new threats are kept under control).
"I think recovery by the second half of the century is reasonable," Professor John Pyle, a leading atmospheric chemist and former Co-Director of the Centre for Atmospheric Science, who was instrumental in the Montreal Protocol, told IFLScience
"It's a slow process, recovery. It's slow because the lifetime of some of these gases is very long, and it's difficult to detect recovery because of interannual variability. But I think, by and large, the story is a good one."
There is good reason to be cautious, though. While the ozone hole is on track to recover, progress is fragile. Rogue emissions of banned substances like CFC-11 have been detected in recent years and traced back to China, suggesting that compliance isn't perfect. Climate change itself could also complicate recovery, as shifting atmospheric temperatures and circulation patterns may influence how ozone forms and depletes.
Early research also suggests that satellite and rocket launches, which are becoming alarmingly common in recent years, may also have a negative impact on the ozone layer, both during launch and upon satellite reentry.
Despite these hurdles, the Montreal Protocol remains a landmark example of global political cooperation in addressing an environmental crisis. It showed that with clear science, coordinated policy, and international commitment, meaningful change is possible. Unfortunately, tackling climate change is proving far more complex.
"The climate story is much, much more difficult than the ozone story," Professor Pyle told IFLScience.
"What the Montreal Protocol showed is that you start with very small steps, but you get it better as the science gets better, and as you get more people onboard. That's not really happening with climate, and for good reasons: Climate is very complicated."
Climate change cannot be solved with a quick fix or a single treaty. Unlike the ozone crisis, which centered on a relatively narrow group of chemicals and had readily available alternatives, climate change touches nearly every part of the global economy and requires deep, sustained changes to how we produce, move, eat, build, and power our lives.
Worse still, politicians are unwilling to face the daunting challenge head-on, fearing short-term costs over long-term consequences.
"That is a lesson the politicians haven't learned: when you have exponential growth, if you cut it off as quickly as possible, you solve a lot of future problems. And they don't want to do that," Shanklin concluded.