Integrated Carbon Observation System Jungfraujoch station in Switzerland. Photo:

Research Signals Milestone in Cutting Gases that Deplete Ozone Layer

Development also a step toward climate change mitigation

Scientists at UC San Diego’s Scripps Institution of Oceanography are part of a new study that reveals significant progress in the drive to reduce levels of chemicals that destroy Earth’s ozone layer, confirming the success of regulations limiting their production.

The findings, led by the University of Bristol and published today in Nature Climate Change, show for the first time a notable decline in the atmospheric levels of potent ozone-depleting substances (ODS) called hydrochlorofluorocarbons (HCFCs). These HCFCs are also harmful greenhouse gases, so a reduction should also lessen global warming.

Countries agreed to enact the Montreal Protocol in 1987 to introduce controls on the production and usage of ODS, which were once widely used in the manufacture of hundreds of products, including refrigerators, aerosol sprays, foams and packaging.

HCFCs were developed as first-generation replacements for chlorofluorocarbons (CFCs). While production and use of CFCs has been banned globally since 2010, HCFC production and usage is still being phased out in developing countries.

The Advanced Global Atmospheric Gases Experiment (AGAGE) monitors levels of HCFCs and other ODS and greenhouse gases in the atmosphere. Scripps is the central calibration and development laboratory of AGAGE. 

"The influence of hydrochlorofluorocarbons (HCFCs) on ozone depletion and climate has peaked about five years before the most recent predictions,” said study co-author Jens Mühle, a Scripps Oceanography atmospheric scientist and AGAGE team member. “This is another milestone for the Montreal Protocol on Substances that Deplete the Ozone Layer, which mandates the phase-out of HCFCs, the first generation replacements of the chlorofluorocarbons (CFCs).” 

Scripps scientists Ray Weiss, Christina Harth and Peter Salameh also contributed to the study.

“The results are very encouraging," said lead author Luke Western, Marie Curie Research Fellow at the University of Bristol’s School of Chemistry. "They underscore the great importance of establishing and sticking to international protocols."

“Without the Montreal Protocol, this success would not have been possible, so it’s a resounding endorsement of multilateral commitments to combat stratospheric ozone depletion, with additional benefits in tackling human-induced climate change,” Western added.

The international study shows the total amount of ozone depleting chlorine contained in all HCFCs peaked in 2021. Because these compounds are also potent greenhouse gases, their contribution to climate change also peaked in that year. This maximum occurred five years before the most recent predictions. Although the drop between 2021 and 2023 was less than 1%, it still shows HCFC emissions are heading in the right direction.

“It validates the scientific basis of pollutants trapping heat within the planet and it is a clear demonstration of how sound climate policies developed with global cooperation can bend the global emissions curve, which in turn can bend the global warming curve,” said Scripps climate scientist Veerabhadran Ramanathan, who has studied the effects of pollutants on climate for more than 50 years and advocated for action to limit the use of CFCs, HCFCs and other heat-trapping gases and compounds. Ramanathan was not part of the study. 

Ramanathan and co-authors predicted in 2018 that the planet has a high probability of crossing the 1.5℃ threshold in about six years. 

“In order to prevent the warming from accelerating quickly to a disastrous 2℃, we have to cut emissions of other heat-trapping super pollutants like HFCs, methane and black carbon soot from diesel vehicles,” he added. “These super pollutants trap 25 to 2,000 times more heat (per ton of emissions) than CO2.”

Study results relied on high-precision measurements at globally distributed atmospheric observatories, using data from AGAGE and NOAA.

Co-author Isaac Vimont, a research scientist at NOAA, added: “This study highlights the critical need to be vigilant and proactive in our environmental monitoring, ensuring other controlled ozone depleting and greenhouse gases follow a similar trend which will help to protect the planet for future generations.”

-- Adapted from University of Bristol

About Scripps Oceanography

Scripps Institution of Oceanography at the University of California San Diego is one of the world’s most important centers for global earth science research and education. In its second century of discovery, Scripps scientists work to understand and protect the planet, and investigate our oceans, Earth, and atmosphere to find solutions to our greatest environmental challenges. Scripps offers unparalleled education and training for the next generation of scientific and environmental leaders through its undergraduate, master’s and doctoral programs. The institution also operates a fleet of four oceanographic research vessels, and is home to Birch Aquarium at Scripps, the public exploration center that welcomes 500,000 visitors each year.

About UC San Diego

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