The varied effect of the major weather elements in different parts of the world and also the varied nature of the earth’s surface give every location a distinct climate. Hence, the number of different climate is large.
In order to easily understand and comprehend this large variety, the climate of the world have been classified into a few major groups, each having certain common important characteristics.
Although several attempts have been made by scholars to classify the climate of the world for the proper understanding of major climate types no single classification is perfect, as climate stands for the generalized and composite weather conditions.
However, the Greeks, perhaps, made the first attempt to classify the world climates on the basis of the distribution of temperature and insolation. They divided the world into five latitudinal thermal zones, The boundary of these zones are fixed on the basis of the angle at which the sun’s rays strike the earth. The following are the five thermal zones.
The Thermal Zones
(i) Torrid Zone
- It is the largest of the thermal zones. It covers, almost half the area of the earth’s surface.
- It is situated between the Tropic of Cancer (23½°N) and Tropic of Capricorn (23½°S).
- The sun’s rays are almost vertical throughout the year in this zone.
- The mid-day sun is overhead at equator on equinoxes, i.e. on 21 st March and 23rd September.
- It is also overhead at Tropic of Cancer on 21st June and at Tropic of Capricorn on 22nd December.
- The duration’s of day and night are always equal i.e. 12 hours each on the equator and they increase to 13 hours 27 minutes at tropics.
- The range of temperature is lowest at the equator and it increases towards the tropics.
(ii) Temperate Zone
- The temperate zones are on either side of the Torrid zone.
- The North Temperate Zone lies between Tropic of Cancer (23½° North) and Arctic Circle (66½° North).
- The South Temperate Zone lies between Tropic of Capricorn (23½° South) and Antarctic Circle (66½° South).
- The sun is never overhead.
- In this zone in winter season, the nights are longer and days are shorter and vice versa in summer.
- The difference between the duration of the day and night increases towards the poles. The maximum duration of day in summer and that of night in winter in the polar circles is 24 hours.
- When it is summer in the northern hemisphere it is winter in the southern hemisphere and vice versa.
(iii) Frigid Zones
- Like the temperate zone, frigid zone is also found in both the hemispheres.
- The North Frigid Zone lies between Arctic Circle (66½°N) and North Pole (90°N).
- The South Frigid Zone lies between Antarctic Circle (66½°S) and South Pole (90°S).
- During winter season, the sun does not rise above the horizon for almost six months.
- These are the coldest regions of the world.
- The surface remains permanently frozen under thick snow.
The concept of thermal zone is theoretical and explains the distribution of solar energy over the earth’s surface.
There are several other factors besides the angle of the sun’s rays which influence the climate of a place. Keeping in view other factors responsible for the distribution and combined influence of temperature and rainfall, modern scientists have arrived to several classifications of climate and its types. The most widely used system of climatic classification in its various modified forms is that of Wladimir koeppen (1846-1940). It is based upon temperature, precipitation and their seasonal characteristics. The relationship of climate with the vegetation is also included with it. According to this scheme, the world has been divided into five climatic groups and they are further sub-divided into 13 climatic types. They are as follows –
|Climatic Groups||Climatic Types|
|(A) Tropical climates (hot all seasons)||(i) Tropical rain forest
(ii) Savanna Climate
(iii) Monsoon Climate
|(B) Dry climates||(iv) Desert Climate
(v) Steppe Climate
|(C) Warm temperate rainy or Middle latitude rainy climates (mild winters)||(vi) Mediterranean Climate
(vii) China Type Climate
(viii)West European Climate
|(D) Humid Middle latitude climates (severe winters)||(ix) Taiga Climate
(x) Cool East-coast Climate
(xi) The Continental Climate
|(E) Polar climates||(xii) Tundra Climate
(xiii) Ice-cap Climate
The earth is divided into five thermal zones on the basis of distribution of insolation and temperature.
Bibliography : NIOS Geography Book
Reference : http://www.nios.ac.in