The Ozone Hole Started in the Tropics — and Decades Earlier Than We Thought

For decades the story of the ozone hole began in Antarctica in 1985. New modelling from MIT rewrites the opening scene: the damage started high above the equator, and the first villain was not the chemical the world blamed.

The image most people carry of the ozone story is the Antarctic one: satellite maps of a blue-painted hole opening above the South Pole, discovered by British scientists led by Joe Farman in 1985, then traced to the chlorofluorocarbons (CFCs) used in fridges and spray cans. That picture shaped one of the great environmental success stories of the twentieth century — the 1987 Montreal Protocol, which phased out ozone-depleting substances across the globe.

A new study published by MIT researchers, led in part by atmospheric chemist Susan Solomon, turns the opening pages of that story around. The team applied modern computational tools to historical records of the atmosphere and found signs of human-driven ozone loss in the tropical upper stratosphere well before the Antarctic hole came into view — a lag of roughly three decades.

The reason has to do with how the atmosphere is wired. Chemicals released at the surface tend to gather first in the warm tropical air, where they rise high into the stratosphere. Once there, ultraviolet light splits them apart and releases the chlorine and bromine atoms that destroy ozone. From the tropics, the weakened air is carried poleward by large-scale circulation, eventually contributing to the severe losses seen over Antarctica and the Arctic. In other words, the tropics are the engine; the poles are where the damage becomes most visible.

The surprise was which chemical arrived first. The model showed that, in the earliest period, the only ozone-depleting substance that was climbing was carbon tetrachloride. As Solomon explained, it had been in industrial use in the United States as early as 1914 and was widespread as a dry-cleaning agent and degreasing solvent by the 1930s — well before CFCs entered the picture. By the time CFCs had scaled up, the atmospheric damage was already underway.

The new picture does not diminish the achievement of the Montreal Protocol; if anything it strengthens the lesson that phasing out all ozone-depleting substances, not just the most famous one, mattered. It also offers a clearer map of where to look for early warnings in the future, and a reminder that the atmosphere does not announce trouble where the trouble begins — it announces it where the effects pile up. The ozone story, it turns out, started far away from the hole everyone saw.