Remember ozone-destroying CFCs? They’re on the rise again. And the source is a mystery

Once, not that long ago, the depletion of the Earth's ozone layer was a terrifying threat. But the phaseout of the man-made chemicals that were destroying it became one of the great environmental success stories of the past century, and a highly touted example of how international cooperation can work to protect people and the planet.

Now, a team of scientists say they've detected small but rapidly rising concentrations of five of these ozone-destroying substances in the atmosphere, starting the year the ban on their use took effect - and that the source of the emissions is a mystery.

Two of the five, in particular, have no known current uses, deepening the mystery of their origins, the researchers say.

We don't really know where it's coming from, and that's really a bit scary," said Stefan Reimann, a researcher at Empa, the Swiss Federal Laboratories for Materials Science and Technology and a co-author of the new research.

The amounts the scientists measured are not enough to set back the slow but steady healing of the ozone layer, according to the study, which was published Monday in the journal Nature Geoscience. But if the levels continue to rise, it could start negating some of our hard-fought progress.

A more pressing concern is that the substances, known as chlorofluorocarbons (CFCs), are highly potent greenhouse gases - thousands of times moreso than carbon dioxide - and can persist for long periods. The five detected ones have atmospheric lifetimes ranging from 52 to 640 years.

The emissions of these gases in 2020 were around the same size as the total carbon emissions for a country like Switzerland. So the climate impact is still quite substantial," said Luke Western, the paper's first author and a researcher with the University of Bristol and the National Oceanic and Atmospheric Administration's Global Monitoring Laboratory.

Scientists not involved in the research say it is an important reminder that the world needs to stay vigilant to this not-yet-dead environmental threat, and tighten up the landmark treaty, the Montreal Protocol, that has been successful so far in fighting it.

This is basically a warning," said Susann Tegtmeier, an atmospheric scientist at the University of Saskatchewan. While the problem is currently small, it is very important to keep an eye on these processes because, as we've learned in the past, these things can grow, and sometimes they can grow quite quickly."

Chlorofluorocarbons were once widely used in refrigerators, air-conditioners, aerosol spray cans and other applications. In the 1970s and 80s, a series of pioneering experiments showed that CFCs were destroying ozone in the earth's stratosphere and, in particular, creating a gaping hole in the layer above Antarctica. Ozone depletion allows harmful ultraviolet radiation to penetrate to the planet's surface, increasing the risks of skin cancers and cataracts in humans and harming plant and ocean life.

In 1987, the Montreal Protocol was adopted - a rare treaty to achieve ratification from every country in the world, and one described by former United Nations secretary-general Kofi Annan as perhaps the single most successful international agreement to date." The protocol phased out CFC production over time, ending with a total ban in 2010.

According to the United Nations Environment Programme's latest assessment, released in January, the ozone layer has been on a slow, steady path toward healing since then, and is expected to recover fully over the coming decades, with the hole over Antarctica estimated to close by 2066.

The international team of scientists involved in the new research used a network of air-sampling instruments across the globe to measure atmospheric concentrations of five now-banned CFCs, and discovered that they have been rising since the ban took effect in 2010, peaking in concentration in 2020.

The Montreal Protocol still allows CFCs to be used as feedstocks" or ingredients in the creation of other substances, in particular to create the safer replacements for CFCs we now use instead. The scientists believe three of the five CFCs they detected, which increased significantly around 2010, are tied to these processes.

Two of them, however, have no known current uses, and even their rare previous uses can't explain the levels the scientists have detected.

All five of them are somewhat worrisome. But in some sense, the ones that we have no idea where they come from, where we have no known byproduct production or no known sources, those might be the most worrisome," said Tegtmeier, adding that while there is no evidence yet, they may be coming from illegal production that contravenes the Montreal Protocol.

The scientists were careful not to name any particular country as a potential source for these newly discovered emissions. But they noted that because of the dense web of air sampling instruments, they are fairly certain" it is not coming from the United States or Europe - and that previously published work has identified East Asia as a source of some of the CFCs, where their sampling network is much more sparse.

I don't think much can be done before we know which processes and which regions are responsible," said Tegtmeier, adding that the seemingly boring work of conducting long-term sampling remains critically important.

An update to the Montreal Protocol called the Kigali Amendment is intended to phase out the replacement chemicals for CFCs which, while not harmful to the ozone, are potent greenhouse gases. The study's suggestion that CFCs are escaping via the production of those replacement chemicals makes this update even more urgent, researchers said.

It does kind of highlight that there are gaps in our current international policy, the Montreal Protocol ... the ratification of the Kigali Amendment is really important," said Karen Smith, an atmospheric scientist at the University of Toronto Scarborough who was also not involved in the new study.

More research will be necessary to find the rogue emissions," all the scientists said. But once they are discovered and stopped, it would be the equivalent of having a small country go carbon-neutral.

Eradicating these emissions is an easy win in terms of the impact on the climate," said Western.

Kate Allen is a Toronto-based reporter covering climate change for the Star. Follow her on Twitter: @katecallen