Farman's team · The ozone hole
Can the gas in a refrigerator put a hole in the sky?
That time, that place
Chlorofluorocarbons were created in the 1930s: refrigerants for fridges and air conditioners, propellants for spray cans.
Their virtues were plain. They do not burn, are not poisonous, and react with nothing. The ammonia and sulphur dioxide used before them killed people when they leaked. CFCs were the safe gas.
Safe also meant they do not break down. Nobody thought about that side of it.
Why this question
In 1974 Molina and Rowland did.
If they do not break down, where do they go? Not vanishing at ground level, they eventually rise. High in the stratosphere there is ultraviolet light that never reaches the ground, and up there CFCs do split — releasing chlorine atoms.
A chlorine atom destroys an ozone molecule and remains, intact, to destroy the next. By calculation a single chlorine atom could take out tens of thousands of ozone molecules before it was removed.
The ozone layer is what blocks ultraviolet. Thin it and more reaches the surface: more skin cancer, more cataracts, less phytoplankton.
When the paper appeared, the chemical industry pushed back — laboratory arithmetic, they said, and the real atmosphere is another matter. Rowland recalled that invitations to industry conferences dried up for some years afterwards.
What was found
In 1985 Farman's team at the British Antarctic Survey published their measurements.
Springtime ozone over Halley Station had fallen to around 60 per cent of its 1970s level. It was far worse than predicted, and concentrated over Antarctica.
They had held the result back for years, suspecting their own instrument. Only after bringing in a new one and measuring again did they publish.
Satellites had been recording the same values for years already — but the processing software was written to discard implausibly low readings as instrument error. The machine had been filing the fact away as an outlier.
What followed was unusual. The Montreal Protocol of 1987 set a phase-out of CFC production. It remains the only treaty every UN member state has ratified.
The ozone layer is recovering, and is expected back at 1980 levels around 2060. It is one of the few cases where science predicted a problem, observation confirmed it, and an international agreement stopped it.
A gas that reacts with nothing does no harm
Years of springtime ozone measurements at Halley Station showing a sharp decline
The 1987 Montreal Protocol phased CFCs out, and the ozone layer entered recovery