Chapter 12. World Climate and Climate Change

Koeppen’s Climate Classification
• This climate classification scheme was developed by Wladimir Peter Koeppen in 1818. He recognized a close relationship between distribution of vegetation and climate. He selected specific values of temperature and precipitation and related them to distribution of vegetation and used these values for classifying climate.
• Koeppen’s climate classification system recognizes five major climatic types and each type is designated by a capital letter – A, B, C, D, E & H. seasons of dryness are indicated by small letters – f, m, w & s. small letters a, b, c & d refer to degree of severity of temperature.

Group Types Letter Code Characteristics
A-Tropical Humid Climate Tropical wet Tropical monsoon Tropical wet and dry Af Am Aw No dry season Monsoonal, short dry season Winter dry season
B-Dry Climate Subtropical steppe Subtropical desert Mid-latitude steppe Mid-latitude desert BSh BWh BSk BWk Low-latitude semi arid or dry Low-latitude arid or dry Low-latitude semi arid and dry Low-latitude arid or dry
C-Warm temperate [mid-latitude] Climates Humid subtropical Mediterranean Marine west coast Cfa Cs Cfb No dry season, warm summer Dry hot summer No dry season, warm & cool summer
E-Cold Climates Tundra Polar ice cap ET EF No true summer Perennial ice
H-Highland Highland H Highland with snow cover

Table: Climatic Types According to Koeppen

Group A : Tropical Humid Climates
• A tropical humid climate exists between Tropic of Cancer and Tropic of Capricorn. sun is overhead throughout year and presence of Inter-Tropical Convergence Zone [ITCZ] makes climate hot and humid.

Tropical Wet Climate [Af]
• This is found near equator. major areas are Amazon Basin in South America, Western Equatorial Africa and Islands of East Indies. A significant amount of rainfall occurs every month of year with thundershowers in afternoon. maximum temperature on any day is around 30˚C while minimum temperature is around 20˚C.

Tropical Monsoon Climate [Am]
• This is found over Indian sub-continent, North Eastern part of South America and Northern Australia. Heavy rainfall occurs mostly in summer and Winters are dry.

Tropical Wet and Dry Climate [Aw]
• Tropical wet and dry climate occurs north and south of Af type climate regions. It borders a dry climate on western part of continent and Cf or Cw on eastern part.
• Extensive Aw climate is found to north and south of Amazon Forest in Brazil and adjoining parts of Bolivia and Paraguay in South America, Sudan & South of Central Africa. annual rainfall in this climate is considerably less than that in Af and Am climate types and is variable also. Deciduous forests and tree-shredded grasslands occur in climate.

Group B – Dry Climate
• These climates cover a very large area of planet extending over large latitudes from 15˚ to 60˚ North and South of equator. At low latitudes, from 15˚ – 30˚, they occur in area of sub-tropical high where subsidence and inversion of temperature do not produce rainfall.
• In middle latitude, from 35˚ – 60˚ North and South of equator, they are confined to interior of continents where maritime – humid winds do not reach to areas often surrounded by mountains.

Subtropical Steppe [BSh] and Subtropical Desert [BWh] Climates
• Located in transition zone between humid and dry climates, subtropical steppe receives slightly more rainfall than desert, adequate for growth of sparse grasslands. rainfall in both climates is highly variable.
• Rain occurs in short intense thundershowers in deserts and is effective in building soil moisture. Fog is common in coastal deserts bordering cold currents. maximum temperature in summer is very high.

Warm Temperature [Mid-Latitude] Climate – C
• Warm temperature [mid-latitude] climates extend from 30˚ to 50˚ latitudes mainly on eastern and western margins of continents. These climates usually have warm summers with mild winters.

Humid Subtropical Climate [Cwa]
• Humid subtropical climate occurs poleward of Tropic of Cancer and Capricorn, mainly in North Indian plains and South China interior plains.
• climate is similar to Aw climate except that temperature in winter is warm.

Mediterranean Climate [Cs]
• It occurs around Mediterranean Sea, along west coast of continents in subtropical latitudes between 30° – 40° latitudes. monthly average temperature in summer is around 25° C and in winter is below 10°C. annual precipitation ranges from 35 – 90 cm

Marine West Coast Climate [Cfb]
• marine west coast climate is located poleward from Mediterranean climate on west coast of continents.
• Due to marine influence, temperature is moderate and in winter, it is warmer than its latitude. mean temperature in summer months ranges from 15° – 20°C and in winter 40° – 10°C. annual and daily ranges of temperature are small. Precipitation varies greatly from 50 –250 cm.

Cold Snow Forest Climates [D]
• It occurs in large continental area in northern hemisphere between 40° – 70° north latitudes in Europe, Asia & North America

Cold Climate with Humid Winters [Df]
• Cold climate with humid winter occurs poleward of marine west coast climate and mid-latitude steppe.
• winters are cold and snowy. frost-free season is short. annual ranges of temperature are large. weather changes are abrupt and short. Poleward, winters are more severe.

Cold Climate with Dry Winters [Dw]
• Cold climate with dry winter occurs mainly over North-eastern Asia. development of pronounced winter, anti-cyclone and its weakening in summer sets in a monsoon-like reversal of wind in this region.
• Pole [ward] summer temperatures are lower and winter temperatures are extremely low with many locations experiencing below freezing point temperatures for up to seven months in a year. Precipitation occurs in summer.

Polar Climate [E]
• It exists poleward beyond 70° latitudes.

Tundra Climate [ET]
• Tundra climate [ET] is so-called after types of vegetation, like low growing mosses, lichens & flowering plants. It is region of permafrost where subsoil is permanently frozen. During summer, tundra regions have a long duration of daylight.

Icecap Climate [EF]
• It occurs over interior Greenland and Antarctica. Even in summer, temperature is below freezing point. This area receives very little precipitation.

Highland Climates [H]
• Highland Climates are governed by topography. In high mountains, a large change in mean temperature occurs over short distances. There is vertical zonation of layering of climatic types with elevation in mountain environment.

Causes of Climatic Change
• causes of climate change are many and can be grouped into Astronomical and Terrestrial causes.
• Astronomical causes are changes in solar output associated with sunspot activities. Sunspots are dark and cooler patches on sun which increase and decrease cyclically.
• Terrestrial causes: Volcanism is considered another cause of climate change. Volcanic eruption throws up lots of aerosols into atmosphere. These aerosols remain in atmosphere for a considerable period reducing sun’s radiation reaching Earth’s surface. most important Anthropogenic effect on climate is increasing trend in concentration of greenhouse gases.

Greenhouse gases [G.H.G’s]
• primary G.H.Gs of concern today are CO2, CFCs, CH4, N2O, & O3. Some other gases such as NO and CO easily react with G.H.G’s and affect their concentration in atmosphere. effectiveness of any given G.H.G molecule will depend on magnitude of increase in its concentration, its lifetime in atmosphere and wavelength of radiation that it absorbs. largest concentration of G.H.G’s in atmosphere is CO2. emission of CO2 comes mainly from fossil fuels combustion [oil, gas & coal].
• Forests and oceans are sinks of CO2. Forest use CO2 in their growth. So, deforestation due to changes in land use increases concentration of CO2. doubling of concentration of CO2 over pre-industrial level is used as an index for estimating changes in climatic models.

Global Warming
• The atmosphere sends out radiation from the sun, but it takes in most of the longwave radiation that comes from the Earth’s surface. Greenhouse gases are gases in the atmosphere that soak up long-wave radiation and are a cause of global warming.

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