What happened to the world’s ozone hole?

In 1974, scientists Mario Molina and F. Sherry Rowland published a paper theorizing that CFCs could destroy ozone in the Earth’s stratosphere. Until then, CFCs were thought to be harmless, but Molina and Rowland suggested that assumption was wrong. Their findings were attacked by industry, which insisted their products were safe. Her research was controversial among scientists. Projections indicated that ozone depletion would be small – between 2 and 4% – and many thought it would occur over a period of centuries.

The use of CFCs continued unabated and by the 1970s they were ubiquitous worldwide, as refrigerants in refrigerators and air conditioners, in aerosol spray cans and as industrial cleaning products.

Just a decade later, in 1985, the British Antarctic Survey confirmed a hole in the ozone layer and suggested a link to CFCs – confirming the work of Molina and Rowland, who eventually won the 1995 Nobel Prize in Chemistry. Worse, the exhaustion came much quicker than expected. “It was really quite shocking,” says Shanklin, now a fellow emeritus at the British Antarctic Survey.

From then on, scientists tried to figure out how and why this happened.

A chemical mystery

In 1986, as the Antarctic winter was drawing to a close, Susan Solomon, a researcher with the US government’s National Oceanic and Atmospheric Administration, led a team of scientists in search of answers to the McMurdo base. At the time, scientists debated three possible theories, one of which Solomon had proposed: that the answer might lie in surface chlorine chemistry on polar stratospheric clouds, which occur at high latitudes and form only at very low temperatures in polar winters.

“It was a big mystery,” says Solomon, now a professor of atmospheric chemistry and climate science at MIT. Her research explained how and why the Antarctic ozone hole occurs. “All the data indicated that the combination of the increase in chlorine from human use of CFCs and the presence of polar stratospheric clouds was the trigger for what happened.”

Satellite monitoring confirmed that ozone depletion spanned a vast region – 7.7 million square miles (20 million square kilometers).

The serious threat posed by ozone depletion – increases in human skin cancer and cataracts, damage to crop growth, crops and animals, and reproductive problems in fish, crabs, frogs and phytoplankton, the basis of the marine food chain – spurred international action and collaboration.

But given how seriously the ozone hole was considered a threat, why don’t we hear about it more often?

“It’s not the same cause for concern that it used to be,” says Laura Revell, associate professor of environmental physics at the University of Canterbury, New Zealand. This is largely due to the unprecedented international steps governments have taken to address the problem.

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