CHAPTER 12
WORLD CLIMATE & CLIMATE CHANGE

–> Meaning of Climate

Climate means the average weather conditions of a place over a long period of time.

The two most important elements used to describe climate are:

• Temperature – how hot or cold a place is.
• Precipitation – rainfall, snowfall, etc.

–> Weather vs Climate

• Weather: Condition of the atmosphere at a particular time.
• Climate: Average weather condition of a place over many years.

–> Koeppen’s Classification of Climate

Wladimir Koeppen was a German climatologist and botanist. He introduced his climate classification in 1918 and revised it in 1936.

His classification was based mainly on:

• Temperature
• Rainfall/precipitation
• Natural vegetation

Koeppen believed that there is a close relationship between climate and vegetation.

He used capital and small letters to represent different climate types.

–> Five Major Climate Groups

• Found mainly between the Tropic of Cancer and Tropic of Capricorn.
• Temperature remains high throughout the year.
• The coldest month has a temperature of 18°C or above.
• These areas generally receive considerable rainfall.
• The climate is generally hot and humid.
• Dense forests are commonly found in areas with heavy rainfall.

Example: Amazon Basin, Congo Basin and parts of Southeast Asia.

B – Dry Climate

• These areas receive very little rainfall.
• Rainfall is not enough for the growth of many plants.
• Potential evaporation is greater than precipitation.
• Deserts and semi-deserts are common.
• These climates are found in many parts of the world.

Examples: Sahara Desert, Arabian Desert and parts of Australia.

C – Warm Temperate / Mid-Latitude Climate

• Mainly found in middle latitudes.
• Summers are generally warm.
• Winters are generally mild.
• These climates occur mainly in parts of the eastern and western margins of continents.

Examples: Parts of Europe, eastern China and the southeastern United States.

D – Cold Snow Forest Climate

• Mainly found in the Northern Hemisphere.
• Common between about 40° and 70° N.
• Winters are very cold.
• The coldest month has a temperature of -3°C or below.
• The warmest month has a temperature of above 10°C.
• Coniferous and other cold-region forests are common.

Examples: Canada, northern Europe and Siberia.

E – Polar Climate

• Found near the North and South Poles.
• Temperatures remain extremely low.
• There is no proper warm summer season.
• Even summer temperatures can remain very low.
• Tundra vegetation is found in some polar regions.
• Antarctica has an extremely cold polar climate.

Examples: Antarctica, Greenland and Arctic regions.

Highland Climate – H

Highland climate is mainly controlled by altitude/elevation.

• Temperature decreases as altitude increases.
• Mountain areas can be cold even when surrounding lowlands are warm.
• Climate changes with height.
• Snowfall may occur at higher elevations.

Examples: Himalayas, Alps and Andes.

–> World Climate According to Temperature

According to temperature, the world can broadly be divided into three major zones:

1. Tropical Zone
2. Sub-Tropical/Temperate Zone
3. Polar Zone

Important Latitudes

Tropical Zone

• Extends between 23½° N and 23½° S.
• It lies between the Tropic of Cancer and Tropic of Capricorn.
• The Sun’s rays are almost vertical.
• Temperatures are generally high throughout the year.
• The coldest month generally has a temperature of 18°C or above.

Main feature: ☀️ Hot throughout the year

Sub-Tropical / Temperate Zone

• Extends roughly from 23½° to 66½° in both hemispheres.
• The Sun’s rays are more inclined than in the tropical zone.
• Temperatures are neither extremely hot nor extremely cold in many areas.
• Seasonal changes are more noticeable.

Main feature: 🌤️ Moderate temperatures with seasons

Polar Zone

• Extends from 66½° to 90° in both hemispheres.
• Includes areas around the North and South Poles.
• The Sun’s rays are highly inclined.
• Winters are extremely cold.
• Summers are short and cool.
• Snow and ice are common.