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A chemical banned around the globe for the last 30 years has made an unfortunate resurgence. And all signs, in a new study, point to China as the culprit.

In the 1980s, countries came together to sign The Montreal Protocol on Substances that Deplete the Ozone Layer, a landmark treaty designed to halt and reduce the production of chlorofluorocarbons (CFC), chemicals used in fridges and foams that had the side effect of tearing through the Earth’s ozone layer.

The Montreal Protocol has been signed by 197 countries around the world, including Canada, the U.S., and China. As the ozone layer in our upper atmosphere slowly depleted — letting in an increasing amount of the sun’s ultraviolet rays — the protocol contributed to a significant reduction in harmful CFCs, which then allowed for a slow healing of the damaged ozone layer.

That is until last year, when scientists from the National Oceanic and Atmospheric Association found that global emissions of Trichlorofluoromethane (CFC-11) have actually been increasing since 2013.

The increase implied that someone was secretly violating the Montreal Protocol. But the limitations of measuring devices meant the location of the polluter could only be traced to somewhere in east Asia.

Now, in a new study published in Nature on May 22, scientists from the University of Bristol, Kyungpook National University, and the Massachusetts Institute of Technology found that between 40 and 60 per cent of total global CFC-11 emissions originate from eastern China.