NCERT Class 11 Part 1 Geography Chapter 12: World Climate & Climate Change YouTube Lecture Handouts

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NCERT Class 11 Part 1 Geography Chapter 12: World Climate & Climate Change


  • Empirical
  • Genetic
  • Applied
  • Empirical based on temperature and precipitation
  • Genetic classification based on causes
  • Applied classification based on specific purpose

Koeppen՚s Classification

  • Relation b/w vegetation and climate (values of temperature and precipitation selected)
  • Empirical based on mean annual and monthly temperature and precipitation (capital and small letters)
  • Developed in 1918
  • 5 groups – 4 on temperature and 1 on precipitation (B as dry while A, C, D and E as humid)
  • Small letters as seasonality of precipitation and temperature
    A Characteristics
  • Seasons of dryness by f, m, w and s
  • f – no dry season
  • m – monsoon
  • w- winter dry
  • s – summer dry
  • Temperature severity by a, b, c and d (small letters)
  • B (dry) has S for Steppe and W for desert

Group a- Tropical Humid

  • b/w tropic of cancer and Capricorn; hot and humid ITCZ
  • Af – Tropical wet
  • Am – Tropical Monsoon
  • Aw – Tropical wet and dry
  • Af – Tropical wet – Amazon basin, equatorial Africa and east Indies, rainfall throughout year with afternoon thunderstorms; high temperature and negligible range, dense canopy and large biodiversity
  • Am – Tropical Monsoon – India, NE of South America and North Australia, heavy rain in summer and dry winter
  • Aw – Tropical wet and dry – North and South of Af; border dry climate of west of Cf/Cw; in north and south of Amazon; less rain than Af and Am; short wet and long dry season; high temperature throughout year with deciduous forests

Group B – Dry Climate

  • Low rain – from 15 to 60 N & S of equator
  • In subtropical high where no rain due to temperature inversion
  • On western margins of the continents
  • BS – Semi-Arid
    • BSh – Subtropical steppe
    • BSk – mid-latitude steppe
  • BW - Arid
    • BWh – Subtropical desert
    • BWk- mid-latitude desert
  • BSh more rainfall than BWh
  • Variable rain affects life in steppes
  • Rain with short intense thundershower in desert
  • Fog in coastal desert near cold currents
  • Annual and diurnal temperature ranges are high

Group C – Warm Temperate Mid Latitude

  • 3 to 50 on east & west margins of continents
  • Warm summer with mild winters
  • Cwa – humid subtropical (dry in winter and hot in summer)
  • Cs – Meditterenean
  • Cfa – Humid subtropical – no dry and mild winter
  • Cfb – marine west coast
  • Cwa – poleward of tropic of cancer and Capricorn in north Indian plain and south china plains. Similar to Aw except temperature in winter is warm
  • Cs – west coast near Mediterranean sea – central Chile, central California, SW and SE Australia – influence of subtropical high in summer and westerly wind in winter. Hot dry summer and mild rainy winter. Rain 35 - 90 mm
  • Cfa – lies on eastern part of continents in subtropical latitudes, unstable airmass and rain throughout – USA, east China, South Japan, NE Argentina, South Africa and east Australia. Rain from 75 to 150 cm. Summer thunderstorm and frontal rain in winter
  • Cfb – poleward from Mediterranean climate on west coast of continents – NW Europe, West of N America, N California, S Chile, SE Australia and New Zealand. Moderate temperature with warm winters as compared to others in that latitude. Rain throughout the year

Group D – Cold Snow Forest

  • 4 to 70 N in Europe, Asia and North America
  • Df – cold climate with humid winter
  • Dw – cold climate with dry winter
  • Df – poleward of marine west coast and mid latitude steppe; cold and snowy winter; frost free season is short, large range of temperature, short weather changes and severe poleward winters
  • Dw – NE Asia, winter anticyclone, weakening in summer sets in monsoons with wind reversals; low summer and extreme low winter temperatures; rain in summers about 12 - 15 cm

Group E – Polar Climate

  • Beyond 70
  • ET – Tundra
  • EF – Ice Cap
  • ET – low growing mosses, lichens and flowering plants, permafrost with subsoil frozen, short growing season, water logging support only low growing crops. In summers have long duration of day light
  • EF – Interior Greenland and Antarctica, summers below freezing point, less rainfall, ice accumulated and deformation of ice sheets occur, move as icebergs over waters

Group H - Highland Climate

  • Governed by topography
  • High mountain – large changes in mean temperature occur over short distance
  • Precipitation type and intensity vary
  • Vertical zonation of climate with elevation

Climate Change

  • Geological records show alternations in glacial and interglacial period
  • In high altitude – retreat and advancement of glaciers
  • Sediments in glacial lakes denote warm and cold period
  • Rings of tree explain wet and dry period
  • Rajasthan desert was wet and cold around 8000 BC. High rain from 1700 to 3000 BC. From 2000 to 1700 BC Harappa civilization and then dry climate
  • Earth warm in Cambrian, Ordovician and Silurian period,
  • Glacial and interglacial period during Pleistocene with last major peak glacial period around 18,000 years. Present interglacial period started 10,000 years ago.

Climate in Recent Past

  • Variability occurs
  • 1990՚s – warmest with worst floods
  • 1967 - 77 – worst drought in Sahel
  • 1930՚s- drought in SW Great Pains of USA – dust bowl
  • 10th -11th century – Vikings settled in Greenland (warm and dry conditions)
  • 1550 - 1850 – Europe witnessed Little Ice age

Causes of Climate Change

  • Astronomical – solar output and sunspots (dark cooler patch that increase and decrease in cyclical manner)
  • Sunspots increase – cold wetter climate and more storms
  • Milankovitch oscillations – variation in orbital characteristics around sun, wobbling and change in axial tilt. Alter insolation from sun
  • Volcanism – throw aerosols in atmosphere and reduce sun radiations reaching earth (e. g. , Pinatoba and El Cion)
  • Anthropogenic effect – higher concentration of CO2 leading to global warming

Global Warming

  • Greenhouse Gases – CO2, CFC, CH4, N2O, O3
  • NO and CO react with GHG and affect their concentration
  • Due to greenhouse gases, earth behaves as greenhouse – transmit incoming shortwave solar radiation but absorb longwave radiations going out (allow temperature inside to rise)
  • CFC are highly effective. It destroys ozone in stratosphere leading to ozone hole.
  • Ozone absorbs UV rays
  • More time GHG molecule remain in atmosphere, longer it will take to recover from changes that are brought about
  • Forest are largest carbon sink, photosynthesis, 20 - 50 years taken to adjust to the changes in source to sink. Rises about 0.5 % annually. Concentration doubles over pre-industrial levels. Fossil fuels, combustion lead to CO2
  • Kyoto protocol proclaimed in 1997 and ratified in 2005 by 141 nations bounds 35 industrialized nations to reduce emissions by 2012 to 5 % less than 1900 levels.
  • Melting of glaciers, ice caps, rise of sea levels, submergence of islands
  • Temperature data is available for Europe with reference period of 1961 - 1990 with annual average sea surface temperature of 14 degree Celsius
  • Maximum warming during 1901 - 44 and 1977 - 99. Globally average temperature at end of 20th century was 0.6 degree Celsius higher than 19th century
  • 7 warmest years in 1856 - 200 were during last decade (with 1998 was the warmest year)

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