World Climate and Climate Change

Three broad approaches have been adopted for classifying climate. The first of the three approaches is the empirical classification used for over a century, which relies on simple monotonic functions of mean or maximum temperature, precipitation, or related variables to define climatic regions. Genetic classification attempts to organize climates according to their causes.

Koeppen’s Scheme of Classification of Climate

The most widely used classification of climate is the empirical climate classification scheme developed by V. Koeppen. Koeppen identified a close relationship between the distribution of vegetation and climate.

The Köppen climate classification divides climates into five main climate groups, with each group being divided based on seasonal precipitation and temperature patterns.

The five main groups are A (tropical), B (dry), C (temperate), D (continental), and E (polar). Each group and subgroup is represented by a letter.

All climates are assigned a main group (the first letter). All climates except for those in the E group are assigned a seasonal precipitation subgroup (the second letter).

For example, Af indicates a tropical rainforest climate. The system assigns a temperature subgroup for all groups other than those in the A group, indicated by the third letter for climates in B, C, and D, and the second letter for climates in E.

For example, Cfb indicates an oceanic climate with warm summers as indicated by the ending b. Climates are classified based on specific criteria unique to each climate type.

The capital letters: A, C, D and E delineate humid climates and B dry climates.

The climatic groups are subdivided into types, designated by small letters, based on seasonality of precipitation and temperature characteristics.

The seasons of dryness are indicated by the small letters : f, m, w and s, where f corresponds to no dry season m – monsoon climate, w- winter dry season and s – summer dry season.

The small letters a, b, c and d refer to the degree of severity of temperature. The B- Dry Climates are subdivided using the capital letters S for steppe or semi-arid and W for deserts.

Group A : Tropical Humid Climates

Tropical humid climates exist between Tropic of Cancer and Tropic of Capricorn.

The sun being overhead throughout the year and the presence of Inter Tropical Convergence Zone (ITCZ) make the climate hot and humid.

Annual range of temperature is very low and annual rainfall is high.

Tropical Wet Climate (Af): Tropical wet climate is found near the equator. The major areas are the Amazon Basin in South America, western equatorial Africa and the islands of East Indies.Significant amount of rainfall occurs in every month of the year as thunder showers in the afternoon.The temperature is uniformly high and the annual range of temperature is negligible.

Tropical Monsoon Climate (Am): Tropical monsoon climate (Am) is found over the Indian sub-continent, North Eastern part of South America and Northern Australia. Heavy rainfall occurs mostly in summer. Winter is dry.

Tropical Wet and Dry Climate (Aw): Tropical wet and dry climate occurs north and south of Af type climate regions. It borders with dry climate on the western part of the continent and Cf or Cw on the eastern part. Extensive Aw climate is found to the north and south of the Amazon forest in Brazil and adjoining parts of Bolivia and Paraguay in South America, Sudan and south of Central Africa.

Dry climates B

Dry climates are characterized by very low rainfall that is not adequate for the growth of plants.

These climates cover a very large area of the planet extending over large latitudes from 15° – 60° north and south of the equator.

At low latitudes, from 15° – 30°, they occur in the area of subtropical high where subsidence and inversion of temperature do not produce rainfall.

Subtropical Steppe (BSh) and Subtropical Desert (BWh) Climates: Subtropical steppe (BSh) and subtropical desert (BWh) have common precipitation and temperature characteristics. Located in the transition zone between humid and dry climates. subtropical steppe receives slightly more rainfall than the desert, adequate enough for the growth of sparse grasslands. The rainfall in both climates is highly variable.

Warm Temperate (Mid-Latitude) Climates-C: Warm temperate (mid-latitude) climates extend from 30° – 50° of latitude mainly on the eastern and western margins of continents. These climates generally have warm summers with mild winters.

Cold Snow Forest Climates (D)

Cold snow forest climates occur in the large continental area in the northern hemisphere between 40°-70° north latitudes in Europe, Asia and North America. Cold snow forest climates are divided into two types:

Df- cold climate with humid winter: Dw- cold climate with dry winter. The severity of winter is more pronounced in higher latitudes. Cold Climate with Humid Winters (Df). Cold climate with humid winter occurs poleward of marine west coast climate and mid-latitude steppe. The winters are cold and snowy. The frost-free season is short. The annual ranges of temperature are large. The weather changes are abrupt and short.

Cold Climate with Dry Winters (Dw): Cold climate with dry winter occurs mainly over Northeastern Asia.The development of pronounced winter anti cyclone and its weakening in summer sets in a monsoon-like reversal of wind in this region. Poleward 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. The annual precipitation is low from 12-15 cm.

Polar Climates (E)

Polar climates exist poleward beyond 70° latitude. Polar climates consist of two types:

Tundra Climate (ET): The tundra climate (ET) is so called after the types of vegetation, like low growing mosses, lichens and flowering plants. This is the region of permafrost where the sub soil is permanently frozen. The short growing season and water logging support only low growing plants. During summer, the tundra regions have very long duration of day light.

Ice Cap Climate (EF): The ice cap climate (EF) occurs over interior Greenland and Antarctica. This area receives very little precipitation. The snow and ice get accumulated and the mounting pressure causes the deformation of the ice sheets and they break. Plateau Station, Antarctica, 79°S, portray this climate.

Highland Climates (H)

Highland climates are governed by topography.

In high mountains, large changes in mean temperature occur over short distances.

Precipitation types and intensity also vary spatially across high lands.

There is vertical zonation of layering of climatic types with elevation in the mountain environment.