They were troubled because everything rested on their calculations. Apart from Lovelock's CFC measurements and a few balloons that had been sent up afterward, Molina and Rowland had no direct measurements from the stratosphere. They had to imagine what might be happening there and then set up artificial stratospheres in the lab to test their ideas. The stratosphere is a strange place; the air is thin, the temperature is warm, and energetic ultraviolet rays abound, ripping apart the molecules that exist in more normal circumstances. Bizarre chemical species that wouldn't last a millisecond down near the ground are common in this maelstrom. And Rowland and Molina had to be sure they had included every one of the possibilities in their figures.
They knew, for instance, of two chemicals that could turn out to be either heroes or villains. Hydrogen chloride (HCl) and chlorine nitrate (ClNO3) are "reservoirs" for chlorine. They are extremely stable even in the stratosphere, and once a chlorine atom gets tied up in one of these two, its destructive habits are over. Molina and Rowland had included both of these chemicals in their calculations. But had they got it right? Give the reservoirs too much credit for their ability to rein chlorine atoms in and you'll seriously underestimate the eventual ozone destruction. Give them too little credit, on the other hand, and your results will seem like fear-mongering. Until the first signs of ozone depletion showed up, nobody would know if Molina and Rowland had got it right.
Eventually, in September 1976, the reports were published. The first concluded that Molina and Rowland's calculations were justified. CFCs posed a threat to ozone. The second declared that, since it was not yet clear how serious the threat might be, it made sense to wait and see rather than to introduce immediate draconian regulations. Molina and Rowland later wrote that the two reports could have been shortened to one word each: "Yes," and "But." Confusion reigned. Newspapers took whichever message they preferred. "Scientists back new aerosol curbs to protect ozone in atmosphere," declared the New York Times. "Aerosol ban opposed by science unit," was how the Washington Post put it.
Still, a certain level of alarm had been raised. By 1978, America had at least banned the use of CFCs as a propellant. Canada, Norway, and Sweden followed suit. But then, in spite of the continued attempts of Molina and Rowland and many of their scientific colleagues to keep the issue alive, ozone and CFCs dropped quietly off the political agenda. Carter was out and Reagan was in; the green 1970s had given way to the greedy 1980s.
The problem was that even Molina and Rowland now thought it could be decades before the first incontrovertible signs of ozone loss appeared. Until then, CFCs would gradually, imperceptibly nibble away at the ozone layer, and by the time we had concrete proof of a serious effect it would be too late. In summer 1984, Rowland gave a dispirited interview to the New Yorker:
From what I've seen over the past 10 years, nothing will be done about this problem until there is further evidence that a significant loss of ozone has occurred. Unfortunately, this means that if there is a disaster in the making in the stratosphere, we are probably not going to avoid it.
Rowland was right that nothing much would happen without new evidence of ozone loss. But he had no idea how quickly and dramatically that would come. For in the autumn of that same year, a scientist who had spent several years adopting a bit of "British caution" decided to abandon his reticence and trumpet his findings to the world.
***
Antarctica in the 1950s was a rugged, macho place, and few stations were more rugged and macho than the British Antarctic Survey's remotest outpost at Halley Bay, which floats on a shelf of ice about a thousand miles from the South Pole. The temperature there never rose above freezing and in the winters plunged to 50 degrees below zero. An even worse problem was the wind, which howled over the flat ice shelf, whisking away any vestiges of bodily warmth as it whipped up snow into blizzard after blizzard and buried those first tough little wooden huts up to their necks.
The old traditions prevailed at Halley long after they had been overtaken in the rest of the world. There were men with beards, with their arcane Antarctic-only slang and coarse humor. There were dogs to pull sledges, and there was the flat white emptiness from horizon to horizon. No room there for softness, or comforts, or women.
Joe Farman, a quiet, pipe-smoking Briton of the old school, had been masterminding research at this bleak outpost since 1957. Every year, during the southern spring and summer, scientists from the British Antarctic Survey had trekked down to Halley to measure the amount of ozone overhead.
Why ozone? And why there? At first, it was an attempt to use movements of ozone to map upper atmospheric currents. Later, it was more out of habit. In the 1970s Molina and Rowland's findings about CFCs had given some extra impetus to this research, but Farman probably would have done it anyway. Long records of interesting atmospheric constituents usually prove useful in the end, for one reason or another. Compiling the records is often thankless, but after all, you never know. Farman didn't receive much money for his project, but it didn't cost that much to do and there were always plenty of volunteers to make the measurements.
Early in 1984, Farman received a visit from his boss at the funding agency, who asked him, yet again, why he was persisting with such an obscure record. "There is a big CFC industry," Farman replied. "And people are writing that ozone will change. And the only way you can tell if ozone has changed is to sit and keep measuring it." His boss's response: "You're making these measurements for posterity. Well tell me, what's posterity done for you?"
It was slightly disingenuous of Joe Farman to say this about CFCs, because he was already nursing a secret. He had been nursing it for three years, but later that same year he decided to divulge it. Something had shown up in this long, repetitive series of measurements that at first Farman didn't quite believe. Ozone always changed a bit at Halley, between the dark winter months and the return of the sun. But in 1977 something different had begun to happen. In October each year, at the onset of spring, the ozone had begun to plummet. Each year the drop was a little worse. In 1983, where Farman would normally expect about three hundred units of ozone, he was seeing less than two hundred.
At first, Farman and his two colleagues kept mum. Above all, they didn't want to look foolish. A NASA satellite had been measuring ozone over the whole of Antarctica for the past five years and had noticed nothing amiss. Perhaps there was something funny about the instruments Farman and his group were using. Perhaps there was something funny about Halley itself. So in the season of 1983-84, Farman sent a new instrument down to Halley. He also took a look at the record from another British station, Argentine Islands, which was more than a thousand miles farther north. Both stations confirmed what Halley had already shown. Now 40 percent of the ozone was disappearing each austral spring. There was a hole in the sky.
When he saw this, Farman threw his British caution to the winds. The paper that he and his two colleagues wrote landed in the offices of Nature on Christmas Eve and was published in May 1985. Molina and Rowland's paper had had little immediate effect, but Farman's caused an uproar. Among the most astonished was Donald Heath's research group at the NASA Goddard Space Flight Center, whose job was to coordinate the ozone measurements made by NASA's Nimbus-7 satellite. They had no hole in their data. What was Farman's group talking about?
Hastily, Heath's group pulled their data out to check it again. They were mortified. The data recovery program had been designed to throw out spurious numbers before the researchers even saw the results; that way they wouldn't have to be bothered by irritating measuring glitches. Any measurement of ozone values that fell below 180 units was obviously ridiculous and had simply been ditched. The satellite had seen Farman's ozone hole all right, but thanks to their overeager program the researchers themselves hadn't seen a thing. Now, using the correct data from 1979 to 1983, they watched a hole the size of the continental United States gradually appear over Antarctica. In some cases, the ozone dropped to less than 150 units.
Heath's group ha
d learned an important lesson about Earth's atmosphere. Even if you are sure you understand the way our ocean of air works, it is still always wise to expect the unexpected.
Meanwhile, the rest of the ozone community was in disarray. Even Molina and Rowland's worst scenarios hadn't predicted something as extreme as this, and so soon. There was no sign of a hole like this anywhere else on Earth, so it must have something to do with the extreme Antarctic conditions. But what?
In research labs and coffee rooms at universities throughout the world, attention began to focus on the first, most obvious characteristic of the Antarctic stratosphere: It is the most isolated air on Earth. Every winter, winds whip up around the edge of the entire ice-covered continent until they form a giant vortex whose walls separate the air from warmer breezes farther north. Trapped inside this vast whirlwind, Antarctic air grows steadily colder, and colder. And then, a new kind of cloud appears in the Antarctic skies.
Normal clouds are formed of liquid water drops, and they can occur at almost all levels in the troposphere—the lower part of the atmosphere—which is the place where we live and experience our wind and weather. As you progress upward through this layer of air, the temperature drops steadily until, at the top of the troposphere, it reaches a minimum. Immediately above this point, the stratosphere begins. Now there are ozone molecules to catch sunlight and warm the air, and the temperature starts to rise. The cold point between these two layers traps any water vapor by turning it into clouds and sending the rain falling back down to Earth. It is a water-tight barrier, stretching around the world like a giant tarpaulin, keeping the lower atmosphere wet and the upper atmosphere bone-dry. That's why the stratosphere almost never has clouds.
But the stratosphere still contains just a little water that has leaked through from below, and—if the temperatures are low enough—this can freeze solid into tiny flecks of ice. That is what happens in the Antarctic stratosphere, in winter.
They are beautiful, these clouds, iridescent like the inside of an abalone shell with hot pinks and purples and shimmering blues, colors that don't belong in the sky. In spring, when the sun has returned after the long polar night, they materialize at sunrise or sunset seemingly out of thin air. In fact, the clouds are there all the time, but it's only as the sun tips over the horizon that it picks them out, shining on them like a spotlight with its final steep rays. And then, suddenly, it's as if the sky is filled with glimmering peacock feathers. The early explorers made exquisite watercolors of the effect. They had no idea how dangerous it would turn out to be.
Many different researchers began to suggest that these high stratospheric clouds might explain the Antarctic ozone hole. Among them was a thirty-year-old theoretician named Susan Solomon, who was working at the National Oceanic and Atmospheric Administration in Boulder, Colorado. Though she was young, Solomon was very talented. She had been one of the original reviewers of Joe Farman's paper, and when she read it she was immediately horrified. Ever since, the data had nagged at her.
Hunched over her computer, Solomon had tried model after model, accounting for every reaction she could think of in the Antarctic stratosphere. None of them made a hole of this magnitude. Then she began thinking about the clouds. What if they made the difference? Perhaps they somehow "primed" the Antarctic atmosphere during the winter, so that when sunlight returned in spring the destruction could begin.
Cloud surfaces can make a big difference to chemical reactions, especially in somewhere as thin as the stratosphere. For any chemistry to happen in the air, two atoms or molecules have to meet. But up where the air is rarefied, such encounters don't happen very often. What's more, the two, or more, participants in the reaction need to be suitably energized. If they're overly lethargic, nothing much will come of their meeting.
But if any of these chemicals can land on the surface of a cloud, they immediately have many more options. The cloud can act as an introduction agency, both bringing species together and giving them an energy boost to get them going. That's what Solomon found when she began to put clouds into her model.
The key seemed to be in those unreactive "reservoir" species that could bind up chlorine atoms and keep them out of trouble. Throughout the long winter nights, these molecules—chlorine nitrate and hydrochloric acid—could be landing on the surface of clouds and reacting. Work through the sequence of reactions and you end up with chlorine gas, Cl2. This molecule detaches itself from the clouds and awaits the return of sunlight. The first ultraviolet rays that appear with the rising sun split the chlorine gas into its individual, deadly atoms, which rip ravenously through the ozone layer. Suddenly a hole made perfect sense. The only wonder was that it wasn't even worse.
Still, this was only a theory. Around the United States, many other research groups had come to similar conclusions, but they all knew that nobody could be sure until they had more data. Someone would have to go south to Antarctica, to measure the reactions as they happened at the end of the twenty-four-hour darkness of winter and on into the first few weeks of spring.
Solomon was as surprised as anyone to find herself volunteering for the job. She was a theoretician. Her work involved sitting at a computer, not going out into the field. For her first-ever venture into experimental science, she would lead a team of twelve people to the coldest, most hostile place on Earth, in the winter.
She still can't explain why she wanted to go. Perhaps because, in spite of the sedentary nature of her chosen profession, she was captivated by the might of the atmosphere. She loved storms, thunder, lightning—anything that reminded her how powerful nature is, and how puny humans are by comparison.
For whatever reason, a few months later Solomon found herself at the airport in Christchurch, New Zealand, sweltering in her red fur-trimmed parka, clutching her standard-issue canvas bag full of safety gear and survival clothing. Ahead was a hazardous eight-hour flight in a Hercules military transport plane. The pilot arrived for the briefing and regarded the twelve men and one young woman in front of him. "Who's in charge here?" he asked. Solomon raised her hand. The pilot regarded her with some astonishment and then managed to stammer out, "Good for you."
Solomon loved Antarctica from the moment she stepped off the plane. She loved the emptiness, the ferocity, the unforgiving wildness. It wasn't beautiful in the usual, picture-postcard sense. Its beauty was fierce, and Solomon reveled in it.
She had arrived at McMurdo, the main American base, which is the unofficial "capital" of the continent. It was August 1986, the tail end of the austral winter. The influx of summer visitors would not begin for another month or so, when the weather warmed and daylight began to stretch toward twenty-four hours. The only occupants of the base were the people who had been isolated there for the whole winter, who had bonded tightly with each other into established cliques and enmities and tended to regard with suspicion newcomers who would unwittingly take the wrong chair at dinner, or hang their coat on "somebody else's" peg.
Solomon's task was to set up an instrument on the roof of one of the buildings. The idea was to use incoming moonlight to pick out and measure the chemicals floating in the intervening stratosphere. The measuring instrument would be inside the building, but up on the roof would be mirrors that would turn to guide the moonlight down into a channel.
The team had only four months' notice of their journey. They hadn't had time to construct a tracking system to turn the mirrors as the moon journeyed across the sky. Instead, someone had to be on hand, braving temperatures of –40 degrees and the occasional fierce wind that could blow up almost out of nowhere.
One night, Solomon was up on the roof taking her turn when the weather turned cloudy. Without moonlight the instrument was useless. Solomon decided to leave the mirrors and climb back down into the lab for a nap. Perhaps when she returned, the moon would be back. In the laboratory, Solomon curled up in her sleeping bag and fell asleep. She woke to a blizzard, the worst kind of white-out, winds screaming past the building with a ferociousness rarely
seen outside the ice. Solomon was aghast. Her mirrors were still on the roof. If they became damaged, the project was over.
Without stopping to think, she climbed back up the wooden ladder onto the roof, bracing her face against the shards of snow that blasted like sand. She flung herself, spread-eagled, onto the roof surface and began to edge her way toward the mirrors, the gusts tugging at her, urging her to fall. But she held onto the mirrors, and the ladder, and managed to scramble back inside.
It was worth it, she says. It was all worth it. Because Solomon's research, and the studies that followed, showed beyond a doubt that high stratospheric ice clouds were indeed doing the damage. Each winter, they took the chlorine reservoirs and activated them, priming the Antarctic air like a grenade. True, this is a problem that is unique to the unoccupied continent of Antarctica; even the Arctic doesn't get cold enough to form stratospheric clouds for long, and there has never been an ozone hole in northern parts. But though you could argue that the Antarctic problem would affect only a few penguins and scientists, the striking image of deadly rays flooding through a hole in the sky turned the ozone tide.
On September 16, 1987, under the auspices of the United Nations Environment Program, twenty-one nations and the European Community signed the famous Montreal Protocol, the first international agreement ever made to restrict the emissions of an environmentally hazardous material. There would be a 50 percent reduction of CFC production by the end of the century.
In March 1988, new analyses of ozone measurements over the United States, Canada, Japan, and northern Europe revealed that, though not as severe as the Antarctic loss, the air was thinning in the north as well. Two weeks later Dupont, the world's largest CFC manufacturer, announced it would cease production.
An Ocean of Air Page 18
