Chapter 2 climate

Chapter 2: Variable Weather and Changing
Climate – A Continuing Challenge
An Introduction

Key Questions of Chapter
1. Why do different
places experience
different weather and
climate?
2. What is
happening to the
Earth’s climate?

Gateway 1: Why do different places experience
different weather and climate?

Section Objectives
Weather vs. Climate
Elements of Weather
Climatic types:
Characteristics & Location
Gateway 1: Why do different places experience

What is the difference between
weather and climate?
• Condition of the
atmosphere at a particular
place and timeWeather
• The average condition of
the atmosphere of a specific
place over a long period of
time – usually over 30 years
Climate

What are the elements of weather?
QUESTION: How would you describe
today’s weather?
Warm?
No rain?
Humid?
Windy?
Cloudy?

What are the elements of weather?
Weather
Temperature
Relative
humidity
Clouds
Rainfall
Pressure &
winds

1) Temperature
• The degree of hotness or coldness
Energy of
sun
Travels
through the
atmosphere
Absorbed
by the
earth’s
surface
Warms up
Heats up
atmosphere

1) Temperature
• Measured in degrees Celsius (⁰C)
• Important terms:
–Maximum and minimum temperature
–Diurnal temperature range
–Mean daily/monthly/annual temperature
–Annual temperature range

Maximum and minimum temp.
• The highest and lowest temperatures
recorded within a day.
• Normally affected most by the presence
or absence of sunlight (key heatsource)

Diurnal Temperature Range
• The difference between the Maximum
and minimum temperature of the day.
January 1 2 3 4 5 6 7 8 9 10 11 12
Maximum 26 27 27 26 28 28 28 28 29 29 27 25
Minimum 25 25 25 24 25 25 24 25 25 26 26 24
QN: What is the diurnal temperature range for
9 January?

Mean Annual Temperature
• The average of all the monthly average
temperatures
• Method 1: Sum of all divided by 12
months.
• Method 2: Sum of highest and lowest
months divided by 2
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
COUNTRYC -30 -28 -25 -20 -16 -15 -10 -16 -22 -29 -30 -35
COUNTRYD 27 27 28 28 29 30 32 30 30 29 28 28

Annual Temperature Range
• The variation of temperature between
the monthly average temperature
readings.
• Difference between the maximum and
minimum mean monthly temperatures
in a year.
QN: What is the annual temperature range for
Country C?

Why and how does temperature vary
over different areas?

Factors affecting the temperature of
locations
Latitude Altitude
Distance
from the sea
Cloud cover

Factors affecting temp: Latitude
• Refers to the imaginary horizontal lines
running east to west around the earth
• Equator = 0⁰
• North / South Pole = 90⁰N / 90⁰S
• Angle of incidence: the angle at which the
sun’s rays hit the earth surface

Factors affecting temp: Latitude
Low AOI:
lower
temperatures
• Sun’s rays strike
at a lower angle
• Solar energy is
spread out over a
wider area
• Sun’s rays strike
at a higher angle
• Solar energy is
concentrated on
a small area
High AOI:
higher
temperatures
Food for thought: the earth tilts at 23.5⁰  results
in some places not receiving sunlight for months.
How is this so?

Video: 30 days of night
http://www.youtube.com/watch?v=GxC0Um9zS
qY

Factors affecting temp: Altitude
• Refers to the
height of a
location in
relation to
the sea level

Factors affecting temp: Altitude (TB p. 76)
• The ___ the altitude, the ___ the temperature
• Temperature decreases with altitude
WHY?!

Reason 1
• Atmosphere is mostly heated by the earth’s
surface
Shortwave
radiation
Longwave
radiation
The higher up the
atmosphere you
go, the further you
are from the
source of heat
(earth’s surface)
 lower
temperature.

Reason 2
• Air is less dense at
higher altitudes
• The lower the
altitudes, the higher
the density of the air
• Dense air is able to
absorb more heat
from LW radiation 
higher temperatures
at lower altitudes
QUESTION: What are the gases that
absorb heat?

Fun Fact 101: How altitude affects
baking

Factors affecting temp: Distance from
the sea

the sea
• The sea heats up and
cools down more
slowly than the land
 difference in rate of
heating & cooling
between coastal and
inland areas 
difference in
temperature
– Maritime vs.
Continental effect

the sea
Maritime effect
• The effect of large ocean bodies on climate of
coastal areas
• During summer the air over the sea remains
cooler than the land as it heats up slower
• During winter the air over the sea remains
warmer than the land as it loses heat slower
• This causes coastal areas to have cooler summers
and warmer winters
• The annual temperature range is thus smaller

the sea
Continental effect
• The effect of continental surfaces on climate of
inland areas
• Inland areas are further from the sea and oceans
• These areas are not influenced by the
temperatures over the sea
• Inland areas tend to have warmer summers and
colder winters
• The annual temperature range is thus larger

Factors affecting temp: Cloud cover
• Refers to the extent of sky that is covered by
clouds
• More cloud cover results in a smaller diurnal
range
• Less cloud cover results in a larger diurnal
range
• This is due to the effect of clouds absorbing
and reflecting the sun’s rays and heat energy
from the earth’s surface

Qn: Why do different places along
the same latitude have different
temperatures?
http://drought.unl.edu/DroughtBasics/WhatisCli
matology/ClimographsforSelectedInternationalC
ities.aspx

Homework: PITSTOP 2 (TB p. 79)
Questions 1, 3 & 6

2) Relative humidity
• Refers to the ratio between the actual amount
of water vapour and the maximum amount of
water vapour that the air can hold at a given
temperature
• Formula:
Actual amount of water vapour in the air (g/m³)
Max. amount of water vapour the air can hold(g/m³)
x 100
EXERCISE: if the air at 15⁰C holds 5g/m³ of water vapour
and can contain a maximum of 10g/m³ of water vapour,
what is its relative humidity?

2) Relative humidity
• Relative humidity varies with temperature
• Warmer air can hold more water vapour
• If temperature rises and the actual amount of
water vapour remains, then relative humidity
will __________

2) Relative humidity – Key terms
• Saturation is when relative humidity =
100%
• Dew point temperature: temperature
at which saturation occurs
• Condensation occurs during dew point
temperature

3) Clouds
• Refer to visible masses of water droplets or ice
crystals suspended in the atmosphere
• When the earth’s surface is heated up…
1. Evaporation: water becoming water vapour
2. When water vapour rises, it cools to dew point
temperature
3. Condensation: water vapour changes to liquid
form
4. To condense, water vapour needs to find
condensation nuclei
5. Coalescence: water droplets bumping into each
other to become larger in size

4) Rainfall
• Precipitation refers to water that falls from the
atmosphere to the earth surface in any form
• E.g. hail, snow, sleet, rain
• In the tropics, precipitation is mainly rain
• Measured using a rain gauge

4) Rainfall
• Rainfall is caused by air instability  when
an air parcel is warmer than its surrounding
air, causing it expand (becomes less dense)
and rise
• Qn: What is air stability?
• Air stability: a parcel of air that is cooler
than its surrounding air and tends to sink
and remain in its original position
• 2 types of rainfall: Convectional and Relief

4) Rainfall
Convectional
• Occurs due to intense heating of earth’s surface
• Warm surface heats the air above it
• Instability causes air to rise and expand
• As air rises, it cools to dew point temperature
• Condensation occurs and clouds are formed
• When water droplets become large enough, they
fall as rain
• Convectional rain is often associated with
lightning and thunder
• Intense rain over a short amount of time

4) Rainfall
Relief
• Also known as Orographic rain
• As air passes over the sea, it picks up moisture
• When it arrives at the coast, moist air is forced to rise
along the windward side of the mountain
• Air is forced to cool and condensation occurs at dew
point temperature
• When water droplets in the clouds become heavy
enough they fall to the ground on the windward side
• On the other side of the mountain, leeward side, it is
dry as most of the moisture is lost on the windward
side (rain shadow)

Video: Formation of Relief Rain
http://www.youtube.com/watch?v=kTc_uS3i9Ps

Qn1: Based on your own
experience with the weather in
Singapore, what type of rain do
you think we experience
dominantly?
Qn2: Explain why the other form of
rain is not common here.

Questions 1, 2, 3 and 5

5) Pressure and winds
• Air pressure: the forced exerted by the weight
a column of air on a unit area of the earth’s
surface
• Measured in millibars (mb) by a barometer
• Air is less dense at higher altitudes
• Thus air pressure decreases as altitude
increases
• The average value of air pressure at sea level
is 1,013mb

Air pressure is
higher at sea
level and lower
at higher
altitudes

• Wind: The movement of air from high
pressure area to low pressure area
• Pressure gradient: The difference in air
pressure between two places
• The greater the pressure gradient, the faster
the wind speed
• Wind can be described by its speed, direction
and frequency.

Wind speed
• The rate at which air is moving
• Measured in kilometres per hour, using an
anemometer
• Wind speed may also be represented by the
Beaufort Scale (TB p. 85, figure 2.23)

Wind direction
• The direction which the wind blows from
• Measured by a wind vane
Wind frequency
• The percentage of time the wind blows from a
particular direction
• Winds that blow most frequently from a specific
direction  prevailing winds
• Information of wind direction and frequency can
be recorded using wind roses

5) Pressure and winds – Wind systems
• Prevailing winds can be categorised by wind
systems
Wind systems
Localised
Land breeze
Sea breeze
Regional
Monsoon Winds
Mid-latitude
Westerlies
Polar Easterlies

Localised wind systems
Land breeze and sea breeze
• Occur in coastal areas due to different rates of
heating between the land and sea
• Recall: maritime effect
• Lowers the temperature of coastal areas
during the day and regulate the temperature
during the night  smaller diurnal
temperature range

Land breeze
• Blows from the land to the sea
• In the night:
–Sea loses heat slower resulting in warm air
above the sea  rises up, leaving a
vacuum (Low pressure)
–Land loses heat/cools down faster than
the sea (High pressure)
–Cooler air above the land rushes towards
the sea as land breeze

Sea breeze
• Blows from the sea to the land
• In the day:
– Land heats up faster than the sea  warm air
above the land rises up, leaving a vacuum (Low
pressure)
– Sea heats up slower than the sea  cooler (High
pressure)
– Cooler air from the sea rushes towards the land as
sea breeze

5) Pressure and winds – Wind systems
Wind systems
Localised
Land breeze
Sea breeze
Regional
Monsoon Winds
Mid-latitude
Westerlies
Polar Easterlies

Regional wind systems
Monsoon winds
• A regional wind pattern
• Brings seasonal changes in precipitation
• Affected by Coriolis effect (a force produced by
the earth’s rotation)
• Northern hemisphere  deflects to the right
• Southern hemisphere  deflects to the left
• Coriolis effect is stronger nearer the poles and
weaker near the equator
• Winds result in monsoons (SW & NE monsoons)

Take a moment to digest…
• You should keep the following background
knowledge that you ALREADY HAVE…
– Summer = Higher Temp, Winter = Lower Temp
– High Temp = Low pressure, Low Temp = High
pressure
– Concept of relief rain and rain shadow
– Coriolis Effect: North = Right and South = Left
• For purpose of study, we will use the monsoon
winds blowing between Asia and Australia as
an example

Southwest monsoon (TB p. 88, figure 2.26)
• June to September
• Summer in northern hemisphere, winter in
southern hemisphere
• Winds move from Australia (south) to Asia
(north)
• From Australia, wind moves as southeast
monsoon
• As it crosses the equator, it deflects to become
southwest monsoon
• The air picks up moisture over Indian Ocean and
brings heavy rain to India

The Southwest monsoons in summer in the
northern hemisphere

Northeast monsoon (TB p. 88, figure 2.27)
• October to February
• Summer in southern hemisphere, winter in
northern hemisphere
• Winds move from Asia (north) to Australia
(south)
• From Asia, wind moves as northeast monsoon
• As it crosses the equator, it deflects to become
northwest monsoon
• The air picks up moisture over Indian Ocean and
brings heavy rain to Australia

The Northeast monsoons in winter in the
northern hemisphere

Qn: How does the NE and SW
monsoon winds affect Singapore in
terms of rainfall?

Questions 2 and 4

Section Objectives
Weather vs. Climate
Elements of weather
Climatic types:
Characteristics & Location
KGQ 1: Why do different places experience

What are the climatic types and where
are they experienced? (TB p. 91)

Climatic types
Equatorial Monsoon
Cool
temperate
Warm
temperate
Dry
Other cool
temperate
Polar Highlands

Climatic type: Equatorial
• Between 10⁰ north and south of the Equator

Characteristics/features Explanation
Temp. • High temp (Mean annual
temp of about 27⁰C)
• Small annual temp range
of 2⁰C to 3⁰C
• High angle of
incidence of the sun’s
rays
Relative
humidity
(RH)
• High RH • High temp  warmer
air  able to hold
more water vapour 
high RH
Rainfall
(RF)
• Convectional rain often
occurs
• Rain throughout the year
with no distinct wet or dry
seasons
• Total annual RF: more than
2,000 millimetres
• High temp  intense
heating of earth’s
surface  instability
 convectional rain

Case study: Weather and climate of
Singapore
• Equatorial climate
– Uniformly high
temperature
– Abundant rainfall
– High relative humidity
• WHY???
– Located at a latitude of
1⁰22’N
-(Latitude, cloud cover,
High humidity)

Climatic type: Monsoon
• Between 5⁰ and 25⁰ north and south of the
Equator (e.g. Chittagong in Bangladesh)

Characteristics/features Explanation
Temp. • High mean annual temp.
• Overall lower mean annual
temp than equatorial climate
• Mean monthly temp about 30⁰C
in May but about 25⁰C in July
• Annual temp range is about 6⁰C
• Located further
from the equator
as compared to
equatorial
regions
Rainfall
(RF)
• Distinct wet and dry seasons
• Concentrated RF in the summer
(June – Sept)
• E.g. Chittagong receives 2,000
mm of RF during the wet
seasons (June – Sept) and only
about 75 mm of RF during the
dry season (Oct – May)
• Monsoon winds

Climatic type: Cool temperate (marine west-
coast) climate
• Between 45⁰and 60⁰ north and south of the equator
(e.g. Paris in France & Toronto in Canada)
• Four distinct seasons (spring, summer, autumn &
winter) due to tilt of the earth and revolution around
the sun

Characteristics Explanation
Temp. • Large annual range of 25⁰C
(temps ranging between -3⁰C
and 22⁰C
• During winter 
shorter days 
less energy from
the sun
Rainfall
(RF)
• Evenly distributed throughout
the year
• However, total annual RF is
lower than in places with the
equatorial or monsoon climate
• Total annual RF ranges
between 300 mm and 900 mm.
• No distinct wet or dry seasons

Questions 1, 2 and 4

KGQ 2: What is happening to the Earth’s
climate?

CHECK-IN: Icebergs on the loose
102
1 2
3

Section Objectives
How has global climate
changed
Natural causes of climate
change
Human causes of climate
change – enhanced greenhouse
effect
Impacts of climate change
Responses to climate change

Global climate change
• Refers to the variation in the global climate or
climatic patterns in the long term
• Happening since the 1800s  significant but
irregular temperature increases (0.3⁰C –
0.6⁰C)

1980 – 2000: rose by 0.4⁰C in
20 years!
Observation 1: The global temperatures
are increasing
Observation 2: The global temperatures are
irregular (they increase and decrease)

Global warming and cooling
• Refers to the climatic changes due to natural
cycles as observed over hundreds to millions
of years
• Global warming: the increase in global
temperatures over a long period of time
• Global cooling: the decrease in global
temperatures over a long period of time

Changes in global climate since 1881
http://www.youtube.com/watch?v=9kFHQpZpg
dg

Changes in global climate since 1881
• The earth has warmed by an average of
0.74⁰C over the last century
• Greatest increases after the 1980s
• The warmest temperatures recorded so far are
between 1990 and 2015

What are the causes of climate
change?
Causes of
climate
change
Natural Human

What are the natural causes of climate
change?
Natural causes
of climate
change
Variations in
solar output
Volcanic
eruptions

Natural causes of climate change:
Variations in solar output
• The amount of solar radiation the sun emits
depends on any changes in its Magnetic field
Magnetic activity
Solar Radiation

Solar activity cycle: 11 years
High Magnetic
Energy
Low Magnetic
Energy

• Sunspots: cooler areas on the sun’s surface
that appear as dark spots
• Sunspot areas—about 4000 degrees Celsius
• Other areas—about 5000 degrees Celsius

Sunspots
• Sunspot activity is linked to the amount of
solar radiation emitted
• E.g. During high solar activity, there are more
sunspots as the areas surrounding the
sunspots release more magnetic energy 
compensates for the lower temperatures
• E.g.

Volcanic eruptions
http://www.youtube.com/watch?v=WecgO8cBc
ZY

Mount Pinatubo, Philippines (1991)

Volcanic eruptions
• When a volcano erupts,
carbon dioxide, water
vapour, sulphur dioxide,
dust and ash are released
into the atmosphere
• Sulphur dioxide + water =
sulphur-based particles 
reflects solar energy back
into space (together with
dust and ash)  Global
dimming

WaterSulphur dioxide Sulphur-based particles
Ash Dust
GLOBAL DIMMING

Volcanic eruptions
Global dimming
• The gradual reduction in the
amount of sunlight reach the
Earth’s surface.
• Cools the Earth for months
or years.
• Dips in global temperatures
occurred in the 1940s and
1960s because of volcanic
activity

Case study: Mount Pinatubo,
Philippines (1991)
• The eruption released 17 million tonnes of
SO2  spread of sulphur based particles
• Lowered temperatures in the northern
hemisphere by as much as 0.6⁰C
• Effects lasted for two years (temporary)

Qn: How long do the effects of volcanic
eruptions last? Why?
Ans: They are temporary! The temporary global
cooling effect will cease once the volcanic dust and
ash settle.

Questions 1, 2, 3 and 4

What is greenhouse effect and how
does it work?
http://www.youtube.com/watch?v=ZzCA60Wno
Mk

does it work?
• Natural process in
which the gases in
the Earth’s
atmosphere trap
longwave radiation
emitted from the
earth’s surface,
warming the
atmosphere.

does it work? (TB p. 102, Fig 2.49)

does it work?
Greenhouse
gases (GHG)
Water vapour
Carbon
dioxide
Methane
Nitrous oxide
Ozone
Halocarbons

What is the enhanced greenhouse
effect?
• The increase in the amount of greenhouse
gases in Earth’s atmosphere due to human
activity
Anthropogenic
factors

Questions 1 & 2

How do human activities lead to the
Enhanced Greenhouse Effect?
Burning fossil
fuels
Deforestation Changing land
use
▪ Agriculture
▪ Industries
▪ Urbanisation

Burning Fossil Fuels
• Formed from dead organic
matter that has been
decomposed over many
millions of years
• E.g. oil, coal and natural gas
• Burnt to produce a large
amount of energy 
important for human
activities (e.g.
transportation, industries,
domestic)

• Estimated to produce more than 80% of
• Large consumers: China, USA, Canada and UK
• In Singapore, most of our electricity is
generated by fossil fuels

• Fossil fuels contribute to an increase in GHG
• High carbon content  produce large
amounts of carbon dioxide when burnt 
highest contributor of GHG
• World’s usage of fossil fuels has increased in
recent years  releases billions of tonnes of
carbon dioxide into the atmosphere each year
• 2010: global CO2 emssions = 30.6 billion
tonnes (5.6% increase from 2009)

Deforestation
• The loss of forests due to the removal of trees
in forested areas
– Wood  paper and building materials
– Clearing of land for human activities e.g. mining,
grazing of animals and planting of crops
(agriculture), construction of infrastructure
How does deforestation result in enhanced
greenhouse effect?

• Deforestation  fewer trees
to absorb CO2  increase in
CO2 levels in the atmosphere
 greenhouse effect
Forests are
absorbers of
carbon dioxide
(through
photosynthesis)
• Deforestation  soil exposed
to sunlight  increase rate of
carbon oxidation of soil 
increase in CO2 levels 
greenhouse effect
Soil is one of the
largest sources of
carbon in the
world
How does deforestation result in enhanced
greenhouse effect?

Deforestation
• 52,000 km² of forest lost every year between
2000 and 2010 (142.5 km² lost every year)
• Great overall loss of forests occurs in S.
America, Southeast Asia, Australia and Africa 
WHY? The need for development: agricultural
and commercial activities (e.g. cattle ranching)

Changing land use
Agriculture
• The practice of
cultivating land,
producing crops
and raising livestock

How does rice cultivation and padi fields
contribute to the increase of greenhouse gases in
the atmosphere?
Tractors run on
fossil fuels which
release CO2
Use of inorganic
fertillisers
increase amount
of nitrous oxide
in soil 
released when
soil is ploughed
or when rain
flows through it
Organic matter such
as dead leaves
releases methane
during
decomposition

How does cattle farming increase greenhouse
gases in the atmosphere?
Cattle release methane as a waste gas!!!

Changing land use
Industries
• The production of
goods and services
within a country
• Secondary industries
(manufacturing)
involve the burning
of fossil fuels 
GHG as by-products

Changing land use
Processes emitting carbon dioxide
Process Kg of CO2
equivalent
Equivalent activity
a) Manufacturing a
mobile phone
60 A car travelling 7 times the length
of the PIE in Singapore
b) Manufacturing a
computer and a monitor
275 A car travelling 31 times the length
of the PIE in Singapore

Changing land use
Urbanisation
• Process by which an increasing number of
people live in urban areas (i.e. cities or towns)
How does urbanisation increase greenhouse

How does urbanisation increase greenhouse

Urbanisation
• Urbanisation: Process by which an increasing
number of people live in urban areas.
159
- Various human
activities are
concentrated or are
necessary in urban
places. All of them
contribute to the
amount of greenhouse
gases in the
atmosphere.

Questions 1 & 2

How has global climate
changed
Natural causes of climate
change
Human causes of climate
change – enhanced greenhouse
effect
Impacts of climate change
Responses to climate change

How does climate change affect
people?
Impacts of climate
change
Sea level rise
Frequent
extreme weather
events
Spread of
infectious insect-
borne diseases
Lengthening the
growing season
in certain regions

Impacts of Climate change
Sea level rise
• Increase in mean height of the sea’s surface
• Causes:
– Higher temperatures  melting of glaciers in
Greenland and Antarctica  addition of meltwater
 rise in sea level
– Higher temperatures  water in seas expand  rise
in sea level

Sea level rise
• Negative impact on places where humans live
• Threatens low-lying areas, coastal areas and
islands
– Over 600 million people live in areas less than 10
metres above sea level
– 33% of coastal land and wetland habitat are
predicted to be lost in the next 100 years

More frequent extreme
weather events
• Extreme weather event:
a severe and rare
weather phenomenon
that results in significant
losses
• E.g. heat waves, floods,
droughts and tropical
cyclones

More frequent extreme weather events
• Causes:
–Higher temperatures  greater amounts of
water vapour and latent heat in a warmer
atmosphere  driving force for extreme
weather events

Spread of infectious insect-borne
diseases
• Increased temperatures and
rainfall  favourable condition
for insects to thrive  spread of
insect-borne diseases
– Climate change results in diseases
occurring in cool climate areas as
well
• E.g. heavy rainfall allowing
mosquitoes to grow in aquatic
habitats  DENGUE fever &
MALARIA

Lengthening the growing season in certain areas
• Growing season: period during which crops can
be grown
• Lengthened growing seasons affect different
crops differently (+ve or –ve)

Lengthening the growing season in certain areas
Advantages Disadvantages
In the United Kingdom, the types of
crops that can be grown increased. E.g.
Blackberries and maize.
In the Yunnan Province, China, the
production of fruits such as apples and
cherries, and nuts such as almonds and
walnuts is reduced as these fruits and
nuts require cool weather conditions.
The production of fruit, soybeans and
potatoes is projected to increase in
Canada.
In Canada, the average wheat grain
yield has reduced.

Questions 1, 2 & 4

What are the responses to climate change?
Responses
International level
Kyoto protocol
Copenhagen
Conference
National level
Case study: Singapore
(e.g. Singapore Green
Plan)
Case study: India (e.g.
National Urban
Transport Policy)

Responses at the international level

Chapter 2 climate

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