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Regeneration of the Ozone Layer


Scientific Assessment of Ozone Depletion: 2022 indicates that the Earth’s protective ozone layer is slowly but noticeably healing at a rate that would close the hole over Antarctica in approximately 43 years.


GS Paper-3: Climate Change and International Conventions; Ozone Layer and Montreal Protocol

Mains Question

What are the Montreal Protocol’s major accomplishments? Discuss the current scientific and policy challenges as well. (250 Words)

Outcomes of the Report

  • Major Montreal Protocol achievements
    • Montreal Protocol actions continued to reduce atmospheric abundances of controlled ozone-depleting substances (ODSs) and advance stratospheric ozone layer recovery.
  • Since the 2018 Assessment, the atmospheric abundances of both total tropospheric chlorine and total tropospheric bromine from long-lived ODSs have continued to decline.
    • New studies back up previous assessments, indicating that compliance with the Montreal Protocol reduces ODS emissions by about 0.5 to 1 degree Celsius by mid-century, compared to an extreme scenario with an uncontrolled increase in ODSs of 3 to 3.5% per year.
    • Montreal Protocol actions continue to contribute to ozone recovery.
  • The recovery of ozone in the upper stratosphere is underway.
  • Despite significant interannual variability in the size, strength, and longevity of the ozone hole, total column ozone (TCO) in the Antarctic continues to recover.
  • TCO is expected to return to 1980 levels in the Antarctic around 2066, in the Arctic around 2045, and in the near-global average (60°N-60°S) around 2040.
  • Compliance with the 2016 Kigali Amendment to the Montreal Protocol, which requires a phase-down of some hydrofluorocarbons (HFCs) production and consumption, is estimated to save 0.3–0.5°C of warming by 2100.
  • Current Scientific and Policy Issues
    • The recent discovery of unexpected CFC-11 emissions prompted scientific inquiries and policy responses.
  • Observations and analyses revealed the source region for at least half of these emissions, resulting in significant emissions reductions.
  • According to regional data, some CFC-12 emissions may have been associated with unreported CFC-11 production.
  • Other ODSs (CFCs-13, 112a, 113a, 114a, 115, and CCl4), as well as HFC-23, have unexplained emissions.
  • Some of these unexplained emissions are most likely caused by leaks of feedstocks or by-products, while the remainder is unknown.
    • Outside of the polar regions, observations and models show that ozone in the upper stratosphere is recovering.
  • In contrast, there has been no sign of recovery of ozone in the lower stratosphere.
  • Models predict a small recovery in mid-latitude lower-stratospheric ozone in both hemispheres, which is not observed.
  • Resolving this discrepancy is critical to gaining a complete understanding of ozone recovery.
    • The existing network of atmospheric monitoring stations collects data on global surface concentrations of long-lived ODSs and HFCs emitted by humans.
  • However, gaps in regional atmospheric monitoring limit the scientific community’s ability to identify and quantify controlled substance emissions from a wide range of source regions.
    • The impact of stratospheric aerosol injection (SAI), which has been proposed as a possible option to offset global warming, on the ozone layer has been assessed in accordance with the terms of reference for the 2022 SAP Assessment Report.
  • Significant potential consequences were identified, including the deepening of the Antarctic ozone hole and a delay in ozone recovery.
    • At this time, many knowledge gaps and uncertainties prevent a more robust evaluation.

The Montreal Protocol

  • The Montreal Protocol is an international treaty designed to protect the ozone layer by phasing out the production of a variety of ozone-depleting substances (known as ozone-depleting substances).
  • It was agreed on September 16, 1987, and went into effect on January 1, 1989.
  • It has undergone nine revisions since then, the most recent being in 2016. (Kigali).
  • For each group of ODSs, the treaty specifies a timetable for reducing and eventually eliminating production of those substances.
  • The Kigali Amendment to the Montreal Protocol entered into force on January 1, 2019.
    • Under the Kigali Amendment, countries committed to cutting HFC use by more than 80% over the next 30 years.
  • Policy Considerations for the Future
    • If ODS feedstock emissions are reduced to current estimates in future years, the return of mid-latitude Equivalent Effective Stratospheric Chlorine (EESC) abundances to 1980 levels could be accelerated by nearly 4 years.
    • Reducing future methyl bromide (CH3Br) emissions from quarantine and pre-shipment applications, as permitted by the Montreal Protocol, would accelerate the return of mid-latitude EESC abundances to 1980 levels by two years.
    • Human-caused emissions of very short-lived chlorine substances, primarily dichloromethane (CH2Cl2), continue to rise and contribute to ozone depletion.
    • A 3% reduction in anthropogenic N2O emissions over the period 2023-2070 would result in an increase in annual averaged global TCO of about 0.5 DU.
    • Global emissions of long-lived HFC-23, a byproduct of HCFC-22 production, are up to eight times higher than expected and are expected to rise unless abatement increases during HCFC-22 production or HCFC-22 feedstock use decreases.


Reducing future CFC and HCFC emissions requires addressing bank releases as well as continuing production and use in allowed manufacturing of feedstocks, by-products, or unknown uses, depending on the compound.

February 2024