After Years Of Rising, Emissions Of An Ozone-Depleting Chemical Have Finally Started To Fall


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

ozone layer

The ozone layer is likely to continue its recovery with the news an increase in emissions of the ozone-destroying chemical CFC-11 has been reversed. Image credit: Yarchanka Siarhei/

The world faces quite enough potential sources of apocalypse to be going on with, so it’s a relief to know one threat is back in its box for the moment. A disturbing increase in emissions of the banned chemical CFC-11 (technically known as trichlorofluoromethane) has reversed, new research shows. Monitoring will go on, but for the moment we can return to worrying about global heating, antibiotic resistance, incoming asteroids, collapsing biodiversity, and the threat of a robot uprising, freed from any immediate threat of death by UV radiation.

Two papers in Nature reveal the success of efforts to control CFC-11, with one indicating low emissions in 2018-19 from East Asia, while the other confirms concentrations are falling in the atmosphere as a whole


When Sherwood Rowland and Mario Molina provided evidence that certain artificial chemicals threatened the ozone layer – and therefore most life on Earth – CFC-11 was the prime culprit. Although very useful for refrigeration and expanding insulating foams, CFC-11 breaks down in the atmosphere into chemicals that rip ozone molecules apart, turning them into ordinary oxygen. Stratospheric ozone blocks almost all the medium-frequency ultraviolet radiation that would give humans and other animals skin cancer and wilt plants if allowed through.

In an admirable – and unusually prompt – response, Jimmy Carter banned CFC-11 in America for certain uses and encouraged chemical companies to find alternatives in other cases. Few other countries followed immediately, but a decade later when the danger was confirmed, replacements were well advanced. The Montreal Protocol banned CFC-11 from 2010, along with different dates for other ozone destroyers.

At first, this went well. Concentrations of the relevant gasses started falling even before their final ban dates. So it was with considerable alarm that atmospheric scientists reported in 2018 that CFC-11 emissions had been rising since 2013. The source of at least half the emissions was traced to north-eastern China.

“The enhanced emissions during this period are unlikely to lead to a substantial delay in ozone recovery, although a delay of years to decades would be expected if emissions continued at the levels observed between 2014 and 2017,” the first paper notes.


Fortunately, those emissions did not continue in 2018-19, possibly as a result of the attention drawn by the previous discovery. Both papers report thousands of tonnes less of the gas was released in 2019 than in 2017.

Air monitoring stations reveal the density of CFC-11 concentrations in north-east China has fallen dramatically. Image credit: AGAGE/NASA Earth Observatory

"The findings are very welcome news and hopefully mark an end to a disturbing period of apparent regulatory breaches," Dr Luke Western of the University of Bristol, co-lead author of one paper, noted in a statement. "Since CFC-11 is also a potent greenhouse gas, the new emissions were contributing to climate change at levels similar to the carbon dioxide emissions of a megacity."

Nevertheless, Weston's paper notes it is likely some of the CFC-11 manufactured during the 2013-2017 period is still in storage and could pose a danger to the atmosphere if eventually released.