Ozone depletion

Thinning of the stratospheric ozone layer, its causes, effects and the legal response

In one minute

The ozone layer is a thin shield of gas high in the atmosphere that blocks most of the Sun's harmful ultraviolet rays. Ozone depletion is the thinning of that shield.

It is caused mainly by man-made chemicals such as CFCs and halons. The world answered with the Montreal Protocol. Exams ask for causes, effects and this legal response.

Exam focus

Frequency: Frequently asked
Usually asked as: Both (long answer and short answer)

Legal provision

Vienna Convention for the Protection of the Ozone Layer: adopted on 22 March 1985, in force from 22 September 1988.
Montreal Protocol on Substances that Deplete the Ozone Layer: concluded on 16 September 1987, in force from 1 January 1989.
Ozone Depleting Substances (Regulation and Control) Rules, 2000: made under the Environment (Protection) Act, 1986 (Gazette notification S.O. 670(E) of 19 July 2000), to regulate and phase out such substances in India.
Section 3(1), Environment (Protection) Act, 1986: the source of the Central Government's power to take measures to prevent and control pollution.

Meaning and definition

Ozone depletion is the thinning of the ozone layer in the stratosphere, caused by the breakdown of ozone (O₃) molecules. The layer lies roughly 10 to 50 kilometres above the Earth's surface. It absorbs most of the Sun's harmful ultraviolet radiation.

How a CFC destroys ozoneHow to read this: follow the boxes from top to bottom. Each step leads to the next. The last box is the result for people and wildlife.

1. A CFC leaks from an old refrigerator or air conditioner.
2. The gas drifts up to the stratosphere.
3. Ultraviolet rays break the CFC and free chlorine atoms.
4. One chlorine atom destroys many ozone molecules.
5. ResultThe layer thins and more ultraviolet rays reach the ground.

Detailed explanation

Step 1: causes

Chlorofluorocarbons (CFCs): once common in refrigerators, air conditioners, solvents and aerosol sprays. In the stratosphere they release chlorine.
Halons: used in fire extinguishers. They release bromine, which destroys ozone even more strongly than chlorine.
Other ozone-depleting substances: carbon tetrachloride, methyl chloroform, methyl bromide and some solvents.

Step 2: effects

More ultraviolet radiation raises the risk of skin cancer and cataracts and weakens the immune system. It harms plankton, which sit at the base of the ocean food chain. It also reduces the yield of some crops.

Example. A fishing community on the Andhra coast depends on a fish stock that feeds on plankton. If extra ultraviolet rays reduce the plankton, the catch can fall, and the families who live by it lose income.

Step 3: the international response

The Vienna Convention of 1985 started international co-operation on the ozone layer. The Montreal Protocol of 1987 made it binding by setting limits on the production and use of the harmful chemicals and phasing them out. It is widely regarded as a successful treaty, since CFC use fell sharply after its limits applied.

Step 4: the Indian response

India acts through the Ozone Depleting Substances (Regulation and Control) Rules, 2000, made under the Environment (Protection) Act, 1986. The Rules regulate the production, sale and use of such substances and aim at their phase-out. Breach of the Act or its rules attracts a penalty under section 15, from ten thousand rupees up to fifteen lakh rupees, with a further ten thousand rupees for each day the contravention continues.

Step 5: the link with global warming

Many ozone-depleting substances, including CFCs, are also strong heat-trapping gases. So one chemical can add to both ozone depletion and global warming, but the two problems are different.

Don't confuse: ozone depletion and global warming

Point	Ozone depletion	Global warming
What happens	The ozone layer thins	The Earth's average surface temperature rises
Main cause	CFCs, halons and similar chemicals	Greenhouse gases such as carbon dioxide and methane
Main harm	More ultraviolet rays reach the ground	Heat, melting ice, rising seas, extreme weather
Main treaty	Montreal Protocol, 1987	UNFCCC, Kyoto Protocol, Paris Agreement

Inside the concept. A leaking old refrigerant destroys ozone in the stratosphere, and a farmer in a high-ultraviolet region sees more crop damage.

Just outside it. A coal power plant releases carbon dioxide. That gas does not thin the ozone layer. It adds to global warming.

Common mistakes

Saying the ozone hole causes global warming. They are two different problems with an overlap in some chemicals.
Putting the ozone layer in the troposphere. It is in the stratosphere.
Mixing up the Montreal Protocol (ozone) with the Kyoto Protocol (climate).
Stating that ozone protects only humans. It protects plants, marine life and wildlife too.

Apply it

Problem

A cold-storage owner in Vijayawada keeps using an old refrigerant that is a controlled ozone-depleting substance. A neighbour asks whether any Indian law can stop this.

Issue. Is the use of such a substance regulated in India?

Rule. The Ozone Depleting Substances (Regulation and Control) Rules, 2000 were made under the Environment (Protection) Act, 1986 to regulate and phase out these substances.

Application. The refrigerant is a controlled substance. Its use is subject to the Rules and to the phase-out under the Montreal Protocol.

Conclusion. The neighbour can give notice of not less than sixty days under section 19 and then complain to the court. The owner risks a penalty for breach of the Rules.

Leading case laws

No case on the cases list of the syllabus turns on ozone depletion. The law here rests on the treaties and the 2000 Rules.

How to write this answer in the exam

5-mark answer

Meaning: thinning of the stratospheric ozone layer.
Causes: CFCs, halons.
Effects on health and ecosystems.
Montreal Protocol, 1987.

10-mark answer

Meaning and position of the ozone layer.
Causes, with the chemicals named.
Effects on people, marine life and crops.
Vienna Convention and Montreal Protocol.
Indian Rules of 2000 under the 1986 Act.
Link and difference with global warming.

Key points to remember

Ozone layer: stratosphere, about 10 to 50 km above the surface.
Causes: CFCs, halons, carbon tetrachloride, methyl chloroform, methyl bromide.
Vienna Convention: 1985. Montreal Protocol: 1987, in force 1989.
India: Ozone Depleting Substances (Regulation and Control) Rules, 2000.
Many such substances are also heat-trapping gases, but ozone depletion is not global warming.

Quick self-test

1. In which layer is the ozone layer?

The stratosphere.

2. Name the treaty of 1987 on ozone-depleting substances.

The Montreal Protocol on Substances that Deplete the Ozone Layer.

3. Under which Act were India's Rules of 2000 made?

The Environment (Protection) Act, 1986.