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← Fundamentals of Physical Geography — all chaptersWorld Climate and Climate Change
Start here: why this chapter matters
In simple wordsWeather is what you wear today; climate is what is in your wardrobe — it tells you what a place is like over many years. This chapter does two jobs: it sorts the world's climates into families (like sorting clothes into summer and winter wear), and it asks why climates change — including the warming the world is living through now.
Chapters 7–10 explained the ingredients: heating, pressure, winds, moisture and rain. This chapter puts them together into the climates of real places, and then looks at how those climates have changed in the past and are changing now. It is the bridge between physical geography and the environment and climate-change topics of GS3.
- Builds on Chapters 8–10: temperature, pressure belts, winds and rainfall decide each climate type.
- Links to Chapter 14 (biodiversity): Koeppen built his scheme on the link between climate and vegetation.
- Links to India — Physical Environment: India's own climate (Am, Aw, BSh, Cwa) and the monsoon.
- UPSC: GS1 (world climatic regions, deserts, monsoon lands) and GS3 (global warming, GHGs, international agreements, sea-level rise).
| Word | What it means here |
|---|---|
| Empirical | Based on observed data (here, temperature and rainfall) |
| Genetic | Based on causes (e.g. air masses, pressure belts) |
| Applied | Made for a specific purpose (e.g. farming) |
| Potential evaporation | How much water could evaporate if it were available |
| Steppe | Semi-arid grassland climate, a little wetter than desert |
| Permafrost | Ground (subsoil) that stays frozen all year |
| Greenhouse gas (GHG) | A gas that lets sunlight in but absorbs the earth's long-wave heat |
| Interglacial | A warmer period between two ice ages |
At a glance — the six ideas to carry away
- Koeppen's scheme is empirical: built from observed temperature and precipitation.
- Groups: A coldest month ≥ 18°C · C −3°C to 18°C · D ≤ −3°C · E all months < 10°C · B evaporation > precipitation.
- Small letters: f no dry season, m monsoon, w dry winter, s dry summer; dry climates: S steppe, W desert.
- Hot deserts lie at 15°–30° under subtropical highs and reach the equator along cold-current west coasts.
- Causes of climate change: sunspots, Milankovitch cycles, volcanic aerosols, greenhouse gases.
- GHGs: CO₂ (largest), CFCs, CH₄, N₂O, O₃; Kyoto Protocol 1997, in force 2005.
1. Classifying climates: Koeppen's scheme
In simple wordsA doctor sorts patients by measurable signs — temperature, pulse — without needing to know the cause first. Koeppen did the same for climates: he used two measurable signs, temperature and rainfall, and drew the lines where the vegetation changes. That makes it an empirical scheme.
| Approach | Basis | Example |
|---|---|---|
| Empirical | Observed data, especially temperature and precipitation | Koeppen |
| Genetic | The causes of climate | e.g. by air masses or circulation (Beyond NCERT example) |
| Applied | A specific purpose | e.g. for agriculture (Beyond NCERT example) |
The most widely used scheme is V. Koeppen's. He found a close relationship between vegetation and climate, chose temperature and precipitation values that matched vegetation boundaries, and used mean annual and mean monthly temperature and precipitation. He used capital and small letters for groups and types. Developed in 1918 and modified since, it is still in use.
Reading NCERT Table 11.1 — Climatic groups according to Koeppen (page 91)
- A — Tropical: average temperature of the coldest month 18°C or higher.
- B — Dry: potential evaporation exceeds precipitation — the only group defined by moisture.
- C — Warm temperate (mid-latitude): coldest month above −3°C but below 18°C.
- D — Cold snow forest: coldest month −3°C or below.
- E — Cold: every month below 10°C.
- A, C, D and E are the humid climates; B is dry (NCERT exercise Q1-v: A—C—D—E).
Reading NCERT Table 11.2 — Climatic types according to Koeppen (page 92)
- 14 types in five groups: Af, Am, Aw · BSh, BWh, BSk, BWk · Cfa, Cs, Cfb · Df, Dw · ET, EF.
- The ‘characteristics’ column gives one-line memory hooks: Af no dry season; Am monsoonal, short dry season; Aw winter dry season; BSh/BWh low-latitude semi-arid/arid; BSk/BWk mid-latitude; Cfa no dry season, warm summer; Cs dry hot summer; Cfb no dry season, warm and cool summer; Df severe winter; Dw winter dry and very severe; ET no true summer; EF perennial ice.
- The table calls Df ‘humid continental’ and Dw ‘subarctic’, while the text calls them ‘cold climate with humid winters’ and ‘with dry winters’.
NCERT inconsistencies
- The text says the distribution of climatic groups and types is ‘shown in Table 11.1’, but there is no map in this reprint — Table 11.1 only lists the groups. Use the idealised continent below.
- The text lists four C types including Cwa (humid subtropical with dry winter — north Indian plains, south China), but Table 11.2 lists only three and leaves out Cwa.
⤵ Find the Koeppen group
Does potential evaporation exceed precipitation?yes → B (dry): S steppe or W desert
If not, look at the coldest month18°C or more → A (tropical)
Above −3°C but below 18°C→ C (warm temperate)
−3°C or below→ D (cold snow forest)
Every month below 10°C?→ E (ET tundra or EF ice cap)
2. Group A: tropical humid climates
In simple wordsIn the tropics it is always summer. The sun is high all year, so the difference between ‘winter’ and ‘summer’ is tiny. What changes from place to place is rain: some places get it every day, some in one long wet season.
Tropical humid climates lie between the Tropic of Cancer and the Tropic of Capricorn. The sun is overhead through the year and the ITCZ is present, so the climate is hot and humid; the annual range of temperature is very low and annual rainfall is high.
| Type | Where (NCERT) | Features |
|---|---|---|
| Af — tropical wet | Near the equator: Amazon Basin, western equatorial Africa, East Indies islands | Rain in every month as afternoon thundershowers; uniformly high temperature, negligible annual range; daily max ~30°C, min ~20°C; tropical evergreen forest, dense canopy, great biodiversity |
| Am — tropical monsoon | Indian subcontinent, north-eastern South America, northern Australia | Heavy rain mostly in summer; dry winter (details in ‘India: Physical Environment’) |
| Aw — tropical wet and dry | North and south of Af: around the Amazon in Brazil, parts of Bolivia and Paraguay, Sudan and south of Central Africa | Less and more variable rain than Af/Am; shorter wet season, longer and harsher dry season; high temperature all year; largest daily range in the dry season; deciduous forest and tree-studded grassland (savanna) |
Aw borders the dry climates on the western side of a continent and Cf or Cw climates on the eastern side.
Beyond NCERT (asked by UPSC)
- UPSC 2015 described an equatorial day — clear morning, heat builds, dark clouds, thunder, short rain — that is Af.
- A definite wet and dry season marks the savanna (Aw) (UPSC 2012; a climograph of it in 1995).
- The seasonal reversal of winds is typical of the monsoon climate (UPSC 2014), and India's climate is ‘monsoonal’ (UPSC 1989).
- Equatorial regions do not have four seasons (UPSC 2002).
- NCERT prints ‘tree-shredded grasslands’ — a misprint for tree-studded.
3. Group B: dry climates
In simple wordsA desert is not defined by heat but by thirst: more water could evaporate than falls as rain. Deserts form where air keeps sinking (sinking air warms and dries, like air from a hair-drier), where cold seas chill the coast, or where mountains and distance block moist winds.
Dry climates have rainfall too low for plant growth and cover large areas from 15° to 60° N and S. At 15°–30° they lie under the subtropical highs, where subsidence and temperature inversion prevent rain. On the western margins of continents next to cold currents — especially the west coast of South America — they reach further towards the equator, right onto the coast. At 35°–60° they lie in continental interiors that moist ocean winds cannot reach, often ringed by mountains.
| Type | Latitude | Features |
|---|---|---|
| BSh subtropical steppe | 15°–35° | Transition between humid and dry; a little more rain than desert — enough for sparse grassland; rainfall very variable, so famine is more common here than in the desert |
| BWh subtropical desert | 15°–35° | Rain in short, intense thundershowers that do not build soil moisture; fog on coastal deserts by cold currents; very high summer maxima; high annual and daily ranges |
| BSk / BWk mid-latitude steppe / desert | 35°–60° | Interior of continents, away from maritime winds |
⤵ Why the great hot deserts sit on west coasts at 15°–30°
Subtropical high pressureair sinks, warms and dries (Chapter 9)
Subsidence and inversionrising air — and rain — are blocked
Cold ocean current offshorecools the air from below; fog, not rain
Trade winds blow offshore heremoisture is carried away from the west coast
Hot desert on the west side of the continentSahara, Atacama, Namib, Australian deserts
Exam traps
- West-coast deserts are linked to cold currents, not warm ones — UPSC 2011 rejected ‘warm ocean currents’ as a reason for the African–Eurasian desert belt but accepted ‘subtropical high pressure cells’.
- UPSC 1992: deserts such as the Sahara lie in the west at 20°–30° because they have offshore winds.
- UPSC 1989: hot deserts do lie on western margins in the trade-wind zone, but trade-wind zones do not have a reversal of planetary winds (assertion true, reason false); UPSC 2009 asked the same idea.
- Mid-latitude deserts (Gobi, Central Asia, Patagonia) are caused by distance from the sea and mountain barriers, not by subtropical highs. UPSC 2013 described the extreme, dry Central Asian steppe of nomadic herders.
Beyond NCERT — a record that no longer standsNCERT quotes 58°C at Al Aziziyah, Libya, on 13 September 1922 as the highest shade temperature. In 2012 the World Meteorological Organization rejected that reading as a measurement error; the official world record is now 56.7°C at Death Valley, California (1913). Quote both if asked, but know the WMO position.
4. Group C: warm temperate (mid-latitude) climates
In simple wordsThe middle latitudes are a tug-of-war between the tropics and the poles. Which side of the continent you are on decides who wins: the west side gets ocean air from the westerlies (mild, often wet); the east side gets warm, humid air from the oceans in summer.
These climates lie between 30° and 50°, mainly on the eastern and western margins of continents. Summers are warm, winters mild.
| Type | Where (NCERT) | Temperature | Rainfall |
|---|---|---|---|
| Cwa humid subtropical, dry winter | Poleward of the tropics: north Indian plains, south China interior plains | Like Aw but warm winters | Hot wet summer, dry winter |
| Cs Mediterranean | Around the Mediterranean; west coasts at 30°–40°: central California, central Chile, south-eastern and south-western Australia | Summer ~25°C, winter below 10°C | 35–90 cm, in winter (subtropical high in summer, westerlies in winter) |
| Cfa humid subtropical | East sides: eastern USA, southern and eastern China, southern Japan, north-eastern Argentina, coastal South Africa, east coast of Australia | Summer ~27°C, winter 5°–12°C; small daily range | 75–150 cm, all year: summer thunderstorms, winter frontal rain |
| Cfb marine west coast | Poleward of Cs on west coasts: north-western Europe, west coast of North America north of California, southern Chile, south-eastern Australia, New Zealand | Summer 15°–20°C, winter 4°–10°C (warmer than its latitude); small ranges | 50–250 cm, all year |
Beyond NCERT (asked by UPSC)
- The Mediterranean is the classic UPSC climate: hot dry summers, mild wet winters (2010 added ‘evergreen oak trees’); a map question in 1988 and 1997; a station with 12.8°C and 54.9 cm (2001); and ‘summer receives more rain’ is false (2002).
- UPSC 2024 lifted NCERT's Cfb line almost word for word: low annual and daily range, rain all year, 50–250 cm → marine west coast. UPSC 1999 gave station data for the ‘West European’ type (= Cfb).
- ‘China type’ = Cfa: rain throughout the year (UPSC 1998, 2002).
- NCERT lists ‘south-eastern Australia’ under both Cs and Cfb; most atlases put Cs in the south-west and south (around Perth and Adelaide) and Cfb in the south-east (Victoria, Tasmania).
5. Groups D and E: cold and polar climates
In simple wordsGo far enough north inside a big continent and winter takes over: long, deep cold with snow on the ground for months. Go further, and summer is too short and cool for trees; further still, and even summer never melts the ice.
| Type | Where (NCERT) | Features |
|---|---|---|
| Df cold, humid winter | Northern hemisphere 40°–70°N in Europe, Asia, North America; poleward of Cfb and mid-latitude steppe | Cold, snowy winters; short frost-free season; large annual range; abrupt, short weather changes; harsher poleward |
| Dw cold, dry winter | Mainly north-eastern Asia | A strong winter anticyclone that weakens in summer gives a monsoon-like reversal of winds; below freezing for up to seven months; summer rain; only 12–15 cm a year |
| ET tundra | Poleward of 70° | Named after its vegetation — low mosses, lichens, flowering plants; permafrost; short growing season and waterlogging; very long summer daylight |
| EF ice cap | Interior Greenland and Antarctica | Below freezing even in summer; very little precipitation; snow and ice pile up, deform and break off as icebergs; e.g. Plateau Station, Antarctica (79°S) |
Exam trapD climates occur only in the northern hemisphere — the southern hemisphere has no large landmass at 40°–70°S. And ‘monsoon-like reversal of winds’ in NCERT is said of Dw (north-east Asia) as well as the true monsoon — but UPSC's ‘seasonal reversal of winds’ answer is the monsoon climate.
Why this picture worksRead it from west to east at any latitude and you see NCERT's logic: deserts and Mediterranean climates on the west (subtropical highs, cold currents), humid subtropical climates on the east (moist onshore winds), and the marine west coast where the westerlies come straight off the ocean.
6. Climate change in the past
In simple wordsThe earth keeps a diary of its old climates: scratches left by glaciers, layers of mud in lakes, rings in old trees, and history books recording famines and floods. Read together, they show that climate has never stood still.
- Today's climate has lasted roughly the last 10,000 years, with small and sometimes large swings.
- Evidence: glacial and interglacial periods in geological records; advances and retreats of glaciers in landforms at high altitudes and latitudes; warm and cold periods in glacial-lake sediments; wet and dry periods in tree rings; historical records.
- India: the Rajasthan desert was wet and cool around 8,000 BC; 3,000–1,700 BC had higher rainfall; 2,000–1,700 BC it was the centre of the Harappan civilisation; dry conditions increased afterwards.
- Geological past: warm some 500–300 million years ago (Cambrian, Ordovician, Silurian); in the Pleistocene, glacials and interglacials alternated; the last major glacial peak was about 18,000 years ago; the present interglacial began about 10,000 years ago.
- Recent past: warm, dry 10th–11th centuries in Europe, when Vikings settled in Greenland; the Little Ice Age (1550 to about 1850); world temperature rising 1885–1940, then rising more slowly; the US dust bowl drought in the 1930s; the devastating Sahel drought of 1967–1977; the 1990s — the century's warmest decade, with some of the worst floods.
NCERT dating slipNCERT says the earth was warm ‘some 500–300 million years ago, through the Cambrian, Ordovician and Silurian periods’. Those three periods actually span roughly 540–420 million years ago; 300 million years ago falls in the Carboniferous, which had a major glaciation (Beyond NCERT). For exams, remember the period names.
7. Causes of climate change
In simple wordsThe earth's temperature is like the warmth of a room: it depends on how strong the heater is (the sun), where the room faces (the earth's orbit and tilt), whether someone draws the curtains (volcanic dust), and how well the room is insulated (greenhouse gases). Change any one and the room's temperature changes.
| Cause | How it works (NCERT) | Note |
|---|---|---|
| Sunspots (astronomical) | Dark, cooler patches on the sun that rise and fall in cycles. Some meteorologists link more sunspots → cooler, wetter, stormier weather and fewer → warmer, drier | NCERT adds these findings are not statistically significant (exercise Q2-iv) |
| Milankovitch oscillations (astronomical) | Cycles in the earth's orbit, its wobble and its axial tilt change the insolation received | NCERT spells it ‘Millankovitch’ |
| Volcanism (terrestrial) | Eruptions throw up aerosols that stay for a long time and cut the sunlight reaching the surface | After ‘Pinatoba and El Cion’ — i.e. Pinatubo (Philippines, 1991) and El Chichón (Mexico, 1982) — the earth's average temperature fell for some years |
| Greenhouse gases (anthropogenic) | Rising concentrations from human activity | The most important human effect — likely to cause global warming |
⤵ Causes of climate change
Climate changenatural and continuous — now sped up by people
Astronomicalsunspot cycles · Milankovitch (orbit, wobble, tilt)
Terrestrial / humanvolcanic aerosols (cooling) · greenhouse gases (warming)
All change the heat budgethow much sunlight arrives, or how much heat escapes (Chapter 8)
8. Global warming and greenhouse gases
In simple wordsSit in a parked car in summer with the windows shut: sunlight pours in through the glass, the seats warm up, but the heat they give off can't escape — it gets hotter inside than outside. Greenhouse gases are the car's windows for the whole planet. Add more of them, and the planet warms.
The atmosphere lets incoming solar radiation through but absorbs most of the long-wave radiation the earth gives off. Gases that absorb long waves are greenhouse gases, and the warming they cause is the greenhouse effect — named after glasshouses in cold places, whose glass lets short waves in but stops long waves leaving.
| Greenhouse gas | What NCERT says |
|---|---|
| Carbon dioxide (CO₂) | Largest concentration; mainly from burning oil, gas and coal; forests and oceans are sinks; deforestation adds to it; rising about 0.5% a year; takes 20–50 years to adjust to changes in sources and sinks; doubling over pre-industrial levels is the benchmark in climate models |
| Chlorofluorocarbons (CFCs) | Made only by people; highly effective GHGs; drift into the stratosphere and destroy ozone |
| Methane (CH₄), nitrous oxide (N₂O) | Listed as primary GHGs of concern |
| Ozone (O₃) | Absorbs UV in the stratosphere; in the lower troposphere it is very effective at absorbing terrestrial radiation |
| Nitric oxide (NO), carbon monoxide (CO) | Not GHGs themselves in NCERT's list, but react with GHGs and change their concentration |
A gas's effect depends on how much its concentration rises, how long it stays in the air, and the wavelengths it absorbs. The longer a molecule stays, the longer the climate takes to recover.
Ozone hole. Ultraviolet rays turn oxygen into ozone in the stratosphere, and that ozone stops UV reaching the ground. CFCs drifting up destroy it; the large depletion over Antarctica is the ozone hole, which lets UV through to the troposphere.
Kyoto Protocol. The most important international effort in NCERT: proclaimed in 1997, in force from 2005, ratified by 141 nations (at that time). It bound 35 industrialised countries to cut emissions to 5% below 1990 levels by 2012.
Effects. Once warming sets in it is hard to reverse, and its effects will not be uniform. Sea level rises through melting glaciers and ice caps and the thermal expansion of seawater, threatening to flood coasts and islands.
- Average near-surface air temperature of the world: about 14°C.
- The 20th century warmed most in 1901–44 and 1977–99 — about 0.4°C each — with slight cooling in between, more marked in the northern hemisphere.
- By the end of the 20th century the global mean was about 0.6°C above the end of the 19th century.
- The seven warmest years of 1856–2000 were all in the last decade; 1998 was the warmest, probably of the whole millennium.
Reading the newspaper collage on page 97
- A page of clippings asks you to ‘write an explanatory note on global warming’. The headlines are your evidence list:
- Ancient air bubbles in Antarctic ice (a European ice-coring station) show greenhouse gases rising alarmingly.
- Gangotri glacier shrinking about 23 m a year; Himalayan glaciers retreating 10–15 m a year, with a satellite image of the Gangotri snout's retreat since 1780 — and a warning of future water shortages for the rivers they feed.
- A warming Arctic could affect global weather; another clipping warns a prolonged chill could follow changes in the North Atlantic.
- A dried-up reservoir with dead fish on Hainan Island, China, after two years without a typhoon.
- Air pollution named the biggest killer in Southeast Asia.
- Use these as examples: ice cores (evidence), glacier retreat (impact on water), the Arctic (feedback), drought (variability).
⤵ From emissions to rising seas
Burning fossil fuels, deforestation, CFCsmore greenhouse gases
More long-wave radiation absorbedthe heat budget tilts (Chapter 8)
Global warmingnot uniform; hard to reverse
Glaciers and ice caps melte.g. Gangotri retreating
Seawater expands as it warmsthermal expansion
Sea level risescoasts and islands flooded; social problems
NCERT figures that have dated
- Kyoto: ‘141 nations’ was the count when it entered into force in 2005; it later had 192 parties. Its target was an average cut of about 5% below 1990 over the commitment period 2008–2012 (Beyond NCERT).
- Warmest year: 1998 was the record when the chapter was written. It has since been overtaken many times, and the WMO confirmed 2024 as the warmest year on record, about 1.55°C above the 1850–1900 average (Beyond NCERT). For NCERT's own MCQ (Q1-iv) the answer is still 1998.
- NCERT says CO₂ adjusts in 20–50 years; the IPCC notes that a substantial part of emitted CO₂ stays in the air for centuries (Beyond NCERT).
Beyond NCERT — current, standard facts
- IPCC (Intergovernmental Panel on Climate Change), Sixth Assessment Report (2021–2023): human influence has unequivocally warmed the atmosphere, ocean and land; global surface temperature in 2011–2020 was about 1.1°C above 1850–1900.
- CO₂: about 280 ppm before industrialisation; now above 420 ppm.
- Paris Agreement (2015, COP21): hold warming well below 2°C above pre-industrial levels and pursue efforts to limit it to 1.5°C; each country sets Nationally Determined Contributions (NDCs), updated every five years. India has announced a net-zero target for 2070 (COP26, Glasgow, 2021).
- Montreal Protocol (1987) phases out ozone-depleting substances such as CFCs; its Kigali Amendment (2016) adds HFCs. Kyoto dealt with greenhouse gases, not the ozone layer (UPSC 2005).
- Ozone holes form over Antarctica because of the strong polar vortex and polar stratospheric clouds, on which CFC-derived chlorine destroys ozone (UPSC 2011).
NCERT exercise — answer outlines
Try each question yourself first, then open the outline to compare. MCQs (i), (ii), (iv) and (v) are in the self-check below.
MCQ (iii): Most of the Indian Peninsula will be grouped according to Koeppen's system under: Af, BSh, Cfb, Am
On Koeppen maps of India (India — Physical Environment), most of the interior peninsula is actually Aw (tropical savanna), which is not among the options; the west coast is Am and the rain-shadow interior BSh. Of the four choices, Am (tropical monsoon) is the answer most guides give, since the peninsula's climate is monsoonal and NCERT places Am over the Indian subcontinent. Af (no dry season) and Cfb (marine west coast) are clearly wrong.
Which two climatic variables are used by Koeppen for classification of the climate? (30 words)
Temperature and precipitation — mean annual and mean monthly values — chosen to match the boundaries of vegetation.
How is the “genetic” system of classification different from the “empirical one”? (30 words)
Empirical classification groups climates by observed data (temperature, precipitation), as Koeppen did. Genetic classification groups them by their causes — e.g. air masses, pressure belts, circulation.
Which types of climates have very low range of temperature? (30 words)
Tropical humid climates, especially Af (negligible annual range; equatorial oceans ~3°C), and the marine west coast (Cfb), where the ocean keeps annual and daily ranges small.
What type of climatic conditions would prevail if the sun spots increase? (30 words)
According to some meteorologists, cooler and wetter weather with more storms; fewer sunspots bring warmer, drier conditions. NCERT notes the link is not statistically significant.
Make a comparison of the climatic conditions between the “A” and “B” types of climate. (150 words)
Definition: A — coldest month ≥ 18°C (humid); B — potential evaporation exceeds precipitation (dry).
Location: A between the tropics (ITCZ, overhead sun); B at 15°–30° under subtropical highs, on cold-current west coasts, and in mid-latitude interiors (35°–60°).
Temperature: A uniformly high, very small annual range (Af: 20–30°C daily); B very high summer maxima (Al Aziziyah 58°C in NCERT), large annual and daily ranges.
Rainfall: A high — every month in Af, summer in Am, a wet and a dry season in Aw; B scanty, highly variable, in short intense showers that do not build soil moisture; fog on coastal deserts.
Vegetation: A evergreen forest (Af), deciduous forest and savanna (Aw); B sparse grassland (steppe), desert scrub.
Human impact: rainfall variability causes famine in steppes.
Diagram: an idealised continent showing A at the equator and B on the west at 15°–30°.
Location: A between the tropics (ITCZ, overhead sun); B at 15°–30° under subtropical highs, on cold-current west coasts, and in mid-latitude interiors (35°–60°).
Temperature: A uniformly high, very small annual range (Af: 20–30°C daily); B very high summer maxima (Al Aziziyah 58°C in NCERT), large annual and daily ranges.
Rainfall: A high — every month in Af, summer in Am, a wet and a dry season in Aw; B scanty, highly variable, in short intense showers that do not build soil moisture; fog on coastal deserts.
Vegetation: A evergreen forest (Af), deciduous forest and savanna (Aw); B sparse grassland (steppe), desert scrub.
Human impact: rainfall variability causes famine in steppes.
Diagram: an idealised continent showing A at the equator and B on the west at 15°–30°.
What type of vegetation would you find in the “C” and “A” type(s) of climate? (150 words)
A climates: Af — tropical evergreen rainforest, dense multi-layered canopy, huge biodiversity (Amazon, Congo, Indonesia); Am — monsoon (tropical deciduous) forests that shed leaves in the dry season; Aw — deciduous forest and tree-studded grassland (savanna) (Brazil, Sudan).
C climates (Beyond NCERT detail): Cs Mediterranean — evergreen, drought-resistant woodland and scrub (cork oak, olive; maquis/chaparral) adapted to dry summers; Cfa humid subtropical — mixed evergreen and broad-leaved forests; Cfb marine west coast — deciduous broad-leaved forests (oak, beech) and coniferous forests in wetter, cooler parts; Cwa — tropical deciduous/subtropical forests (north India, south China).
Link: Koeppen drew his boundaries along exactly these vegetation changes.
Conclude with one example each and a small table.
C climates (Beyond NCERT detail): Cs Mediterranean — evergreen, drought-resistant woodland and scrub (cork oak, olive; maquis/chaparral) adapted to dry summers; Cfa humid subtropical — mixed evergreen and broad-leaved forests; Cfb marine west coast — deciduous broad-leaved forests (oak, beech) and coniferous forests in wetter, cooler parts; Cwa — tropical deciduous/subtropical forests (north India, south China).
Link: Koeppen drew his boundaries along exactly these vegetation changes.
Conclude with one example each and a small table.
What do you understand by the term “Greenhouse Gases”? Make a list of greenhouse gases. (150 words)
Define: gases that are transparent to incoming short-wave solar radiation but absorb outgoing long-wave radiation from the earth, warming the atmosphere — the greenhouse effect (glasshouse/closed-car analogy).
List (NCERT): carbon dioxide (largest concentration; fossil fuels, deforestation), chlorofluorocarbons (man-made, highly effective, also destroy ozone), methane, nitrous oxide, ozone (effective in the lower troposphere); NO and CO affect their concentrations. (Water vapour is also a natural GHG — Chapter 7.)
Effectiveness: depends on rise in concentration, lifetime, wavelength absorbed.
Consequences: global warming — 0.6°C rise in the 20th century, 1998 warmest (NCERT); sea-level rise from melting ice and thermal expansion.
Response: Kyoto Protocol 1997/2005; (Beyond NCERT) Paris Agreement 2015 — well below 2°C, aiming for 1.5°C.
Diagram: greenhouse sketch.
List (NCERT): carbon dioxide (largest concentration; fossil fuels, deforestation), chlorofluorocarbons (man-made, highly effective, also destroy ozone), methane, nitrous oxide, ozone (effective in the lower troposphere); NO and CO affect their concentrations. (Water vapour is also a natural GHG — Chapter 7.)
Effectiveness: depends on rise in concentration, lifetime, wavelength absorbed.
Consequences: global warming — 0.6°C rise in the 20th century, 1998 warmest (NCERT); sea-level rise from melting ice and thermal expansion.
Response: Kyoto Protocol 1997/2005; (Beyond NCERT) Paris Agreement 2015 — well below 2°C, aiming for 1.5°C.
Diagram: greenhouse sketch.
What to remember
Numbers
Koeppen's scheme developed1918
A group: coldest month18°C or more
C group: coldest monthabove −3°C, below 18°C
D group: coldest month−3°C or below
E group: every monthbelow 10°C
Dry climates span15°–60° N and S
Af daily max / min~30°C / ~20°C
Mediterranean rainfall35–90 cm (summer ~25°C, winter < 10°C)
Cfa rainfall / Cfb rainfall75–150 cm / 50–250 cm
Dw annual precipitation12–15 cm
Polar climatesbeyond 70°
Last glacial peak / present interglacial~18,000 / ~10,000 years ago
Little Ice Age (Europe)1550–about 1850
Sahel drought1967–1977
Kyoto Protocol1997; in force 2005; 5% below 1990
World mean surface air temperature~14°C
20th-century warming~0.6°C; warmest year (NCERT) 1998
One-liners
- Koeppen = empirical; based on temperature, precipitation and vegetation.
- A, C, D, E are humid; B is dry.
- f no dry season · m monsoon · w dry winter · s dry summer.
- Hot deserts: subtropical highs + cold currents + offshore trades on west coasts.
- Mediterranean: hot dry summer, mild rainy winter.
- CO₂ has the largest concentration; CFCs are man-made and destroy ozone.
- Sea-level rise = melting ice + thermal expansion.
- More sunspots → cooler, wetter (not statistically significant).
Traps to avoid
- Koeppen's scheme is empirical, not genetic.
- Humid groups are A, C, D, E — B is dry.
- West-coast deserts lie next to cold currents, not warm ones.
- Mediterranean rain falls in winter, not summer.
- Kyoto is about greenhouse gases; Montreal is about the ozone layer.
- 1998 was NCERT's warmest year; today the record is 2024 (WMO).
- The 58°C Al Aziziyah record was rejected by the WMO in 2012.
- Table 11.2 omits Cwa, which the text describes.
- D climates exist only in the northern hemisphere.
How to strategise
Prelims — what UPSC asks
- Identify-the-climate questions are a UPSC staple: from a description (2010, 2013, 2015, 2024), station data (1999, 2001), a climograph (1995) or a map (1988, 1997). Learn each type's temperature, rainfall season and amount, and two locations — UPSC 2024 copied NCERT's Cfb line.
- Deserts on west coasts: 1989, 1992, 2009, 2011 — subtropical high, offshore winds, cold currents.
- Monsoon and savanna: seasonal reversal of winds (2014), India monsoonal (1989), savanna wet and dry seasons (2012), China type and Mediterranean statements (1998, 2002).
- Greenhouse gases and treaties: greenhouse effect (1989, 2025), CFCs and ozone (1992, 2011), Kyoto (1998, 2005). Know Kyoto vs Montreal vs Paris.
Mains — where it appears and how to answer
- GS1: why hot deserts lie at 20°–30°N on western sides (2013); the monsoon climate that feeds half the world (2017); shrinking Himalayan glaciers and climate change (2014); the cryosphere and global climate (2017); sea-level rise and island nations (2025).
- GS3: global warming, its effects and the Kyoto Protocol (2022); IPCC's projected sea-level rise and the Indian Ocean region (2023); how India's Himalayan and coastal states will be affected (2017).
- Answer frame: define → mechanism (greenhouse effect, Hadley-cell subsidence) → evidence (temperature record, ice cores, glacier retreat) → impacts (sea level, water, agriculture) → global and Indian response (Kyoto → Paris, NDCs, net zero 2070).
- Draw the idealised continent for any world-climate answer; draw the greenhouse sketch for any warming answer.
Self-check
Tap an option. NCERT's own exercise questions come first; the rest test the figures and common confusions.
1. Which one of the following is suitable for Koeppen's “A” type of climate?
2. Koeppen's system of classification of climates can be termed as:
3. Which one of the following years is supposed to have recorded the warmest temperature the world over (as per NCERT)?
4. Which one of the following groups of four climates represents humid conditions?
5. Hot, dry summers and mild, rainy winters on west coasts at 30°–40° describe:
6. Which statement about the Kyoto Protocol is correct?
7. Volcanic eruptions such as Pinatubo tend to:
UPSC questions from this chapter
Open any question to attempt it in the Question bank — your attempt is saved to your progress.