Class 11 Geography Chapter 11 World Climate and Climate Change NCERT Exercise Solution (English Medium)
NCERT EXERCISES
1. Multiple choice questions.
(i) Which one of the following is
suitable for Koeppen’s “A” type of climate?
(a) High rainfall in all the
months
(b) Mean monthly temperature of
the coldest month more than freezing point
(c) Mean monthly temperature of
all the months more than 18°C
(d) Average temperature for all
the months below 10°C
Ans. (c) Mean monthly
temperature of all the months more than 18°C
(ii) Koeppen’s system of
classification of climates can be termed as :
(a) Applied (b) Systematic (c)
Genetic (d) Empirical
Ans. (d) Empirical
(iii) Most of the Indian Peninsula
will be grouped according to Koeppen’s system under:
(a) “Af” (b) “BSh” (c) “Cfb” (d)
“Am”
Ans. (d) “Am”
(iv) Which one of the following
years is supposed to have recorded the warmest temperature the world over?
(a) 1990 (b) 1998 (c) 1885 (d)
1950
Ans. (b) 1998
(v) Which one of the following
groups of four climates represents humid conditions?
(a) A—B—C—E
(b) A—C—D—E
(c) B—C—D—E
(d) A—C—D—F
Ans. (b) A—C—D—E
2. Answer the following
questions in about 30 words.
(i) Which two climatic variables
are used by Koeppen for classification of the climate?
Ans. The most widely used
classification of climate is the empirical climate classification scheme
developed by V. Koeppen. Koeppen identified a close relationship between the
distribution of vegetation and climate. He selected certain values of
temperature and precipitation and related them to the distribution of
vegetation and used these values for classifying the climates. It is an
empirical classification based on mean annual and mean monthly temperature and
precipitation data. He introduced the use of capital and small letters to
designate climatic groups and types. Although developed in 1918 and modified
over a period of time, Koeppen’s scheme is still popular and in use.
(ii) How is the “genetic” system
of classification different from the “empirical one”?
Ans. The world climate can be
studied by organising information and data on climate and synthesising them in
smaller units for easy understanding, description and analysis. Three
broad approaches have been adopted for classifying climate. They are empirical,
genetic and applied.
·
Empirical classification is based on observed data,
particularly on temperature and precipitation.
·
Genetic classification attempts to organise climates
according to their causes.
·
Applied classification is for specific purpose.
(iii) Which types of climates have
very low range of temperature?
Ans. Tropical humid climates
exist between Tropic of Cancer and Tropic of Capricorn. The sun being overhead
throughout the year and the presence of Inter Tropical Convergence Zone (ITCZ)
make the climate hot and humid. Annual range of temperature is very low and
annual rainfall is high.
(iv) What type of climatic
conditions would prevail if the sun spots increase?
Ans. Sunspots are dark and
cooler patches on the sun which increase and decrease in a cyclical manner. According
to some meteorologists, when the number of sunspots increase, cooler and wetter
weather and greater storminess occur. A decrease in sunspot numbers is
associated with warm and drier conditions. Yet, these findings are not
statistically significant.
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3. Answer the following questions in
about 150 words.
(i) Make a comparison of the climatic conditions between the “A” and “B” types of climate. (ii) What type of vegetation would you find in the “C” and “A” type(s) of climate? OR Classify the world climate according to Koeppen’s Scheme of Classification of Climate
Ans. The most widely used
classification of climate is the empirical climate classification scheme
developed by V. Koeppen. Koeppen identified a close relationship between the
distribution of vegetation and climate. He selected certain values of
temperature and precipitation and related them to the distribution of
vegetation and used these values for classifying the climates. It is an
empirical classification based on mean annual and mean monthly temperature and
precipitation data. He introduced the use of capital and small letters to
designate climatic groups and types. Although developed in 1918 and modified
over a period of time, Koeppen’s scheme is still popular and in use.
Koeppen recognised five
major climatic groups; four of them are based on temperature and one on
precipitation. Table 12.1 lists the climatic groups and their characteristics
according to Koeppen. The capital letters: A, C, D and E delineate humid
climates and B dry climates.
Group A: Tropical Humid
Climates
Tropical humid climates exist
between Tropic of Cancer and Tropic of Capricorn. The sun being overhead
throughout the year and the presence of Inter Tropical Convergence Zone (ITCZ)
make the climate hot and humid. Annual range of temperature is very low and
annual rainfall is high.
The tropical group is divided into
three types, namely (i) Af- Tropical wet climate; (ii) Am - Tropical monsoon
climate; (iii) Aw- Tropical wet and dry climate.
Tropical Wet Climate (Af)
Tropical wet climate is
found near the equator. The major areas are the Amazon Basin in South America, western
equatorial Africa and the islands of East Indies. Significant amount of
rainfall occurs in every month of the year as thunder showers in the afternoon.
The temperature is uniformly high and the annual range of temperature is
negligible. The maximum temperature on any day is around 30°C while the
minimum temperature is around 20°C. Tropical evergreen forests with dense
canopy cover and large biodiversity are found in this climate.
Tropical monsoon climate (Am) is
found over the Indian sub-continent, North Eastern part of South America
and Northern Australia. Heavy rainfall occurs mostly in summer. Winter is
dry. The detailed climatic account of this climatic type is given in the
book on India: Physical Environment.
Tropical Wet and Dry
Climate (Aw)
Tropical wet and dry climate
occurs north and south of Af type climate regions. It borders with dry
climate on the western part of the continent and Cf or Cw on the eastern
part. Extensive Aw climate is found to the north and south of the Amazon forest
in Brazil and adjoining parts of Bolivia and Paraguay in South America, Sudan
and south of Central Africa. The annual rainfall in this climate is considerably
less than that in Af and Am climate types and is variable also. The wet season
is shorter and the dry season is longer with the drought being more severe. Temperature
is high throughout the year and diurnal ranges of temperature are the greatest
in the dry season. Deciduous forest and tree-shredded grasslands occur in
this climate.
Dry climates are characterised by
very low rainfall that is not adequate for the growth of plants. These climates
cover a very large area of the planet extending over large latitudes from 15° -
60° north and south of the equator. At low latitudes, from 15° - 30°, they
occur in the area of subtropical high where subsidence and inversion of
temperature do not produce rainfall. On the western margin of the
continents, adjoining the cold current, particularly over the west coast of
South America, they extend more equatorwards and occur on the coast land. In
middle latitudes, from 35° - 60° north and south of equator, they are
confined to the interior of continents where maritime-humid winds do not reach
and to areas often surrounded by mountains.
Dry climates are divided
into steppe or semi-arid climate (BS) and desert climate (BW). They are further
subdivided as subtropical steppe (BSh) and subtropical desert (BWh) at
latitudes from 15° - 35° and mid-latitude steppe (BSk) and mid-latitude desert
(BWk) at latitudes between 35° - 60°.
Subtropical Steppe (BSh)
and Subtropical Desert (BWh) Climates
Subtropical steppe (BSh) and
subtropical desert (BWh) have common precipitation and temperature
characteristics. Located in the transition zone between humid and dry
climates, subtropical steppe receives slightly more rainfall than the desert,
adequate enough for the growth of sparse grasslands. The rainfall in both
the climates is highly variable. The variability in the rainfall affects the
life in the steppe much more than in the desert, more often causing famine.
Rain occurs in short intense thundershowers in deserts and is ineffective in
building soil moisture. Fog is common in coastal deserts bordering
cold currents. Maximum temperature in the summer is very high. The
highest shade temperature of 58° C was recorded at Al Aziziyah, Libya on
13 September 1922. The annual and diurnal ranges of temperature are also
high.
Warm temperate (mid-latitude)
climates extend from 30° - 50° of latitude mainly on the eastern and western
margins of continents. These climates generally have warm summers with mild
winters. They are grouped into four types: (i) Humid subtropical, i.e.
dry in winter and hot in summer (Cwa); (ii) Mediterranean (Cs); (iii) Humid
subtropical, i.e. no dry season and mild winter (Cfa); (iv) Marine west coast
climate (Cfb).
Humid Subtropical
Climate (Cwa)
Humid subtropical climate occurs
poleward of Tropic of Cancer and Capricorn, mainly in North Indian plains and
South China interior plains. The climate is similar to Aw climate except that
the temperature in winter is warm.
As the name suggests,
Mediterranean climate occurs around Mediterranean sea, along the west coast of
continents in subtropical latitudes between 30° - 40° latitudes e.g. — Central
California, Central Chile, along the coast in south eastern and south western
Australia. These areas come under the influence of sub-tropical high in summer
and westerly wind in winter. Hence, the climate is characterized by hot, dry summer and mild, rainy
winter. Monthly average temperature in summer is around 25° C and in winter
below 10°C. The annual precipitation ranges between 35 - 90 cm.
Humid subtropical climate lies on
the eastern parts of the continent in subtropical latitudes. In this region the
air masses are generally unstable and cause rainfall throughout the year.
They occur in eastern United States of America, southern and eastern China,
southern Japan, northeastern Argentina, coastal South Africa and eastern coast
of Australia. The annual averages of precipitation vary from 75-150 cm.
Thunderstorms in summer and frontal precipitation in winter is common. Mean
monthly temperature in summer is around 27°C, and in winter it varies from
5°-12° C. The daily range of temperature is small.
Marine West Coast
Climate (Cfb)
Marine west coast climate is
located poleward from the Mediterranean climate on the west coast of the
continents. The main areas are: Northwestern Europe, west coast of North
America, north of California, southern Chile, southeastern Australia and
New Zealand. Due to marine influence, the temperature is moderate and in
winter, it is warmer than for its latitude. The mean temperature in summer
months ranges from 15°-20°C and in winter 4°-10°C. The annual and daily ranges
of temperature are small. Precipitation occurs throughout the year.
Precipitation varies greatly from 50-250cm.
Cold snow forest climates occur in
the large continental area in the northern hemisphere between 40°-70° north
latitudes in Europe, Asia and North America. Cold snow forest climates are
divided into two types: (i) Df- cold climate with humid winter; (ii) Dw- cold climate
with dry winter. The severity of winter is more pronounced in higher latitudes.
Cold Climate with Humid
Winters (Df)
Cold climate with humid winter
occurs poleward of marine west coast climate and mid latitude steppe. The
winters are cold and snowy. The frost free season is short. The annual ranges
of temperature are large. The weather changes are abrupt and short. Poleward,
the winters are more severe.
Cold climate with dry winter
occurs mainly over Northeastern Asia. The development of pronounced winter anti
cyclone and its weakening in summer sets in monsoon like reversal of wind in
this region. Poleward summer temperatures are lower and winter temperatures are
extremely low with many locations experiencing below freezing point
temperatures for up to seven months in a year. Precipitation occurs in summer.
The annual precipitation is low from 12-15 cm.
Polar Climates (E)
Polar climates exist poleward
beyond 70° latitude. Polar climates consist of two types: (i) Tundra (ET); (ii)
Ice Cap (EF).
Tundra Climate (ET)
The tundra climate (ET) is so
called after the types of vegetation, like low growing mosses, lichens and
flowering plants. This is the region of permafrost where the sub soil is
permanently frozen. The short growing season and water logging support only low
growing plants. During summer, the tundra regions have very long duration of
day light.
Ice Cap Climate (EF)
The ice cap climate (EF) occurs
over interior Greenland and Antarctica. Even in summer, the temperature is
below freezing point. This area receives very little precipitation. The snow
and ice get accumulated and the mounting pressure causes the deformation
of the ice sheets and they break. They move as icebergs that float in the
Arctic and Antarctic waters. Plateau Station, Antarctica, 79°S, portray this
climate.
Highland climates are governed by
topography. In high mountains, large changes in mean temperature occur over
short distances. Precipitation types and intensity also vary spatially across
high lands. There is vertical zonation of layering of climatic types with
elevation in the mountain environment.
(iii) What do you understand by
the term “Greenhouse Gases”? Make a list of greenhouse gases.
Ans. The
term greenhouse is derived from the analogy to a greenhouse used in cold
areas for preserving heat. A greenhouse is made up of glass. The glass which is
transparent to incoming short wave solar radiation is opaque to outgoing
long wave radiation. The glass, therefore, allows in more radiation and
prevents the long wave radiation going outside the glass house, causing the
temperature inside the glasshouse structure warmer than outside. When you enter
a car or a bus, during summers, where windows are closed, you feel more heat
than outside. Likewise during winter the vehicles with closed doors and windows
remain warmer than the temperature outside. This is another example of the
greenhouse effect.
Greenhouse Gases (GHGs)
The primary GHGs of
concern today are carbon dioxide (CO2), Chlorofluorocarbons
(CFCs), methane (CH4), nitrous oxide (N2O) and ozone (O3). Some other gases such
as nitric oxide (NO) and carbon monoxide (CO) easily react with GHGs and affect
their concentration in the atmosphere.
The effectiveness of any given GHG
molecule will depend on the magnitude of the increase in its concentration, its
life time in the atmosphere and the wavelength of radiation that it absorbs. The
chlorofluorocarbons (CFCs) are highly effective. Ozone which
absorbs ultra violet radiation in the stratosphere is very effective in
absorbing terrestrial radiation when it is present in the lower troposphere.
Another important point to be noted is that the more time the GHG molecule
remains in the atmosphere, the longer it will take for earth’s atmospheric
system to recover from any change brought about by the latter.
The largest
concentration of GHGs in the atmosphere is carbon dioxide. The emission of CO2 comes mainly from
fossil fuel combustion (oil, gas and coal). Forests and oceans are the sinks
for the carbon dioxide. Forests use CO2 in their growth. So,
deforestation due to changes in land use also increases the concentration of Co2. The time taken for
atmospheric CO2 to adjust to changes in sources to sinks is 20-50 years. It
is rising at about 0.5 per cent annually. Doubling of concentration of CO2 over pre-industrial
level is used as an index for estimating the changes in climate in climatic
models.
Chlorofluorocarbons (CFCs) are
products of human activity. Ozone occurs in the
stratosphere where ultra-violet rays convert oxygen into ozone. Thus, ultra
violet rays do not reach the earth’s surface. The CFCs which drift into the
stratosphere destroy the ozone. Large depletion of ozone occurs over Antarctica. The depletion of
ozone concentration in the stratosphere is called the ozone
hole. This allows the ultra violet rays to pass through the troposphere.
International efforts have been
initiated for reducing the emission of GHGs into the atmosphere. The most important
one is the Kyoto protocol proclaimed in 1997. This protocol went into
effect in 2005, ratified by 141 nations. Kyoto protocol bounds the 35
industrialised countries to reduce their emissions by the year 2012 to 5 per
cent less than the levels prevalent in the year 1990.
The increasing trend in
the concentration of GHGs in the atmosphere may, in the long run, warm up the
earth. Once
the global warming sets in, it will be difficult to reverse it. The effect of
global warming may not be uniform everywhere. Nevertheless, the adverse
effect due to global warming will adversely affect the life supporting system.
Rise in the sea level due to melting of glaciers and ice-caps and thermal
expansion of the sea may inundate large parts of the coastal area and islands,
leading to social problems. This is another cause for serious concern for
the world community. Efforts have already been initiated to control the
emission of GHGs and to arrest the trend towards global warming. Let us
hope the world community responds to this challenge and adopts a
lifestyle that leaves behind a livable world for the generations to come.
One of the major concerns
of the world today is global warming. Let us look at how much
the planet has warmed up from the temperature records.
Temperature data are available
from the middle of the 19th century mostly for Western Europe. The reference
period for this study is 1961-90. The temperature anomalies for the earlier and
later periods are estimated from the average temperature for the period
1961-90. The annual average near-surface air temperature of the world is
approximately 14°C. The time series show anomalies of annual near surface
temperature over land from 1856-2000, relative to the period 1961-90 as normal
for the globe.
An increasing trend in
temperature was discernible in the 20th century. The greatest warming of
the 20th century was during the two periods, 1901-44 and 1977-99. Over each of
these two periods, global temperatures rose by about 0.4°C. In between, there
was a slight cooling, which was more marked in the Northern Hemisphere.
The globally averaged
annual mean temperature at the end of the 20th century was about 0.6°C above
that recorded at the end of the 19th century. The seven warmest years
during the 1856-2000 were recorded in the last decade. The year 1998 was the
warmest
year,
probably not only for the 20th century but also for the whole millennium.
(iv) Write an explanatory note on “Climate
Change and global warming”.
Ans. Climate Change - The type of climate we
experience now might be prevailing over the last 10,000 years with minor and
occasionally wide fluctuations. The planet earth has witnessed many variations
in climate since the beginning. Geological records show alteration of glacial
and inter-glacial periods. The geomorphological features, especially in high
altitudes and high latitudes, exhibit traces of advances and retreats of
glaciers. The sediment deposits in glacial lakes also reveal the occurrence of
warm and cold periods. The rings in the trees provide clues about wet and dry
periods. Historical records describe the vagaries in climate. All these
evidences indicate that change in climate is a natural and continuous process.
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In the geological past, the earth
was warm some 500-300 million years ago, through the Cambrian, Ordovician and
Silurian periods. During the Pleistocene epoch, glacial and inter-glacial
periods occurred, the last major peak glacial period was about 18,000 years
ago. The present inter-glacial period started 10,000 years ago.
Climate in the recent
past - Variability
in climate occurs all the time. The nineties decade of the last century
witnessed extreme weather events. The 1990s recorded the warmest temperature of
the century and some of the worst floods around the world. The worst
devastating drought in the Sahel region, south of the Sahara desert,
from 1967-1977 is one such variability. During the 1930s, severe drought
occurred in southwestern Great Plains of the United States, described as
the dust bowl. Historical records of crop yield or crop failures, of
floods and migration of people tell about the effects of changing climate. A
number of times Europe witnessed warm, wet, cold and dry periods, the
significant episodes were the warm and dry conditions in the tenth and eleventh
centuries, when the Vikings settled in Greenland. Europe witnessed “Little
Ice Age” from 1550 to about 1850. From about 1885-1940 world
temperature showed an upward trend. After 1940, the rate of increase in
temperature slowed down.
Causes of Climate Change
The causes for climate change are
many. They can be grouped into astronomical and terrestrial causes. The
astronomical causes are the changes in solar output associated with sunspot
activities. Sunspots are dark and cooler patches on the sun which increase and
decrease in a cyclical manner. According to some meteorologists, when the number
of sunspots increases, cooler and wetter weather and greater storminess occur.
A decrease in sunspot numbers is associated with warm and drier conditions.
Yet, these findings are not statistically significant.
An another astronomical theory is Millankovitch
oscillations, which infer cycles in the variations in the earth’s orbital
characteristics around the sun, the wobbling of the earth and the changes in
the earth’s axial tilt. All these alter the amount of insolation received from
the sun, which in turn, might have a bearing on the climate.
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Due to the presence of
greenhouse gases, the atmosphere is behaving like a greenhouse. The
atmosphere also transmits the incoming solar radiation but absorbs the vast
majority of long wave radiation emitted upwards by the earth’s surface. The
gases that absorb long wave radiation are called greenhouse gases. The
processes that warm the atmosphere are often collectively referred to
as the greenhouse effect.
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