Climate is the long-term average of weather conditions over a large area, usually calculated over 30 years or more. While weather describes the day-to-day conditions of the atmosphere, climate describes the prevailing conditions that characterise a region. The study of world climates helps us understand why some regions are hot and humid, others hot and dry, and others cold throughout the year. This chapter examines the classification of world climates, the influence of latitude, altitude and distance from the sea, and the growing issue of climate change.
The climate of a place is determined by several factors, including latitude, altitude, distance from the sea, ocean currents, prevailing winds and relief. The global distribution of climates was classified by several geographers, most notably Wladimir Koppen, whose classification is based on temperature and precipitation. Climate change, driven by natural factors and increasingly by human activities, is modifying these climate patterns. In this chapter we study the major climate groups, the natural and human causes of climate change, and the international response to the problem.
Climate is the aggregate of weather conditions over a long period. The major controls of climate are: 1. Latitude: Determines the amount of insolation and hence temperature. The tropics are hot, the polar regions are cold. 2. Altitude: Higher altitudes have cooler temperatures; highlands are colder than lowlands at the same latitude. 3. Pressure and wind systems: They determine the movement of air masses, moisture and precipitation. 4. Distance from the sea (continentality): Coastal areas have equable climates while continental interiors have extremes. 5. Ocean currents: Warm currents warm the coasts, cold currents cool them. 6. Relief: Mountains act as barriers to winds and influence precipitation (rain shadow effect).
The Koppen classification scheme, devised by the German-Russian climatologist Wladimir Koppen, is based on mean monthly temperature, mean monthly precipitation and annual temperature and precipitation. He divided the world's climates into five major groups, designated by the letters A to E: - Type A (Tropical humid climate): Found between the tropics, with high temperatures throughout the year. Subtypes: Af (tropical wet), Am (tropical monsoon), Aw (tropical wet and dry/savanna). - Type B (Dry climate): Where evaporation exceeds precipitation. Subtypes: BWh (hot desert), BSh (hot steppe), BWk (cold desert), BSk (cold steppe). - Type C (Warm temperate or humid subtropical climate): With mild winters and warm summers. Subtypes: Cfa (humid subtropical), Cfb (marine west coast), Csa (mediterranean). - Type D (Cold or snow climate): Cold winters and warm summers, found in the high mid-latitudes of the Northern Hemisphere. Subtypes: Df (cold with humid winters), Dw (cold with dry winters). - Type E (Polar climate): Very cold throughout the year. Subtypes: ET (tundra) and EF (ice cap).
G. T. Trewartha modified Koppen's scheme, and Thornthwaite used the concept of potential evapotranspiration for classification. In India, the classification of climate is important for agriculture, with monsoon climate dominating most of the country.
Located near the equator, with heavy rainfall throughout the year and no dry season. Temperature is high and uniform (about 25-27 deg C). Supports tropical rainforests. Example: the Amazon Basin, Congo Basin.
The tropical monsoon climate has a short dry season with heavy rain during the monsoon; the savanna climate has distinct wet and dry seasons. Example: most of India (Am/Aw), African savannas (Aw).
Found in the subtropical high pressure belts, with very low rainfall, high daytime temperatures and large diurnal temperature ranges. Example: Sahara, Thar, Arabian desert.
Found on the western margins of continents between 30 and 45 degrees, with hot, dry summers and mild, wet winters. Examples: the Mediterranean region, central California, parts of Chile and South Africa.
Found on the eastern margins of continents, with warm, humid summers and mild winters, with rainfall throughout the year. Example: south-eastern USA, eastern China, parts of India (Punjab area).
Found on the western margins of continents in mid-latitudes, with mild, wet conditions throughout the year. Example: western Europe.
Cold climates of the interior of continents with cold, snowy winters and warm summers, supporting coniferous forests (taiga) and grasslands (steppe). Example: Siberia, Canada.
Tundra (ET) with short cool summers and the ice cap (EF) with permanent ice. Example: northern Canada, Greenland, Antarctica.
Climate has changed naturally over geological time. The natural causes include: - Volcanic eruptions: Ash and aerosols in the atmosphere can block sunlight and cause temporary cooling. - Changes in solar output: Variations in solar radiation affect global temperatures. - Changes in Earth's orbit: Milankovitch cycles (changes in the Earth's orbit, tilt and wobble) cause long-term glacial and interglacial periods. - Continental drift: Movement of continents changes ocean currents and climate patterns.
Since the Industrial Revolution, human activities have intensified climate change: - Greenhouse gas emissions: Burning of fossil fuels releases carbon dioxide and methane, strengthening the greenhouse effect. - Deforestation: Reduces the removal of carbon dioxide from the atmosphere. - Industrial processes and agriculture: Release methane, nitrous oxide and other gases. - Urbanisation and land-use change: Alter local and global climate.
The average global temperature has risen by about 0.6 degrees Celsius over the last century. The effects include the melting of glaciers and polar ice, rising sea levels, changing rainfall patterns, more frequent extreme weather events, and threats to biodiversity and agriculture. Low-lying coastal areas and small island nations are especially vulnerable.
The international community has responded through agreements such as the United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol (1997) and the Paris Agreement (2015), which aim to reduce greenhouse gas emissions and limit global warming to well below 2 degrees Celsius.
| Group | Name | Characteristics |
|---|---|---|
| A | Tropical humid | High temperature throughout the year |
| B | Dry | Evaporation exceeds precipitation |
| C | Warm temperate | Mild winters, warm summers |
| D | Cold/Snow | Cold winters, warm summers |
| E | Polar | Very cold throughout the year |
| Climate Type | Koppen Symbol | Example Region |
|---|---|---|
| Equatorial wet | Af | Amazon Basin |
| Tropical monsoon | Am | Most of India |
| Savanna | Aw | African savannas |
| Hot desert | BWh | Sahara, Thar |
| Mediterranean | Csa | Mediterranean coast |
| Humid subtropical | Cfa | South-eastern USA |
| Marine west coast | Cfb | Western Europe |
| Taiga (boreal) | Df | Siberia, Canada |
| Tundra | ET | Arctic coasts |
| Ice cap | EF | Antarctica, Greenland |
| Type | Cause | Effect |
|---|---|---|
| Natural | Volcanic eruptions, solar variation, Milankovitch cycles | Long-term natural variability |
| Human | Fossil fuel burning, deforestation, agriculture | Enhanced greenhouse effect, warming |
World climate is determined by latitude, altitude, pressure systems, distance from the sea, ocean currents and relief. The Koppen classification divides the world's climates into tropical, dry, warm temperate, cold and polar groups, each with characteristic temperature and rainfall regimes. However, the Earth's climate is not static; it has always changed through natural processes such as volcanic eruptions and orbital variations. Since the Industrial Revolution, human activities have accelerated climate change by releasing greenhouse gases, leading to global warming with serious consequences such as rising sea levels and more extreme weather. International cooperation through agreements like the Kyoto Protocol and the Paris Agreement represents the global response to this challenge. Understanding world climate and climate change is essential for environmental planning and sustainable development.
Keywords: Climate, Koppen, tropical, desert, Mediterranean, polar, greenhouse effect, global warming, Kyoto Protocol, Paris Agreement.