Reducing Ozone Depletion

The Montreal Protocol, signed in 1987, phased out production of CFCs (chlorofluorocarbons), the refrigerants and propellants that were ripping apart stratospheric ozone. It worked where so many global agreements stall because the problem was narrow: a short list of identifiable chemicals, made by a handful of companies, with substitutes already on the shelf. Nearly every country signed on, production dropped, and stratospheric chlorine has been declining ever since. Compare that to carbon dioxide, woven into every power plant, car, and factory on Earth — there's no single valve to shut.

The phase-out happened in stages. CFCs gave way first to HCFCs (hydrochlorofluorocarbons), which still contain chlorine and still damage ozone, just less efficiently — a stopgap. HCFCs are now being phased out in favor of HFCs (hydrofluorocarbons), which contain no chlorine and don't touch ozone at all. But HFCs trade one problem for another: many are potent greenhouse gases, so fixing ozone depletion can worsen warming unless HFCs are also phased down.

The hole doesn't close the year emissions stop because CFCs already aloft are chemically stubborn. Once released, they drift up into the stratosphere and persist for decades to over a century, continuing to catalyze ozone destruction long after production ends. The chlorine already up there has to slowly break down and settle out before the ozone layer can fully rebuild, which is why full recovery is projected around the 2060s. That multi-decade lag is also the catch in the story: any illegal CFC production, like the unexpected emissions traced to eastern China in the late 2010s, directly slows the whole timeline back down.