By Sarah-Jane O'Connor 23/05/2019

Thirty years ago, in May 1989, global leaders gathered in Helsinki to sign into force the Montreal Protocol.

You might not be familiar with it by name, but you certainly know its effects: the Montreal Protocol phased out the use of chlorofluorocarbons, or CFCs, and other ozone-depleting substances in an effort to reverse the damage to the ozone layer.

It’s one of the few global achievements we can rightfully crow about. Researchers say if we hadn’t phased the chemicals out, the ozone hole over Antarctica would have been 40 per cent larger by 2013. In 2016, a paper in Science reported the hole had begun to ‘heal’, showing an increase in ozone. (It’s worth pointing out that through to the mid 1980s the CFC industry, including Du Pont, was still arguing that the science was still too uncertain to justify action… Sound familiar?)

There are still some complications, including warnings that now we’ve phased out the worst offenders, we should turn our attention to other chemicals such as dichloromethane. But overall, the Montreal Protocol has been a success.

A suspicious finding

So it was something of a shock a year ago when researchers reported in Nature that they’d found something suspicious…

Levels of a particular CFC – trichlorofluoromethane, CFC-11 – had declined steadily between 2002 and 2012, but then the decline slowed by about half.

This was in contrast to the two other most abundant CFCs – CFC-12 and CFC-13 – which showed the expected decline due to halted production and as leftover emissions from existing equipment and products gradually escape and diminish. CFC-11 should have done the same as reported production went down to zero.

And so, the hunt was on. Was this just some kind of scientific error, or was there foul play afoot? Running simulations on the emissions data, the researchers ruled out increases in emissions from the demolition of buildings, or changes in how fast the chemicals were released from old equipment.

Rather, they suspected the reason for the lag in decline is that someone was still making CFC-11.  (Cue dramatic music.)

When I saw this study come across my desk last year, I was instantly fascinated. Here is this epic global accord that has seen definitive proof of its effectiveness, and through careful and thorough monitoring an international team of scientists have found evidence that suggests someone, somewhere is breaking the rules.


In that first paper, the researchers reported CFC-11 emissions were about 7,000,000 kilograms per year higher over eastern mainland China between 2014 and 2017, compared to 2008-2012. Primarily, this was around the provinces of Shangdong and Hebei.

Today they’ve published their follow-up research, and they’ve zeroed in on the two provinces, saying they account for at least 40-60 per cent of the increase. Most likely, this is the result of new production: a clear breach of the Montreal Protocol.

Professor Ian Rae, a chemist from the University of Melbourne who was a technical advisor to the Montreal Protocol for ten years, told the Australian Science Media Centre that CFC-11 was mainly used for ‘foam blowing’ – “that is, the process of producing the voids in plastic foams”.

“Because it’s very effective at what it does, however, there have been rogue users of old supplies and rogue producers who flout international agreements that their governments have signed up to.”

He said that while regulated production of ozone-depleting substances had been phased out, “regulators like China EPA and some in other countries have found it difficult to deal with the rogues”.

Despite the headlines proclaiming that researchers have “pinpointed” the source of the banned chemicals, there’s still work to be done to figure out who is making them. But given many countries, including China, are not well covered by existing monitoring it’s impressive that this level of deduction has allowed researchers to know that CFC-11 is being produced somewhere – even if we don’t yet know who’s responsible.

It makes me feel hopeful that we are able to enforce these global agreements, especially as we move into figuring out how to enact the promises made in the Paris Agreement. It also shows that this stalwart of the scientific method – simply looking to find out what’s out there – continues to be an essential part of spotting these bad actors.

I’m waiting with bated breath to find out the next chapter of this scientific mystery story.