Montreal Protocol

Topic: Atmosphere: Composition, Structure and Elements of Weather · NCERT: Beyond NCERT

Meaning

The Montreal Protocol on Substances that Deplete the Ozone Layer is a binding global treaty, adopted on 16 September 1987 under the Vienna Convention (1985). It sets deadlines to stop making and using ozone-depleting substances (ODS) (man-made chemicals that carry chlorine or bromine up to the stratosphere and destroy ozone).

It matters because it worked. About 99% of the ODS it controls have been phased out [2], and the ozone layer is now on track to recover. Since the Kigali Amendment (2016), it also protects the climate.

Explanation

The problem it was built to solve

• Ozone layer: the part of the stratosphere that holds most ozone (O3). About 90% of all atmospheric ozone is here, mostly at 15–35 km (NCERT: 10–50 km).
• It absorbs harmful UV-B and UV-C rays.

• This protects people from skin cancer and cataracts (clouding of the eye lens). It also protects crops and ocean plankton (tiny drifting plants and animals at the base of the sea food chain).

• The chemicals that harm it:

• CFCs (refrigerators, ACs, aerosol sprays, foams) carry chlorine.
• Halons (fire extinguishers) carry bromine.
• Carbon tetrachloride (solvent) carries chlorine.
• Methyl bromide (fumigant for soil and stored grain) carries bromine.

• HCFCs (stop-gap substitutes for CFCs) carry chlorine, but harm ozone less.

• How they destroy ozone:

• These gases are very stable, so they do not break down in the lower air. They slowly drift up to the stratosphere.
• There, strong UV light breaks them apart and frees chlorine and bromine.
• Over Antarctica, the polar vortex (a ring of strong west winds around the pole in winter) traps air colder than about −78°C. In this cold, polar stratospheric clouds form, and their surfaces turn chlorine into an active, ozone-attacking form.

• When spring sunlight returns in September, a catalytic cycle begins. The chlorine is not used up, so one chlorine atom destroys ozone again and again.

• The result is the Antarctic ozone hole, a region where total ozone falls below 220 Dobson units. It was reported in 1985 by the British Antarctic Survey.

How the treaty works

• Framework first, then action:
• The Vienna Convention (1985) set up research and cooperation. It had no binding cuts.

• The Montreal Protocol (1987) added binding phase-out schedules. This means legal deadlines to stop each chemical completely.

• Common but different timelines:

• Developed countries cut first.

• Developing countries (Article 5 parties) get more time.

• It can be tightened over time:

• Parties meet regularly and can bring deadlines forward.

• Example: the 19th Meeting of the Parties (2007) moved the HCFC phase-out 10 years earlier [3].

• Science drives the reviews:

• Regular scientific assessments track progress. One example is the WMO/UNEP Scientific Assessment of Ozone Depletion 2022.

• Universal membership:

• In 2009 it became the first UN treaty ratified by every country.

Results and recovery

• About 99% of controlled ODS have been phased out worldwide [2].
• Since peaking around 2000, ODS in the Antarctic stratosphere have fallen by about one-third relative to pre-ozone-hole levels [6].
• Expected return to 1980 ozone levels (if current policies stay in place) [4][5]:

Region	Year
Rest of the world	About 2040
Arctic	About 2045
Antarctic	About 2066

• The 2025 ozone hole shows the recovery:
• Its average size from 7 September to 13 October 2025 was about 18.71 million km². This made it the 5th smallest since 1992 [6][7].
• Its largest one-day size was 22.86 million km² on 9 September 2025. That is about 30% smaller than the record hole of 2006 (average 26.60 million km²) [6].
• It broke up nearly three weeks earlier than the average of the past decade. A weaker-than-normal polar vortex in August 2025 kept temperatures higher [6].

The Kigali Amendment: from ozone to climate

• The new problem:
• CFCs and HCFCs were replaced by HFCs (hydrofluorocarbons).
• HFCs have no chlorine, so they do not harm ozone.

• But they are very strong greenhouse gases, often thousands of times stronger than CO2.

• The fix:

• The Kigali Amendment was agreed in 2016 at Kigali, Rwanda. It came into force on 1 January 2019.
• It phases down HFCs. This means it reduces them step by step; it does not ban them outright.
• Full compliance could avoid 0.3–0.5°C of global warming by 2100 [4].

Where it occurs

• Worldwide: every country has ratified it (universal ratification since 2009). It is named after Montreal (Canada), where it was adopted in 1987.
• Antarctica: this is where its main target, the ozone hole, forms every southern spring (September–October).

• The continent is ringed by open ocean, and few mountains disturb the winds. So the polar vortex stays closed and very cold.

• Arctic: here ozone only thins in some very cold years. Land, sea and mountain ranges (Rockies, Himalaya) create waves that break up the vortex.

• Kigali, Rwanda: where the HFC amendment was agreed in 2016.
• India:
• India joined in 1992. The Ozone Cell of the Ministry of Environment, Forest and Climate Change (MoEFCC) runs India's programme [2].
• CFCs, carbon tetrachloride and halons were all phased out by 2010 [2].
• HCFCs are being cut under the HCFC Phase-out Management Plan (HPMP). Its roadmap was launched in 2009 with industry and research institutions. By 2025, India had cut HCFC production and consumption by 67.5% [3].
• Kigali: the Union Cabinet approved ratification in August 2021 [1].
  • India's baseline is 2024–26, with a freeze in 2028.
  • Cuts come in four steps: 10% by 2032, 20% by 2037, 30% by 2042 and 85% by 2047 [1].
  • A national HFC phase-down strategy was to be drawn up with industry by 2023 [1].
• India Cooling Action Plan (ICAP, 2019): a 20-year plan (2017–18 to 2037–38) to cut cooling demand and refrigerant use. It supports the Kigali targets.

Don't confuse with

• Vienna Convention (1985): a framework treaty for research and cooperation with no binding cuts. The Montreal Protocol (1987) made the legally binding phase-out deadlines.
• Kigali Amendment (2016): an amendment to the Montreal Protocol, not a separate treaty. It targets HFCs, which do not harm ozone but heat the climate. It is a phase-down, not a full phase-out.
• Kyoto Protocol: a climate treaty on greenhouse gases. HFCs are controlled under Kigali (a Montreal Protocol amendment), not by the Kyoto Protocol alone.
• Ground-level ozone: a pollutant near the ground. It forms when vehicle and factory fumes react in sunlight, and it is part of urban smog. The Montreal Protocol protects stratospheric ("good") ozone, not this one.

Prelims Hooks

• Chronology: Vienna Convention 1985 → Montreal Protocol 1987 → universal ratification 2009 → Kigali 2016 (in force 1 January 2019).
• World Ozone Day = 16 September, the date the Montreal Protocol was adopted in 1987.
• Recovery to 1980 levels, from earliest to latest: Rest of world ~2040 → Arctic ~2045 → Antarctic ~2066 [4].
• Trap: Halons carry bromine, while CFCs carry chlorine. HFCs carry no chlorine, so they do not deplete ozone, but they are strong greenhouse gases.
• India's Kigali path: baseline 2024–26, freeze 2028, cuts of 10% (2032) → 20% (2037) → 30% (2042) → 85% (2047) [1].
• The 2025 Antarctic ozone hole was the 5th smallest since 1992. The largest on record was in 2006 [6].

Mains Points

• A model for global environmental action (GS-III):
• Its key features: universal ratification (2009), binding deadlines, extra time for developing (Article 5) countries, and science-based reviews such as the 2022 Assessment.
• The results: about 99% of ODS phased out [2] and ozone recovery expected by about 2040–2066 [4].

• It is often called the most successful environmental treaty and offers lessons for climate agreements.

• Ozone–climate link (GS-III):

• Replacing CFCs with HFCs swapped an ozone problem for a climate problem.
• Kigali fixes this and could avoid 0.3–0.5°C of warming by 2100 [4].

• For India, AC demand is rising fast in hot cities. This makes the Kigali steps (2028 freeze; 85% cut by 2047) [1], the HPMP and ICAP 2019 important.

• Threats to recovery (GS-I/GS-III):

• Recovery depends on current policies staying in place [4][5].
• Stratospheric aerosol injection (a geoengineering idea to spray sulphate particles into the stratosphere to cool the Earth) could deepen the Antarctic ozone hole and delay recovery [4].
• Any such plan therefore needs careful, multilateral governance.

Related concepts

• Ozone layer
• Dobson unit
• Ozone hole
• Polar stratospheric clouds
• Kigali Amendment
• Stratospheric aerosol injection

Read more

• The ozone layer, its depletion and the Montreal Protocol