Ozone depletion

Topic: Environment and Sustainable Development · NCERT: Class 11, Ch 7 "Environment and Sustainable Development"

Meaning

Ozone depletion is the thinning of the ozone layer in the stratosphere (the layer of air about 10-50 km above the earth). It happens when high levels of chlorine and bromine compounds build up there. These compounds come from man-made ozone-depleting substances (ODS) such as CFCs and halons. It matters because the ozone layer absorbs harmful ultraviolet (UV) rays from the sun. When the layer thins, more UV-B reaches the earth and harms human health, crops and ocean life. It is also the base of the Montreal Protocol (1987), often called the most successful environmental treaty in the world.

Explanation

How the damage happens

• Ozone (O3) is a gas. In the stratosphere it forms a shield against UV rays.
• The chain reaction:
• CFCs are very stable, so they drift up into the stratosphere without breaking down.
• Strong UV light there breaks the CFCs apart and frees chlorine atoms.

• One chlorine atom can destroy thousands of ozone molecules, because the same atom is used again and again.

• The Antarctic "ozone hole":

• Over Antarctica, very cold polar clouds speed up this reaction.

• So an "ozone hole" forms every spring (September-October).

• NCERT records a ~5% fall in the ozone layer between 1979 and 1990.

The ozone-depleting substances (ODS)

Substance	Key element	Main use
Chlorofluorocarbons (CFCs)	Chlorine	Coolants in refrigerators and ACs; aerosol propellants (the gas that pushes spray out of a can)
Halons (bromofluorocarbons)	Bromine	Fire extinguishers
Carbon tetrachloride	Chlorine	Industrial solvent
Methyl chloroform (trichloroethane)	Chlorine	Industrial solvent

Effects of more UV-B

• Human health: more skin cancer and more eye cataracts.
• Oceans: phytoplankton (tiny floating plants at the base of the ocean food chain) produce less, so aquatic food chains suffer.
• Farming: land plants grow less well, so crop yields fall.

The economics: why a treaty was needed

• The ozone layer is a global public good. Everyone benefits from it, and no one can be kept out.
• A firm that released CFCs did not pay for the harm it caused. This is a negative externality (a cost that falls on others and not on the one who causes it).
• No single country could fix the problem alone, so the world needed a treaty:

Step	Year	What it did
Vienna Convention	1985	A framework for cooperation, with no binding cuts
Montreal Protocol	1987	Set binding phase-outs of ODS (CFCs, halons, CCl4, methyl chloroform). Every country has ratified it
Multilateral Fund	1990	Pays developing countries the extra costs of phasing out ODS
Kigali Amendment	2016	Phases down HFCs

• Results:
• Nearly 99% of banned ODS have been phased out [4].

• ODS are also greenhouse gases, so cutting them has helped avoid about 0.5°C of global warming [4].

• When the layer is expected to recover to 1980 levels (UNEP/WMO Scientific Assessment 2022, released January 2023):

• Near-global average (60°N-60°S): around 2040 [5][4].
• Arctic: around 2045 [5].
• Antarctic: around 2066 [5][4].

In India

• Under the Montreal Protocol: as a developing country, India got delayed deadlines and money through the Multilateral Fund. This is CBDR (Common But Differentiated Responsibilities: every country must act, but not in the same way or to the same degree) in practice.
• Kigali Amendment:
• It was adopted at the 28th Meeting of the Parties in Kigali, Rwanda (October 2016) [2].

• The Union Cabinet approved India's ratification in August 2021, and India ratified in September 2021 [2].

• Why Kigali matters for ozone:

• HFCs replaced CFCs. They do not harm ozone.
• But they are strong greenhouse gases. Their Global Warming Potential (GWP: how much heat a gas traps compared with the same mass of CO2) runs into hundreds or thousands.

• So fixing the ozone problem created a climate problem.

• India's HFC path: a freeze in 2028, then cumulative cuts of 10% by 2032, 20% by 2037, 30% by 2042 and 85% by 2047 [2].

• Benefit: the global HFC phase-down may prevent up to 105 million tonnes of CO2-equivalent emissions and avoid up to 0.5°C of warming by 2100 [2].
• India Cooling Action Plan (ICAP, 2019):
• It was the world's first cooling action plan, with a 20-year outlook [3].
• Its targets for 2037-38 are to cut cooling demand by 20-25%, energy used for cooling by 25-40% and refrigerant demand by 25-30% [3].
• It supports the HFC phase-down through better energy efficiency and climate-friendly refrigerants [3].

Don't confuse with

• Global warming: this is warming of the lower atmosphere because greenhouse gases trap heat. Ozone depletion is a thinning of the stratospheric shield that lets in more UV-B. They are different problems, but CFCs and HFCs link them.
• Tropospheric (ground-level) ozone: this is the "bad" ozone. It is a pollutant and a greenhouse gas. Stratospheric ozone is the "good" ozone that shields us from UV.
• HFCs vs CFCs: CFCs deplete ozone and are controlled under Montreal (1987). HFCs do not deplete ozone, but they are powerful greenhouse gases. They are controlled under the Kigali Amendment (2016).
• Vienna Convention vs Montreal Protocol: Vienna (1985) was only a framework with no binding cuts. Montreal (1987) set the binding phase-out schedules.

Prelims Hooks

• Ozone depletion is a stratospheric problem, and it increases UV-B radiation reaching the earth. It is not a tropospheric problem.
• Halons contain bromine and are used in fire extinguishers. CFCs contain chlorine and are used as coolants and aerosol propellants.
• Vienna 1985 was a framework. Montreal 1987 set binding phase-outs. The Multilateral Fund was created in 1990. Kigali 2016 phases down HFCs.
• The Antarctic ozone hole forms every spring (September-October), because very cold polar clouds speed up ozone loss.
• Ozone recovery to 1980 levels: global ~2040, Arctic ~2045, Antarctic ~2066 [5].
• India's HFC steps: freeze 2028, then 10% (2032), 20% (2037), 30% (2042) and 85% (2047) [2].

Mains Points

• Montreal as a model for climate diplomacy:
• It worked because substitutes for ODS were available, there was a dedicated fund, developing countries got delayed timelines, and every country ratified it.
• It also avoided about 0.5°C of warming [4].

• Climate deals do not yet have an equally credible package of finance and technology. This is a lesson for CBDR debates under the Paris framework.

• Linked problems, linked solutions:

• The HFCs that replaced CFCs solved the ozone problem but worsened the climate problem.

• This shows that environmental policy must be integrated. Kigali corrected the gap, which fits SDG 13 (Climate Action) and the Brundtland idea of sustainable development.

• Cooling as a development need:

• India's demand for cooling will rise with heat waves and the growth of cities.
• ICAP links energy efficiency, control of refrigerants and heat-related health [3].
• The trade-off is that HFC cuts must not make cooling unaffordable for poor households [3][2].

Related concepts

• Global warming
• Greenhouse gases
• Carbon budget
• Chlorofluorocarbons

Read more

• Global environmental issues: global warming, greenhouse gases and ozone depletion