Ozone-depleting gas emissions back on the decline

The emissions of a banned ozone-depleting gas have dropped rapidly following a previously unexpected spike.

A team of international researchers analysed global air measurements of the ozone-depleting chemical chlorofluorocarbon CFC-11. The analysis involved the use of detailed atmospheric models to remove the effects of natural meteorological variations.

They found that five years after an unexpected rise in emissions of the gas – which were linked to China – emissions dropped sharply between 2018 and 2019.

The abrupt turnaround of CFC-11 – the production of which should have been phased out worldwide by 2010 – is revealed in a paper published in the journal Nature.

Co-author, Professor Martyn Chipperfield, of the School of Earth and Environment and the National Centre for Earth Observation, said: “This is a good news story. It was surprising to detect the recent rapid decline in CFC-11 emissions but very welcome.

“The alarm raised by the scientific community in 2018 has had a positive impact and we can expect the continued repair of the ozone layer.”

Co-author Dr Wuhu Feng, also from the School of Earth and Environment, and the National Centre for Atmospheric Science, added: “This work shows the importance of maintaining global observation networks and modelling capabilities so that we can detect and understand these atmospheric changes.”

CFC-11 was originally developed in the 1930s and widely used in fridges, aerosols and thermal insulation.

But by the 1980s it was blamed for causing depletion of the ozone layer – which protects us from harmful ultraviolet light – most dramatically with the large hole over Antarctica.

The alarm raised by the scientific community in 2018 has had a positive impact.


A legally binding global treaty – the 1987 Montreal Protocol – called for production and trade of CFC-11 to be phased out by 2010.

With compliance to the protocol, research predicts that the hole over the Antarctic could be fully repaired by the 2060s.

However, two years ago, an unexpected rise in CFC-11 emissions were detected and attributed to the production of polyurethane insulation in eastern provinces of China.

Members of the treaty called for immediate action, and China announced renewed enforcement and inspection measures, with scientists monitoring the results. 

The resulting sharp fall in emissions was detected by two independent observation networks, the Global Monitoring Laboratory, run by the US National Oceanic and Atmospheric Administration (NOAA), and the Advanced Global Atmospheric Gases Experiment. Global atmospheric modelling from the University of Leeds was used to help derive the change in CFC-11 emissions.

Dr Stephen Montzka, an atmospheric scientist at NOAA, led the research team that first documented the 2018 spike. 

He said that the paper indicated that efforts to address the first known substantive violation of the international treaty were working.

“This was a major test of the Montreal Protocol, and it appears to have passed,” he said. “This is a great example of how important early warnings from observational systems can be. It’s pretty hard to solve a problem you don’t know exists.”

In 2018, the research team led by Dr Montzka announced that from 2014 to 2016, emissions of CFC-11 had increased by more than 13,000 tonnes per year to about 59,000 tonnes.

The new results show that from 2018 to 2019, emissions CFC-11 decreased globally by 18,000 tonnes per year to 52,000 tonnes per year. Current annual emissions now appear to have returned to pre-2012 levels.

The coming years will also see the phase-out of two further families of chemicals – hydrofluorocarbons and hydrochlorofluorocarbons (HFCs and HCFCs) – that replaced the main ozone-depleting substances and which do less damage to the ozone layer, but like CFCs are still very potent greenhouse gases that contribute to climate change. It will be important to monitor, through atmospheric observation and modelling, that these phase-outs proceed as expected.

Further information

"A decline in global CFC-11 emissions during 2018−2019", is published in Nature on 10 February 2021. DOI 10.1038/s41586-021-03260-5

The research at the University of Leeds was supported by the UK Natural Environment Research Council (NERC).

Image credit: jcrane on Pixabay