World Climate and Climate Change Class 11 Geography Chapter 11 CBSE Notes 2025-26

The study of world climate involves organizing information and analysing data to understand patterns and causes of various climatic zones across the globe. Climate classification helps in simplifying this diversity for description and analysis. There are three main approaches to climate classification: empirical (based on observed temperature and precipitation data), genetic (focused on causes of climate), and applied (for specific applications such as agriculture or tourism). The most widely used system for global climate classification is the empirical system by V. Koeppen, which links vegetation and climate using specific values of temperature and precipitation.

Koeppen’s Classification of Climate Koeppen’s system identifies five major climate groups—A: Tropical, B: Dry, C: Warm Temperate (Mid-latitude), D: Cold Snow Forest, and E: Cold—using capital letters. These main groups are further subdivided using small letters based on temperature severity and seasonality of precipitation, such as ‘f’ for no dry season, ‘w’ for winter dry, ‘s’ for summer dry, and ‘m’ for monsoon. For dry climates (B), 'S' is used for steppe (semi-arid) and 'W' for desert (arid) types.

Summary Table: Major Koeppen Climatic Groups

Group	Characteristic
A – Tropical	Coldest month’s mean temperature 18°C or above
B – Dry	Evaporation exceeds precipitation
C – Warm Temperate (Mid-latitude)	Coldest month’s mean temperature above -3°C but below 18°C
D – Cold Snow Forest	Coldest month’s mean temperature -3°C or below
E – Cold	All months’ mean temperature below 10°C

Types of World Climates (Koeppen Codes)

• Af: Tropical Wet — uniform rainfall throughout year, equatorial regions.
• Am: Tropical Monsoon — heavy summer rainfall and dry winters, seen in Indian subcontinent.
• Aw: Tropical Wet and Dry — pronounced dry winter season, areas north and south of equator.
• BSh, BWh: Subtropical Steppe and Desert — arid to semi-arid, low rainfall, hot summers.
• BSk, BWk: Mid-latitude Steppe and Desert — drier and colder than low-latitude types.
• Cwa, Cfa: Humid Subtropical — warm, humid summers, mild winters; Cwa has dry winters.
• Cs: Mediterranean — hot, dry summers, mild, rainy winters.
• Cfb: Marine West Coast — moderate temperature, rain all year, small annual variation.
• Df, Dw: Cold Snow Forest — severe winters, Df has year-round precipitation, Dw has dry winters.
• ET: Tundra — very cold, short growing season, permafrost conditions.
• EF: Polar Ice Cap — temperature always below freezing, permanent ice.

Tropical Humid Climates (A Group) Tropical regions between the Tropic of Cancer and Tropic of Capricorn have hot and humid conditions due to high sun angle throughout the year and presence of the Inter Tropical Convergence Zone (ITCZ). These areas have low annual temperature range and high rainfall.

• Af: Equatorial areas (Amazon, West Africa) — high rainfall all year, evergreen forests.
• Am: Monsoon areas (India, South America) — summer rains, dry winter.
• Aw: Wet & dry climates — shorter wet season, longer dry season with possible droughts, more grasslands.

Dry Climates (B Group) These are found in areas where rainfall is too low to support much vegetation, often between 15°–60° latitude. Subtropical deserts occur under high pressure belts, while mid-latitude dry regions are usually in continental interiors or rain-shadow areas. Steppe (semi-arid) zones have more rain and grasses, while true deserts support very sparse life.

Warm Temperate (C Group) Found typically between 30°–50° latitude. These include Mediterranean climate (hot, dry summers and cool, wet winters), marine west coast (mild, rainy throughout), and humid subtropical climate (hot, humid summers, mild winters). Vegetation can range from evergreen broadleaf to deciduous forests and temperate grasslands.

Cold Snow Forest (D Group) and Polar Climates (E Group) Cold climates predominate across northern continents between 40°–70° latitude. Df climates have year-round precipitation while Dw climates have dry winters due to monsoonal effects (especially in NE Asia). E group includes Tundra (ET) with permafrost and short vegetation, and Ice cap (EF) with permanent snow and ice. Both are marked by extremely cold conditions and short or no summers.

Climate Change: Evidence and Causes Throughout history, the earth’s climate has naturally changed, alternating between wet and dry periods or glacial and interglacial phases. Examples include a wetter Rajasthan desert around 8,000 BC and the wetter Harappan period in India. The last millennium has recorded both slight ice ages (1550–1850 AD in Europe) and warming trends, especially since the 20th century.

Climate can be affected by astronomical (sunspot cycles, Earth’s orbital variations) and terrestrial (volcanoes, atmospheric composition) factors. Major volcanic eruptions can temporarily cool earth by reflecting sunlight. Earth's orbital features (tilt, shape, wobble) lead to long-term changes, as described by Milankovitch cycles. Recently, human-caused greenhouse gas emissions have emerged as a vital cause of present day global warming.

Global Warming and Greenhouse Gases The atmosphere behaves like a greenhouse due to certain gases which absorb and re-radiate infrared radiation, leading to an overall rise in global temperature. Key greenhouse gases include carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), ozone (O₃), and chlorofluorocarbons (CFCs). CO₂, mainly produced by burning fossil fuels, is the largest contributor and its concentration is rising yearly.

CFCs, fully manufactured by humans, also damage the ozone layer, causing more ultraviolet radiation to reach Earth’s surface. International agreements such as the Kyoto Protocol seek to limit the emissions of such gases, yet reversing the warming trend is challenging. Potential effects of global warming include faster melting of glaciers and ice caps, sea level rise, and loss of habitats, especially in coastal and island areas.

Trends in Global Temperature

• The global average near-surface air temperature is about 14°C.
• Most 20th-century warming occurred during 1901–44 and 1977–99, with about 0.4°C rise in each period.
• By the end of the 20th century, temperatures were about 0.6°C higher than at the end of the 19th century.
• 1998 was likely the warmest year of the millennium.

Important MCQs and Short Questions

• Koeppen’s "A" type climate is where all months’ mean temperature is above 18°C.
• Most of the Indian peninsula falls under ‘Am’ (tropical monsoon) climate in Koeppen’s classification.
• Main variables used by Koeppen are temperature and precipitation.
• Genetic classification is based on causes, empirical on observed data.

Practice and Project Work

• Students should collect and discuss information about the Kyoto Declaration and international efforts regarding climate change.
• Prepare notes on how different vegetation types correspond to ‘A’ and ‘C’ climate groups using real-world examples.

CBSE Class 11 Geography Chapter 11 Notes – World Climate and Climate Change: Key Points for Quick Revision

These concise notes for Class 11 Geography Chapter 11 cover all key aspects of world climates and climate change, making them ideal for thorough last-minute revision. Gain a clear understanding of Koeppen’s climate classification, causes of climate change, and the effects of global warming through simplified explanations and tables. Use these revision notes to reinforce core concepts and boost your exam confidence in Geography.

With a blend of bullet points and summary tables, these World Climate and Climate Change notes make complex information accessible for CBSE students. They are valuable for answering short and long questions, practicing MCQs, and remembering important data about greenhouse gases and climate trends. Strengthen your Geography fundamentals quickly with these well-organized study notes.