World Climate and Climate Change

WORLD CLIMATE AND CLIMATE CHANGE

CLIMATE CLASSIFICATION APPROACHES

Climate classification is the systematic organization of climate data and information into manageable units for analysis and understanding. Three broad approaches are used:

**Empirical Classification**: Based on observed climate data, particularly temperature and precipitation records. Does not explain the causes of climate patterns.

**Genetic Classification**: Organizes climates according to their causes — atmospheric pressure systems, wind patterns, and air masses that produce specific climates.

**Applied Classification**: Developed for specific purposes such as agriculture, urban planning, or resource management.

KOEPPEN'S SCHEME OF CLIMATE CLASSIFICATION

**Definition**: The most widely used empirical climate classification system developed by **Wladimir Koeppen in 1918** and refined over time. It relates climate to vegetation distribution and uses temperature and precipitation data.

**Key Characteristics**:

Based on mean annual and mean monthly temperature and precipitation data

Uses capital letters (A, B, C, D, E) for major climatic groups

Uses small letters (a, b, c, d, f, m, w, s) to designate climatic types

Identifies close relationship between climate and vegetation zones

Still widely used in geography and meteorology despite being over a century old

**Five Major Climatic Groups**:

1. **Group A — Tropical Humid Climates**: Average temperature of coldest month ≥ 18°C

2. **Group B — Dry Climates**: Potential evaporation exceeds precipitation

3. **Group C — Warm Temperate (Mid-Latitude) Climates**: Average temperature of coldest month > -3°C but < 18°C

4. **Group D — Cold Snow Forest Climates**: Average temperature of coldest month ≤ -3°C

5. **Group E — Cold/Polar Climates**: Average temperature for all months < 10°C

**Small Letter Designations**:

**f** = No dry season (from German "feucht" meaning moist)

**m** = Monsoon climate (short dry season)

**w** = Winter dry season

**s** = Summer dry season

**a, b, c, d** = Degree of temperature severity (a = hot summers; b = warm summers; c = cool summers; d = extremely cold winters)

**B Group Subdivisions**:

**BS** = Steppe or semi-arid climate (transition between humid and desert)

**BW** = Desert or arid climate (annual precipitation very low)

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GROUP A: TROPICAL HUMID CLIMATES

Tropical humid climates exist between the **Tropic of Cancer (23.5°N) and Tropic of Capricorn (23.5°S)**.

**Characteristics**:

Overhead sun throughout the year creates intense solar radiation

**Inter-Tropical Convergence Zone (ITCZ)** brings persistent rainfall

Annual temperature range is **very low** (< 5°C) — uniformly hot year-round

High annual rainfall (1500-2500 mm minimum)

Weathering is intense; laterite soils common

Dense vegetation with high biodiversity

Tropical Wet Climate (Af)

**Distribution**: Equatorial regions — Amazon Basin (South America), Western equatorial Africa, East Indies

**Characteristics**:

Rainfall **every month** in the form of afternoon thundershowers

Total annual rainfall: 1500-2250 mm minimum

Maximum temperature: ~30°C; Minimum: ~20°C

Annual temperature range: < 3°C

High humidity and cloud cover typical

No true dry season

**Vegetation & Soils**:

**Tropical evergreen rainforests** with dense canopy

Largest repository of biodiversity on Earth

Red laterite soils develop due to intense leaching

Thick humus layer despite heavy rainfall

**Example**: Amazon rainforest experiences Af climate with rainfall throughout the year.

Tropical Monsoon Climate (Am)

**Distribution**: **Indian sub-continent**, northeastern South America, northern Australia

**Characteristics**:

Heavy rainfall concentrated in **summer season** (monsoon season)

Distinct **dry winter** season

Short dry season distinguishes it from Af

Temperature high throughout year

Monsoonal wind reversal brings seasonal rainfall

**Vegetation**: Tropical deciduous and semi-evergreen forests adapted to dry season

**Note**: Detailed discussion in *India: Physical Environment* textbook as this is crucial for Indian climate.

Tropical Wet and Dry Climate (Aw)

**Distribution**: North and south of Af regions — northern and southern Amazon basin (Brazil, Bolivia, Paraguay), Sudan, Central Africa

**Characteristics**:

**Shorter wet season and longer dry season** compared to Am and Af

Annual rainfall significantly lower and **highly variable** — 750-1500 mm

Pronounced dry season creates water stress

**Drought more severe** than in Am type — affects livestock and agriculture

Temperature high throughout year

**Greatest diurnal temperature range during dry season** due to clear skies

**Seasonality**:

Wet season: 4-6 months

Dry season: 6-8 months of minimal precipitation

**Vegetation & Soils**:

**Deciduous forests** — trees shed leaves during dry season

**Tree-shredded grasslands** (savannas) — interspersed trees with grassland

Dark clay soils; some laterization

Sparse tree cover compared to Af region

**Example**: Brazilian cerrado (grasslands) and African savanna experience Aw climate with distinct wet-dry seasons.

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GROUP B: DRY CLIMATES

**Definition**: Climates where **potential evaporation exceeds precipitation**, making rainfall inadequate for vegetation growth. Covers largest latitudinal range (15°-60° N and S).

**Characteristics**:

Annual precipitation insufficient for plants — typically < 500 mm

High evaporation rates due to temperature and wind

Sparse vegetation or bare land

Large temperature ranges (diurnal and annual)

Subsurface storage of salt due to evaporation

Minimal cloud cover; high insolation

**Distribution Pattern**:

**Low Latitudes (15°-30°)**:

Located in **subtropical high-pressure belts** — descending dry air

Subsidence and temperature inversion prevent rainfall

Western continental margins with cold ocean currents (Peru, SW Africa, California) — cool currents suppress convection

**Mid-Latitudes (35°-60°)**:

**Interior continental locations** — far from maritime air masses

**Rain shadow areas** — windward mountains intercept moisture

Surrounded by mountains blocking humid winds

Examples: Central Asia, interior North America

Subtropical Steppe Climate (BSh) and Subtropical Desert Climate (BWh)

**Distribution**: Latitudes 15°-35° (both hemispheres)

Sahara Desert, Arabian Desert, Kalahari, Australian Desert

Southwestern United States, northwestern Mexico

Parts of Peru and Chile

**Characteristics (both BSh and BWh)**:

**Precipitation**:

**Highly variable and unreliable** — major issue for people

Short, intense thundershowers in deserts — water runs off, doesn't soak in

Rainfall ineffective in building soil moisture

BSh receives slightly more than BWh — enough for sparse grasslands

Variability in steppe causes frequent famines more than in desert

**Temperature**:

Extremely high summer temperatures — **highest recorded: 58°C at Al Aziziyah, Libya (September 1922)**

Large **annual temperature range** (20-30°C) — cold winters possible

Large **diurnal temperature range** (15-20°C) — intense daytime heating, rapid nighttime cooling due to low cloud cover

Winter frosts common in inland areas

**Distinguishing Feature**:

**Steppe (BSh)**: Sparse short grass, scrub vegetation — transition zone between humid and desert

**Desert (BWh)**: Bare ground, scattered shrubs, minimal vegetation

**Special Feature**: **Fog common in coastal deserts** bordering cold ocean currents (Peru, Namibia, California coasts) — cold water cools air, causes condensation

**Vegetation & Soils**:

Hardy grasses, cacti, thorny shrubs

Brown, gray soils with salt accumulation

Minimal organic matter

**Example**: Sahara Desert experiences BWh with extreme heat and minimal rainfall; Sahel region shows BSh with sparse grasslands.

Mid-Latitude Steppe Climate (BSk) and Mid-Latitude Desert Climate (BWk)

**Distribution**: Latitudes 35°-60°

Central Asia (Mongolia, Kazakhstan), interior of continents

Great Basin (USA), Patagonia (Argentina)

Interior Scandinavia, interior Russia

**Characteristics**:

Similar precipitation patterns to subtropical B climates — variable and low

Colder than subtropical counterparts — winters can be severe

Annual temperature range greater due to latitude

Summer temperatures still high in continental interiors

Vegetation: short grass (steppe) to barren (desert)

Often rain-shadow regions on lee side of mountains

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GROUP C: WARM TEMPERATE (MID-LATITUDE) CLIMATES

**Distribution**: 30°-50° latitude, mainly on **eastern and western continental margins**

**General Characteristics**:

**Warm summers and mild winters** — moderate year-round

Transition between tropical and cold climates

Four distinct types based on precipitation seasonality and temperature

Humid Subtropical Climate (Cwa)

**Distribution**: **North Indian plains, interior South China plains**, southeastern USA, southeastern Brazil

**Characteristics**:

**Similar to Aw tropical wet-dry** but with **warmer winters**

Winter dry season less pronounced than Aw

Summer hot and humid with convective rainfall

Mean annual temperature range: 15-20°C

**Precipitation**:

Variable, mostly summer concentration

Annual total: 750-1500 mm

**Example**: North Indian plains (Delhi, Lucknow) experience Cwa with hot summers, mild winters, and concentrated monsoon rainfall.

Mediterranean Climate (Cs)

**Distribution**: Around Mediterranean Sea; west coasts of continents at 30°-40° latitudes

Central California, central Chile

Southeastern and southwestern Australia

Mediterranean Europe

**Characteristics**:

**Hot, dry summer** and **mild, rainy winter** — opposite of monsoon pattern

Summer temperatures: ~25°C

Winter temperatures: < 10°C (mild, not freezing)

Annual precipitation: 35-90 cm (moderate, concentrated in winter)

Dominated by subtropical high in summer (dry) and westerlies in winter (wet)

**Why This Pattern**:

Summer: subtropical high-pressure system moves poleward, bringing dry, stable air

Winter: westerly winds bring mid-latitude cyclones with rain

**Vegetation & Soils**:

**Sclerophyll vegetation** — hard-leaved, drought-adapted shrubs

Cork oak, olive trees, Mediterranean pine

Brown soils; water stress in summer

Wildfires common in dry summers

**Example**: California coast and Mediterranean coast experience hot dry summers and cool rainy winters.

Humid Subtropical Climate (Cfa)

**Distribution**: **Eastern margins of continents** in subtropical latitudes

Eastern USA, southern and eastern China, southern Japan

Northeastern Argentina, coastal South Africa, eastern Australia

**Characteristics**:

**No dry season** — rain throughout year

**Warm summer** (mean ~27°C) and **cool winter** (mean 5°-12°C)

Small daily temperature range due to maritime influence and cloud cover

Air masses unstable — frequent rainfall

**Precipitation**:

Annual total: 75-150 cm well-distributed

Thunderstorms in summer (convective)

Frontal precipitation in winter (cyclonic)

**Weathering & Soil**:

Moderate to intense weathering

Red and yellow soils with good fertility

Humid subtropical forests — broadleaf evergreen and deciduous mix

**Example**: Southeastern USA (Georgia, Florida) with year-round rainfall and warm summers.

Marine West Coast Climate (Cfb)

**Distribution**: Poleward from Mediterranean climate on **west coasts of continents**

Northwestern Europe (British Isles, Scandinavia)

West coast North America (north of California)

Southern Chile, southeastern Australia, New Zealand

Generally 40°-60° latitude

**Characteristics**:

**Temperature**:

Summer: 15°-20°C (cool, not hot)

Winter: 4°-10°C (mild due to marine influence)

Small annual range due to oceanic effect

Small diurnal range — ocean moderates temperature fluctuations

**Warmest month cooler than Cfa** — distinguishing feature

**Precipitation**:

Occurs throughout year — no dry season

Highly variable: 50-250 cm depending on exposure to moisture and orographic effect

Frequent cyclonic activity in westerlies brings frequent overcast days

Morning fog common

**Vegetation & Soils**:

Mixed evergreen-deciduous forests (temperate rainforests in some areas)

Podzolic soils — acidic, low fertility under coniferous forest

Extensive grasslands in rain-shadow areas

Dense vegetation due to abundant moisture

**Example**: British Isles, coastal Scandinavia, and coastal Pacific Northwest (Seattle) experience cool summers, mild winters, and year-round rainfall.

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GROUP D: COLD SNOW FOREST CLIMATES

**Distribution**: **Large continental areas in northern hemisphere** — 40°-70° N latitude

Northern Europe, Asia, and North America

Boreal forest (taiga) zone

**General Characteristics**:

**Long, severe, snowy winters** and short summers

Winters extremely cold; summers provide only brief relief

Large annual temperature range (30-50°C difference)

Low precipitation, mostly summer

**Permafrost** in poleward areas — permanently frozen subsurface

Boreal forests and tundra vegetation

**Two Types**:

Cold Climate with Humid Winters (Df)

**Distribution**: Poleward from marine west coast climate and mid-latitude steppe

Central and northern Europe, central North America, southern Siberia

**Characteristics**:

**Winters cold and snowy** — below freezing for long periods

**Frost-free season short** — only 3-4 months for plant growth

Summer temperatures reach 15°-20°C, adequate for coniferous growth

Annual precipitation low but fairly well-distributed — 50-100 cm

**Large annual temperature range** — summer warmth vs. winter cold

Weather changes abrupt and frequent

**Snowfall**:

Heavy snow cover during winter — 30-100 cm common

Snow reflects solar radiation, contributing to cold

**Vegetation & Soils**:

Boreal forests (taiga) — dominated by conifers (spruce, fir, pine)

Thick moss and lichen understory

Podzolic soils — acidic, thin humus, little fertility

Permafrost in poleward areas

**Example**: Moscow, Canada's interior, and Scandinavia experience long cold snowy winters and short summers.

Cold Climate with Dry Winters (Dw)

**Distribution**: **Mainly northeastern Asia** — Siberia, Mongolia, Manchuria, parts of northern Japan

**Characteristics**:

**Wind Pattern**:

**Pronounced winter anticyclone** (Siberian high) brings extremely cold, dry air

Summer monsoon brings moisture reversal

Creates monsoon-like wind reversal despite continental location

**Temperature**:

**Extremely severe winters** — often below -30°C

**Many locations experience below freezing temperatures for 7+ months**

Very short summer

Temperature extremes extreme — Verkhoyansk, Siberia: -67.7°C (world's coldest inhabited place)

**Precipitation**:

**Very low annual total** — 12-15 cm (semi-desert characteristics)

Most precipitation in summer months

Winter extremely dry due to high pressure and cold air's inability to hold moisture

**Permafrost**:

Continuous and thick permafrost — active layer only 30-50 cm

Ground ice, ice-wedge polygons, thermokarst features common

**Vegetation & Soils**:

Sparse boreal forest with stunted trees (taiga)

Transition to tundra in poleward areas

Permafrost-adapted vegetation

Humus accumulates (active layer thin)

**Example**: Yakutsk and Verkhoyansk in eastern Siberia with temperatures dropping below -60°C in winter and minimal precipitation.

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GROUP E: POLAR CLIMATES

**Distribution**: Poleward beyond **70° latitude** — Arctic and Antarctica

**General Characteristics**:

**Coldest climates on Earth** — average temperature below 10°C for all months

Very low precipitation (polar deserts)

Long winter darkness; long summer daylight

Strong temperature inversions

Thin atmosphere

**Two Types**:

Tundra Climate (ET)

**Distribution**: Fringes of Arctic Ocean — Arctic tundra of Canada, Greenland, northern Scandinavia, Siberia (66°-74°N)

**Characteristics**:

**Temperature**:

At least one month with mean temperature > 0°C (distinguishes from ice cap)

All other months below freezing

Mean annual temperature: -5° to -10°C

Large annual temperature range (20-30°C)

**Precipitation**:

Very low — 12-25 cm annually (polar desert)

Mostly summer snow; winter too dry and cold for precipitation

Snowfall light but doesn't melt — accumulates

**Daylight**:

**Midnight sun in summer** — continuous daylight for weeks/months

Polar night in winter — continuous darkness

Provides brief growing season of 2-3 months

**Vegetation & Soil**:

**Tundra vegetation**: Low-growing mosses, lichens, flowering plants (no trees)

Ground vegetation hugs surface for warmth and wind protection

**Permafrost** — subsurface permanently frozen (active layer 0.5-1 m)

Waterlogging in summer — permafrost prevents drainage

Dark, acidic humus soils

**Permafrost Features**:

Ice-wedge polygons

Thermokarst depressions

Pingos (ice-cored mounds)

Solifluction (soil creep on slopes)

**Example**: Northern Canada, Alaska, Siberia, Greenland tundra regions.

Ice Cap Climate (EF)

**Distribution**: **Interior Greenland and Antarctica** (poleward of 80° or extreme cold areas)

**Characteristics**:

**Temperature**:

**Below freezing even in summer** — no month > 0°C

Extremely severe — mean annual temperature: -20° to -60°C

Antarctica: mean annual -57°C (Plateau Station)

Coldest temperature on Earth: -89.2°C (Vostok Station, Antarctica)

**Precipitation**:

**Extremely low** — < 10 cm annually (polar desert)

Almost all falls as snow due to extreme cold

Clouds rare — very dry atmosphere

**Ice Sheets**:

Permanent ice and snow cover — multi-year ice accumulation

Mounting pressure compresses and deforms ice sheets

Ice breaks into icebergs that float in Arctic/Antarctic waters

Glacial features dominate landscape

**Glaciology**:

Ice flows slowly outward toward coasts

Calving produces icebergs

Blue ice surfaces (dense, compressed ancient ice)

Sastrugi (wind-carved ice ridges)

**Life**:

Virtually no vegetation on land

Only microbial life in ice

Marine life in surrounding ocean

**Example**: Antarctic plateau (Plateau Station at 79°S) and Greenland ice sheet.

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CLIMATE CHANGE

**Definition**: Variations in climate patterns over geological and historical timescales — natural and ongoing process.

**Time Scales**:

Geological time (millions of years): glacial-interglacial cycles

Historical time (centuries): documented variability

Recent time (decades): instrumental records

EVIDENCE OF CLIMATE CHANGE

**Geological Evidence**:

**Glacial-interglacial alternation** — 40,000-100,000 year cycles during Pleistocene

**Geomorphological features** — moraines, striations, U-shaped valleys indicate glacier advances and retreats

**Terminal moraines in high altitudes and latitudes** show evidence of past glaciation

Sediment layers in glacial lakes alternate between coarse (cold) and fine (warm) deposits

**Paleontological Evidence**:

Fossil records show climate-adapted species changes

Pollen analysis (palynology) reveals past vegetation changes

Tree rings (dendrochronology) show wet (wide rings) and dry (narrow rings) periods

**Historical Records**:

Written records of crop failures, floods, droughts, famines

Chronicles of temperature extremes

Migration patterns of peoples following climate

CLIMATIC VARIATIONS IN EARTH'S PAST

**Geological History**:

**Warm Periods (500-300 Million Years Ago)**:

Cambrian, Ordovician, Silurian periods — tropical conditions globally

No polar ice caps

Frequent rainfall, warm oceans

**Pleistocene Epoch (2.6 Million - 11,700 Years Ago)**:

Multiple glacial and interglacial periods

**Last major glacial peak: ~18,000 years ago** (Last Glacial Maximum)

Ice sheets covered much of North America, Europe, Asia

Sea levels 130 m lower

Deserts expanded poleward

**Present interglacial: started 10,000 years ago** (Holocene)

Glaciers retreated

Sea levels rose

Humans developed agriculture

**Historical Variability in India**:

**Rajasthan desert** (currently arid): Wet and cool around **8,000 B.C.**

Period **3,000-1,700 B.C.**: Higher rainfall — supported Harappan civilization (2,000-1,700 B.C.)

**Since 1,700 B.C.**: Dry conditions increasingly dominant — desert expansion

Archaeological evidence in settlement patterns and artifact types

CLIMATE IN THE RECENT PAST

**Medieval Warm Period (10th-11th Centuries)**:

Europe experienced warm, dry conditions

**Vikings settled Greenland** — agriculture possible

Expanded agriculture in northern regions

**Little Ice Age (1550-1850)**:

Cooling period across Northern Hemisphere

Glaciers advanced in Alps and other mountains

Extended sea ice in Arctic — disrupted navigation

Cold, harsh winters — crop failures in Europe

Hardships for populations dependent on agriculture

**Modern Warming Trend (1885-1940)**:

Global temperatures showed upward trend

World average temperature rose ~0.5°C

Agricultural advancement in previously marginal lands

**Mid-20th Century Cooling (1940-1970)**:

Rate of temperature increase slowed

Some regions experienced cooling

Caused concerns about ice age recurrence

Likely due to industrial aerosols masking greenhouse warming

**Recent Extreme Weather (1990s)**:

**Warmest decade of the century** — 1990s

Worst floods globally — increased precipitation extremes

Severe droughts — Sahel region (1967-1977), Dust Bowl in southwestern USA (1930s)

Increased frequency of hurricanes and extreme weather events

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CAUSES OF CLIMATE CHANGE

Climate change causes grouped into two categories:

ASTRONOMICAL CAUSES

**Sunspot Activity**:

**Sunspots** — dark, cooler patches on sun's photosphere

Increase and decrease in **cyclical manner** (11-year cycle)

**Proposed correlation** (NOT statistically confirmed):

High sunspot numbers → cooler, wetter weather, more storms

Low sunspot numbers → warm, dry conditions

**Critical limitation**: Correlation weak; sunspot forcing ~0.2 W/m² vs. greenhouse gas forcing ~2 W/m²

**Milankovitch Oscillations**:

Cycles in Earth's orbital characteristics affecting insolation:

1. **Orbital eccentricity** (100,000-year cycle) — orbit varies from nearly circular to elliptical

2. **Axial tilt variation** (41,000-year cycle) — obliquity changes from 22.1° to 24.5°

3. **Precession of axis** (26,000-year cycle) — wobbling of axis

All three affect seasonal and latitudinal distribution of solar radiation

Likely explains glacial-interglacial cycles during Pleistocene

Changes in insolation received → climate changes

TERRESTRIAL/ATMOSPHERIC CAUSES

**Volcanism**:

**Mechanism**:

Volcanic eruptions eject massive quantities of **aerosols** (fine particles) into atmosphere

Aerosols concentrated in **stratosphere** — persist 1-3 years

Aerosol particles **scatter and absorb incoming solar radiation**

Reduces solar radiation reaching Earth's surface

**Net result: cooling effect on climate**

**Historical Examples**:

**Mount Pinatubo (1991, Philippines)**: Eruption ejected 20 million tons of SO₂; global temperature fell 0.5°C for 2-3 years

**El Chichón (1982, Mexico)**: Similar cooling effect

**Limitations**: Volcanic cooling temporary — returns to normal once aerosols settle

**Terrestrial/Anthropogenic Causes**:

**Most important modern cause**: Increasing greenhouse gas concentration

Industrial emissions, fossil fuel combustion, deforestation

Agricultural practices (methane from livestock, rice paddies)

Cement production and chemical industries

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GLOBAL WARMING AND GREENHOUSE EFFECT

**Definition of Greenhouse Effect**: Process by which certain atmospheric gases absorb and trap outgoing long-wave radiation, warming the atmosphere and Earth's surface.

MECHANISM OF GREENHOUSE EFFECT

**Step-by-Step Process**:

1. **Incoming Solar Radiation**: Short-wave solar radiation (wavelength 0.3-3 μm) enters atmosphere

2. **Atmospheric Transmission**: ~50% penetrates atmosphere (atmosphere relatively transparent to short waves)

3. **Surface Absorption**: Short-wave radiation reaches surface, absorbed, converted to heat

4. **Outgoing Terrestrial Radiation**: Warm surface emits long-wave radiation (infrared, wavelength 4-100 μm)

5. **GHG Absorption**: Greenhouse gases in atmosphere absorb long-wave radiation (opaque to these wavelengths)

6. **Re-radiation**: Absorbed radiation re-radiated back toward surface

7. **Net Result**: More heat trapped in lower atmosphere — warming

**Analogy to Greenhouse/Car**:

**Glass/Window**: Transparent to short-wave solar radiation, opaque to long-wave terrestrial radiation

**Greenhouse**: Heat enters as light, but cannot escape as heat — interior warms

**Closed car in summer**: Same effect — interior temperature rises to 50°C+ even on mild days

**Closed vehicle in winter**: Trapped heat keeps interior warmer than outside

PRIMARY GREENHOUSE GASES (GHGs)

**Carbon Dioxide (CO₂)**:

**Primary concern** — most abundant anthropogenic GHG

Sources: Fossil fuel combustion, cement production, deforestation

Atmospheric concentration: ~280 ppm (pre-industrial) → 410+ ppm (2020)

Lifetime: 100-300 years (accumulates over centuries)

**Global warming potential (GWP)**: 1 (reference standard)

**Methane (CH₄)**:

**20-25 times more effective** than CO₂ over 100 years

Sources: Livestock digestion, rice paddies, landfills, natural gas leaks, termites

Concentration: ~700 ppb (pre-industrial) → 1800+ ppb (2020)

Lifetime: ~12 years (shorter than CO₂)

**GWP**: 28-34 (100-year basis)

**Nitrous Oxide (N₂O)**:

Sources: Fertilizers, industrial processes, animal waste, soil microbes

Lifetime: ~120 years

**GWP**: 265-298 (100-year basis) — very potent despite low concentration

Concentration: ~270 ppb (pre-industrial) → 330+ ppb (2020)

**Chlorofluorocarbons (CFCs)**:

**Highly effective** greenhouse gases

Sources: Refrigerants, foam blowing agents, solvents (now banned by Montreal Protocol)

**GWP**: 4,000-10,000+ — extremely potent but low concentration

Lifetime: 50-100+ years — persist long in atmosphere

Also cause ozone depletion in stratosphere

**Ozone (O₃)**:

**Dual role**:

Stratospheric O₃ (good ozone) — absorbs UV radiation, protects life

Tropospheric O₃ (bad ozone) — greenhouse gas, air pollutant

When present in lower troposphere, absorbs terrestrial radiation

Formed by photochemical reactions of NOₓ and hydrocarbons

**GWP**: ~270 (100-year basis)

**Other Gases**:

**Nitric oxide (NO)** and **carbon monoxide (CO)** — react with GHGs, affect their atmospheric concentrations

Don't directly absorb long-wave radiation but indirectly affect climate

FACTORS AFFECTING GHG EFFECTIVENESS

**Three Key Parameters**:

1. **Concentration Change**: Larger increase in atmospheric concentration = stronger warming effect

CO₂ increased 40% (pre-industrial to present)

CH₄ increased 150%

2. **Atmospheric Lifetime**: Longer a molecule persists, longer climate system takes to recover

CO₂: 100-300 years — cumulative effect over centuries

CH₄: 12 years — turnover rapid but production increasing

CFCs: 50-100+ years — slow removal

3. **Spectral Properties**: Wavelength of radiation absorbed determines effectiveness

Different GHGs absorb different wavelengths of terrestrial radiation

Some gases absorb in spectral regions where other gases are transparent — "radiative forcing"

CO₂ and CH₄ absorb overlapping wavelengths — saturation effects weaken additional forcing

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EXAM IMPORTANT POINTS

**Map-Based Questions**:

Identify climate zones on world maps using latitude, continental position, ocean currents

Tropical humid (A) — equatorial belt

Dry (B) — subtropical highs (15-30°), continental interiors (35-60°)

Temperate (C) — eastern margins (Cfa), western margins (Cs, Cfb), 30-50° latitude

Cold (D) — 40-70° N (continental)

Polar (E) — poleward of 70°

**Climatic Feature Identification**:

High temperature range → continental interior, high latitude, or dry climate

Low temperature range → maritime location, equatorial region

Highly variable rainfall → transition zones (BSh), monsoon regions (Am)

No dry season → eastern continental margins, equatorial region

Summer dry → Mediterranean (Cs), monsoon region winter dry (Aw)

**Climate-Vegetation Relationships**:

Af → tropical rainforest (dense, evergreen, biodiversity hotspot)

Aw → deciduous forests and savannas (adapt to dry season)

BS → grasslands (sparse, short grass)

BW → desert shrubs or barren

Cs → sclerophyll vegetation (hard-leaved, drought-adapted)

Cf → temperate forests (deciduous or mixed)

D → boreal forest/taiga (coniferous)

E → tundra (dwarf vegetation) or ice cap (no vegetation)

**Climate Change Mechanisms**:

Greenhouse effect: Short-wave radiation in → long-wave radiation trapped

GHG effectiveness depends on: concentration increase, lifetime, spectral absorption

Natural causes: Sunspots (weak), Milankovitch cycles (proven), volcanoes (temporary)

Anthropogenic cause: Industrial greenhouse gas emissions (dominant modern effect)

**Historical Climate Events**:

Last glacial maximum: 18,000 years ago

Present interglacial: 10,000 years ago

Medieval Warm Period: 10-11th centuries (Vikings in Greenland)

Little Ice Age: 1550-1850

Modern warming: 1885-1940, acceleration since 1970s