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
Classification
- Empirical
- Genetic
- Applied
- Empirical based on temperature and precipitation
- Genetic classification based on causes
- Applied classification based on specific purpose
KoeppenΥs 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 β 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
- Seasons of dryness by f, m, w and s
- f β no dry season
- m β monsoon
- w- winter dry
- s β 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 β Tropical wet
- Am β Tropical Monsoon
- Aw β Tropical wet and dry
- Af β Tropical wet β Amazon basin, equatorial Africa and east Indies, rainfall throughout year with afternoon thunderstorms; high temperature and negligible range, dense canopy and large biodiversity
- Am β Tropical Monsoon β India, NE of South America and North Australia, heavy rain in summer and dry winter
- Aw β Tropical wet and dry β 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 β Dry Climate
- Low rain β 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 β Semi-Arid
- BSh β Subtropical steppe
- BSk β mid-latitude steppe
- BW - Arid
- BWh β 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 β Warm Temperate Mid Latitude
- 3 to 50 on east & west margins of continents
- Warm summer with mild winters
- Cwa β humid subtropical (dry in winter and hot in summer)
- Cs β Meditterenean
- Cfa β Humid subtropical β no dry and mild winter
- Cfb β marine west coast
- Cwa β 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 β west coast near Mediterranean sea β central Chile, central California, SW and SE Australia β influence of subtropical high in summer and westerly wind in winter. Hot dry summer and mild rainy winter. Rain 35 - 90 mm
- Cfa β lies on eastern part of continents in subtropical latitudes, unstable airmass and rain throughout β 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 β poleward from Mediterranean climate on west coast of continents β 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 β Cold Snow Forest
- 4 to 70 N in Europe, Asia and North America
- Df β cold climate with humid winter
- Dw β cold climate with dry winter
- Df β 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 β 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 β Polar Climate
- Beyond 70
- ET β Tundra
- EF β Ice Cap
- ET β 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 β 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 β 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 β 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
- 1990Υs β warmest with worst floods
- 1967 - 77 β worst drought in Sahel
- 1930Υs- drought in SW Great Pains of USA β dust bowl
- 10th -11th century β Vikings settled in Greenland (warm and dry conditions)
- 1550 - 1850 β Europe witnessed Little Ice age
Causes of Climate Change
- Astronomical β solar output and sunspots (dark cooler patch that increase and decrease in cyclical manner)
- Sunspots increase β cold wetter climate and more storms
- Milankovitch oscillations β variation in orbital characteristics around sun, wobbling and change in axial tilt. Alter insolation from sun
- Volcanism β throw aerosols in atmosphere and reduce sun radiations reaching earth (e. g. , Pinatoba and El Cion)
- Anthropogenic effect β higher concentration of CO2 leading to global warming
Global Warming
- Greenhouse Gases β CO2, CFC, CH4, N2O, O3
- NO and CO react with GHG and affect their concentration
- Due to greenhouse gases, earth behaves as greenhouse β 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)
β Manishika