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An article on a new tool to measure ozone recovery has been published in Nature. The Integrated Ozone Depletion (IOD) metric is being suggested as a tool to assess the effects of ozone-destroying substances and their impact on the recovery of the ozone layer.

The ozone depletion potential of atmospheric compounds has been a key metric in measuring the ability of those chemicals to deplete stratospheric ozone and guiding the phase-out of the most highly depleting substances under the Montreal Protocol. A recent scientific study by a team of researchers from the National Centre for Atmospheric Science and the University of Cambridge suggests that the current recovery phase in monitoring the success of the Protocol might require additional metrics.

The article suggests that rather than measuring the “delay in ozone return” to some previous value, often taken to be the 1980 value, the IOD metric may be used. IOD provides a straightforward means of calculating the impact of any new emissions, regardless of their size, on the ozone layer based on the strength of the particular emission, how long it will remain in the atmosphere, and how much ozone is chemically destroyed by it. The study argues that the IOD could provide a useful complementary metric of the impact of specific emissions of ozone-depleting substance for both policy makers and scientists.

Continued vigilance and monitoring of controlled substances (and those unregulated by the Protocol i.e. short-lived substances), as well as the need to address any gaps in atmospheric monitoring for early detection of emissions and their sources is critical to successful ozone depletion mitigation. This was recently reaffirmed when in 2018 scientists alerted the world of an unexpected increase in emissions of a banned chlorofluorocarbon (CFC), CFC-11. Such an increase would have been detrimental to the ozone layer had this gone on unchecked.

35 years since the adoption of the Protocol, it is recognised that threats to ozone layer and its recovery, including breaches of the Protocol and emissions of unregulated ozone-depleting substances, remain. As ozone layer recovery enters a new phase, scientific assessments of the state of ozone depletion and recovery are key.