Ozone Layer Depletion and Montreal Protocol (UPSC Prelims + Mains)
Think of the ozone layer as Earth's "invisible sunscreen." You cannot see it, but it quietly blocks a large part of the Sun's harmful ultraviolet (UV) radiation. When this layer becomes thinner, more UV reaches the ground—raising risks of skin cancer, cataracts, damage to crops, and harm to marine life. That is why ozone layer depletion is one of the most important environment topics for UPSC, especially because it connects science + international treaties + India's environmental governance + climate change.
Ozone Layer
A region in the stratosphere (roughly 15–35 km above Earth) where ozone gas (O3) is present in higher concentration and absorbs most harmful UV-B and almost all UV-C radiation.
Ozone Layer Depletion
A long-term reduction in stratospheric ozone caused mainly by man-made chemicals (especially those releasing chlorine and bromine) that destroy ozone molecules through catalytic reactions.
Ozone Hole
A seasonal and severe thinning of ozone over Antarctica during Southern Hemisphere spring (around September–November), driven by polar weather conditions and ozone-depleting substances.
1) Why this topic is in news
- Ozone layer is recovering, and recent scientific bulletins continue to track its healing trend and yearly ozone hole size variations.
- Recovery timeline is a popular fact in UPSC: scientific assessments project recovery to 1980 levels around 2040 (most regions), 2045 (Arctic), and 2066 (Antarctica) if current commitments continue.
- Kigali Amendment (2016) expanded the Montreal framework to phase down HFCs (not ozone-depleting, but strong greenhouse gases). India accepted/ratified it in September 2021.
2) Basics you must be clear about: stratospheric ozone vs tropospheric ozone
UPSC often tests confusion points. Ozone is "good" in the stratosphere but "bad" near the ground.
| Aspect | Stratospheric Ozone ("Good ozone") | Tropospheric Ozone ("Bad ozone") |
|---|---|---|
| Where? | Stratosphere (about 15–35 km) | Near Earth's surface (0–10 km) |
| Role | Absorbs harmful UV radiation | Air pollutant; part of smog |
| Impact | Protects life | Harms lungs, crops; greenhouse gas |
Dobson Unit (DU)
A unit used to measure the total amount of ozone in a column of air above a location. (UPSC may ask the term even if not the number.)
3) How ozone is formed and naturally destroyed (simple science)
Ozone in the stratosphere is continuously formed and broken down:
- Formation: UV splits oxygen (O2) into oxygen atoms (O). Then O combines with O2 to form O3.
- Natural breakdown: UV can also split ozone back to O2 + O.
In a healthy atmosphere, formation and destruction remain in balance. The problem starts when human-made chemicals add extra destruction pathways that are much faster.
4) What causes ozone depletion?
The main reason is the release of ozone-depleting substances (ODS) that contain chlorine or bromine. These substances are stable in the lower atmosphere, so they survive long enough to reach the stratosphere. There, sunlight breaks them and releases chlorine/bromine atoms.
Ozone Depleting Substances (ODS)
Man-made chemicals (mainly containing chlorine or bromine) that destroy ozone in the stratosphere. Examples: CFCs, halons, carbon tetrachloride, methyl chloroform, HCFCs, methyl bromide.
4.1) The "catalytic" nature (why one atom can destroy thousands of ozone molecules)
Chlorine works like a catalyst:
- Cl + O3 → ClO + O2
- ClO + O → Cl + O2
- Net: O3 + O → 2O2
Because chlorine is regenerated, it can keep repeating the cycle many times. Bromine is even more efficient per atom, which is why halons were extremely damaging.
5) Why is the Antarctic "ozone hole" special?
The Antarctic ozone hole is not simply "more pollution." It is strongly linked to polar stratospheric conditions:
- Polar vortex: Strong winds isolate Antarctic air in winter.
- Very low temperatures: Form polar stratospheric clouds (PSCs).
- PSCs trigger chemistry: Convert chlorine into reactive forms.
- When sunlight returns in spring: Rapid ozone destruction happens, creating the "hole."
So, the ozone hole peaks around September–October and then reduces as the vortex weakens.
6) Major ODS and where they were used (UPSC-friendly)
| ODS group | Common uses (classic UPSC areas) | Key point to remember |
|---|---|---|
| CFCs | Refrigeration, air-conditioning, foam blowing, aerosol propellants, cleaning solvents | High ozone damage; long atmospheric life |
| Halons | Fire extinguishers (especially aviation, defence, high-value equipment) | Very high ozone damage per molecule |
| Carbon tetrachloride | Solvent; chemical feedstock (earlier widespread use) | Strong ozone-depleting chemical |
| Methyl chloroform | Industrial cleaning solvent | Controlled under Montreal system |
| HCFCs | Transitional refrigerants, foam sector (used as replacements for CFCs) | Lower ozone damage than CFCs but still harmful; being phased out |
| Methyl bromide | Fumigant (agriculture/quarantine uses) | Ozone-depleting; controlled with exemptions for critical uses |
India notified domestic controls through the Ozone Depleting Substances (Regulation and Control) Rules, 2000, which include schedules and restrictions on production, trade, and use of ODS.
7) Impacts of ozone depletion
- Human health: Higher UV-B exposure increases risk of skin cancer, cataracts, and immune suppression.
- Agriculture: UV can reduce crop productivity and damage plant tissues.
- Marine ecosystems: UV harms phytoplankton (base of ocean food chain), affecting fisheries.
- Materials: Faster degradation of plastics, paints, rubber, and fabrics.
Indian context: With high sunshine conditions in many parts of India (plains, deserts, high-altitude regions), protection from UV is an everyday health and productivity issue, not just an "Antarctica problem."
8) International response: Vienna Convention (1985) → Montreal Protocol (1987)
Ozone protection is a textbook example of how science pushed global governance.
Vienna Convention (1985)
A framework convention to promote cooperation on research, monitoring, and data-sharing on ozone depletion. It created the base on which the Montreal Protocol was later built.
Montreal Protocol (1987)
A legally binding treaty to phase out ozone-depleting substances. Adopted on 16 September 1987 and entered into force in 1989. It is widely cited as having achieved universal ratification.
16 September is observed globally as the International Day for the Preservation of the Ozone Layer.
9) Montreal Protocol: key features UPSC expects
| Feature | What it means (simple) | Why UPSC likes it |
|---|---|---|
| Binding phase-out schedules | Countries must reduce/stop production and consumption of listed chemicals | Concrete timelines = easy to test |
| Article 5 provisions | Developing countries get longer timelines and support | Links with equity and CBDR-like approach |
| Multilateral Fund (MLF) | Financial mechanism to help developing countries with technology transition | Shows "finance + tech transfer" working |
| Trade provisions + licensing | Regulates/bans trade with non-parties for controlled substances | Enforcement tool in an international treaty |
| Adjustments and amendments | Targets were tightened and new chemicals added over time | "Dynamic treaty" example |
| Science-based monitoring | Regular assessments guide policy decisions | Evidence-based global governance |
The Montreal Protocol is administered under the UNEP ozone system, and Parties meet regularly to take decisions.
10) Major amendments (important years for Prelims)
| Year | Amendment | UPSC-level takeaway |
|---|---|---|
| 1990 | London Amendment | Strengthened controls; helped broaden ODS coverage |
| 1992 | Copenhagen Amendment | Accelerated phase-out; more stringent measures |
| 1997 | Montreal Amendment | Further tightening; licensing/trade-related measures strengthened |
| 1999 | Beijing Amendment | Added/strengthened controls (including some production controls) |
| 2016 | Kigali Amendment | Phase-down of HFCs (climate focus) under Montreal framework |
11) Why Montreal Protocol is considered a global success
(A) Ozone recovery is on track
- Scientific assessments project that ozone levels could return to 1980 values around 2040 (most regions), 2045 (Arctic), and 2066 (Antarctica) under continued compliance.
- Recent WMO bulletins have reported continuing recovery signals and noted that some recent ozone holes (e.g., 2024) were smaller than several recent years.
(B) Climate co-benefits
Many ODS are also powerful greenhouse gases. So, phasing them out helped both ozone protection and climate mitigation. The Kigali Amendment further strengthens climate benefits by cutting HFCs, which can prevent significant warming by 2100 according to major global assessments and reporting.
(C) Strong "compliance design"
The combination of legal obligations, financial support, technology transfer, and trade measures made compliance feasible and attractive, especially for developing countries.
12) India and ozone protection: treaties, laws, achievements
12.1) India's treaty timeline (very important for Prelims)
- India became a Party to the Vienna Convention on 18 March 1991.
- India became a Party to the Montreal Protocol on 19 June 1992.
- India accepted/ratified the Kigali Amendment on 27 September 2021 (deposit date in UN treaty records).
12.2) India's domestic institutional setup
- MoEFCC Ozone Cell / National Ozone Unit: Nodal body for implementing Montreal commitments (policy, coordination, projects, reporting).
- ODS (Regulation and Control) Rules, 2000: Legal framework for controlling ODS production, import/export, sale, and use in India.
12.3) India's phase-out achievements
As per official Government of India releases, India has phased out controlled uses of CFCs, carbon tetrachloride, halons, methyl bromide, and methyl chloroform in line with Montreal schedules (notably by 1 January 2010 for controlled uses).
12.4) Current focus: HCFC phase-out (2030 target with servicing tail)
India's strategy for HCFCs is through phased programmes (HPMP). Official programme documents state that India aims to phase out HCFCs by 2030, with a small 2.5% servicing tail allowed until 2040.
Under HPMP Stage II (2017–2023), official releases note funding support from the Multilateral Fund and enterprise conversion in sectors like foam and air-conditioning manufacturing.
13) Kigali Amendment (2016): Montreal Protocol's climate upgrade
Hydrofluorocarbons (HFCs)
Refrigerants commonly used as replacements for CFCs/HCFCs. They have zero ozone depletion potential but can have very high global warming potential (GWP).
The Kigali Amendment was agreed in October 2016 to phase down HFC production and consumption under the Montreal framework. The UNEP OzonAction factsheet explains that Article 5 (developing) Parties are divided into two groups, and India is in Article 5 Group 2.
13.1) What India's schedule looks like (Article 5 Group 2)
| Item | Article 5 Group 2 (includes India) |
|---|---|
| Baseline years | Average HFC consumption/production in 2024–2026 + 65% of HCFC baseline |
| Freeze year | 2028 |
| Reduction steps | 10% (2032), 20% (2037), 30% (2042), 85% (2047) |
These steps and Group 2 membership details (including listing India among Group 2 countries) are given in UNEP's Kigali factsheet.
The factsheet also highlights key governance aspects such as reporting in CO2-equivalents and trade restrictions with non-parties beginning from 1 January 2033.
14) India's sustainable cooling link (very relevant for GS3 + Essay)
India's rising cooling demand makes Kigali implementation strategically important. The Government launched the India Cooling Action Plan (ICAP) in March 2019 with goals such as:
- Reduce cooling demand by 20–25% by 2037–38
- Reduce refrigerant demand by 25–30% by 2037–38
- Reduce cooling energy requirements by 25–40% by 2037–38
- Training and certification of 100,000 servicing technicians (skill ecosystem for leak reduction, safe alternatives, efficiency)
These targets are clearly stated in official PIB communication on ICAP.
15) Quick Revision Points (Prelims-Friendly)
- Montreal Protocol is mainly about ozone-depleting substances (CFCs, halons, HCFCs, etc.), not general CO2 reduction.
- Kigali Amendment is about HFC phase-down (climate), even though it is inside the Montreal system.
- Ozone hole ≠ a literal hole. It is a region of very low ozone concentration.
- Stratospheric ozone depletion is different from tropospheric ozone pollution.
- Why Antarctica? PSCs + polar vortex + spring sunlight trigger rapid depletion.
16) Mains answer framework (write like GS3)
How to structure a 10-marker:
- Intro (2–3 lines): Define ozone layer depletion and why it matters (UV shield).
- Causes: ODS → chlorine/bromine catalytic destruction; highlight Antarctic mechanism.
- Impacts: Health, agriculture, marine ecosystems, materials.
- Global response: Vienna Convention + Montreal Protocol; mention Article 5 + Multilateral Fund.
- India's actions: ODS Rules 2000; phase-out achievements; HCFC phase-out; Kigali acceptance.
- Way forward: Kigali implementation + energy-efficient cooling + technician training + low-GWP transition.
For a 15-marker: Add a short paragraph on "lessons for climate governance" (science-based targets, finance & technology transfer, compliance design, trade measures).
UPSC Question (Prelims 2012)
Q. Chlorofluorocarbons, known as ozone-depleting substances, are used:
1) in the production of plastic foams
2) in the production of tubeless tyres
3) in cleaning certain electronic components
4) as pressurizing agents in aerosol cans
Which of the statements given above is/are correct?
Answer: 1, 3 and 4 only
Explanation: CFCs were widely used as foam-blowing agents, cleaning solvents (electronics), and aerosol propellants; tubeless tyres are not the standard CFC use category in such questions.
17) Practice MCQs (UPSC Prelims level) with answers and explanations
1. The Montreal Protocol primarily aims to:
- (A) Reduce CO2 emissions
- (B) Phase out ozone-depleting substances
- (C) Stop deforestation
- (D) Control ocean acidification
Answer: (B)
Explanation: Montreal Protocol is the global treaty to phase out ODS responsible for ozone depletion.
2. "Ozone hole" is most strongly associated with:
- (A) Summer monsoon over India
- (B) Antarctic polar vortex and polar stratospheric clouds
- (C) Ocean currents in the Pacific
- (D) Desertification in Africa
Answer: (B)
Explanation: PSCs + polar vortex create conditions for rapid springtime ozone destruction over Antarctica.
3. Which of the following is NOT an ozone-depleting substance?
- (A) CFCs
- (B) Halons
- (C) HFCs
- (D) HCFCs
Answer: (C)
Explanation: HFCs have zero ODP (they do not deplete ozone) but have high GWP; hence Kigali targets them.
4. India became a Party to the Montreal Protocol in:
- (A) 1987
- (B) 1989
- (C) 1992
- (D) 2000
Answer: (C)
Explanation: India's accession/Party date is listed as 1992-06-19 in UNEP ozone country profile.
5. The Kigali Amendment deals with phase-down of:
- (A) CO2
- (B) Methane
- (C) HFCs
- (D) SO2
Answer: (C)
Explanation: Kigali adds HFC controls (Annex F) under Montreal system.
6. Which statement is correct?
- (A) Tropospheric ozone protects life from UV rays
- (B) Stratospheric ozone is a major air pollutant in cities
- (C) Stratospheric ozone absorbs harmful UV radiation
- (D) Ozone is absent in the atmosphere
Answer: (C)
Explanation: Stratospheric ozone forms the protective "UV shield."
7. Under Kigali, India is grouped as:
- (A) Non-Article 5 Party
- (B) Article 5 Group 1
- (C) Article 5 Group 2
- (D) Observer only
Answer: (C)
Explanation: UNEP Kigali factsheet lists India under Article 5 Group 2.
8. Which is the best reason why CFCs were especially damaging?
- (A) They are quickly washed out by rain
- (B) They are highly reactive in the troposphere
- (C) They are stable enough to reach stratosphere and release chlorine under UV
- (D) They only exist naturally
Answer: (C)
Explanation: CFC stability lets them survive long enough to reach stratosphere, where UV breaks them.
9. India's HCFC phase-out target is primarily:
- (A) 2020
- (B) 2030 (with a small servicing tail allowed till 2040)
- (C) 2050
- (D) No target exists
Answer: (B)
Explanation: Indian programme documents state phase-out by 2030 with 2.5% servicing tail until 2040.
10. The projected recovery of Antarctic ozone to 1980 levels is around:
- (A) 2025
- (B) 2040
- (C) 2066
- (D) 2100
Answer: (C)
Explanation: Scientific assessments commonly project ~2066 for Antarctic recovery under continued compliance.
18) Mains practice questions (GS3)
Explain the causes of ozone layer depletion and assess the effectiveness of the Montreal Protocol as an international environmental agreement.
Discuss how the Kigali Amendment links ozone protection institutions with climate mitigation goals. Highlight India's opportunities and challenges in the cooling sector.
"The Montreal Protocol is a model for future climate agreements." Comment with suitable examples (finance, technology transfer, compliance, trade measures).
19) Conclusion
The ozone layer story is one of humanity's environmental success stories. The Montreal Protocol proved that when science, policy, and international cooperation come together, global environmental problems can be solved. For UPSC aspirants, this topic offers rich material connecting atmospheric science, international treaties, India's environmental governance, and climate change linkages through the Kigali Amendment. Understanding the difference between stratospheric and tropospheric ozone, knowing India's treaty timelines, and grasping the HFC-climate connection are essential for both Prelims and Mains success.