In 1985, scientists «accidentally» discovered a massive hole in the ozone layer over Antarctica. Initial studies suggested the issue originated in the late 1970s, but a new analysis conducted by the Massachusetts Institute of Technology (MIT) indicates that human activity began interfering with the ozone layer decades earlier. The new research was published in the journal Proceedings of the National Academy of Sciences.
“The fact that ozone depletion occurred as early as the late 1950s, much earlier than I ever expected, completely stunned me,” stated Professor Susan Solomon, one of the pioneering researchers on ozone’s impact on the atmosphere and the Lee and Geraldine Martin Professor of Environmental Studies and Chemistry at MIT.
This discovery emerged while the team was investigating whether other chemicals could deplete the ozone layer long before chlorofluorocarbons (CFCs) appeared.
The Antarctic ozone hole is attributed to the release of chlorofluorocarbons—chemicals once widely used in refrigerants, propellants, and solvents—which, upon entering the atmosphere, rise to the upper layers. In the stratosphere, the gas is broken down by the Sun’s ultraviolet radiation, releasing chlorine atoms that catalyze the destruction of ozone molecules.
However, this latest study highlights the impact of another ozone-depleting chemical that was in widespread use long before CFCs: carbon tetrachloride.
“From textbooks, we learned that CFCs lead to ozone depletion,” said co-author Jian Guan of MIT. “It turned out there was another compound causing ozone depletion much earlier than CFCs. That was a big surprise.”
To delve deeper into this idea, the team devised a “thought experiment” to determine when human-induced ozone depletion might first have been detected if scientists had access to modern technology and knowledge over the past century.
They used 16 different models simulating the atmospheric chemistry of the last hundred years, attempting to identify any unusual changes in the ozone layer that could be attributed to human activity rather than natural phenomena, such as volcanic eruptions or El Niño, which can also influence ozone levels.
Each model was expanded to include industrial chemicals that began production at various points during the past century.
Their analysis revealed that a signal emerged as early as 1957. The only likely culprit, they found, was carbon tetrachloride.
“It is the only ozone-depleting substance whose concentration began rising that early,” explained Solomon. “We started using carbon tetrachloride in the 1930s as a dry-cleaning agent and degreasing solvent. We began using CFCs much later.”
However, the signal appeared high above the tropics, not over Antarctica, where the infamous hole eventually formed. This is because natural atmospheric fluctuations over the equator are smaller, making any anomalies “stand out” more and easier to detect.
It’s important to note that this is somewhat different from the Antarctic ozone hole problem, which arose because chlorofluorocarbons (CFCs) accumulated in such quantities that, combined with Antarctica’s uniquely cold and isolated winter atmosphere, caused an explosive seasonal collapse of the ozone layer every spring.
Nevertheless, the new research shows that human activity has been interfering with the ozone layer for much longer than previously thought.
The good news is that the use of carbon tetrachloride and CFCs has been halted, and as a result, the ozone hole has significantly recovered.
Still, the new research indicates that CFCs are not the only ozone-depleting chemicals that warrant concern. Many such substances have been banned, but numerous others are emerging that could also pose a threat. For example, preliminary studies suggest that satellite and rocket launches, which have become alarmingly frequent in recent years, may also negatively impact the ozone layer both during launch and when satellites re-enter the atmosphere.
For the planet to remain healthy, balanced, and habitable for its current inhabitants, we must remain vigilant about the chemicals we release into the atmosphere.
“We put enormous effort into getting rid of these chemicals,” says Solomon. “Don’t we have a duty to continue monitoring to ensure the atmosphere is responding the way we think it should?”
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