Scientists find ozone depletion began decades before discovery of ozone hole and was caused by carbon tetrachloride since the 1930s

Amazing stuff!

These authors seem to be obsessed with the instrument of a thought experiment! In this particular study it might have been overused.

"... In a study ... the scientists suggest that the first signs of ozone depletion appeared as early as 1957 — about 30 years before the ozone hole was discovered. And, this first signal of ozone loss popped up not in the Antarctic, but in the upper stratosphere of the tropics. What’s more, the cause of this early depletion was not due to CFCs, but to another industrial chemical: carbon tetrachloride.  ..."

From the significance and abstract:

"Significance

This paper examines the earliest emergence of human-caused ozone depletion: the when, the where, and the why.  ...

The “when” is as early as the late 1950s—about 30 y before the Antarctic ozone hole was discovered and 20 y before the Molina–Rowland theory. The “where” is the tropical upper stratosphere, where a relatively small signal stands out against even smaller noise, allowing the earliest emergence. The “why” is the use of carbon tetrachloride as a solvent decades before chlorofluorocarbons became common in refrigeration and spray cans.

Abstract

The Antarctic ozone hole was first reported in 1985, and small ozone losses at the global scale were also observed in the late 1980s. The combination of field and laboratory measurements, together with modeling, quickly established anthropogenic chlorofluorocarbons (CFCs) as the cause of both the Antarctic and global ozone depletion.

However, when, where, and why the earliest ozone depletion could have been detected has not been determined.  ...

We find that human-caused ozone depletion was likely identifiable as early as 1957 in the tropical upper stratosphere. This region’s low internal variability enables the earliest detection of the anthropogenic signal, even though tropical ozone losses in the upper stratosphere were smaller than those in higher-latitude regions. ... 

Further, while CFCs are widely recognized as the primary drivers of current ozone depletion, we find that early ozone loss was primarily caused by human-made carbon tetrachloride (CCl4), used mainly as a solvent. These findings suggest that a clear human influence on the stratospheric ozone layer began nearly 70 y ago, even before substantial emissions of CFCs from spray cans or air conditioning."

Scientists find ozone depletion began decades before discovery of ozone hole | MIT News | Massachusetts Institute of Technology "Using modern tools, they also determined that carbon tetrachloride, used as a dry-cleaning and degreasing agent as early as the 1930s, was at the root of early ozone loss."

The emergence of human influence on the ozone layer by the 1960s

Resonance structures of ozone with lone pairs indicated (Source)

Polarity of Carbon Tetrachloride (CCl4) (Source)