The Proof That Worked

Sit with that for a second. On a planet hurtling around a fusion reactor at 67,000 miles per hour, on a wet rock whose only real defense against that reactor's ultraviolet output is a faint smear of three-oxygen molecules eight miles up, a clever ape figured out how to make excellent refrigerants — and accidentally started dissolving its own sunscreen. The ozone layer is, no exaggeration, the thin film that keeps DNA from getting cooked across an entire continent. And in the twentieth century we were quietly thinning it with the stuff we put in aerosol cans.

This is the part of the story where the species usually does nothing. We are spectacular at noticing slow catastrophes and then arguing about them until they become fast ones. So here is the genuinely strange fact: this time, we didn't.

In 1987 nearly every nation on Earth signed the Montreal Protocol and agreed to stop manufacturing chlorofluorocarbons — the CFCs in refrigeration, dry cleaning, and hairspray. No world government forced it. No single benevolent genius solved it. A bunch of countries that could barely agree on anything looked at the same atmospheric chemistry and quietly changed what they were willing to put in a spray can.

And then — this is the part that should make you put your coffee down — the sky started healing.

In June 2016, MIT atmospheric chemist Susan Solomon and her colleagues published the receipt in Science. Tracking the September ozone hole with weather balloons, satellites, and volcanic sulfur measurements from 2000 to 2015, they found it had shrunk by more than four million square kilometers. That is roughly half the area of the contiguous United States, healed. Solomon was careful to note that more than half of that shrinkage came from one thing and one thing only: less chlorine in the air. Not a megaproject. Not a technological miracle. Just us, having stopped.

The universe, naturally, could not let the moment be clean. In 2015 the Calbuco volcano in Chile erupted and flung enough sulfur skyward to puff the ozone hole back to record size that year — a cosmic reminder that the planet keeps its own chaos on retainer regardless of our paperwork. But the underlying trend held. The chlorine is still falling. Solomon's projection: the hole should keep shrinking and close permanently around midcentury, barring some volcano deciding otherwise.

Here is what undoes me about this. We have closed loops before — we pulled lead out of gasoline once we saw what it did to children's brains, we capped the sulfur emissions that were acidifying the rain. But the Montreal Protocol is the cleanest case we have where the species detected a planetary-scale threat, agreed on it across borders, signed something binding, and then — decades later — got to point a telescope at the wound and watch it scar over. Global, binding, verified from space. We are a civilization that mostly leaves its problems running like background processes until the machine crashes. And here, at least once, we ran the full loop at the largest possible scale: notice, agree, act, verify. The proof came back positive.

The CFCs didn't vanish, by the way. Nothing does. Those molecules broke apart in the stratosphere, surrendered their chlorine, and the atmosphere folded the wreckage back into its slow chemistry. The leaf that falls doesn't disappear; it composts. We poured a mistake into the sky and the sky, given a few decades of us simply not making it worse, turned the mistake back into ordinary air.

But notice why it worked, because the reason is the whole lesson. Montreal didn't run on willpower. It ran on the luck of its structure: CFCs had drop-in substitutes already sitting on the shelf, a mere handful of companies — DuPont and a few others — made almost all of them, and the harm was bounded and legible enough that everyone on Earth could see the same hole in the same sky. Cooperation was cheap. That is the uncomfortable footnote stapled to the hope. Climate change is the inverse on every axis — no cheap substitute for the fuels, billions of diffuse producers instead of a handful, harm smeared so thin across decades and continents that no two people are ever looking at the same wound. Montreal is not proof that we can simply decide to cooperate. It is proof of how cheap cooperation has to get before we actually do.

It is almost unbearably hopeful, which is a strange note for a column that mostly specializes in cosmic vertigo. But that's the joke, isn't it. We spend so much energy convinced that nothing we do matters at the scale of the heavens. And then a species that can barely agree on lunch, handed exactly the kind of problem it was equipped to solve, reached eight miles up and changed the color of the sky over an entire continent.

The void is enormous and indifferent. The hole in it, this once, is closing. Sleep well.