Environment and Sustainable Development — Class 12 Economics Notes & Practice

What You’ll Learn

Your Game Plan

Chapters like this one go wrong when students read them like a story. Work through it like this instead:

1. Read the first five sections in one sitting. They build a single idea — the environment as an economic asset. Do not break them up.
2. Draw the two flow diagrams yourself on rough paper, from memory, before moving on. If you can draw them, you understand them.
3. Do the global warming and ozone sections carefully and separately. These are the two topics students mix up most, and mixing them up costs marks in almost every board sitting.
4. Cover the sustainable development strategies last, and learn them as a list of six with one line of explanation each. Lists are what six-mark questions want.
5. Attempt the worksheet with your book closed. Write the answer out in full sentences, then open the reveal and mark yourself.
6. Come back after two days and re-read only the sticky notes. That second pass is what moves it into long-term memory.

What “Environment” Really Means in Economics

Let us start with the word itself, because the everyday meaning and the economics meaning are not quite the same.

In ordinary conversation, “environment” usually means nature — trees, rivers, clean air, animals. In economics the word is wider. Environment means the total sum of everything that surrounds us, living and non-living. That includes the biotic things (plants, animals, birds, micro-organisms, human beings themselves) and the abiotic things (air, water, soil, rocks, sunlight, minerals underground).

So a coal seam a kilometre below Jharkhand is part of the environment. So is the monsoon. So is the population of earthworms in a field. So, for that matter, is the city you live in, because the buildings and roads are part of what surrounds you. It is a genuinely all-inclusive word.

Why does an economics textbook care? Because economics is the study of how we use scarce resources, and the environment is the ultimate source of every resource we have ever used. Every rupee of output in the country began life as something taken out of the environment — iron ore, cotton, water, sunlight, land to stand a factory on. And every rupee of output ends life as something put back into the environment — smoke, effluent, scrap, packaging.

Here is the picture I want you to hold. Think of the environment as a very generous but very old relative who gives you pocket money every month and quietly cleans your room afterwards. For years it seems free and endless. It is neither. There is a limit to how much pocket money is available, and there is a limit to how much mess can be cleaned up. This chapter is about what happens when we cross both limits at once.

Biotic and Abiotic — A Quick Sorting Exercise

You will occasionally be asked to classify. The line is simple: if it is alive or was alive, it is biotic; if it never was, it is abiotic.

• Biotic: a mango tree, a fish, bacteria in the soil, a farmer, a flock of migratory birds.
• Abiotic: river water, sunlight, bauxite, the air in your room, a mountain, the temperature.

Do not move on until the word “environment” feels bigger in your head than it did five minutes ago. That widening is the whole point of this first section.

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The Four Functions of the Environment

Now to the heart of the chapter. Economists say the environment performs four functions. If you learn nothing else from this chapter, learn these four, because almost every question can be traced back to them.

I will give you the list first and then walk through each one slowly.

Function 1 — Supply of Resources

Everything a factory uses arrives, ultimately, from the environment. Steel begins as iron ore. Cloth begins as cotton or as petroleum. Electricity begins as coal, falling water, wind or sunlight. A cup of tea begins as a tea bush, water, and the gas that boiled it.

The economics word for these is resources — things drawn from the environment that are useful in production or consumption. Some renew themselves; some do not. We will separate those two carefully in a moment because that distinction drives the whole chapter.

Function 2 — Assimilation of Waste

This one gets forgotten, and it is the one that matters most for the second half of the chapter. The environment does not only hand things out. It also takes things back.

When a village throws vegetable peel onto a compost heap, soil organisms break it down and within weeks it is manure. When a small amount of organic waste enters a river, bacteria digest it and the river runs clean again a few kilometres downstream. This is called assimilation of waste — the environment absorbing our by-products and neutralising them.

Think of it as nature’s dustbin service. And like every dustbin service, it has a capacity. One family’s vegetable peel disappears into the soil; the daily waste of a city of ten million does not.

Function 3 — Sustaining Life

The environment supports life through what is called genetic and biodiversity — the enormous variety of species and the genetic variety inside each species. This is not decoration. It is load-bearing.

Bees and other insects pollinate a large share of the crops we eat. Earthworms and soil microbes keep soil fertile. Mangroves and coral reefs shelter the fish that coastal families sell. Forests hold soil in place on hillsides so that it does not slide into rivers. Remove enough of these quiet workers and agriculture itself starts to wobble.

The economic point is that biodiversity is an input we never pay for and rarely notice until it fails.

Function 4 — Aesthetic Services

Finally, the environment provides beauty and enjoyment: a view of the hills, a clean beach, the sound of a river, a tree-lined street. These are called aesthetic services.

It sounds like the soft one on the list, but it has hard money behind it. Tourism in Himachal Pradesh, Kerala, Goa, Sikkim and Rajasthan rests directly on the environment being pleasant to look at. When a hill station’s slopes are stripped bare or a beach fills with plastic, tourist arrivals fall and real incomes fall with them. Aesthetic services show up in the accounts.

Sit with Figure 1 for a minute before moving on. Notice that all four functions run simultaneously from the same environment — the river that supplies water is also the river that absorbs waste, sustains fish and looks beautiful. That is exactly why damaging it for one purpose damages the other three.

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Growth policy sits behind every environmental trade-off — revise Liberalisation, Privatisation and Globalisation notes.

How the Economy and the Environment Are Joined

Here is the single most useful picture in the chapter. Look at Figure 2 and notice what it is really saying: the economy is not beside the environment, it is inside it. Every economy is a machine that sits within nature, takes material in at one end and pushes material out at the other.

Follow the green arrow along the top. The environment hands over resources — ore, timber, water, fuel, land. Those resources go into the economy, where firms and households turn them into goods and services. That is production and consumption.

Now follow the coral arrow along the bottom. Nothing vanishes. Everything the economy consumes eventually comes back out as waste — exhaust gases, effluent, ash, scrap metal, food waste, old phones. That waste returns to the environment, which is expected to absorb it.

The Two Checks in the Middle

Look at the two notes in the middle of Figure 2. They are the questions that decide whether an economy is sustainable or not, and I want you to be able to state both from memory.

Check 1 (extraction): Is the rate at which we take resources out less than or equal to the rate at which nature can regenerate them?

Check 2 (waste): Is the volume of waste we generate less than or equal to the volume the environment can absorb and neutralise?

Answer yes to both and the economy can carry on for centuries. Answer no to either and you are, in plain language, spending your savings.

A Small Analogy That Makes It Click

Picture a family with a fixed monthly income and a house with one dustbin that the municipality empties once a week.

For years the family spends less than it earns and produces less rubbish than one bin holds. Life is comfortable and nobody thinks about limits. Then the family starts spending more than it earns — the savings begin to fall. At the same time it starts producing three bins of rubbish a week — and the extra piles up outside the door.

Nothing dramatic happens on day one. That is the danger. The savings fall slowly and the rubbish accumulates slowly, and by the time anyone notices, both problems are expensive to fix. An economy that exceeds the two checks behaves exactly like that family.

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Carrying Capacity: The Environment’s Quiet Limit

You have now met the two checks. The idea that sits behind both of them has a name: carrying capacity.

Carrying capacity means the environment’s ability to keep doing its job indefinitely — to keep supplying resources and to keep absorbing waste — without itself being damaged. It is a limit, and it is a limit on both sides of the flow.

Why Both Conditions, Not One?

Students often learn only the first condition, and it costs them. Think about why both are needed.

An economy could, in theory, cut only as many trees as grow back each year — passing check one perfectly — while still choking its rivers with untreated chemicals. It would be depleting nothing but poisoning everything. Equally, an economy could produce almost no waste while mining out its entire mineral wealth in thirty years.

Sustainability needs both taps turned to the right setting: the one that lets resources out, and the one that lets waste back in.

The Village Pond — A Picture Worth Keeping

Here is the example I find works best. Imagine a village pond.

The pond is fed by rain and springs, so it refills itself. Families draw water for cooking and for cattle. They also wash clothes at the edge, and a small amount of soap goes in. For decades this works: the pond refills as fast as it is drawn down, and the small quantity of soap and organic matter is broken down by the pond’s own bacteria and plants. The pond is within its carrying capacity.

Now the village grows. Twice as much water is drawn, more than the springs can replace, so the level falls each year. At the same time a small workshop starts rinsing its equipment there. The bacteria cannot cope. The water turns green, then foul.

Notice the pond did not fail because people were wicked. It failed because the demands on it grew past a limit that nobody could see and nobody had measured. That invisibility is the real problem with carrying capacity.

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Rural livelihoods depend directly on these resources; see our Rural Development chapter notes.

Renewable and Non-Renewable Resources

Before we can talk about running out of things, we have to separate the things that can run out from the things that cannot — at least not in the same way.

The Subtle Point Everyone Misses

Here is something worth pausing on, because it turns up in application questions.

Renewable does not mean inexhaustible. A forest is renewable, but a forest cut faster than it regrows disappears. Groundwater is renewable, but an aquifer pumped faster than the monsoon recharges it falls year after year until the borewell runs dry. Fish stocks are renewable, and fisheries around the world have still collapsed.

So the word “renewable” is a statement about the mechanism, not a guarantee about the outcome. The outcome depends entirely on whether we respect check one.

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Why Environmental Problems Arise: The Reversal of Supply and Demand

We now have all the pieces. Let us put them together and answer the question the chapter is really built around: why did environmental problems appear at all?

For most of human history they did not — not at any serious scale. Something changed. Understanding what changed is worth several marks, and it is genuinely interesting.

The World Before the Problem

In the early stages of civilisation, the demands humans placed on the environment were small relative to what the environment could provide and absorb.

Population was low. Production was mostly agricultural and local. The waste generated was overwhelmingly organic — crop residue, animal dung, food scraps, human waste — and organic waste is exactly what soil bacteria are good at digesting. The environment’s supply comfortably exceeded demand, and its absorptive capacity comfortably exceeded the waste load.

In economic language: for both resources and waste, supply exceeded demand. There was no scarcity, so there was no economic problem. Environmental resources were free goods — available in quantities greater than anyone wanted, so nobody had to pay for them or ration them.

What Changed

Then came a combination of forces, and they all pushed the same way:

• Population growth. More people means more resources drawn and more waste produced, from the same fixed environment.
• Industrialisation. Factories consume raw materials and energy on a scale no farming society ever did, and they emit at that same scale.
• Urbanisation. Concentrating millions of people in one city concentrates the waste load into one place, which overwhelms local absorptive capacity even when the national average looks fine.
• Intensive agriculture. Higher yields came partly from chemical fertilisers, pesticides and heavy irrigation — each of which loads the soil and water systems.
• New kinds of waste. This is the one students forget. Pre-industrial waste was organic and biodegradable. Modern waste includes plastics, heavy metals, synthetic chemicals and radioactive material — substances the environment has no biological machinery to break down at all.

This is the sentence that earns marks: environmental resources have changed from free goods into economic goods. A free good is one whose supply exceeds demand at zero price. An economic good is scarce and therefore has an opportunity cost. Clean air over an industrial city is no longer free in the economic sense — getting it costs real resources, and using it up denies it to somebody else.

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The Environmental Opportunity Cost of Our Growth Path

Now that environmental resources are scarce, they behave like every other scarce thing in economics — using them for one purpose means giving up another. That sacrifice has a name you already know from the very first weeks of Class 11: opportunity cost.

The opportunity cost of an environmental decision is the value of the next best alternative that we gave up. And the striking thing about the growth path most countries have followed is how large that forgone alternative has turned out to be.

The Three Bills That Arrive Later

When growth damages the environment, three separate bills eventually land on the table. It helps to name them because they make natural sub-headings in a long answer.

1. The health bill. Air and water pollution cause respiratory illness, waterborne disease and reduced life expectancy. Treating those illnesses uses doctors, hospitals and medicines — resources that could have built schools or roads. Illness also means working days lost, which lowers output directly.
2. The clean-up bill. Cleaning a polluted river, restoring degraded farmland or treating contaminated groundwater is expensive and slow. Prevention would have cost a fraction of what restoration costs.
3. The substitution bill. When a non-renewable resource nears exhaustion, an economy must spend heavily on research, imports and new infrastructure to find and switch to alternatives — spending it would not otherwise have needed to do.

Add to those three a fourth that is harder to measure but very real: the loss of the environment’s own services — the fertile soil that no longer holds, the fishery that no longer yields, the hillside that no longer stops the landslide.

Why the Bills Get Ignored at the Time

Here is the piece of economics underneath it all. Environmental damage is a classic externality — a cost imposed on people who are not party to the transaction.

When a factory saves money by not treating its effluent, the saving appears in the factory’s accounts. The cost appears in the illness of families downstream, who never signed a contract with the factory and receive no compensation. Because the cost falls outside the market transaction, the market price of the good does not reflect it, and society ends up producing more of that good than is genuinely worthwhile.

That is why environmental problems rarely fix themselves and why government action, regulation and public investment appear in every answer about solutions.

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India’s First Big Problem: Land Degradation

The syllabus asks you to know the two major environmental issues India faces. They are land degradation and pollution (of air and water). We will take one section each, starting with land.

India’s position is genuinely difficult, and it helps to say why in one sentence: India supports a very large share of the world’s people and livestock on a much smaller share of the world’s land. That arithmetic puts intense and continuous pressure on every hectare.

What Land Degradation Means

Land degradation means a decline in the quality and productive capacity of land — loss of topsoil, loss of fertility, waterlogging, salinity, or the land turning to scrub and desert. Degraded land does not vanish; it simply produces less and less, and in the worst cases produces nothing at all.

For a country where a large part of the population depends on agriculture for a living, this is not an aesthetic issue. It is an income issue.

The Main Causes in India

These are the ones to learn. I have grouped them so they are easier to remember — three about pressure on the land, three about how it is farmed, and two about what is dumped on it.

• Loss of vegetation cover and deforestation. Once tree and grass cover goes, rain strikes bare soil directly and washes the fertile topsoil away.
• Overgrazing. Livestock numbers beyond what the pasture can support strip the grass cover and compact the soil, leaving it open to erosion.
• Encroachment into forests and shifting cultivation. Cultivating fragile forest and hill land clears the cover that was holding the soil together.
• Improper crop rotation and over-cropping. Growing the same demanding crop season after season without rotation or rest strips the soil of specific nutrients.
• Excessive use of chemical fertilisers and pesticides. Heavy chemical use can damage soil structure and soil organisms, so that ever more fertiliser is needed for the same yield.
• Faulty irrigation and unplanned canal irrigation. Over-watering raises the water table and causes waterlogging; when that water evaporates it leaves salts behind, causing salinity and alkalinity. Both make land progressively less fertile.
• Extraction of groundwater beyond recharge. Falling water tables dry out the soil profile and, in coastal areas, can draw in saline water.
• Improper planning of industrial and mining activity, and dumping of untreated waste. Mining spoil, industrial effluent and solid waste degrade land directly and often permanently.

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India’s Second Big Problem: Air and Water Pollution

The second major issue is pollution — principally of air and water. Pollution is the waste-assimilation function failing: we are putting more into the environment’s sinks than those sinks can neutralise.

Air Pollution

Where does it come from? Broadly three places, and it is worth being able to name all three because questions often ask for sources.

• Vehicular emissions. The number of vehicles on Indian roads has grown enormously, and older or poorly maintained vehicles emit disproportionately. In dense cities this is often the single largest contributor at street level.
• Industry and thermal power. Burning coal for electricity and running industrial processes releases particulate matter, sulphur dioxide and oxides of nitrogen.
• Domestic and other sources. Burning firewood, dung cakes and crop residue — including the burning of crop stubble after harvest in parts of north India — along with construction dust and waste burning.

The consequences run straight into the economy. Respiratory and cardiac illness raises health spending and lowers the number of working days. Reduced visibility disrupts transport. Airborne pollutants damage crops and corrode buildings and monuments.

There is also a form of air pollution that is easy to overlook because it happens indoors. In households that still cook on firewood, dung cakes or crop residue over an open stove, the smoke inside the kitchen is a serious health hazard, and it falls hardest on the women and small children who spend the most time there. Remember this point — it is exactly why LPG and gobar gas appear later as sustainable-development strategies.

Water Pollution

Water pollution in India comes from three main streams too:

• Untreated municipal sewage. A large volume of domestic sewage from towns and cities still reaches rivers without adequate treatment. This is, by volume, the biggest single source of river pollution in India.
• Industrial effluent. Discharge from tanneries, textile dyeing units, chemical plants, paper mills, distilleries and metal-processing units, often containing chemicals and heavy metals that no bacteria can digest.
• Agricultural run-off. Fertiliser and pesticide residues washed off fields into streams, canals and groundwater.

The economic consequences are severe: waterborne disease, contaminated groundwater used for drinking, loss of fish stocks that people depend on for a living, and land damaged by irrigating with polluted water.

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Global Warming: The Mechanism, Step by Step

This section and the next are the two most commonly muddled topics in the whole chapter, so we are going to go slowly and get each one exactly right. Read this section, then read the next one, and only then read the comparison table. Do not shuffle them.

Let us build global warming from the ground up.

Step 1 — Energy Arrives From the Sun

The Sun sends energy to the Earth mostly as short-wavelength radiation, including visible light. Some of it is reflected straight back by clouds and bright surfaces such as ice. The rest passes through the atmosphere and is absorbed by the land and the oceans, which warm up.

Step 2 — The Earth Radiates Heat Back Out

A warm object radiates energy. The Earth’s surface, having absorbed sunlight, sends energy back outwards — but at a much longer wavelength. This outgoing energy is infrared radiation, which is what we experience as radiant heat.

If nothing stopped that outgoing infrared, it would escape to space and the Earth would settle at a very cold average temperature.

Step 3 — Greenhouse Gases Intercept the Outgoing Heat

Certain gases in the lower atmosphere — the troposphere — are transparent to incoming sunlight but very good at absorbing outgoing infrared. These are the greenhouse gases. The main ones are water vapour, carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and the industrial halocarbons including CFCs.

When these gases absorb outgoing infrared, they re-emit it in all directions — including back down towards the surface. Some of the heat that was on its way out is therefore returned. The lower atmosphere and the surface stay warmer than they otherwise would be. This is the greenhouse effect.

Step 4 — What Human Activity Added

The concentration of greenhouse gases has risen because of:

• Burning fossil fuels — coal, petroleum and natural gas — for electricity, industry and transport. This is the largest source of additional CO₂.
• Deforestation. Two effects at once: burning or decaying trees release stored carbon, and the forest that would have absorbed CO₂ in future is no longer there to do so.
• Agriculture and livestock. Cattle and other ruminants release methane during digestion, and flooded paddy fields are a significant methane source.
• Nitrogen fertilisers, which lead to emissions of nitrous oxide.
• Industrial processes and waste. Cement manufacture releases CO₂ chemically as well as through fuel use, and decomposing landfill waste releases methane.

Step 5 — The Consequences

A warmer atmosphere and ocean produce a chain of effects:

• Rising average global temperature.
• Melting of glaciers, ice sheets and snow cover, including the Himalayan glaciers that feed several of India’s major rivers.
• Rising sea levels, from two causes: water expands slightly as it warms, and land-based ice melts and adds water to the ocean. Low-lying coasts and island nations are threatened.
• More frequent and more intense extreme weather — heatwaves, heavy rainfall events, droughts and cyclones.
• Disruption to agriculture, through altered rainfall patterns, shifting growing seasons and heat stress on crops. For a country as monsoon-dependent as India, this is the most economically serious effect.
• Spread of vector-borne diseases as warmer areas become hospitable to the insects that carry them.
• Loss of biodiversity, as species cannot shift their ranges fast enough to keep up with a changing climate.

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Ozone Depletion: A Separate Problem With a Separate Cause

Now put global warming completely out of your mind for the next few minutes. This is a different problem, in a different layer of the atmosphere, caused by different substances, doing different damage. I mean that literally — almost nothing carries over.

What Ozone Is and Where It Sits

Ozone is a form of oxygen whose molecule has three oxygen atoms instead of the usual two. It is written O₃.

Most of the Earth’s ozone sits in the stratosphere, the layer of the atmosphere roughly 15 to 35 kilometres above the surface — well above the troposphere where weather and greenhouse warming happen. This concentration of ozone is called the ozone layer.

What the Ozone Layer Does For Us

The ozone layer absorbs most of the Sun’s harmful ultraviolet (UV) radiation before it reaches the surface. Think of it as the planet’s sunscreen. Ultraviolet is not heat — it is high-energy radiation that damages living tissue and DNA.

How It Gets Destroyed — The Chain Reaction

This is the part worth understanding properly, because the mechanism is genuinely elegant and it is also what the examiner is testing.

1. Human industry produced a family of very stable synthetic chemicals called chlorofluorocarbons (CFCs), used as refrigerants in refrigerators and air-conditioners, as propellants in aerosol sprays, as solvents and in making foam. Related substances include halons (in fire extinguishers), carbon tetrachloride and methyl bromide. Together these are called ozone-depleting substances.
2. Because they are so chemically stable, they are not broken down in the lower atmosphere. They simply drift upward over years and decades until they reach the stratosphere.
3. In the stratosphere the ultraviolet radiation is intense enough to break them apart, releasing free chlorine (or bromine) atoms.
4. A free chlorine atom reacts with an ozone molecule and destroys it — and then emerges from the reaction unchanged, ready to destroy another. It acts as a catalyst. This is why a small quantity of CFC does a disproportionately large amount of damage: one chlorine atom can go on to destroy a great many ozone molecules in a chain reaction.
5. The result is a thinning of the ozone layer. The most dramatic case is the seasonal severe thinning over Antarctica, popularly called the ozone hole — not literally a hole, but a region where ozone concentration falls very low each southern spring.

The Consequences

• Human health: higher incidence of skin cancer, cataracts and eye damage, and suppression of the immune system.
• Agriculture: reduced yields in UV-sensitive crops.
• Marine life: damage to phytoplankton, the microscopic organisms at the base of the entire ocean food chain — which matters for fisheries and therefore for coastal livelihoods.
• Materials: faster degradation of plastics, paints and other materials exposed to sunlight.

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Global Warming vs Ozone Depletion: Telling Them Apart

Now, and only now, let us put the two side by side. I am giving this its own section because the confusion between them is the single most common factual error in this chapter — and it appears in student answers, in guide books, and occasionally in classroom explanations too.

The One Genuine Connection

Having separated them firmly, honesty requires me to mention the one real link, because a sharp student will ask.

CFCs happen to be both. They are ozone-depleting substances and they are extremely potent greenhouse gases. So phasing them out under the Montreal Protocol helped on both fronts at once — it protected the ozone layer and it also avoided a considerable amount of warming. That is a genuine overlap.

But notice what the overlap is: one shared culprit, not one shared mechanism. The ozone hole still does not cause warming, and warming still does not cause the ozone hole. If you mention the CFC overlap in an answer, say it exactly that way and it will read as sophistication rather than confusion.

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The State of India’s Environment

Let us now look at India specifically. The picture is genuinely mixed, and I want to give you both halves of it, because a balanced answer reads far better than a purely gloomy one.

The Pressures

India’s environmental difficulty starts with a simple ratio. India supports a very large share of the world’s human and livestock population on a comparatively small share of the world’s land area. Every hectare therefore does a great deal of work, and rarely gets a rest.

On top of that sits rapid economic growth, rapid urbanisation and rising energy demand — all of which are desirable in themselves and all of which press on the environment.

• Land. ISRO’s Desertification and Land Degradation Atlas of India has reported that roughly 29.7 per cent of the country’s geographical area was undergoing land degradation in its 2018-19 assessment, up from about 28.8 per cent in the 2003-05 assessment — a slow but persistent worsening.
• Forests. According to the India State of Forest Report 2023 published by the Forest Survey of India, forest cover stood at about 21.76 per cent of the geographical area, with forest and tree cover together at about 25.17 per cent. Both figures have been broadly stable or very slightly rising in recent assessments, but they remain below the one-third of land area that India’s National Forest Policy has long held up as a goal.
• Air. Several Indian cities record air quality well below health-based guideline levels, particularly during the winter months in the northern plains. This is one of the country’s most visible environmental costs.
• Water. Groundwater tables are falling in several intensively irrigated regions, and a substantial part of urban sewage still reaches rivers without adequate treatment.

The Progress

Now the other half, which students almost never write and which lifts an answer noticeably.

• Energy transition. India has expanded non-fossil electricity generation capacity rapidly. Government statements and press releases indicate that non-fossil sources crossed 50 per cent of India’s total installed electricity generation capacity in mid-2025 — reaching this milestone about five years ahead of the target India had set under its Nationally Determined Contribution to the Paris Agreement.
• Climate commitments. At the COP26 conference in Glasgow in 2021, India announced a set of five climate commitments described as the Panchamrit. These included reaching 500 GW of non-fossil electricity capacity by 2030, meeting half of energy requirements from renewable sources by 2030, reducing the emissions intensity of GDP, reducing projected emissions, and achieving net-zero emissions by 2070.
• Cleaner transport fuels. The conversion of Delhi’s public transport fleet to CNG in the early 2000s, following orders of the Supreme Court in the M. C. Mehta case, remains the standard Indian example of a successful, targeted intervention on urban air pollution.
• Institutional framework. India has a body of environmental legislation and a system of pollution control boards at central and state level, alongside programmes for river cleaning, afforestation and renewable energy promotion.

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Sustainable Development: What the Word Actually Promises

We have spent a long time on the problem. Now the answer — and it is a genuinely hopeful idea, so let us treat it properly.

The phrase sustainable development came into wide use after the World Commission on Environment and Development, chaired by Gro Harlem Brundtland, published its report Our Common Future in 1987. The definition it offered has been quoted ever since.

What Sustainable Development Is Not

It is worth clearing away three misunderstandings, because each of them shows up in weak answers.

It is not anti-growth. The definition explicitly requires that present needs be met. A country where people go hungry is not practising sustainable development by leaving its coal in the ground. Sustainable development is about the manner of growth, not the absence of it.

It is not only about the environment. The idea covers economic and social sustainability too — growth that collapses after ten years, or that leaves most of the population behind, is not sustainable either.

It is not about never using non-renewable resources. That would be impossible. It is about using them efficiently, recycling where we can, and investing in substitutes so that when a resource does run low the economy has somewhere to go.

The Four Conditions, in Practical Terms

If you want a checklist for whether a development path is sustainable, this is a fair one:

1. Renewable resources are used no faster than they regenerate. Cut no more timber than grows back; catch no more fish than breed.
2. Non-renewable resources are used efficiently, and substitutes are developed. The stock will fall — the requirement is that we are ready before it runs out.
3. Waste generation stays within the environment’s absorptive capacity. Treat effluent; reduce, reuse and recycle; move to cleaner processes.
4. The stock of natural capital passed on is not reduced. The next generation should inherit an environment capable of supporting at least the standard of living we enjoy.

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For the planning era that shaped India’s resource use, read Indian Economy 1950-1990 explained.

Intergenerational Equity: Fairness Across Time

Sitting inside the definition of sustainable development is a moral and economic idea worth pulling out and naming, because questions ask about it directly: intergenerational equity.

The Inheritance Analogy

Here is the picture that makes it stick.

Imagine you inherit a farm from your grandparents. You are entitled to live off it — that is what it is for. You may take the harvest every year, and nobody would call you selfish for doing so.

But suppose that instead of harvesting, you sell the topsoil, cut down the orchard for timber and sell the tubewell. You will have a very good few years. Your children will inherit a patch of bare, unproductive ground.

The first behaviour is living off the income of the asset. The second is consuming the asset itself. Intergenerational equity says: live off the income, and hand on the asset intact.

That distinction — income versus capital — is the economics underneath the whole idea, and if you can express it in those words in an answer, it reads extremely well.

Why the Future Generation Needs Protecting

There is a hard-headed reason why this needs to be a stated principle rather than left to good intentions.

The future generation is not in the room. They cannot vote in today’s elections, they cannot bid in today’s markets, and they cannot sue over decisions taken now. Every ordinary economic mechanism we rely on to balance competing interests — prices, voting, contracts — systematically leaves them out.

So their interest has to be built in deliberately, through policy, regulation and public commitment. That is a large part of why the government has such a prominent role in every list of environmental solutions.

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Strategies for Sustainable Development: The Big Picture

This is the section that six-mark questions come from, so let us organise it properly.

The strategies fall into three natural groups, and grouping them makes them far easier to recall under exam pressure:

1. Change the source of energy — move from fossil fuels to non-conventional sources: solar, wind and mini-hydel.
2. Change the fuel people actually burn — LPG and gobar gas in rural kitchens, CNG in urban transport.
3. Change how we farm — use traditional and local knowledge, biocomposting and biopest control instead of heavy chemical inputs.

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Non-Conventional Energy: Solar, Wind and Mini-Hydel

India’s electricity has historically leaned heavily on conventional sources — coal, petroleum and natural gas. These are called conventional because they have long been the standard, and they share three problems: they are non-renewable, they pollute when burnt, and a large part of the oil and gas has to be imported.

Non-conventional sources — solar, wind, small hydro, biomass, geothermal, tidal — are renewable, far cleaner in use, and domestically available. India is unusually well placed for two of them in particular.

Solar Power and Photovoltaic Cells

India lies largely in the tropical belt and receives strong sunshine over most of its area for most of the year. That is a genuine natural advantage.

The key technology to name is the photovoltaic cell — a device that converts sunlight directly into electricity, with no burning, no moving parts and no emissions during operation. Panels of these cells can be installed at almost any scale: a single rooftop, a village mini-grid, or a very large solar park.

Why this matters especially for India: many remote settlements are expensive to reach with transmission lines. A decentralised solar installation can supply a hamlet without any grid connection at all — which is why solar is not only an environmental strategy but a rural development strategy.

Wind Power

Where the wind blows steadily — along parts of the western and southern coasts and across some open inland plains — windmills can turn turbines to generate electricity.

Once the structure is built, the fuel is free and permanent, and there is no combustion and no emission. The land between and beneath the turbines can usually continue to be farmed or grazed, so the land-use cost is much lower than it first appears.

Mini-Hydel Plants

This one is distinctively Indian and worth learning carefully, because it is a favourite in questions.

In hill regions there are many perennial streams carrying water down the slopes. A mini-hydel plant uses the energy of such a stream to turn a small turbine and generate electricity, and then returns the water to the stream for irrigation and other uses downstream.

The advantages are considerable and specific:

• They generate enough for a small local area — a village or a cluster of villages — without needing a national grid connection.
• They cause minimal environmental disturbance: no large dam, no large reservoir, no submergence of forest or farmland, and no displacement of people.
• The water is not consumed; it passes through and continues downstream, so irrigation is unaffected.
• They suit terrain where extending the main grid would be extremely expensive.

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Cleaner Fuels: LPG and Gobar Gas in Villages, CNG in Cities

The previous section was about where electricity comes from. This one is about the fuel people burn directly — in the kitchen and in the vehicle. Both matter enormously for air quality, and both are firmly on the syllabus.

LPG and Gobar Gas in Rural Areas

Start with the problem. In households that cook on firewood, dung cakes and crop residue over a traditional stove, two things go wrong at once.

First, indoor air pollution. The smoke from these fuels fills the kitchen, and it contains particulate matter and gases that cause respiratory illness and eye problems. The burden falls hardest on women, who do most of the cooking, and on the small children who are with them. This is one of the most serious and least visible health problems in rural India.

Second, pressure on forests and on soil. Collecting firewood contributes to the loss of tree cover. And burning dung as fuel means it is not being returned to the field as manure, which quietly lowers soil fertility — a real cost that nobody records anywhere.

There is a third cost that is easy to miss: the time spent collecting fuel, often several hours a week, usually by women and girls. Hours spent gathering firewood are hours not spent in school, in paid work or in rest.

The solutions.

• LPG (liquefied petroleum gas) supplied in cylinders burns far more cleanly than solid biomass, produces very little smoke, and cooks faster. It is not renewable — it is a fossil fuel — but the improvement in indoor air quality and in health, and the relief of pressure on forests, make it a substantial net gain over firewood and dung.
• Gobar gas (biogas). This is the elegant one. Cattle dung is fed into a sealed digester where, in the absence of oxygen, bacteria break it down and release a combustible gas — largely methane — which is piped to the kitchen stove. Crucially, the residual slurry that comes out of the digester is an excellent organic manure. So a single plant supplies clean cooking fuel and high-quality fertiliser from the same input, using a resource the household already has. It is renewable, it is decentralised, and it turns a waste-disposal problem into two useful outputs.

CNG in Urban Transport

Now the cities. Vehicular emissions are a leading contributor to urban air pollution, and the fuel a vehicle burns makes a large difference to what comes out of its exhaust.

CNG — compressed natural gas — burns considerably more cleanly than petrol and, especially, than diesel. In particular it produces far less particulate matter, which is the pollutant most closely linked to respiratory harm in cities.

The Indian example to cite is Delhi. Following orders of the Supreme Court of India in the M. C. Mehta public interest litigation in the late 1990s, Delhi’s public transport fleet — buses, auto-rickshaws and taxis — was converted to run on CNG in the early 2000s. It is widely cited as one of the clearest demonstrations that a targeted, enforced switch of fuel can measurably improve urban air quality.

Be balanced, though: it improved air quality, but it did not solve Delhi’s air pollution, which has many other sources — private vehicles, construction dust, industry, waste burning and seasonal crop-residue burning in neighbouring states. A good answer says the intervention worked on the problem it targeted. That nuance reads very well.

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Traditional Knowledge, Biocomposting and Biopest Control

The last group of strategies is about farming and about knowledge, and it carries a nice underlying message: some of the answers we need are not new inventions but old practices we set aside too quickly.

Traditional and Local Knowledge

Indian agricultural, health and housing traditions developed over a very long period in close contact with local conditions, and many of them are inherently resource-conserving.

Traditional water harvesting structures suited to local rainfall; crop varieties adapted to local soil and to erratic monsoons; mixed cropping that keeps soil covered and spreads risk; building designs that stay cool without air-conditioning; systems of traditional medicine using local plants. These were not adopted for environmental reasons — they were adopted because they worked with limited resources, which amounts to the same thing.

The economic argument for reviving them is straightforward: they are typically low-cost, locally available and locally understood, so they need little imported input and little external expertise. For a country with limited foreign exchange and large rural populations, that combination is valuable.

Biocomposting

Here is the problem it answers. Intensive chemical fertiliser use over many years can damage soil structure and harm the soil organisms that keep land productive, so that more and more fertiliser is needed for the same yield — an expensive treadmill for the farmer and a degrading one for the land. Residues also wash into water bodies.

Biocomposting means converting organic waste — crop residue, cattle dung, kitchen and farm waste — into compost, which is then returned to the field as organic manure. Earthworms are often used to speed the process up and improve the product; this is called vermicomposting.

The benefits stack up neatly:

• It restores soil structure and organic content, so the soil holds water and nutrients better.
• It reduces dependence on chemical fertilisers, cutting the farmer’s cash costs.
• It disposes of agricultural waste productively instead of leaving it to be burnt — which matters, because crop-residue burning is itself a significant source of seasonal air pollution.
• It reduces run-off of chemical residues into rivers and groundwater.

Biopest Control and Integrated Pest Management

The same logic applies to pesticides. Heavy chemical pesticide use kills the target pest, but it also kills the pest’s natural predators, leaves residues on food, contaminates soil and water, and over time selects for resistant pest populations — so that stronger and more frequent doses are needed.

Biopest control means managing pests using biological methods rather than synthetic chemicals:

• Natural predators. Encouraging or introducing the insects, birds and other creatures that eat the pest — ladybirds, spiders, certain wasps, insect-eating birds.
• Plant-based preparations. Neem-based preparations are the best known Indian example, used against a wide range of pests.
• Mixed cropping and crop rotation. Changing what grows where breaks the pest’s life cycle, since most pests specialise in one crop.
• Pest-resistant varieties, so the crop defends itself.

Used together and combined with careful monitoring, so that chemicals are used only as a last resort and in minimum quantity, this approach is called integrated pest management.

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How to Write This Chapter in the Board Exam

Let us finish with the practical business of converting all this into marks. This section is short, and it is the one I would re-read the night before the paper.

Match the Shape of Your Answer to the Marks

The Five Sentences Worth Memorising Word for Word

Not whole answers — just these five. Each is a mark or more on its own, and each can be dropped into several different questions.

1. “Environment is the total sum of all surroundings, comprising both biotic and abiotic elements and the interaction between them.”
2. “The environment performs four functions: supply of resources, assimilation of waste, sustaining life through genetic and biodiversity, and providing aesthetic services.”
3. “Environmental problems arose because environmental resources changed from free goods into scarce economic goods, as demand overtook supply.”
4. “Carrying capacity means resource extraction must not exceed regeneration, and waste generation must not exceed absorptive capacity.”
5. “Sustainable development means meeting the needs of the present generation without reducing the ability of future generations to meet their own needs.”

Three Errors That Cost Real Marks

• Confusing global warming with ozone depletion. Different layers, different substances, different radiation. Never write that one causes the other.
• Calling LPG or CNG renewable. They are cleaner fossil fuels. Gobar gas is the renewable one.
• Writing feeling instead of economics. “We must save our planet for our children” earns nothing. “The present generation must not reduce the stock of natural capital available to future generations” says the same thing and earns the mark.

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Practice Worksheet

Ten questions, mixed marks, all original. Here is how to use them so that they actually help.

Close the notes. Write each answer out in full on paper, in the format the marks call for — numbered points for three and four markers, lettered parts for six markers. Only when you have finished writing should you open the reveal.

Then mark yourself honestly against the model. If your answer is shorter than the model, ask which point you missed. If it is much longer, ask which sentences were not earning anything. Both questions are useful.

A Last Word Before You Close the Page

You do not have to master this chapter today. You really do not.

What works — and I have watched it work for a lot of students — is small, steady, unglamorous improvement. Get one more question right than you did yesterday. Just one. Learn one definition properly today, and tomorrow learn the next one while the first is still fresh. Write one full six-mark answer this week instead of reading five of them.

A single extra correct answer each day sounds like almost nothing. Over a month it is thirty. Over the run-up to the board exam it is the difference between an answer script that trails off and one that finishes strongly.

So pick one thing from this page — the four functions, or the difference between global warming and ozone depletion, or the six strategies — and make it genuinely solid before you move on. Then come back tomorrow and add the next one.

You have got this. Go slowly, and go every day.