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Global Warming, India Concerns & Exercises

🎓 Class 11 Social Science CBSE Theory Ch 4 — Climate ⏱ ~22 min
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Class 11 · Geography · India: Physical Environment · Unit III

Chapter 4 · Climate — Global Warming, NCERT Exercises & Chapter Summary

Climate is never frozen in time. The earth has gone through ice ages and warm interglacials; it is changing even now, but so slowly that the change can only be read across decades. Today, however, the natural pace of change is being amplified by humans. This final part of Chapter 4 looks at global warming — its mechanism, its consequences for India, and what a 50 cm rise in sea level might mean for our coasts. Then we work carefully through the full set of NCERT exercises with model answers, and close with a chapter summary and key terms.

4.15 Climate Change in the Long Run

Change is the law of nature. Climate has changed in the past at both global and local scales, and it is changing even now — but the change is imperceptible. Geological evidence makes it clear that, once upon a time, much of the earth was buried under thick ice cover. We are now living through one of the warmer phases of that long history. What is new is that the natural pace of change has been overlaid by a human signal of unprecedented strength.

4.16 Global Warming — The Greenhouse Effect

You have probably heard the on-going debate around global warming?. Apart from natural causes, large-scale industrialisation and the build-up of polluting gases in the atmosphere are also major factors. The temperature of the world is significantly increasing.

📖 Core Definition
The greenhouse effect is the process by which certain atmospheric gases — known as greenhouse gases — trap part of the long-wave radiation emitted by the earth's surface, keeping the lower atmosphere warmer than it would otherwise be. Strengthening this natural effect by adding more greenhouse gases is what causes global warming.

4.16.1 The Main Greenhouse Gases

Carbon dioxide (CO₂) produced by human activity is the major source of concern. Released to the atmosphere in large quantities by the burning of fossil fuels, it is increasing gradually. Other gases — present in much smaller concentrations — are also important contributors:

  • Methane (CH₄)
  • Chlorofluorocarbons (CFCs)
  • Nitrous oxide (N₂O)

Together with carbon dioxide, these are known as greenhouse gases?. They are better absorbers of long-wave radiation than carbon dioxide, and so are even more effective at enhancing the greenhouse effect, molecule for molecule. The contribution of these gases to global warming is significant.

The Greenhouse Effect — How Earth Stays Warm SUN Short-wave solar radiation EARTH'S SURFACE Greenhouse gas layer (CO₂, CH₄, CFCs, N₂O) Long-wave radiation trapped & re-emitted A small portion escapes to space Solar radiation enters as short-wave; earth re-radiates long-wave; greenhouse gases trap part of it — surplus warmth = global warming.

4.16.2 Consequences of Global Warming

It is widely said that, due to global warming, the polar ice caps and mountain glaciers will melt and the volume of water in the oceans will rise. The mean annual surface temperature of the earth has increased over the past 150 years. By the year 2100, global temperature is projected to rise by about 2°C. This rise will trigger many other changes:

🌊
Sea-Level Rise
Melting glaciers and sea-ice will raise sea level by an estimated 48 cm on average by the end of the 21st century. This will increase the incidence of annual flooding.
🦟
Insect-Borne Diseases
Climate change would promote the spread of insect-borne diseases like malaria, as warmer regions expand and mosquito habitats shift.
🌾
Agricultural Shift
Climatic boundaries would shift — making some regions wetter and others drier. Agricultural patterns and human populations will have to adjust.
🌳
Ecosystem Change
Both human populations and natural ecosystems will experience change. Species migration, forest dieback, and the loss of cold-adapted habitats are expected.
🚨 What If Indian Sea Levels Rise by 50 cm?
Most of India's coastal cities — Mumbai, Chennai, Kolkata, Visakhapatnam, Kochi, Surat — sit on low-lying ground. A 50 cm rise above present sea level would: (i) flood the Sundarbans and large parts of the Ganga–Brahmaputra delta; (ii) salinise groundwater along coastal aquifers in Tamil Nadu, Andhra Pradesh and Gujarat; (iii) increase the storm-surge risk during tropical cyclones; (iv) threaten the entire low islands of Lakshadweep. Adaptation would require coastal embankments, mangrove restoration and a long-term re-design of urban infrastructure.

Figure 4.C: Indicative trend of global mean surface temperature anomaly (illustrative). Final value is the projected 2100 anomaly of about +2°C.

4.16.3 Concerns Specific to India

  • Himalayan glacier retreat: the rivers Ganga, Indus and Brahmaputra all draw a substantial part of their lean-season flow from glacial melt. As glaciers shrink, the long-term water security of north India is at stake.
  • Monsoon variability: rising sea-surface temperatures over the Indian Ocean may be making the monsoon both wetter overall and more unstable — fewer rainy days but more extreme rainfall events.
  • Heat-wave intensity: the loo months are getting hotter and lasting longer, with adverse impacts on agricultural workers and outdoor labourers.
  • Cyclone behaviour: warmer Bay of Bengal waters fuel more intense tropical cyclones.
  • Sea-level threat to deltas: the Sundarbans, Krishna, Godavari and Kaveri deltas are among the world's most exposed flood-prone regions.
THINK ABOUT IT — Greenhouse Effect: Friend or Foe?
Bloom: L5 Evaluate

The greenhouse effect is sometimes called both "essential for life on earth" and "the cause of catastrophic climate change". Both statements are true. In a 6–7 sentence response, evaluate this paradox: explain (i) why the natural greenhouse effect is necessary, (ii) why human enhancement of it is harmful, and (iii) what a 2°C rise by 2100 would specifically imply for India's monsoon-dependent agriculture.

✅ Pointers
Without the natural greenhouse effect, earth's surface temperature would be far below freezing — life would be impossible. Human-emitted CO₂, CH₄, CFCs and N₂O over-strengthen this effect, raising temperatures faster than ecosystems can adapt. For India, a 2°C rise means stronger heat-waves, faster Himalayan glacier melt, more variable monsoon rainfall (longer dry spells punctuated by cloudbursts), and rising seas threatening deltas like the Sundarbans.
IMAGINE — A Letter From 2100
Bloom: L6 Create

Imagine you are a climate scientist living in the year 2100. Write a 250-word "letter to the past" — addressed to a class-11 student in 2026 — describing what worked, what failed and what you wish had been done about global warming. Reference at least three specific Indian features (e.g. Mawsynram, Sundarbans, Himalayan glaciers, Coromandel cyclones).

✅ Pointers
Possible content: Mawsynram still rains heavily but with longer dry breaks; Himalayan glaciers have lost 40–60% of their 2000 volume; the Sundarbans have been largely abandoned; Coromandel cyclones are now stronger and more frequent. Solutions you wish had been adopted: rapid renewable-energy roll-out, mangrove restoration, basin-scale water management, climate-resilient agriculture.

4.17 NCERT Exercises — with Model Answers

Q1. Multiple-Choice Questions

(i) What causes rainfall on the coastal areas of Tamil Nadu in the beginning of winters?

  • (a) South-West monsoon
  • (b) Temperate cyclones
  • (c) North-Eastern monsoon
  • (d) Local air circulation
Answer: (c) North-Eastern monsoon. During October–November the retreating monsoon, while crossing the Bay of Bengal, picks up moisture and dumps torrential rain on the Tamil Nadu coast, southern Andhra Pradesh, south-east Karnataka and south-east Kerala. Coromandel coast gets most of its annual rainfall in this period.

(ii) What is the proportion of area of India which receives annual rainfall less than 75 cm?

  • (a) Half
  • (b) One-third
  • (c) Two-third
  • (d) Three-fourth
Answer: (b) One-third. Roughly one-third of India — covering parts of the Peninsula, Ladakh, most of western Rajasthan, Gujarat and Haryana — receives less than 75 cm of rainfall per year. These are the "low" and "inadequate" rainfall belts.

(iii) Which one of the following is not a fact regarding South India?

  • (a) Diurnal range of temperature is less here.
  • (b) Annual range of temperature is less here.
  • (c) Temperatures here are high throughout the year.
  • (d) Extreme climatic conditions are found here.
Answer: (d) Extreme climatic conditions are found here. South India has an equable climate because of the moderating influence of the surrounding seas and proximity to the equator. Diurnal and annual temperature ranges are small, temperatures stay high through the year, and extremes are absent.

(iv) Which one of the following phenomenon happens when the sun shines vertically over the Tropic of Capricorn in the southern hemisphere?

  • (a) High pressure develops over north-western India due to low temperatures.
  • (b) Low pressure develops over north-western India due to high temperatures.
  • (c) No changes in temperature and pressure occur in north-western India.
  • (d) 'Loo' blows in the north-western India.
Answer: (a) High pressure develops over north-western India due to low temperatures. When the sun is vertical over the Tropic of Capricorn (around 22 December), it is winter in the Northern Hemisphere. North-western India cools, a feeble high-pressure cell develops, and dry north-westerly winds blow outward to the low-pressure region over the Indian Ocean.

Q2. Answer in About 30 Words

(i) What is the Inter-Tropical Convergence Zone?

Model Answer: The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure belt near the equator where the trade winds of both hemispheres converge and the air rises. It shifts north to about 20–25°N over the Gangetic plain in July (the monsoon trough) and south of the equator in January, driving the seasonal reversal of Indian winds.

(ii) What is meant by 'bursting of monsoon'? Name the place of India which gets the highest rainfall.

Model Answer: The sudden onset of the moisture-laden south-west monsoon, accompanied by violent thunder and lightning that drops temperatures by 5–8°C in a single day, is called the "burst" or "break" of the monsoon. Mawsynram, located on the crest of the Khasi hills (Meghalaya), receives the highest average annual rainfall in the world.

(iii) Which type(s) of cyclones cause rainfall in north-western India during winter? Where do they originate?

Model Answer: Winter rainfall in north-western India is caused by weak temperate cyclones (western disturbances). They originate over the eastern Mediterranean Sea and travel eastwards across West Asia, Iran, Afghanistan and Pakistan, picking up moisture from the Caspian Sea and the Persian Gulf en route, before reaching India steered by the westerly jet stream.

Q3. Answer in Not More Than 125 Words

(i) Notwithstanding the broad climatic unity, the climate of India has many regional variations. Elaborate this statement giving suitable examples.

Model Answer: India shares a monsoon climate with the rest of south and south-east Asia, yet its sheer size and varied relief produce striking regional differences.

Temperature contrasts: in summer, the mercury touches 55°C in western Rajasthan but only 19°C at Tawang on the same June day. In winter, Drass (Ladakh) drops to −45°C while Thiruvananthapuram stays around 22°C.

Rainfall contrasts: Cherrapunji and Mawsynram receive over 1,080 cm annually while Jaisalmer rarely exceeds 9 cm. The Ganga delta is hit by storms every third or fifth day in July–August, while the Coromandel coast stays dry.

Seasonal contrasts: while north India shivers in January, peninsular south India shows hardly any seasonal change. These regional variations are all sub-types of the same monsoon climate, produced by latitude, altitude, distance from sea, relief and the path of monsoon branches.

(ii) How many distinct seasons are found in India as per the Indian Meteorological Department? Discuss the weather conditions associated with any one season in detail.

Model Answer: The IMD recognises four seasons: (i) Cold weather (December–February), (ii) Hot weather (March–May), (iii) South-west monsoon (June–September), and (iv) Retreating monsoon (October–November).

The South-west Monsoon Season begins in early June. Intense low pressure over north-west India attracts the SE trade winds across the equator; after deflection, they become south-westerlies. The monsoon "bursts" with violent thunder and lightning, dropping day temperatures by 5–8°C between mid-June and mid-July. It approaches India in two branches:
• Arabian Sea branch — splits into three sub-branches; the Western Ghats sub-branch causes 250–400 cm of rain on the windward slope and a rain-shadow east of the Ghats.
• Bay of Bengal branch — deflected by the Arakan Hills, enters Bengal from the south-east, splits into a westward arm along the Ganga plains and a north-eastward arm up the Brahmaputra valley; its sub-branch hits the Garo-Khasi hills (Mawsynram).
Tamil Nadu coast remains dry because it lies parallel to the Bay of Bengal branch and in the rain-shadow of the Arabian Sea branch.

Project / Activity

On the outline map of India, show the following:

  1. Areas of winter rain
  2. Wind direction during the summer season
  3. Areas having less than 15°C temperature in January
  4. Isohyte of 100 cm
Map Pointers:
  1. Areas of winter rain — shade Punjab, Haryana, Delhi, western UP, Jammu & Kashmir, Himachal (from western disturbances) and the Tamil Nadu coast / southern Andhra Pradesh / south-east Karnataka / south-east Kerala (from north-east monsoon).
  2. Summer wind direction — draw arrows showing south-westerlies hitting the Western Ghats, the Saurashtra/Kachchh strand striking westward Rajasthan, and the Bay of Bengal branch curving up from the SE through Bengal and bifurcating along the Ganga and Brahmaputra valleys.
  3. Areas with January temperature < 15°C — shade the Himalayan belt (J&K, Himachal, Uttarakhand high zones), most of Punjab, Haryana, Delhi, western UP, and high parts of north-east India (Sikkim, Arunachal high reaches).
  4. 100 cm isohyte — draw a single line that runs roughly along: north Gujarat → eastern MP → northern Bihar → West Bengal → eastern hills, separating the medium-rainfall belt (> 100 cm to the east/south of the line) from the low-rainfall belt (< 100 cm to the west/north).

4.18 Chapter Summary

Weather vs Climate

Weather is the momentary state of the atmosphere; climate is the long-period average. India has a hot monsoon climate with great regional variations — 55°C in Rajasthan summer, −45°C around Leh winter; 1,080 cm at Mawsynram, 9 cm at Jaisalmer.

Climatic Controls

Latitude (Tropic of Cancer through middle), altitude (Agra 16°C vs Darjiling 4°C in January), distance from sea, the Himalayan shield, ocean currents, relief and the seasonal pressure-and-wind cycle together make India's climate.

Monsoon Mechanism

The ITCZ shifts to about 20–25°N in July, becoming a monsoon trough; SE trades cross the equator between 40°E–60°E, become SW monsoon; the easterly jet stream at 15°N triggers the burst over Kerala by 1 June, engulfing all India by mid-July.

El Niño & Southern Oscillation

Warm Pacific currents off Peru once every 3–7 years (El Niño) distort equatorial circulation and weaken the Indian monsoon. La Niña does the opposite. The pressure difference between Tahiti and Port Darwin tracks the Southern Oscillation; IMD forecasts use 16 indicators.

Four IMD Seasons

Cold (Dec–Feb), Hot (Mar–May, with Loo, mango showers, blossom showers, Nor'westers/Kal Baisakhi), SW monsoon (Jun–Sep, with Arabian Sea and Bay of Bengal branches), Retreating (Oct–Nov, with October heat and Andaman cyclones).

Rainfall Distribution

Average about 125 cm. High (> 200 cm): West coast, Western Ghats, NE hills. Medium (100–200 cm): southern Gujarat, eastern TN, Odisha–Jharkhand–Bihar belt. Low (50–100 cm): western UP, Punjab, Haryana, Deccan. Inadequate (< 50 cm): western Rajasthan, Ladakh.

Köppen Climate Regions

Amw (west coast south of Goa), As (Coromandel), Aw (Peninsular plateau), BShw (NW Gujarat, parts of W Rajasthan), BWhw (extreme W Rajasthan), Cwg (Ganga plain), Dfc (Arunachal), E (high Himalayas).

Monsoon & Economy

Monsoon is the axis of Indian agriculture (about 64% of population dependent). Variability brings droughts and floods every year. Sudden bursts cause soil erosion. Winter rainfall by temperate cyclones is highly beneficial for rabi crops.

Global Warming

Carbon dioxide, methane, CFCs and nitrous oxide trap long-wave radiation. By 2100, global temperature is projected to rise by about 2°C and sea level by an average 48 cm. India faces glacier retreat, monsoon variability, intensified cyclones and delta inundation.

4.19 Key Terms — Quick Glossary

Weather — Momentary state of the atmosphere at a place.
Climate — Average pattern of weather over decades.
Monsoon — Climate of seasonal wind reversal.
ITCZ — Inter-Tropical Convergence Zone, the migrating low-pressure belt where trade winds converge.
Jet Stream — Fast narrow upper-air current; westerly in winter, easterly (15°N) in summer.
El Niño — Warming of waters off Peru every 3–7 years; tends to weaken the Indian monsoon.
La Niña — Cool phase of the Pacific oscillation; tends to strengthen the Indian monsoon.
Southern Oscillation — Pressure see-saw between Tahiti (E Pacific) and Port Darwin (W Pacific).
Burst of Monsoon — Sudden, violent onset of SW monsoon rainfall, with thunder and lightning.
Break in Monsoon — Multi-day dry spell during the rainy season.
Mawsynram — Place on Khasi hills receiving the world's highest average annual rainfall.
Loo — Hot, dry afternoon winds across the Northern plains in summer.
Kal Baisakhi / Nor'westers — Dreaded evening thunderstorms in Bengal & Assam (also called Bardoisila in Assam).
Mango Showers — Pre-monsoon showers in Kerala & coastal Karnataka helping mangoes ripen.
Blossom Showers — Showers helping coffee flowers blossom in Kerala.
Arabian Sea Branch — Branch of SW monsoon that strikes the west coast and splits into three.
Bay of Bengal Branch — Branch of SW monsoon deflected by Arakan Hills into West Bengal & the Brahmaputra valley.
Retreating Monsoon — October–November withdrawal of SW monsoon; brings rain to Tamil Nadu and Andaman-Sea cyclones to Coromandel.
October Heat — Oppressive weather of high temperature + high humidity during retreating monsoon.
Köppen Classification — World climate scheme with letter codes; India hosts Amw, As, Aw, BShw, BWhw, Cwg, Dfc and E types.
Greenhouse Effect — Trapping of long-wave radiation by atmospheric gases.
Greenhouse Gases — CO₂, CH₄, CFCs, N₂O.
Global Warming — Human-driven rise in earth's mean temperature; ~2°C projected by 2100.
Western Disturbance — Temperate cyclone from the Mediterranean bringing winter rain to NW India.
📋

Competency-Based Questions — Global Warming & Whole Chapter Synthesis

Case Study: The Sundarbans, the world's largest mangrove forest, sits at the mouth of the Ganga–Brahmaputra. With a projected sea-level rise of 48 cm by 2100 and rising Bay-of-Bengal sea-surface temperatures, climate scientists warn the region is among the most vulnerable on earth. Aanya is preparing a school presentation on "Climate of India and the threat of global warming" and she wants to connect every part of Chapter 4 — monsoon mechanism, four seasons, Köppen, El Niño and global warming.
Q1. Which of the following gases is NOT considered a greenhouse gas in the NCERT discussion?
L1 Remember
  • (A) Carbon dioxide
  • (B) Methane
  • (C) Oxygen
  • (D) Chlorofluorocarbons
Answer: (C) Oxygen. NCERT lists CO₂, methane, CFCs and nitrous oxide as the major greenhouse gases. Oxygen is the dominant atmospheric gas after nitrogen but is not a greenhouse gas.
Q2. By the year 2100, NCERT projects an average sea-level rise of approximately:
L1 Remember
  • (A) 8 cm
  • (B) 48 cm
  • (C) 1.5 m
  • (D) 5 m
Answer: (B) 48 cm. The current prediction in NCERT is that, on an average, sea level will rise 48 cm by the end of the 21st century — enough to dramatically increase coastal flooding.
Q3. The greenhouse gases listed in NCERT (other than CO₂) are described as:
L2 Understand
  • (A) Less effective absorbers of long-wave radiation than CO₂
  • (B) Equally effective as CO₂
  • (C) Better absorbers of long-wave radiation than CO₂ molecule for molecule
  • (D) Reflective gases that cool the atmosphere
Answer: (C). Methane, CFCs and nitrous oxide are present in much smaller concentrations than CO₂, but they are better absorbers of long-wave radiation molecule for molecule, so they are more effective at enhancing the greenhouse effect.
Q4. Which of the following Indian impacts of climate change is NOT mentioned by NCERT?
L4 Analyse
  • (A) Rise in sea level due to melting glaciers and sea-ice
  • (B) Increased incidence of annual flooding
  • (C) Spread of insect-borne diseases like malaria
  • (D) Permanent disappearance of the south-west monsoon
Answer: (D). NCERT mentions sea-level rise, annual flooding, malaria spread, shifting climatic boundaries and shifting agriculture — but does not say the SW monsoon will permanently disappear; it would be variable, not absent.
HOT Q. Design a 1-page "Action Plan for Climate-Resilient India" that draws on at least four ideas from Chapter 4: (i) monsoon variability, (ii) Köppen climate zones, (iii) El Niño/Southern Oscillation forecasting, and (iv) coastal sea-level rise. Suggest one policy or technical intervention for each, ending with a justification rooted in the NCERT text.
L6 Create
Hint: (i) For monsoon variability — develop drought-tolerant crops in Köppen Aw and BShw zones; (ii) For El Niño forecasting — strengthen IMD's 16-indicator forecasting system; (iii) For glacier-melt risk in E and Dfc zones — Himalayan basin water-storage planning; (iv) For coastal sea-level rise — mangrove restoration along Sundarbans, Coromandel and Konkan coasts. Justification: each intervention addresses a vulnerability that NCERT explicitly names — variability, El Niño impacts, melting glaciers, 48 cm sea-level rise.
⚖️ Assertion–Reason Questions — Global Warming & Synthesis
Options:
(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.
Assertion (A): Although CO₂ is the most-discussed greenhouse gas, methane, CFCs and nitrous oxide also play a major role in global warming.
Reason (R): These gases, despite being present in much smaller concentrations than CO₂, are better absorbers of long-wave radiation than CO₂ molecule for molecule.
Answer: (A) — Both A and R are true and R is the correct explanation. NCERT explicitly notes that these gases are more effective at enhancing the greenhouse effect even though they are present in much smaller concentrations.
Assertion (A): A 50 cm rise in sea level would have devastating consequences for India's coasts.
Reason (R): India's coasts are formed entirely of high cliffs that will trap rising waters and prevent inland flooding.
Answer: (C) — A is true (NCERT projects ~48 cm rise; the consequences would be severe — flooding, salinisation, cyclone surges, delta loss). R is false: most of India's coasts are low-lying, including the deltas of the Ganga–Brahmaputra, Krishna, Godavari and Kaveri, and the populous cities of Mumbai, Chennai, Kolkata and Kochi.
Assertion (A): Climate change would shift India's climatic boundaries, making some regions wetter and others drier.
Reason (R): A rise in global temperature alters atmospheric circulation and ocean–atmosphere coupling (including ENSO), redistributing rainfall across regions.
Answer: (A) — Both A and R are true, and R correctly explains A. The Köppen boundaries we mapped in Part 2 are not fixed; under continued warming, the BWhw desert may expand, the Cwg humid sub-tropical belt may shift north, and the high-altitude E zone may shrink.
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