“The atmospheric concentration of five theoretically banned chlorofluorocarbons (CFCs) has increased between 2010 and 2020,” said Luke Western of the University of Bristol in Britain during a press conference. “In two cases, we don’t understand what’s going on. It’s worrying. »

The three explainable phenomena described by the study published Monday in the journal Nature Geoscience – namely the increase in the levels of CFC-113a, CFC-114a and CFC-115 – are linked to chemical production. “There is no reason to have so many emissions of these three CFCs,” says another co-author, Stefan Reimann, of the Swiss Federal Laboratories in Dübendorf. “It’s a problem, but we can fix it. »

Of greater concern: no known industrial process can explain such high levels for the other two CFCs whose levels are increasing. “So it must be unexpected by-products of certain reactions,” Western speculates.

The hole in the ozone layer is formed in Antarctica, because it takes cold for the chemical reaction involving CFCs responsible for the destruction of ozone molecules to take place. It peaks in September or October each year. The ozone layer protects the Earth from the Sun’s ultraviolet rays, which notably increase the risk of cancer. As CFCs take a century to degrade, the hole in the ozone layer – which has been shrinking since 2010 – will not disappear until 2080. This hole was detected in 1989 and the production of most CFCs has been banned from 2009.

So far, this increase in levels of five CFCs has not compromised the closing of the hole in the ozone layer, according to Western. “But who knows what’s in store for us if we don’t tackle the problem? On the other hand, the five CFCs identified in the Nature Geoscience study add about 1% to global warming, because they are particularly potent greenhouse gases.

The successors to CFCs as refrigerants, hydrofluorocarbons (HFCs), are benign to the ozone layer, but have almost the same global warming potential. For this reason, their elimination and replacement by other molecules, probably hydrofluoroolefins (HFOs), were provided for in 2016 by the Kigali agreement (ratified in 2017 by Canada and in 2022 by the United States).

“The question now is whether there will be any by-products of HFO production that will be CFCs,” Western said. Parisa Ariya, a chemist at McGill University, says HFC use is declining across the West, including Canada. “But the ozone layer is complex and so are its interactions with the climate,” she warns.

His colleague Patrick Hayes, from the University of Montreal, is also worried about seeing a new pitfall in the healing of the ozone layer. “It’s quite surprising. After the controversy over illegal CFC emissions in China, here comes another problem. When is this going to stop? »

Illegal production of CFC-11 in China was detected in 2018 and factories were shut down. But this remains a delicate subject. “We don’t have access to Chinese data on CFC emissions despite our collaborations with Chinese researchers,” says Western. His colleague Stefan Reimann reports that measuring stations in South Korea can cover part of China. “Let’s say there is room for improvement in data sharing. »