Event 06 · History as decisions
The hole in the sky that the world agreed to fix
Scientists warned in 1974 that common chemicals could destroy the ozone layer, a hole was measured over Antarctica in 1985, and in 1987 countries signed the Montreal Protocol to phase those chemicals out.
- The ozone hole and the Montreal Protocol
- Antarctica and Montreal, Canada
- 1987
- 3 min read
On this page
Before you readWhat would you do?
Your team's AI dashboard shows a sudden, huge drop in customer satisfaction that seems too big to be true. What is the best first step?
Pick an answer now. The file tells you whether you were right.
01The file in one minute
1The warning
In 1974 Molina and Rowland showed that CFCs from sprays and fridges could destroy ozone high in the atmosphere.
2The evidence
In 1985 British Antarctic Survey scientists reported a large seasonal ozone loss over Antarctica.
3The decision
The 1987 Montreal Protocol phased out CFCs. The Antarctic ozone layer is expected to recover by around 2066.
4The lesson for AI
Good rules for technology rest on careful evidence, help people adapt and can be updated.
02Timeline
1974
Molina and Rowland publish their warning about CFCs and ozone.
May 1985
Farman, Gardiner and Shanklin report the Antarctic ozone loss.
16 September 1987
Countries sign the Montreal Protocol.
1995
Molina, Rowland and Crutzen share the Nobel Prize in Chemistry.
2023
A UN assessment says the ozone layer is on track to recover.
03What happened
The ozone layer high in the atmosphere blocks much of the sun's harmful ultraviolet light. In 1974 the chemists Mario Molina and Sherwood Rowland showed that chlorofluorocarbons, or CFCs, used in spray cans, fridges and air conditioners, could rise into the stratosphere and destroy ozone.
In 1985 scientists from the British Antarctic Survey, Joe Farman, Brian Gardiner and Jonathan Shanklin, published measurements showing a large seasonal drop in ozone over Antarctica. The loss was far bigger than expected, and they checked their instruments carefully before publishing.
On 16 September 1987, countries signed the Montreal Protocol, agreeing to cut the production of CFCs and related chemicals, with later changes tightening the limits. It became the first UN treaty ratified by every country. Molina, Rowland and Paul Crutzen shared the 1995 Nobel Prize in Chemistry. A 2023 UN assessment said the ozone layer is on track to recover over Antarctica by around 2066.
04The decisions that shaped it
Governments acted before every detail was settled, because the science was strong enough and the harm, more skin cancers and damage to crops, would be serious and slow to reverse. Industry had substitutes it could develop, and richer countries funded poorer ones to make the switch. The treaty also allowed rules to tighten as new evidence came in.
The AI angle: rules for a powerful technology can work when they are based on evidence, give people time and help to adapt, and can be updated as we learn more. They also depend on careful measurement, like the Antarctic team checking its surprising data.
The idea behind this caseLesson: Check what AI tells you →
05What to take from it
- When data shows something surprising, check your instruments and methods, then share it.
- Act on strong evidence of serious harm, even before every detail is known.
- Design rules that can be tightened or loosened as new evidence arrives.
- Help the people and businesses who have to change, so they can follow the rules.
07 — Sources
- Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction · Nature · 1985-05-16
- The Montreal Protocol on Substances that Deplete the Ozone Layer · UN Environment Programme, Ozone Secretariat · 1987-09-16
- Ozone layer recovery is on track, helping avoid global warming by 0.5°C · World Meteorological Organization · 2023-01-09