The Montreal Protocol, signed in 1987, is often presented as a model of environmental effectiveness. But a crack in this framework now threatens the healing of the ozone layer: a global leak of industrial chemicals, though permitted by an exception, is proving to be far more massive than anticipated.
Concretely, this exception allows the use of certain ozone-depleting products as raw materials to manufacture plastics, non-stick coatings, or other substances. Industry estimated that only 0.5% of these products would escape into the atmosphere. But recent measurements indicate that leaks actually reach 3.6%, or even more for some compounds.
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To measure the impact of these leaks, an international study published in
Nature Communications quantified their scale for the first time. Using data from the AGAGE monitoring network, researchers compared different scenarios. If current emissions persist, the return of the ozone layer to its 1980 state would be delayed from 2066 to 2073, a setback of about seven years.
Faced with this finding, the authors believe that solutions exist. Reducing leaks to 0.5% or completely eliminating these raw materials would save years. The chemical industry has already shown its capacity for innovation, as noted by Susan Solomon, a researcher at MIT. Many substitutes are available, and increased awareness could be enough to tighten processes.
Moreover, the signatory countries of the Montreal Protocol meet annually to discuss emerging issues. Emissions from raw materials are already on the agenda. According to Stefan Reimann, lead author of the study, reducing these leaks would prevent thousands of skin cancers. The stakes are therefore very real.
The chemistry of ozone destruction
Chlorofluorocarbons (CFCs) are stable compounds used in refrigeration, air conditioning, and aerosols. Once released, they slowly rise into the stratosphere, where the Sun's ultraviolet rays break them down. This reaction releases chlorine, which then destroys ozone molecules catalytically: one chlorine atom can destroy thousands of ozone molecules before being neutralized.
This destruction creates a "hole" in the ozone layer, mainly over Antarctica. Without this protection, UV radiation increases, causing skin cancers, cataracts, and damage to ecosystems. The Montreal Protocol banned the production of CFCs, but replacement substances, such as HCFCs and HFCs, also have harmful effects, though to a lesser extent.
Emissions from raw materials, such as dichloromethane, can also release chlorine into the stratosphere. Although less potent than CFCs, these compounds accumulate and contribute to ozone degradation. Their control is therefore essential for a complete recovery of Earth's ozone.