Research in Reducing Ozone-Depleting Substances Suggests Positive Trend for Climate Change Mitigation and Ozone Recovery

Recent research by the University of Bristol has marked a significant milestone in the global effort to combat climate change and protect the ozone layer. The study showcases significant achievement in phasing out of ozone-depleting substances, indicating a positive trend for both climate change mitigation and ozone recovery. 

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A June 2024 study led by the University of Bristol and published in Nature Climate Change marks pivotal advancements in the reduction of hydrochlorofluorocarbons (HCFCs), gases notorious for depleting the ozone layer and exacerbating global warming. The international research indicates that the total ozone-depleting chlorine from all HCFCs reached its highest level in 2021. 

These substances, which contribute to greenhouse gas emissions, similarly reached their peak contribution to climate change in the same year, five years earlier than the latest forecasts had suggested. While the reduction in HCFC emissions between 2021 and 2023 was less than 1%, it nonetheless demonstrates a positive trend in decreasing emissions. 

The breakthrough highlights the effectiveness of international agreements like the Montreal Protocol and its amendments in phasing out these substances.

More on the topic: Ozone Layer Restoration Is Back on Track as Harmful Chemicals Phased Out, UN Says

The Problem with Hydrochlorofluorocarbons (HCFCs)

Hydrochlorofluorocarbons (HCFCs) are a group of man-made compounds primarily used in refrigeration, air conditioning, foam blowing, and as solvents. HCFCs were initially developed to replace chlorofluorocarbons (CFCs), which were found to significantly deplete the ozone layer. HCFCs are less damaging to the ozone layer compared to CFCs; you would have to release around 10 times as much HCFC to have a comparable impact on the ozone layer. However, they still pose significant threats due to their potent greenhouse gas properties and ability to persist in the atmosphere. 

HCFCs have a high global warming potential, meaning they can trap significantly more heat in the atmosphere compared to carbon dioxide (CO2). The most commonly used HCFC, HCFC-22, has a global warming potential of 1,760 times on a ten-year time scale – meaning that 1 tonne of HCFC-22 would trap 1,760 times more heat than 1 tonne of CO2.

HCFCs also still contribute to the degradation of the ozone layer, which protects life on Earth from harmful ultraviolet (UV) radiation. The release of HCFCs into the atmosphere leads to their breakdown by UV light, releasing chlorine atoms that then participate in ozone destruction. In cold temperatures, such as over the Antarctic and the Arctic, a singular chlorine atom can destroy thousands of ozone molecules.

The Montreal Protocol and Its Impact

Established in 1987, the Montreal Protocol on Substances That Deplete the Ozone Layer is a landmark international treaty designed to phase out the production and consumption of substances that deplete the ozone layer, including chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which developed and developing countries agreed to stop producing and using by 2020 and 2030, respectively.

In 2016, the Kigali Amendment to the Montreal Protocol was adopted, targeting hydrofluorocarbons (HFCs), which are used as replacements for HCFCs and CFCs. Although HFCs do not deplete the ozone layer, they are still potent greenhouse gases that contribute significantly to global warming. The global warming potentials for the most abundant HFCs are as large as 14,800 – meaning that 1 tonne of an HFC would trap 14,800 times more heat than 1 tonne of CO2. The Kigali Amendment aims to reduce HFC production and consumption by over 80% over the next 30 years, potentially avoiding up to 0.4C of global warming by the end of the century.

The Montreal Protocol has already been widely successful. According to a 2022 United Nations report, if current policies remain in place, the ozone is expected to recover to 1980 values by 2040. It has already benefited efforts to mitigate climate change, helping avoid global warming by an estimated 0.5C.

A Decrease in Radiative Forcing

The study indicates that between 2021 and 2023, there was a decline in both the global direct radiative forcing and the equivalent effective chlorine (EECl) of HCFCs, which measure the atmospheric chlorine content from ozone-depleting substances, indicating a decrease in their contribution to global warming. Researchers found that HCFC radiative forcing peaked in 2021 at 61.75 mW m−2 and EECl at 321.69 ppt. By 2023, these values had decreased slightly to 61.28 mW m−2 and 319.33 ppt, respectively. 

This trend, particularly rapid in the Northern Hemisphere, was largely driven by reductions in HCFC-22, the most abundant HCFC, and a decline in HCFC-141b emissions, mainly released from ageing appliance foams and their use in polymer production. One of the standout findings of the research is that this reduction in harmful emissions has been achieved five years earlier than predicted.

Several minor HCFCs, with concentrations below 1 ppt, present varied trends. HCFC-124 levels are declining, while HCFC-31, HCFC-133a, and HCFC-132b have either remained stable or increased in recent years. These emissions are likely due to leaks during the production of other chemicals. The production of HCFCs and other ozone-depleting substances (ODS) during the manufacture of other chemicals, as feedstocks, intermediates, or by-products, is not regulated under the Montreal Protocol. This lack of regulation is based on the assumption that emissions from these processes are negligible, although studies suggest otherwise.

However, the speed at which the total radiative forcing and equivalent effective chlorine (EECl) from HCFCs will decrease remains uncertain. Projections indicate that HCFC levels will return to their 1980 values by 2082 for radiative forcing and by 2087 for EECl, based on the dominant three HCFCs. Although the production and consumption of HCFCs are being phased out, emissions from appliances and foams will persist unless there are efforts to reclaim HCFCs before they are released. To avoid future increases in radiative forcing and EECl from HCFC emissions during chemical manufacturing, changes to the Protocol are needed. The Kigali Amendment has already implemented controls on by-product emissions of HFC-23. Any future rise in HCFC radiative forcing and EECl would conflict with the Protocol’s goals.

More on the topic: Ozone Layer Hole is Healing, But Australian Wildfires Threaten Progress

Analysis and Implications for Climate Change and Ozone Layer Recovery

The results highlight the Montreal Protocol’s success, reinforced by the Kigali Amendment, in curbing global temperature increases and reducing stratospheric ozone depletion. It highlights the effectiveness of global collaborative efforts in environmental protection and the potential for further advancements in reducing ozone-depleting substances and greenhouse gases. 

Lead author Dr Luke Western, Marie Curie Research Fellow at the University’s School of Chemistry, said: “The results are very encouraging. 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.”

However, the study’s findings also emphasise the necessity of maintaining global environmental agreements. While the Montreal Protocol and its amendments have demonstrated substantial success, the ongoing challenge of emissions from HCFCs during the manufacture of other chemicals, which are not yet controlled under the Protocol, highlights areas needing further regulatory attention. Amendments must be made when new research comes out, and studies like this underscore the importance of adapting and strengthening these agreements. Moving forward, policymakers need to act on these insights, ensuring that regulations are updated and strengthened as new research emerges.