Geography: Class 112 — Chapter 11: World Climate and Climate Change

Introduction to Climate Classification

The world climate can be studied by organising information and data into smaller units for systematic description and analysis. Three broad approaches are adopted for classifying climate:

Empirical Classification: Based on observed data, particularly temperature and precipitation.
Genetic Classification: Attempts to organise climates according to their causes and atmospheric dynamics.
Applied Classification: Designed for specific purposes or environmental applications.

Koeppen's Scheme of Climate Classification

Developed by V. Koeppen in 1918 and subsequently modified, this widely used empirical classification scheme establishes a close relationship between the distribution of vegetation and climate. It uses numerical values of temperature and precipitation (mean annual and mean monthly) designated by capital and small letters to define climatic groups and types.

Koeppen's Major Climatic Groups

Koeppen recognised five major climatic groups. Four are based on temperature characteristics, and one (Group B) is based on precipitation.

Group	Characteristics
A - Tropical	Average temperature of the coldest month is 18°C or higher
B - Dry Climates	Potential evaporation exceeds precipitation
C - Warm Temperate	The average temperature of the coldest month of the (Mid-latitude) climates is higher than minus 3°C but below 18°C
D - Cold Snow Forest Climates	The average temperature of the coldest month is minus 3°C or below
E - Cold Climates	Average temperature for all months is below 10°C

Koeppen's Climatic Types

Climatic groups are subdivided into types designated by small letters based on the seasonality of precipitation and temperature severity:

f: No dry season
m: Monsoon climate
w: Winter dry season
s: Summer dry season
a, b, c, d: Degree of temperature severity
S: Steppe or semi-arid (used with Group B)
W: Desert or arid (used with Group B)

Group	Type	Letter Code	Characteristics
A-Tropical Humid Climate	Tropical wet	Af	No dry season
	Tropical monsoon	Am	Monsoonal, short dry season
	Tropical wet and dry	Aw	Winter dry season
B-Dry Climate	Subtropical steppe	BSh	Low-latitude semi-arid or dry
	Subtropical desert	BWh	Low-latitude arid or dry
	Mid-latitude steppe	BSk	Mid-latitude semi-arid or dry
	Mid-latitude desert	BWk	Mid-latitude arid or dry
C-Warm temperate (Mid-latitude) Climates	Humid subtropical	Cfa	No dry season, warm summer
	Mediterranean	Cs	Dry hot summer
	Marine west coast	Cfb	No dry season, warm and cool summer
D-Cold Snow-forest Climates	Humid continental	Df	No dry season, severe winter
D-Cold Snow-forest Climates	Subarctic	Dw	Winter dry and very severe
E-Cold Climates	Tundra	ET	No true summer
E-Cold Climates	Polar ice cap	EF	Perennial ice

Detailed Climatic Groups and Types

Group A: Tropical Humid Climates

Located between the Tropic of Cancer and Tropic of Capricorn. Characterised by high solar insolation, the presence of the Inter Tropical Convergence Zone (ITCZ), low annual temperature range, and high rainfall.

Tropical Wet Climate (Af): Found near the equator (Amazon Basin, western equatorial Africa, East Indies). Features afternoon convective thundershowers, uniformly high temperatures (30°C max, 20°C min), and tropical evergreen forests.
Tropical Monsoon Climate (Am): Found over the Indian sub-continent, North Eastern South America, and Northern Australia. Heavy summer rainfall and dry winters.
Tropical Wet and Dry Climate (Aw): Occurs north and south of Af regions. Features a shorter wet season, longer dry season, and deciduous forests or grasslands.

Group B: Dry Climates

Characterised by very low rainfall where potential evaporation exceeds precipitation. Extends from 15° to 60° latitude north and south of the equator.

Subtropical Steppe (BSh) & Subtropical Desert (BWh): Located between 15° - 35° latitudes. BSh acts as a transition zone receiving slightly more rainfall than the desert BWh. High summer temperatures (e.g., 58°C recorded at Al Aziziyah, Libya in 1922).
Mid-latitude Steppe (BSk) & Mid-latitude Desert (BWk): Located between 35° - 60° latitudes. Confined to deep continental interiors or rain-shadow zones.

Group C: Warm Temperate (Mid-Latitude) Climates

Extend from 30° - 50° latitude, mainly on continental margins. Characterised by warm summers and mild winters.

Humid Subtropical Climate (Cwa): Poleward of the Tropics (e.g., North Indian plains, South China). Dry winters and warm summers.
Mediterranean Climate (Cs): Occurs around the Mediterranean Sea, Central California, Central Chile, and southwestern Australia. Characterised by hot, dry summers and mild, rainy winters under the influence of westerlies.
Humid Subtropical Climate (Cfa): Located on eastern continental margins (e.g., Eastern USA, Southern China, Japan). Rainfall occurs throughout the year.
Marine West Coast Climate (Cfb): Located poleward of Cs climates (e.g., Northwestern Europe, Western North America). Moderated by marine influences with mild winters and cool summers.

Group D: Cold Snow Forest Climates

Occur in large continental areas of the Northern Hemisphere between 40° - 70° north latitudes.

Cold Climate with Humid Winters (Df): Cold, snowy winters with short, frost-free summers. Abrupt weather changes.
Cold Climate with Dry Winters (Dw): Occurs mainly over Northeastern Asia. Characterised by strong winter anticyclones and extremely low temperatures.

Group E: Polar Climates

Exist poleward beyond 70° latitude.

Tundra Climate (ET): Named after low-growing vegetation (mosses, lichens). Characterised by permafrost where the subsoil is permanently frozen.
Ice Cap Climate (EF): Occurs over interior Greenland and Antarctica. Temperatures remain below freezing even in summer. Accumulates ice sheets that deform and break into icebergs.

Climate Change

Climate change is a natural, continuous process. Geological, geomorphological, and historical records show that Earth's climate has experienced major variations since its formation, alternating between glacial and inter-glacial periods.

Evidence of Climate Change

Glacial landforms showing advances and retreats of glaciers.
Sediment deposits in glacial lakes.
Dendroclimatology (tree ring analysis) indicating wet and dry periods.
Historical records of crop yields, floods, and human migrations.

Causes of Climate Change

Astronomical Causes:
- Changes in solar output associated with sunspot activities (cyclical dark/cool patches on the sun).
- Milankovitch oscillations: Cycles in Earth's orbital characteristics, axial tilt, and wobbling.
Terrestrial Causes:
- Volcanism: Volcanic eruptions release aerosols that block solar radiation, lowering global temperatures temporarily.
Anthropogenic Causes:
- Increasing concentration of greenhouse gases due to industrialisation, deforestation, and fossil fuel combustion.

Global Warming and Greenhouse Effect

The atmosphere transmits incoming shortwave solar radiation but absorbs longwave terrestrial radiation emitted by the Earth. This process is known as the Greenhouse Effect.

Greenhouse Gases (GHGs)

The primary greenhouse gases of concern include:

Carbon Dioxide (CO2): Emitted mainly from fossil fuel combustion and deforestation.
Chlorofluorocarbons (CFCs): Synthetic products of human activity that also destroy the stratospheric ozone layer.
Methane (CH4): Released from agricultural activities, wetlands, and livestock.
Nitrous Oxide (N2O) and Ozone (O3).

International Initiatives

The Kyoto Protocol, proclaimed in 1997 and effective in 2005, was a major international treaty that bound industrialised nations to reduce greenhouse gas emissions to mitigate global warming.