How Scientists Contained a Threat That Could Have Destroyed Humanity

There are not many stories in which humanity sees a catastrophe coming, understands it, and then actually stops it. The rescue of the ozone layer is one of them — and it remains the clearest proof we have that scientific warning, public alarm and political cooperation can add up to something other than paralysis.

The threat began, as many do, with an invention that looked like a gift. Chlorofluorocarbons, or CFCs, were stable, cheap, nonflammable and seemingly harmless. They chilled refrigerators and air-conditioners, propelled hairspray out of aerosol cans and blew foam into insulation. Their great virtue — chemical inertness — turned out to be their great danger. Because nothing in the lower atmosphere broke them down, they drifted upward for years until ultraviolet light tore them apart high in the stratosphere, releasing chlorine atoms into the thin layer of ozone that shields the planet’s surface from the sun’s most damaging radiation.

In 1974, the chemists Mario Molina and F. Sherwood Rowland published the theory that those chlorine atoms could destroy ozone catalytically — a single atom wrecking many molecules before being neutralized. The idea was met with skepticism and, from parts of the chemical industry, hostility. It described damage that no one could yet see, in a place no one could visit, caused by products consumers loved.

Then, in 1985, scientists with the British Antarctic Survey reported something that turned an abstraction into an emergency: a vast seasonal thinning of ozone over Antarctica. The measurements were so extreme that they had initially been treated as possible instrument error. They were not. A hole had opened in the planet’s sunscreen.

What made the discovery terrifying was what a weakened ozone layer implies. More ultraviolet radiation reaching the ground means more skin cancers and cataracts, weakened immune systems, damage to crops and to the microscopic plankton at the base of the ocean food web. Left unchecked, the erosion would not have stopped at the poles. Scientists later described the trajectory the world avoided as a kind of slow unraveling of the conditions that make surface life comfortable, and in places survivable.

The response was unusually fast. Just two years after the Antarctic findings, negotiators produced the Montreal Protocol, an international agreement to phase out ozone-depleting substances. It was strengthened repeatedly as the science sharpened, and it eventually won ratification from every country in the world. Industry, which had resisted, found substitutes. Molina, Rowland and Paul Crutzen shared the Nobel Prize in Chemistry in 1995 for the atmospheric chemistry that made the danger legible.

The recovery has been slow, because the chemicals already aloft persist for decades. Scientists monitoring the stratosphere have tracked a gradual healing, with full repair projected to take much of this century. There have been setbacks, including detected emissions of banned compounds that required diplomatic pressure to halt, and the awkward discovery that some CFC replacements are themselves potent greenhouse gases — a problem addressed by later amendments.

Still, the arc of the story is the point. A hazard was identified by basic research that had no obvious commercial purpose. It was confirmed by patient, unglamorous monitoring at the ends of the earth. It was communicated clearly enough to move publics and governments. And it was contained by a treaty with teeth.

It is a template, not a guarantee. But at a moment when global problems often feel too large to solve, it is worth remembering that one of them already was. Read More