It might destroy the world, despite passing every known safety test. If we wait for a “warning shot” before we act, it might be too late. And action requires global coordination, because if anyone makes it, everyone dies. Sound familiar?

It should, because it already happened half a century ago, with chlorofluorocarbons (CFCs). Despite seemingly impossible odds, we got our act together and completely solved the problem through unprecedentedly successful international coordination. The Montreal Protocol banning CFCs, signed 39 years ago today, is the only treaty that has ever been ratified by every single country in the entire world.

Total Montreal protocol victory

Making AI go well is going to be a lot harder than fixing the ozone hole. Nonetheless, the similarity is uncanny, and we don’t have any other choice. Understanding how we did the impossible once before may teach us something about how to do it again.

The theory is born

The year is 1973. The slow televised unraveling of the Nixon administration is already well underway. DDT finally got banned last year by the newly created EPA. A river got so polluted that it literally caught on fire.

The Cuyahoga River Fire

Environmentalism looms large in the public consciousness, and trust in the government’s competence is at a nadir. There are some people explicitly trying to anticipate catastrophic environmental risks, but beyond the known quantities like DDT, it’s hard to predict much more than the abstract possibility of delayed effects and catastrophic threshold effects from as-yet unknown pollutants.^[1]

Scientific discovery is often serendipitous. At an obscure conference, during a coffee break (the most important part of any conference), a Professor F. Sherwood Rowland of UC Irvine would by chance learn about some intriguing new findings from a meteorologist, who found evidence that these gases called CFC were accumulating in the atmosphere. Something about this direction piqued Rowland’s interest, and he filed it away in his mind.

After this direction collects dust for about a year, he assigns it to one of his postdocs, Mario Molina. Molina works through the theory of what happens to CFCs in the atmosphere, not expecting to find anything super interesting. Instead, he discovers something alarming: the chlorine from the CFCs will break off in the upper atmosphere, and then catalyze reactions that destroy large amounts of ozone.

Without the ozone layer, nothing prevents intense UV rays from sterilizing everything under the sun.^[2] Vast swathes of vegetation would be obliterated, walking around outside for too long would become a death sentence, and billions would die.

After checking and rechecking the results with Rowland, the result is undeniable. Something needed to be done, and quick.

“The work is going well,” [Rowland] told his wife, Joan. “But it looks like the end of the world.”

The world reacts

Despite an initial media reaction comparable in volume to the average cricket, their persistence pays off, and their theory eventually catches the attention of the nation. Industry lashes back, describing the new theory as ridiculous sci-fi theorizing. CFCs had already established an illustrious (not to mention, lucrative) decades-long career of being inert nontoxic chemicals. Why throw them out because of some theory? Every safety eval had shown that CFCs were far safer than their decidedly non-inert predecessors, which would happily burst into flames, or non-theoretically rearrange the insides of the lungs of unlucky families with leaky refrigerators.

State governments became the first to regulate this new danger. Within a year, Oregon enacted a ban on CFCs in aerosols—^[3]comprising a small fraction of all CFC usage, to be fair, but substantial nonetheless. Other states followed quickly. Industry officials viewed these bills with distrust. After all, how could a patchwork of local regulations ever solve a global issue?

More effective than these early state regulations, however, was consumer choice. Despite its rocky start, public awareness of the CFC issue kept mounting. Concerned members of the public launch a boycott of spray cans and other CFC-containing products, putting a huge dent in sales many years before any federal or international regulations were introduced.

This decimation of the CFC market due to boycotts was one of the key enablers of later regulation—it’s easier to ban something that’s already on the way out than something that’s rapidly growing.

CFC sales per year (Solomon, 2024). The hole left by the Molina-Rowland paper is clearly visible. Just think, we could have been exploring ultra skin cancer by now.

After successful state legislation, the next step was to go federal. Many scientific debates, some political finagling, and one report from a National Academy of Sciences panel later, the EPA finally announced a ban of some “nonessential” uses of CFCs in aerosols, such as spray cans. While this didn’t solve the core problem—the “essential” uses were going to be a lot harder to replace—it was a big step in the right direction.

Clearly, the only reasonable next move would be to expand federal regulations to cover all CFC uses, and then to propose and ratify an international agreement, solving the problem once and for all, and then everyone stood up and clapped. That treaty negotiator’s name? Albert Einstein.

Just kidding! After the 1978 federal ban on nonessential aerosol CFCs, the field of CFC notkilleveryoneism enters what one contemporary advocate for regulations refers to ominously as The Dark Years.

The dark years

After these early wins, the next 8 years were a rough time for ozone safety advocates. A frustrating stalemate ensued: The government wasn’t willing to fully ban such a big industry without airtight evidence, but there was no empirical evidence that the ozone layer was diminishing.

The researchers continued to insist that the potential harm was so serious that prudence demanded immediate action even just on theory. There could be a decades-long delay between CFC emission and ozone layer damage, so we might already be past the point of no return by then.

Caught in this impossible dilemma, the only thing the researchers could do was to further refine the theory. The original Rowland-Molina theory was simple: the chlorine catalyzes the decomposition of ozone into oxygen. As with all simple theories, this one is useful but incomplete.

Every few months, someone would discover a new chemical reaction relevant to ozone depletion, or run a more detailed computer simulation, and the ozone depletion estimates would swing around wildly. Rowland and Molina themselves were even responsible for discovering a reaction that made the models suggest bizarrely that CFCs would increase ozone. Despite the inevitable weaponization this data would find in the hands of DuPont, they decided out of a sense of scientific honor that it would be wrong to withhold publishing it. Although later research suggested these reactions were not enough to exculpate CFCs, their commitment to scientific integrity earned Rowland and Molina a good deal of respect, even from those who disagreed.

These mercurial predictions did not exactly earn the trust of policymakers. Even though chemistry is a very mature scientific field, it turns out that predicting things from theory is just really hard. It didn’t help that a lot of ozone research came from industry trying to muddy the waters, though even the industry researchers themselves often weren’t so confident that all was going to be well.

Industry scientists are used to letting the PR people talk for them. But privately: “But there were nights, over drinks in hotel bars, when industry scientists seemed as concerned as anyone.” “Look, I’m a person. I have children. I want to have grandchildren. We’re interested in the future, too.”

With the dawn of the ‘80s and the anti-regulation Reagan administration, the possibility of anyone ever doing anything felt more and more distant with every day.

An unexpected finding from an unexpected finder

In one of the most bizarre twists of the ozone story, we might not have found empirical evidence of the ozone hole for many more years, if it weren’t for one extremely stubborn scientist.

Joe Farman had spent 25 years of his life measuring trace gases in the atmosphere above the dark cold Antarctic skies, including CFCs. He toiled in obscurity; nobody else in the ozone research space had heard of him, and his work received only paltry and precarious funding.^[4]

“Oh,” Farman’s superior mused slowly. “You’re making these measurements for posterity! Well, tell me, what’s posterity done for you?”

In 1982, Farman started to see strange data coming in, indicating a huge drop in ozone. His first guess was just equipment failure, but measurements in subsequent years from multiple different instruments continued to show the same thing.

Although Farman was expecting to see a decline in ozone, these results were completely inconsistent with the Rowland-Molina theory. First, rather than a gradual thinning of ozone, the results showed ozone levels dipping only during a 30 day period at the end of the austral winter, and recovering afterwards. Second, it wasn’t just a few percent, but nearly half of all ozone gone, for a few months every year. Farman had no idea what was going on, but it was definitely a big deal.

The initial reaction to their paper was skeptical. If the British Antarctic Survey had gotten unlucky with their panel of reviewers at Nature, their result might have been completely ignored. Nobody had ever heard of these underfunded British people, and the ground-based instruments used had a reputation for being quite flaky. And the results didn’t make any sense given the Rowland-Molina theory.

Most importantly, these results contradicted NASA’s satellite data, which hadn’t seen much ozone loss at all. Something was amiss.

The warning shot

It turns out that NASA had occasionally seen similar numbers. But they had dropped those numbers from the data, because they were so bizarre that NASA assumed it must have been a bug. Upon reexamining the data, it became irrefutable that a huge ozone hole was opening up above the Antarctic every winter.

The hole was the warning shot—a striking and easily-understandable visual that did much more for resurrecting concerns than any theory or expert exhortations. Shortly afterwards, the EPA announced its intent to schedule a new round of international workshops and to make a final decision on regulations by the end of 1987.

Industry responded by saying that clearly banning CFCs domestically would be a terrible idea because other countries wouldn’t ban them, and that we couldn’t allow a CFC gap the US would be hurt economically.

Several competing theories burst into the scientific debate to square the theory with this strange new result. The dynamicists claimed that the hole was simply because of seasonal air currents that moved the ozone away temporarily. The odd-nitrogen theorists claimed that the hole was because of solar activity. And of course, a variant of the chemical theory lived on, claiming that the bulk of the reactions occurred on the surfaces of the microscopic ice crystals that make up the polar stratospheric clouds that show up every winter in the Antarctic skies. The two non-chemical theories brought back some hope for CFC defenders. If the hole was because of air currents or solar activity, then CFCs were innocent after all.

The only way to be sure would be to actually directly observe the chemical reactions in the wild.

A journey to the edge of the world

“We’d like to get some scientists to Antarctica to make some measurements,” Margitan said.

“When?” Lynch said.

“August.”

“Well, we want to do something in August of [next year].”

“No, no, we want to do something this August.”

“Impossible. […] Well, maybe.”

Antarctica is not a place that gives up its secrets easily. A hastily assembled expedition in 1986 ruled out the odd-nitrogen theory, but the dynamicists only became more adamant about their theory.

To put the final nail in the coffin, one final expedition was planned for 1987, to directly analyze the air in the stratosphere. A plane loaded with scientific instrumentation would fly deep into the polar ice clouds and collect the data that would settle the question once and for all.

This would not be easy, but with the immense weight of the future on their shoulders, they had no other choice. The team requisitioned the ER-2, the only plane capable of flying at this altitude. This was met with some resistance by NASA officials—the ER-2 was not designed to handle the wind, ice, or cold of Antarctica, and so the mission would be exceedingly risky—but they were ultimately persuaded that it was important enough to be worth the risk.

The scientific instruments were built and tested. A team of meteorologists was assembled to monitor the weather conditions and give the daily go/no-go. The potholes in the airstrip were repaved. As the expedition drew near, everything started to come together.

Flying into the storm

On August 17, 1987, the ER-2 ascended from Punta Arenas, Chile for the first time. It plunged deep into the vortex of ice crystals, until its fuel lines were close to freezing, before landing back at base with flying colors. With bated breath, the scientific team inspected the data from the instrument. Nothing. Although the instrument had worked well during test flights in sunny California, it had failed the moment the plane plunged into the ice cloud. Staying up all night to debug the instrument before the next day’s flight, the team debugged the issue and tracked it down to a single faulty connector.

When the second flight came back, disappointment struck again. A different connector had failed this time. The scientists felt the pressure mounting; the entire expedition depended on this data, which the pilots were risking their lives to collect.

Finally, on the third flight, the instrument worked successfully, and the resulting data was exactly what the chemical theory had predicted. Several more flights were conducted immediately afterwards, collecting even more data. The scientists were elated. By the end of the expedition, the theory that CFCs were responsible for ozone depletion had been confirmed.

The world listens

Following the second Antarctic expedition, the tone of the field shifted dramatically. Adherents of competing theories changed their minds en masse given the strength of the evidence, and a consensus developed rapidly among scientists around the CFC theory. Evidence continued to roll in over the next half-year to solidify the case, but there was no longer much doubt that CFCs were the culprit.

For industry, even this smoking gun was not enough. DuPont made one last stand, announcing that “scientific evidence does not point to the need for dramatic CFC emission reductions” and that ceasing CFC production was “unwarranted and counterproductive”, before finally capitulating in the spring of 1988 when the accumulated evidence had made their position completely untenable.

The expedition also pushed politicians towards more durable action. International coordination had already been moving along since the first satellite images of the ozone hole—the Montreal protocol was signed just 2 weeks before the announcement of the expedition results. However, because of the lack of evidence for the CFC theory, it was hard to negotiate for strong restrictions, and so the original treaty only paced the level of CFCs.^[5] The expedition results and other subsequent experimental evidence over the next half-year were a critical part of changing the tone of international coordination towards a complete ban.

But all of this is a story for another time. While we’ve covered the scientific angle today, Part 2 will cover the international coordination angle of the ozone hole crisis and how we managed to make it all work out.

1. ^{^}

   The 1972 book Limits to Growth is a model of the world that contains, among other things, a surprisingly deep analysis of key ideas, like delayed impacts and the global coordination difficulties of pollution, using familiar examples like DDT. In retrospect, it was somewhat too pessimistic about technology, but it’s aged surprisingly well, especially compared to terrible books from the same era, like the Population Bomb. Limits to Growth feels a bit like the ‘70s equivalent of AI 2027.

2. ^{^}

   

   
   

3. ^{^}

   You will tear my em-dashes out of my cold dead hands.

4. ^{^}

   Farman was getting only about $50k/year (2026 dollars) in funding for his research program.

5. ^{^}

   The original treaty initially froze production at 1986 levels, and then slowly tapered to a 50% reduction by 1998.