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Climate Change, Greenhouse Effect & Exercises

🎓 Class 11 Social Science CBSE Theory Ch 11 — World Climate and Climate Change ⏱ ~28 min
🌐 Language: [gtranslate]

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11.8 Climate Change — A Natural and Continuous Process

The earlier sections of this chapter summarised our understanding of the climate as it prevails now. The kind of climate we currently experience may have been with us for the last 10,000 years or so, with minor and occasionally wide fluctuations. But planet Earth has witnessed many variations in climate since its very beginning. Geological records show alternating glacial? and inter-glacial periods. The geomorphological features of high altitudes and high latitudes — U-shaped valleys, moraines, drumlins, glacial cirques — exhibit traces of advances and retreats of glaciers. Sediment deposits in glacial lakes also reveal the occurrence of warm and cold periods. The rings in trees provide clues about wet and dry periods. Historical records describe the vagaries in climate. All these evidences indicate that change in climate is a natural and continuous process.

📖 Definition — Palaeoclimatology
Palaeoclimatology? is the study of climates of the past. By reading proxy records — fossils, sediment layers, ice cores, tree rings, pollen and corals — palaeoclimatologists reconstruct temperatures and rainfall stretching back thousands and even millions of years.

Evidence — How Do We Know What Past Climates Were Like?

🦴
Fossils & Pollen
Plant and animal remains preserved in rock or peat reveal the temperature and moisture in which the species lived.
🧊
Ice Cores
Cores drilled from Greenland and Antarctic ice sheets trap tiny air bubbles that preserve the atmosphere of the moment the snow fell.
🌳
Tree Rings (Dendrochronology)
Wide rings indicate warm, wet years; narrow rings record cold or dry years — yielding annual climate records for centuries.
🪨
Sediments & Landforms
Glacial moraines, lake-bed varves and ocean-floor sediments record the comings and goings of ice ages.

India and the Indian Subcontinent — Wet and Dry Cycles

India also witnessed alternating wet and dry periods. Archaeological findings show that the Rajasthan desert experienced wet and cool climate around 8,000 BC. The period 3,000–1,700 BC had higher rainfall. From about 2,000–1,700 BC, this region was the centre of the Harappan civilisation. Dry conditions accentuated since then — pushing Harappan settlements to migrate eastward and leaving behind buried cities in the now-arid Saraswati and Ghaggar river valleys.

Climate Change in the Geological Past

In the geological past, the earth was warm some 500–300 million years ago, through the Cambrian, Ordovician and Silurian periods. During the Pleistocene? epoch (the most recent ice age), glacial and inter-glacial periods alternated repeatedly. The last major peak glacial period was about 18,000 years ago. The present inter-glacial period (the Holocene)? started 10,000 years ago — and it is in this comparatively warm and stable inter-glacial that all of human civilisation, agriculture and recorded history have developed.

Climate Through Time — A Schematic Timeline

Cambrian–Silurian 500–300 Ma · Warm Pleistocene Ice Ages Glacial & inter-glacial cycles · last peak 18,000 yr ago Holocene Last 10,000 yr · stable warm inter-glacial Little Ice Age 1550–1850 Modern Warming +0.6°C in 20th c. PAST PRESENT Climate Has Always Been Changing — But Today It Is Changing Fast

11.9 Climate in the Recent Past

Variability in climate occurs all the time. The 1990s witnessed extreme weather events. That decade recorded the warmest temperatures of the 20th century and some of the worst floods around the world. The devastating drought in the Sahel region (south of the Sahara) from 1967 to 1977 is one such variability. During the 1930s, severe drought struck the south-western Great Plains of the United States — described as the Dust Bowl. Historical records of crop yields, of crop failures, of floods and migration of people all tell about the effects of changing climate. A number of times Europe witnessed warm, wet, cold and dry periods. The significant episodes were the warm and dry conditions in the 10th and 11th centuries, when the Vikings settled in Greenland.

❄️ The Little Ice Age (1550–1850)
Europe witnessed the "Little Ice Age" from 1550 to about 1850. Glaciers advanced in the Alps, Norwegian farms were abandoned under fresh ice, the Thames in London froze regularly enough for "frost fairs" to be held on it, and severe winters extended across the entire North Atlantic. From about 1885–1940 world temperature showed an upward trend. After 1940, the rate of increase in temperature slowed down — only to accelerate again towards the end of the century.

11.10 Causes of Climate Change

The causes of climate change are many. NCERT groups them broadly into astronomical and terrestrial causes.

Astronomical Causes

Astronomical causes are changes in solar output associated with sunspot activity. Sunspots are dark and cooler patches on the Sun which increase and decrease in a cyclical manner (about an 11-year cycle). According to some meteorologists, when the number of sunspots increases, cooler and wetter weather and greater storminess occur; a decrease in sunspot number is associated with warm and drier conditions. Yet, these findings are not statistically significant — sunspot effects on terrestrial climate are real but small.

Another astronomical theory is the Milankovitch oscillations, which refer to long, slow cycles in the variations of:

  • the earth's orbital characteristics around the Sun (the eccentricity of its ellipse);
  • the wobbling of the earth (precession of the equinoxes);
  • the changes in the earth's axial tilt (obliquity).

All these alter the amount of insolation received from the Sun, which in turn might have a bearing on climate — particularly on the timing of ice ages.

Terrestrial Causes — Volcanism

Volcanism is considered another cause for climate change. A volcanic eruption throws lots of aerosols into the atmosphere. These aerosols remain in the atmosphere for a considerable period of time, reducing the Sun's radiation reaching the earth's surface. After the recent Pinatubo and El Chichón volcanic eruptions, the average temperature of the earth fell to some extent for some years.

Anthropogenic Causes — The Greenhouse Effect

The most important anthropogenic? effect on climate is the increasing trend in the concentration of greenhouse gases in the atmosphere, which is likely to cause global warming. This is the change that today dominates the discussion of climate.

11.11 Global Warming and the Greenhouse Effect

Due to the presence of greenhouse gases?, the atmosphere behaves like a greenhouse. It transmits the incoming short-wave solar radiation but absorbs the vast majority of the long-wave radiation emitted upwards by the earth's surface. The gases that absorb long-wave radiation are called greenhouse gases. The processes that warm the atmosphere in this way are collectively called the greenhouse effect.

🌱 Why "Greenhouse"?
The term is borrowed from the glasshouses used in cold areas to grow plants. Glass is transparent to incoming short-wave solar radiation but opaque to outgoing long-wave radiation. The glass therefore allows in more radiation than it lets out, so the air inside becomes warmer than outside. When you enter a parked car or bus on a summer afternoon — windows up — you feel more heat than outside. Likewise, a winter vehicle with closed doors and windows stays warmer than the air outside. The atmosphere does the same thing on a planetary scale.

How the Greenhouse Effect Works

SUN Short-wave solar radiation (passes through) Some escape to space CO₂ CH₄ N₂O CFCs EARTH'S SURFACE Surface emits long-wave (infrared) radiation upward

11.12 Greenhouse Gases (GHGs)

The primary GHGs of concern today are carbon dioxide (CO₂), chlorofluorocarbons (CFCs), methane (CH₄), nitrous oxide (N₂O) and ozone (O₃). Some other gases such as nitric oxide (NO) and carbon monoxide (CO) easily react with GHGs and affect their concentration in the atmosphere. Water vapour is also a powerful greenhouse gas, but its concentration is regulated by temperature itself, and it acts as a feedback rather than as a primary forcing agent.

CO₂
Carbon Dioxide
From fossil fuel combustion (oil, gas, coal) and deforestation. Largest concentration among GHGs.
CH₄
Methane
From paddy fields, livestock, wetlands and natural gas leaks.
N₂O
Nitrous Oxide
From fertilisers, industrial processes and biomass burning.
CFCs
Chlorofluorocarbons
Purely human-made. Used in refrigeration, aerosols. Highly effective greenhouse and ozone-destroying gas.
O₃
Ozone
Stratospheric ozone shields life from UV; tropospheric ozone is a strong greenhouse gas.
H₂O
Water Vapour
Most abundant greenhouse gas; acts as a feedback that amplifies warming from CO₂.

The effectiveness of any GHG molecule depends on three things: the magnitude of the increase in its concentration, its lifetime in the atmosphere and the wavelength of radiation that it absorbs. CFCs are highly effective per molecule. Ozone, which absorbs ultra-violet radiation in the stratosphere, is very effective in absorbing terrestrial radiation when it is present in the lower troposphere. The longer a GHG molecule remains in the atmosphere, the longer it will take for the earth's atmospheric system to recover from any change.

Carbon Dioxide — The Big One

The largest concentration of GHGs in the atmosphere is carbon dioxide. Emissions of CO₂ come mainly from fossil fuel combustion (oil, gas and coal). Forests and oceans are the sinks for carbon dioxide. Forests use CO₂ in their growth, so deforestation due to changes in land use also increases the concentration of CO₂. The time taken for atmospheric CO₂ to adjust to changes in sources to sinks is 20–50 years. It is rising at about 0.5 per cent annually. Doubling of the concentration of CO₂ over the pre-industrial level is used as an index for estimating climatic changes in climate models.

CFCs and the Ozone Hole

Chlorofluorocarbons (CFCs) are products of human activity. Ozone occurs in the stratosphere where ultra-violet rays convert oxygen into ozone — and so UV rays do not reach the earth's surface. The CFCs which drift into the stratosphere destroy the ozone. Large depletion of ozone occurs over Antarctica. The depletion of ozone concentration in the stratosphere is called the ozone hole. This allows ultra-violet rays to pass through into the troposphere — a serious threat to plant and animal life.

11.13 International Responses

International efforts have been initiated for reducing the emission of GHGs into the atmosphere. The most important early treaty is the Kyoto Protocol? proclaimed in 1997. This protocol went into effect in 2005, ratified by 141 nations. The Kyoto Protocol bound the 35 industrialised countries to reduce their emissions by the year 2012 to 5 per cent less than the levels prevalent in 1990.

🌐 Beyond Kyoto — The Continuing Effort
After Kyoto, the world community moved through a series of UNFCCC Conferences of the Parties (COP) meetings. The Paris Agreement (2015) at COP21 set the goal of holding global warming "well below 2°C above pre-industrial levels", and pursuing efforts to limit it to 1.5°C. Each country submits its own Nationally Determined Contribution (NDC). The IPCC Assessment Reports (1990, 1995, 2001, 2007, 2014, 2021–23) have, in successive volumes, made the scientific basis for action ever more certain.

India's Climate Action

India's role in the climate negotiations rests on the principle of "common but differentiated responsibilities". India ratified the Paris Agreement in 2016, has set targets for renewable energy capacity (500 GW non-fossil by 2030), launched the International Solar Alliance (ISA) with France and announced a long-term goal of net-zero emissions by 2070. Domestic missions such as the National Action Plan on Climate Change, the National Solar Mission and the LIFE (Lifestyle for Environment) campaign extend climate policy from the international stage to households.

11.14 How Much Has the Planet Warmed?

One of the major concerns of the world today is global warming. Let us look at how much the planet has warmed up from the temperature records.

📊 The Numbers (NCERT)
  • The annual average near-surface air temperature of the world is approximately 14°C.
  • An increasing trend in temperature was discernible in the 20th century.
  • The greatest warming was during two periods: 1901–44 and 1977–99. Over each of these two periods, global temperatures rose by about 0.4°C.
  • In between, there was a slight cooling, more marked in the Northern Hemisphere.
  • The globally averaged annual mean temperature at the end of the 20th century was about 0.6°C above that recorded at the end of the 19th century.
  • The seven warmest years between 1856 and 2000 were recorded in the last decade of the century.
  • The year 1998 was the warmest year — probably not only of the 20th century but of the whole millennium.

Global Temperature Anomaly (illustrative — based on NCERT figures)

The two warming pulses (1901–44 and 1977–99) each added about 0.4°C; together with the 1998 spike, the late-20th-century world ended about 0.6°C above the late-19th-century baseline.

Atmospheric CO₂ Concentration — Rising Steadily

Atmospheric CO₂ is rising at about 0.5 per cent annually. The pre-industrial level was around 280 ppm (parts per million); it has now crossed 420 ppm — a growth steeper than any in 800,000 years of ice-core records.

11.15 Effects of Climate Change

🌊
Sea Level Rise
Thermal expansion of seawater + melting of glaciers and ice caps. Inundation of coastal areas and low islands.
🏔️
Glacier Retreat
Himalayan, Alpine and Andean glaciers retreating. Threat to dry-season river flow for billions downstream.
🌪️
Extreme Weather
More intense heat waves, droughts, floods and tropical cyclones. The 1990s recorded the worst floods of the century.
🌾
Agriculture & Food
Shifting cropping zones; yield declines for staples in tropical regions; rising risk of crop failure.
🦋
Biodiversity
Range shifts, coral bleaching, mismatched timing of flowering and pollinators, extinction risk.
🩺
Human Health
Heat-stroke, vector-borne diseases (malaria, dengue) spreading to higher latitudes; air-pollution mortality.

The increasing trend in the concentration of GHGs may, in the long run, warm up the earth. Once global warming sets in, it will be difficult to reverse. The effect of global warming may not be uniform everywhere. The adverse effect will affect the life-supporting system. Rise in sea level due to melting of glaciers and ice caps and thermal expansion of the sea may inundate large parts of the coastal area and islands, leading to social problems. This is another cause for serious concern for the world community. Efforts have already been initiated to control the emission of GHGs and to arrest the trend towards global warming. Let us hope the world community responds to this challenge and adopts a lifestyle that leaves behind a livable world for the generations to come.

Think About It — Write an Explanatory Note on "Global Warming"

(NCERT in-text task) Write an explanatory note on global warming.

Sample answer: Global warming is the long-term rise in the average near-surface temperature of the earth due to the increasing concentration of greenhouse gases (CO₂, CH₄, N₂O, CFCs and ozone) in the atmosphere. The atmosphere is transparent to incoming short-wave solar radiation but opaque to outgoing long-wave radiation, so the additional GHGs trap more heat near the surface — the greenhouse effect. Globally averaged temperature at the end of the 20th century was about 0.6°C above that of the end of the 19th century, with the warmest year being 1998. Major causes include fossil-fuel combustion, deforestation, agriculture and industrial CFC emissions. Effects include sea-level rise, glacier retreat, extreme weather events, biodiversity loss and threats to agriculture and human health. International responses include the Kyoto Protocol (1997, in force 2005) and the Paris Agreement (2015), supplemented by the IPCC Assessment Reports.

Discuss — Lifestyle Changes That Cut GHG Emissions

Discuss in groups: name five everyday actions an Indian school student can take to reduce GHG emissions.

  • Switch off appliances, lights and fans when not in use — every kWh saved means less CO₂ from coal-fired power.
  • Walk, cycle or use public transport for short distances instead of private cars.
  • Eat less meat — particularly red meat — to reduce livestock methane.
  • Plant and care for trees — small school-and-home plantations are local CO₂ sinks.
  • Avoid single-use plastics and reduce waste — landfill methane is a strong GHG.
Source — IPCC Assessment Reports

What do the IPCC reports say, in increasing certainty?

IPCC Assessment Reports — paraphrased summary

The successive IPCC reports have moved from "warming is likely" (1990) to "warming is unequivocal and human-caused" (2014, 2021). The reports also underline that limiting warming to 1.5°C requires roughly halving global CO₂ emissions by 2030 and reaching net-zero around 2050.

🎯 Competency-Based Questions — Climate Change & Global Warming

A UN climate-change youth panel is preparing a brief for delegates. Use the chapter to answer the questions on causes, effects and policy.
1. Atmospheric CO₂ takes 20–50 years to adjust to changes in its sources and sinks. What is the policy significance of this residence time?
L4 Analyse
Answer: Even if we cut emissions today, the CO₂ already in the air will continue warming the planet for decades. Therefore, climate-policy targets must be set early — waiting to act only locks in further warming. This is why the Paris Agreement set a 1.5°C "carbon budget" goal and emphasised peaking emissions now rather than at the end of the century.
2. Compare the role of volcanism and greenhouse-gas emissions as drivers of climate change. Which is more important on the timescale of decades, and why?
L5 Evaluate
Answer: A large volcanic eruption (Pinatubo, El Chichón) injects sulphate aerosols into the stratosphere and cools the earth by about 0.3–0.5°C, but this cooling lasts only 1–3 years before aerosols rain out. GHGs like CO₂ remain for 20–50 years and accumulate. Over decades, the warming pulse from rising GHGs dwarfs the brief cooling from any single volcano. Hence, on the human-policy timescale, anthropogenic GHGs are the dominant driver.
3. The 1990s recorded both the warmest temperatures and "some of the worst floods around the world". Are these two observations connected? Justify in 4–5 lines.
L4 Analyse
Answer: Yes — the two are connected. A warmer atmosphere holds more water vapour (about 7% more for every 1°C of warming), so when rain does fall it falls more intensely. Warmer oceans also fuel stronger tropical cyclones. Both effects translate higher mean temperatures into more frequent and severe floods. The 1990s pattern is consistent with this physical link, which is why the IPCC reports flag extreme precipitation as one of the most confidently attributable signals of warming.
4. HOT — Higher Order Thinking: Design a simple "Climate Action Pledge" for your classroom that targets the three biggest sources of household GHGs in India. Justify each target with a number.
L6 Create
Answer (sample): Three pledges — (i) Save electricity: switch off ACs, lights, and devices when leaving a room; one ceiling fan running 24×7 unnecessarily wastes ≈ 600 kWh/year ≈ 480 kg of CO₂. (ii) Choose plant-rich meals: a kilogram of beef emits about 60 kg CO₂-eq, while a kilogram of pulses emits under 2 kg; replacing meat once a week saves ≈ 200 kg CO₂/year per person. (iii) Walk-cycle short trips: a petrol two-wheeler emits ≈ 35 g CO₂/km; replacing a daily 4-km school trip with cycling saves ≈ 100 kg CO₂/year. Total per student: roughly 0.8 tonnes CO₂/year — multiplied by a class of 40, the saving = 32 tonnes per year.
⚖️ Assertion–Reason Questions — Climate Change
Assertion (A): The atmosphere acts like a greenhouse.
Reason (R): The atmosphere transmits incoming short-wave solar radiation but absorbs much of the long-wave radiation emitted by the earth's surface.
Correct: Both A and R are true and R is the correct explanation of A.
The wavelength-selective behaviour of GHGs (transparent to short-wave, opaque to long-wave) is precisely what makes the atmosphere greenhouse-like. Without it, mean surface temperature would be near −18°C instead of 14°C.
Assertion (A): The Kyoto Protocol binds developed and developing countries equally to reduce emissions.
Reason (R): The Kyoto Protocol came into force in 2005, ratified by 141 nations.
Correct: A is false but R is true.
Kyoto bound only the 35 industrialised countries to reduce emissions by 2012 to 5% below 1990 levels. Developing countries had no binding emission target — that asymmetry was deliberate, reflecting "common but differentiated responsibilities". The Paris Agreement (2015) extended commitments to all parties, but in the form of voluntary NDCs.
Assertion (A): CFCs are particularly damaging because they destroy stratospheric ozone.
Reason (R): CFCs are products of human activity that drift up into the stratosphere where they release chlorine atoms.
Correct: Both A and R are true and R is the correct explanation of A.
Chlorine atoms catalyse the breakdown of ozone molecules in the stratosphere; large depletion has been observed over Antarctica, called the ozone hole. CFCs are also a powerful greenhouse gas — making them doubly damaging.

📝 NCERT Exercises — Chapter 11

Complete model answers for all NCERT exercises and project work.

1. Multiple Choice Questions

(i) Which one of the following is suitable for Köppen's "A" type of climate?

  1. High rainfall in all the months
  2. Mean monthly temperature of the coldest month more than freezing point
  3. Mean monthly temperature of all the months more than 18°C
  4. Average temperature for all the months below 10°C
Answer: (c) Mean monthly temperature of all the months more than 18°C. Köppen's A is defined by the coldest month being 18°C or higher, so all months will be above 18°C. (Option (b) describes group C; (d) describes E.)

(ii) Köppen's system of classification of climates can be termed as:

  1. Applied
  2. Systematic
  3. Genetic
  4. Empirical
Answer: (d) Empirical. Köppen's scheme uses observed temperature and precipitation values to set boundaries — the very definition of an empirical classification.

(iii) Most of the Indian Peninsula will be grouped according to Köppen's system under:

  1. "Af"
  2. "BSh"
  3. "Cfb"
  4. "Am"
Answer: (d) Am. Most of the Indian Peninsula has a tropical monsoon climate — heavy summer rainfall and a short dry winter — fitting Köppen's Am category.

(iv) Which one of the following years is supposed to have recorded the warmest temperature the world over?

  1. 1990
  2. 1998
  3. 1885
  4. 1950
Answer: (b) 1998. NCERT specifically notes that 1998 was the warmest year — probably for the entire 20th century and the millennium up to that point.

(v) Which one of the following groups of four climates represents humid conditions?

  1. A — B — C — E
  2. A — C — D — E
  3. B — C — D — E
  4. A — C — D — F
Answer: (b) A — C — D — E. Köppen distinguishes humid climates (A, C, D, E) from dry climates (B). Therefore the four humid groups are A, C, D and E.

2. Answer the following questions in about 30 words

(i) Which two climatic variables are used by Köppen for classification of the climate?

Answer: Köppen used temperature (mean annual and mean monthly) and precipitation as the two climatic variables. Capital-letter groups are based on temperature thresholds — except group B, which is based on precipitation (potential evaporation exceeding rainfall).

(ii) How is the "genetic" system of classification different from the "empirical" one?

Answer: The empirical system (e.g. Köppen's) starts from observed temperature and precipitation data, drawing climatic boundaries where the numbers change. The genetic system, by contrast, organises climates by their causes — air masses, pressure belts, ocean currents and global wind systems.

(iii) Which types of climates have very low range of temperature?

Answer: The tropical wet (Af) climate — near the equator with the Sun overhead all year — has an extremely low annual range of temperature. The marine west coast (Cfb) climate also has small annual and daily ranges due to the moderating influence of the sea.

(iv) What type of climatic conditions would prevail if the sunspots increase?

Answer: According to some meteorologists, when the number of sunspots increases, conditions become cooler and wetter, with greater storminess. Decreasing sunspots are associated with warmer, drier conditions. NCERT also notes that these findings are not statistically very strong.

3. Answer the following questions in about 150 words

(i) Make a comparison of the climatic conditions between the "A" and "B" types of climate.

Answer: The A — Tropical Humid climates lie between the Tropics of Cancer and Capricorn. They are hot and humid: the average temperature of the coldest month is 18°C or higher, the annual range is very low, and rainfall is high (up to 200+ cm). Three sub-types — Af (rain every month, max 30°C / min 20°C, evergreen forest), Am (heavy summer monsoon rain, short dry winter), and Aw (long dry winter, savanna with deciduous forest) — cover the equatorial belt.

The B — Dry climates, on the other hand, are defined by moisture deficit: potential evaporation exceeds precipitation. They cover 15°–60° latitude in both hemispheres, occupying the subtropical highs (15°–35° → BSh, BWh) and continental interiors (35°–60° → BSk, BWk). Rainfall is meagre and highly variable; diurnal and annual ranges of temperature are large; the highest shade temperature on earth (58°C, Al Aziziyah, Libya, 13 September 1922) was recorded here. Vegetation is sparse — short grasses or scattered xerophytic shrubs. Thus A is hot-wet and biologically lush, while B is hot-dry and biologically sparse.

(ii) What type of vegetation would you find in the "C" and "A" type(s) of climate?

Answer: The A — Tropical Humid climates support three distinct vegetation types. The Af — Tropical Wet climate of the Amazon, Congo and East Indies hosts tropical evergreen forest — a dense, multi-storey canopy with extraordinary biodiversity. The Am — Tropical Monsoon climate of the Indian sub-continent supports tropical monsoon (deciduous) forest, where teak and sal shed leaves in the dry season. The Aw — Tropical Wet and Dry climate of Brazil, Sudan and central Africa supports savanna — tree-shredded grasslands with deciduous forest.

The C — Warm Temperate (mid-latitude) climates support equally varied vegetation. The Cs — Mediterranean climate produces sclerophyll evergreen scrub with olives, citrus, vines and cork oak — adapted to the hot dry summer. The Cfa — humid subtropical climate supports mixed deciduous and evergreen forest. The Cfb — marine west coast climate supports temperate deciduous and mixed forest (oak, beech, pine), and the Cwa belt supports the cultivated subtropical landscape of the North Indian and South Chinese plains.

(iii) What do you understand by the term "Greenhouse Gases"? Make a list of greenhouse gases.

Answer: Greenhouse gases (GHGs) are atmospheric gases that transmit incoming short-wave solar radiation but absorb the outgoing long-wave (infrared) radiation emitted by the earth's surface. By trapping this heat, they keep the lower atmosphere warmer than it would be otherwise — a process called the greenhouse effect. Without natural GHGs, the earth's mean surface temperature would be around −18°C; with them, it is about 14°C. The greenhouse effect is therefore essential for life. The problem today is the rising concentration of GHGs from human activity, which is enhancing this effect and causing global warming.

List of greenhouse gases:
  • Carbon dioxide (CO₂) — from fossil-fuel combustion and deforestation; the largest concentration of GHGs.
  • Methane (CH₄) — from paddy fields, cattle, landfills.
  • Nitrous oxide (N₂O) — from fertilisers and industrial processes.
  • Chlorofluorocarbons (CFCs) — purely human-made; also destroy stratospheric ozone.
  • Ozone (O₃) — stratospheric ozone shields life, but tropospheric ozone is a strong GHG.
  • Water vapour (H₂O) — most abundant; acts as a feedback amplifier.
  • Reactive helpers: nitric oxide (NO) and carbon monoxide (CO), which alter GHG concentrations.

📚 Project Work

Collect information about the Kyoto declaration related to global climate changes.

Project Outline — The Kyoto Protocol

Background: Adopted at Kyoto, Japan, 11 December 1997 at the third Conference of the Parties (COP3) to the UN Framework Convention on Climate Change. Came into force on 16 February 2005, after ratification by 141 nations.

Key features:
  • Binding emission-reduction commitments for 35 industrialised countries ("Annex I" parties).
  • Target: 5% below 1990 emission levels on average, to be achieved during the 2008–2012 commitment period.
  • Six greenhouse gases covered: CO₂, CH₄, N₂O, HFCs, PFCs and SF₆.
  • Three "flexibility mechanisms" — Clean Development Mechanism (CDM), Joint Implementation, and Emissions Trading.
  • Developing countries (including India) had no binding targets — reflecting the principle of common but differentiated responsibilities.

India's role: Ratified Kyoto in 2002. Hosted many CDM projects in renewable energy and methane capture. Argued strongly that industrialised countries — historically the largest emitters — must lead.

Successor: The Doha Amendment (2012) extended Kyoto to 2020. The Paris Agreement (2015, COP21) succeeded Kyoto and now applies to all parties through Nationally Determined Contributions (NDCs), with the goal of limiting warming to well below 2°C and pursuing 1.5°C.

Sources to consult: UNFCCC website (unfccc.int), IPCC AR4–AR6 reports, Ministry of Environment, Forest and Climate Change (India) website, news archives 1997 and 2005.

📌 Chapter Summary

  • Climate can be classified by three approaches — empirical (data-driven), genetic (cause-driven) and applied (purpose-driven).
  • Köppen's empirical scheme (1918) uses temperature and precipitation thresholds and is still the most widely used.
  • Köppen identified five major groups: A (Tropical), B (Dry), C (Warm Temperate), D (Cold Snow-forest), E (Polar) — plus H (Highland).
  • A: Af — tropical wet; Am — monsoon; Aw — wet & dry savanna. B: BS steppe, BW desert with h (hot) and k (cold) subtypes. C: Cwa (China), Cs (Mediterranean), Cfa (humid subtropical), Cfb (marine west coast). D: Df (humid winter), Dw (dry winter Eurasian taiga). E: ET (tundra), EF (ice cap).
  • Climate change is natural and continuous — geological evidence (fossils, ice cores, tree rings, sediments) shows alternating glacial–interglacial periods. The Pleistocene last peak was 18,000 years ago; the present Holocene interglacial began 10,000 years ago.
  • Europe's Little Ice Age ran from about 1550 to 1850; world temperature rose 1885–1940, slowed after 1940, and rose strongly again in the late 20th century.
  • Causes of climate change are astronomical (sunspots, Milankovitch oscillations), terrestrial (volcanism) and increasingly anthropogenic (greenhouse gases).
  • The greenhouse effect: GHGs (CO₂, CH₄, N₂O, CFCs, O₃, H₂O) transmit short-wave solar radiation but absorb outgoing long-wave radiation. CO₂ rises ~0.5%/year; residence time 20–50 years.
  • 20th century warming totalled about 0.6°C, with two pulses (1901–44 and 1977–99 of ~0.4°C each); 1998 was the warmest year.
  • International responses: Kyoto Protocol (1997, in force 2005); the Paris Agreement (2015); successive IPCC Assessment Reports; India's NDCs, ISA and net-zero-2070 pledge.

📚 Key Terms

Climate ClassificationThe systematic grouping of world climates into manageable units.
Empirical ApproachClimate classification based on observed temperature and precipitation data.
Genetic ApproachClimate classification based on the causes — air masses, pressure belts, currents.
Köppen's Scheme1918 empirical scheme of climate classification using temperature and precipitation thresholds.
ITCZInter Tropical Convergence Zone — the equatorial belt of converging trades.
Steppe (BS)Semi-arid dry climate with sparse grassland.
Desert (BW)Arid dry climate with very low rainfall.
Mediterranean (Cs)Hot dry summer, mild rainy winter — subtropical west-coast climate.
Marine West Coast (Cfb)Mild, rainy, small-range climate of west-coast mid-latitudes.
Taiga / Subarctic (Dw)Cold dry winter, summer rain — boreal coniferous belt of NE Asia.
Tundra (ET)Cold polar climate of permafrost, mosses and lichens.
Ice Cap (EF)All months below freezing — Greenland and Antarctica.
PalaeoclimatologyStudy of climates of the past from proxy records.
PleistoceneRecent geological epoch of repeated glacial–interglacial cycles.
HolocenePresent interglacial epoch, beginning 10,000 years ago.
Little Ice AgeCool period in Europe from 1550 to about 1850.
Milankovitch OscillationsLong cycles in earth's orbit, wobble and tilt that alter insolation.
SunspotsDark, cooler patches on the Sun varying on an 11-year cycle.
AnthropogenicCaused or produced by human activity.
Greenhouse EffectWarming caused by atmospheric absorption of long-wave radiation.
Greenhouse Gas (GHG)Atmospheric gas that traps long-wave radiation: CO₂, CH₄, N₂O, CFCs, O₃, H₂O.
CFCsChlorofluorocarbons — synthetic greenhouse and ozone-destroying gases.
Ozone HoleSevere depletion of stratospheric ozone, especially over Antarctica.
Kyoto Protocol1997 treaty binding 35 industrialised nations to cut emissions by 5% below 1990 levels by 2012.
Paris Agreement2015 climate treaty under UNFCCC limiting warming to well below 2°C, pursuing 1.5°C.
IPCCIntergovernmental Panel on Climate Change — issues Assessment Reports synthesising science.
COPConference of the Parties — annual UNFCCC negotiating meeting.
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Class 11 Geography — Fundamentals of Physical Geography
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