EconomicsCBSE Class 12 · Environment and Sustainable Development

Functions of the Environment, Global Warming and Ozone Depletion (Class 12)

Updated 17 October 2026 · Fact-checked

The environment supplies resources, assimilates waste, sustains life and provides aesthetic services. It performs these only if resources are extracted no faster than they regenerate and waste stays within its absorptive capacity. When these limits are crossed, an environmental crisis follows, seen in global warming and ozone depletion.

Before industrialisation supply exceeded demand; after it, demand crossed the environment's capacity, causing crisis in its four functions.

Illustration drawn for QuestionBuddy.

Understand Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion

Environment. The totality of all resources: biotic elements (plants, animals, birds, forests, fisheries) and abiotic elements (air, water, land, rocks, sunlight).

Four functions.
1. Supplies resources: renewable resources (trees, fish) can be used without exhaustion if used carefully; non-renewable resources (fossil fuels) are exhausted with use.
2. Assimilates waste: absorbs and breaks down wastes.
3. Sustains life: provides genetic diversity and biodiversity.
4. Provides aesthetic services: scenery and enjoyment.

Carrying capacity and absorptive capacity. The environment can perform its functions only if (i) resources are extracted no faster than they regenerate, and (ii) wastes are within its absorptive capacity (its ability to absorb degradation). If these limits are crossed, the environment cannot sustain life: an environmental crisis.

Why the problem is recent. Earlier, with a small population and before industrialisation, the supply of environmental resources and services was greater than demand. With population growth and the Industrial Revolution, demand overtook regeneration and absorptive capacity: a reversal of the supply-demand relationship.

Costs. Polluted or dried-up rivers make water an economic good; exhausted resources force spending on research for substitutes; poor air and water raise health costs; global problems add to government commitments. Hence the opportunity cost of environmental damage is high.

Global warming. The slow rise in the mean temperature of the air near the earth's surface, caused by more greenhouse gases since the Industrial Revolution, largely human-induced. NCERT: since 1750, carbon dioxide has risen 31% and methane 149% above pre-industrial levels; over the past century temperature rose 0.6 degrees Celsius and sea level by several inches.

Causes: burning coal and petroleum (carbon dioxide, methane, nitrous oxide, ozone), deforestation, methane from animal waste and more cattle.
Effects: melting polar ice, rising sea level and coastal flooding; disruption of snow-melt water supplies; extinction of species; more tropical storms and diseases.
Response: the Kyoto conference (1997) produced an agreement calling on industrialised nations to cut emissions.

Ozone depletion. The reduction of ozone in the stratosphere, caused by chlorine and bromine compounds from chlorofluorocarbons (CFCs) (air-conditioners, refrigerators, aerosol propellants) and halons (fire extinguishers). More ultraviolet radiation reaches the earth, linked to skin cancer, lower phytoplankton production and effects on plants. NCERT notes a reduction of about 5% in the ozone layer from 1979 to 1990. The Montreal Protocol banned CFCs and other ozone-depleting chemicals.

Neighbouring topics. India's environmental state, sustainable development and strategies have their own page.

Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion: key facts

Sustainable extraction (renewable): Rate of extraction <= rate of regeneration; Otherwise the stock falls.
Waste condition: Waste generated <= absorptive capacity of the environment; Excess waste = pollution/crisis.
Percentage rise over pre-industrial level: New level = old level x (1 + rise/100); Use NCERT rises of 31% (CO2) and 149% (methane).
Four functions: Supplies resources
Assimilates waste
Sustains life
Provides aesthetic services; Mnemonic S-A-S-A.

How to answer Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion questions

Questions ask for functions, the logic of carrying capacity, causes and effects of global warming and ozone depletion, and sometimes simple stock-flow or percentage sums.

1List the four functions with one example each.
2State the two conditions of carrying capacity, then explain what an environmental crisis is.
3For global warming give causes (greenhouse gases, fossil fuels, deforestation), effects and the Kyoto agreement.
4For ozone give CFCs and halons, the UV effects and the Montreal Protocol.
5For sums, compare extraction with regeneration or waste with absorptive capacity, then state the consequence.

Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Extraction versus regeneration

Suppose a lake has 50,000 tonnes of fish that regenerate by 12% a year, and local boats catch 8,000 tonnes a year.

Is the fishing sustainable?

Try it first, then show the solutionSolution

Regeneration = 12% of 50,000 = 6,000 tonnes a year.
Catch 8,000 > regeneration 6,000, so the stock falls by 2,000 tonnes in a year.
Next year, a smaller stock regenerates even less.

Answer: Not sustainable: the catch exceeds regeneration by 2,000 tonnes, so the stock declines. Fishing should be cut to at most 6,000 tonnes.

Memory hook: Take no more than nature grows back.

Absorptive capacity

Imagine a small river that can break down 500 tonnes of organic waste a year. Local industries and households now release 650 tonnes.

What happens and by how much is the limit exceeded?

Try it first, then show the solutionSolution

Excess waste = 650 - 500 = 150 tonnes, i.e. 30% above capacity.
The river cannot assimilate it, so water quality falls and diseases rise.

Answer: The river's absorptive capacity is exceeded by 150 tonnes (30%), leading to pollution and costs to health and cleaning.

Memory hook: A river is a sink, not a bottomless one.

Tricks to remember Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion

Short memory aids. Say each one aloud once, then use it on a question the same day.

S-A-S-A
Supplies, Assimilates, Sustains, Aesthetic: four functions.
Use it when: Functions of environment.
Two limits
Extract slower than regrowth; dump less than absorption.
Use it when: Carrying capacity.
CFC is the ozone killer, CO2 the heater
Global warming: greenhouse gases; ozone depletion: CFCs and halons.
Use it when: Separating the two problems.

Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Function of the environment · 1 mark · MCQBoard level

When a river dilutes and breaks down the wastes released into it, the environment is performing the function of:
(a) supplying resources
(b) assimilating waste
(c) sustaining life
(d) providing aesthetic services

Try it first, then show the solutionSolution

Absorbing and breaking down waste is assimilation.

Answer: (b) assimilating waste

Example 2: Environmental crisis · 3 marks · Short answerBoard level

Explain how an environmental crisis arises. Why is it a recent problem? (3 marks)

Try it first, then show the solutionSolution

Two limits: extraction vs regeneration, waste vs absorptive capacity.
Earlier supply exceeded demand; now demand exceeds supply.

Answer: The environment can function only if resources are extracted no faster than they regenerate and wastes stay within absorptive capacity. When these limits are crossed, it cannot sustain life, which is an environmental crisis. It is recent because population growth and industrialisation made demand for environmental resources exceed their regeneration and absorptive capacity, reversing the earlier surplus of supply.

Example 3: Sustainable fishing quota · 4 marks · Short answerHarder board level

Suppose a fishery has a stock of 80,000 tonnes with a regeneration rate of 10% a year. Boats catch 11,000 tonnes in year 1. (i) Find regeneration in year 1. (ii) Find the stock at the start of year 2 (stock - catch + regeneration). (iii) Find the maximum sustainable catch in year 2 at that stock. (4 marks)

Try it first, then show the solutionSolution

(i) Regeneration = 10% of 80,000 = 8,000 tonnes.
(ii) Stock in year 2 = 80,000 - 11,000 + 8,000 = 77,000 tonnes.
(iii) Sustainable catch = 10% of 77,000 = 7,700 tonnes.

Answer: Regeneration 8,000 tonnes; year-2 stock 77,000 tonnes; maximum sustainable catch in year 2 is 7,700 tonnes. Over-fishing (11,000 > 8,000) shrinks the stock and later sustainable yield.

Example 4: Greenhouse gases · 5 marks · Short answerHarder board level

NCERT says that since 1750 carbon dioxide has risen 31% and methane 149%. Suppose the pre-industrial levels were 280 units for carbon dioxide and 700 units for methane (assumed figures). Find the present levels and the increases in units. Name two causes and two effects of global warming. (5 marks)

Try it first, then show the solutionSolution

CO2 now = 280 x 1.31 = 366.8 units; increase = 86.8 units.
Methane now = 700 x 2.49 = 1,743 units; increase = 1,043 units.
Causes: burning fossil fuels; deforestation (also methane from cattle).
Effects: melting ice and rising sea level; more frequent storms and tropical diseases.

Answer: CO2 about 366.8 units (+86.8); methane 1,743 units (+1,043) on the assumed base. Causes include fossil fuel burning and deforestation; effects include rising sea level and extreme storms.

Example 5: Policy mix for a coastal city · 5 marks · Long answerHOTS / competency

Suppose a coastal city faces higher sea level, hotter summers and rising skin problems among its residents, and its industries use CFC-based refrigerants. Explain which global environmental problems these indicate, link each effect to its cause, and suggest two measures. (5 marks)

Try it first, then show the solutionSolution

Higher sea level and hotter summers: global warming from greenhouse gas build-up.
More skin problems: ozone depletion raising ultraviolet radiation.
CFC-based refrigerants are ozone-depleting; the Montreal Protocol banned CFCs.
Measures: switch to non-ozone-depleting refrigerants; cut fossil fuel use by shifting to wind and solar power; protect forests and mangroves.

Answer: Global warming explains the sea-level and heat effects; ozone depletion explains the skin problems. Replace CFC refrigerants, adopt clean energy and protect coastal vegetation.

Where students lose marks in Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion

The slips examiners see most often, and what to write instead.

Mistake: Confusing global warming with ozone depletion
Both are atmospheric.
Wrong working
CFCs cause global warming by melting ice.
Right working
Greenhouse gases cause global warming; CFCs and halons deplete the ozone layer.
Do this: Match gas to problem.
Usually costs: 1 to 2 marks.
Mistake: Writing only three functions of the environment
Forgetting aesthetic services.
Wrong working
Supplies resources, assimilates waste, sustains life.
Right working
Four functions: also provides aesthetic services.
Do this: S-A-S-A.
Usually costs: 1 mark.
Mistake: Adding the percentage instead of multiplying
Misreading '31% above'.
Wrong working
CO2 now = 280 + 31 = 311.
Right working
CO2 now = 280 x 1.31 = 366.8.
Do this: Level x (1 + rise/100).
Usually costs: 1 mark.

Exam tips

Define carrying capacity with both conditions, extraction and waste.
Quote NCERT figures with the right unit: 31%, 149%, 0.6 degrees Celsius, about 5% ozone reduction (1979-90).
In 'suggest measures' answers, link each measure to a cause.

Practice questions on Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The Montreal Protocol is related to:
(a) reducing carbon dioxide emissions by industrialised nations
(b) banning CFCs and other ozone-depleting chemicals
(c) protecting wildlife
(d) sharing river water
Hint
Ozone layer.
Answer
(b) banning CFCs and other ozone-depleting chemicals
Q2 · 2 marks · Short answerBoard level
Give one example each of a renewable and a non-renewable resource, and explain why over-use of the renewable one can make it behave like the non-renewable one. (2 marks)
Hint
Extraction faster than regeneration.
Answer
Fish (renewable) and coal or petroleum (non-renewable). A renewable resource regenerates only if extraction stays below its regeneration rate; if it is extracted faster, the stock falls and may be exhausted, as non-renewable resources are.
Q3 · 3 marks · Short answerHarder board level
A forest regenerates 9,000 tonnes of wood a year (assumed). Villagers collect 6,500 tonnes for fuel and a contractor fells another 4,000 tonnes. Find total extraction, the shortfall against regeneration, and say what happens to the forest stock over 5 years if this continues. (3 marks)
Hint
Total extraction first.
Answer
Total extraction = 6,500 + 4,000 = 10,500 tonnes. Shortfall = 10,500 - 9,000 = 1,500 tonnes a year. In 5 years the stock falls by 1,500 x 5 = 7,500 tonnes (ignoring changes in regeneration). Extraction exceeds regeneration, so deforestation and loss of carrying capacity follow.
Q4 · 4 marks · Short answerHarder board level
Explain four effects of global warming and state what the Kyoto conference (1997) called on industrialised nations to do. (4 marks)
Hint
NCERT's list of effects; Kyoto 1997.
Answer
Effects: melting polar ice and rising sea level causing coastal flooding; disrupted supplies of drinking water from snow melt; extinction of some species; more frequent tropical storms and tropical diseases. The Kyoto conference (1997) produced an agreement calling on industrialised nations to cut their greenhouse gas emissions.
Q5 · 1 mark · Assertion-reasonHOTS / competency
Assertion (A): Environmental problems have become serious in recent times.
Reason (R): Population growth and industrialisation made demand for environmental resources exceed their regeneration and absorptive capacity.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Supply-demand reversal.
Answer
(a) Both A and R are true and R is the correct explanation of A.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Name the four functions of the environment.Show answer
Supplies resources, assimilates waste, sustains life, provides aesthetic services.
2.What is absorptive capacity?Show answer
The environment's ability to absorb degradation and waste.
3.Which chemicals deplete the ozone layer?Show answer
CFCs and halons.
4.In which year was the Kyoto conference on greenhouse gases held?Show answer
1997.
5.Which greenhouse gas has shown the larger percentage rise since 1750, carbon dioxide or methane?Show answer
Methane (149%, against 31% for carbon dioxide).

Functions of the Environment, Carrying Capacity, Global Warming and Ozone Depletion: frequently asked questions

What is the difference between global warming and ozone depletion?

Global warming is a rise in the earth's mean temperature from greenhouse gases; ozone depletion is thinning of the stratospheric ozone layer by CFCs and halons, letting in more ultraviolet radiation.

What is an environmental crisis?

A situation in which resource extraction and waste exceed the environment's regeneration and absorptive capacity, so it cannot sustain life.

Why is the opportunity cost of environmental damage high?

Money spent on cleaning, health care and finding substitutes could have been used elsewhere.

Are the quantities in the sums actual data?

No. Stocks, catches and base levels are assumed for practice; the 31%, 149%, 0.6 degrees and 5% figures are NCERT's.