A short-lived resurgence in the emission of ozone-depleting pollutants in Eastern China will not significantly delay the recovery of Earth’s protective ‘sunscreen’ layer, according to new research published in Nature.
NASA computer models helped scientists identify an uptick in atmospheric emissions of an ozone-depleting gas called CFC-11. NASA and the National Oceanic and Atmospheric Administration (NOAA) work together as part of a long-running research partnership to monitor emissions of stratospheric ozone and to support ozone scientists at the Massachusetts Institute of Technology (MIT) and the University of Bristol.
In 1987, the Montreal Protocol – an international treaty enacted to protect the ozone layer from additional degradation – banned new production and trade of ozone-depleting substances like CFC-11, and 198 nations have since signed on to the agreement.
After production ceased, scientists still expected CFC-11 to continue leaking over the years from existing products, but at a gradually declining rate. Because of this, the gas is among those monitored at the global scale by NOAA’s Global Monitoring Division and the Advanced Global Atmospheric Gases Experiment (AGAGE) – a network of monitoring stations funded by NASA and several environmental agencies, and headed by the Center for Global Change Science at MIT and the Scripps Institution of Oceanography.
In 2018, NOAA first reported a smaller decrease in the decline of atmospheric CFC-11 than expected. The numbers didn’t align with trajectories based on CFC-11’s production ban, hinting that something had changed. “The slow-down in the rate of decline indicated that somebody was emitting again, or in larger quantities than we were expecting, we just didn’t know where,” noted Matt Rigby, a University of Bristol (UK) scientist and one of the lead authors of the new study.
It was the AGAGE network that helped track down the origins of much of the new emission of CFC-11 thanks to its geographic distribution. Two of its stations, the South Korean Gosan AGAGE station, run by Kyungpook National University in South Korea, and the AGAGE-affiliated station on Hateruma Island in Japan, run by Japan’s National Institute For Environmental Studies, were both positioned close enough to the source for researchers to track much of the new emissions back to their source: Eastern China.
“This is very much like detective work,” said Qing Liang, a research scientist at NASA Goddard’s Space Flight Center in Greenbelt, Maryland, and co-author of the study. “We figured out there was a problem, then we tracked down where the problem was regionally, and it seems that the actions taken in China, and perhaps elsewhere, have resulted in a big drop in the unexpected emissions [since 2018].”
Due in large part to effective monitoring, and subsequent reaction to the 2018 report, data and analysis in these two papers (published in February 2021) suggest that both the renewed Eastern Chinese and overall global emissions of CFC-11 after mandated global phase out in 2010, have returned to previous levels.
The observed levels of increased emission were comparable to the carbon dioxide emissions of a city roughly the size of London. In other words, closing off CFC-11 emissions has an additional climate benefit similar to that of shutting off a megacity.
Despite the monitoring success story, some emissions are still unaccounted for – and scientists have been unable to pinpoint where they are coming from due to current limitations of the monitoring network.
“The one critical piece of information we need is atmospheric observations,” added Liang. “That’s the reason why it is really important for NASA and NOAA, together with their international partners, to continue making measurements of these gases.”
Monitoring networks like the AGAGE stations are a valuable tool for understanding the role atmospheric chemistry plays in our changing climate.