The global increase in ozone-depleting chlorofluorocarbon-11 (CFC-11) emissions, which was first detected in 2013 and continued to rise in the following years, appears to have been halted.
- A mystery surge in CFC-11 was detected between 2014-17
- The source of 60 per cent was traced to China, but 40 per cent is still unknown
- CFC emissions have returned to normal and researchers believe restoration of the ozone layer is still on track
Data from monitoring stations in South Korea (AGAGE station), Japan (NIES), and Hawaii (NOAA), showed that global CFC-11 emissions began dropping in 2019, after inexplicably surging between 2014-17, according to two research papers published in Nature today.
And preliminary data from late 2019 and early 2020 shows the atmospheric CFC-11 concentration decline during that period was “the fastest since measurements began”.
“The increase [in atmospheric CFC-11] we noticed and announced in 2018 was the most surprising thing I’d seen in 30 years of my work here at NOAA (National Oceanic and Atmospheric Administration),” lead author of the first paper, Stephen Montzka from NOAA said.
“To tell the truth, these new results were a close second.”
The rapid turnaround of a trend that could have seen further damage to the ozone layer is reassuring evidence that the Montreal Protocol is working as intended, said researcher Luke Western from the University of Bristol, the lead author of the second paper.
“The initial discovery of rising [CFC] emissions was unexpected,” Dr Western said.
“It’s pleasing to see that the mechanisms of the Montreal Protocol … enabled a rapid and effective response to its first major violation.”
The Montreal Protocol was an international agreement made in 1987 to phase out the use of ozone-depleting substances (ODS), principally CFCs used as propellants in things like aerosol sprays, as refrigerants in fridges and freezers, and as blowing agents for foams.
Globally, CFCs including CFC-11 — the second most commonly used chlorofluorocarbon — were completely banned in 2010, after which point researchers expected to see rapid declines in atmospheric levels, according to Dr Montzka.
“The Montreal Protocol phased out CFC production in developed countries in the ’90s,” he said.
By analysing the chemical signals from their monitoring stations and combining that with a knowledge of atmospheric circulation, researchers were able to pinpoint the source of around 60 per cent of the new CFC emissions to north-eastern mainland China.
It was suspected that the CFCs were mostly used illegally in the manufacture of closed-cell foams.
Using the leverage of the Montreal Protocol, combined with scientific knowledge and industry expertise, China was asked to crack down on the source of emissions, according to Dr Western.
“In 2018 and 2019, Chinese authorities discovered small quantities of manufactured CFCs and confirmed seizures of the chemicals and closure of factories,” he said.
Those reported seizures amounted to tens of tonnes. While not enough in itself to explain the 26 per cent drop in emissions between 2018 and 2019, the message sent by China’s crackdown may have had the desired effect on illegal manufacturing.
Mystery emissions sources a wake-up call
Although the manufacture of CFCs was banned in 2010, there is what is called a global “bank” of chlorofluorocarbons that will continue to produce emissions into the future, even if our use of new CFCs is zero.
The CFC bank refers to the CFCs already contained in products like refrigerants and foams and which will continue to leak into the atmosphere until their end of life, according to Paul Krummel from the CSIRO.
“[Refrigerators] often have slow, small leaks and when they give out, they dump all their CFCs to the atmosphere,” Mr Krummel said.
“For foam blowing, there’s some released at the time the foam is blown but then there’s residual amounts in the foam that slowly leaks out over many years.”
Prior to the surge in emissions in 2013, it was believed that all the annual CFC emissions were coming from products already in existence.
“We were under the impression that there was no new production,” Mr Krummel said.
And since late 2018, it seems that is again the case.
But the issue worrying researchers is that they still don’t know the source of around 40 per cent of the increased emissions during the 2014-17 period.
The danger is that a future emissions spike that cannot be traced, may not be able to be shut down so quickly.
“Absolutely that is somewhat of a concern,” Mr Krummel said.
Being able to increase the global coverage of atmosphere observation stations would help, Mr Krummel said.
“There’s a gap in our observing network and it would be fabulous if we could fill it in,” he said.
Ozone layer back on track for recovery by late century
The processes through which CFCs harm the ozone layer are the same as the ones that eventually help remove CFCs from the atmosphere.
Ultra-violet rays in the stratosphere separate chlorine molecules from the CFC (carbon + chlorine + fluorine) compound, and the chlorine molecules then react with ozone.
But chlorine, once separated from the CFC compound, can also react with other compounds such as methane.
This eventually leads to the reduction of chlorine in the atmosphere, according to Dr Western.
“CFC-11 has an atmospheric lifetime of around 52 years,” he said.
“Each year there should be smaller CFC emissions as the [CFC] banks get smaller and smaller. For CFC-11, each year around 3 per cent of the bank is emitted.”
Although the bank was added to during the 2014-17 period, the researchers estimate that 2019 emissions were still slightly lower than the 2008-2012 average.
What that means is that the natural depletion rate of CFCs from the atmosphere is still greater than the rate that they are being emitted from the bank.
This in turn means that the ozone layer is still on track for recovery late in this century, Mr Krummel said.
“It’s a good news story. It’s absolutely fantastic that it’s going down again, we’re extremely happy about that. If it didn’t start to decline again it would have been a major problem for the recovery of the Antarctic ozone hole,” he said.
As well as restoring the hole in the ozone layer, reducing CFCs also helps combat climate change.
“Most of these chemicals that have been regulated or banned are actually extremely potent greenhouse gases as well,” Mr Krummel said.
“To date [the Montreal Protocol] is still the most effective international treaty that’s combatting climate change as well as the ozone problem.”
The success thus far of the effort to cut out CFCs and help restore the ozone layer demonstrates that international cooperation is possible when dealing with things like climate change, according to Dr Western.
“I think that the Montreal Protocol proves that global cooperation is both possible and successful in addressing global environmental threats,” he said.