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Key Questions of Chapter
1. Why do different places experience different weather and climate?
2. What is happening to the Earth’s climate?
Chapter 2: Variable Weather and Changing Climate – A Continuing Challenge
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 different weather and climate?
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 Ener
gy 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 12Maximum 26 27 27 26 28 28 28 28 29 29 27 25Minimum 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 DecCOUNTRY C -30 -28 -25 -20 -16 -15 -10 -16 -22 -29 -30 -35COUNTRY D 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?
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: LatitudeLow 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=GxC0Um9zSqY
Factors affecting temp: Altitude (TB p. 76)
• The ___ the altitude, the ___ the temperature• Temperature decreases with altitude
WHY?!
Factors affecting temp: AltitudeReason 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.
Factors affecting temp: AltitudeReason 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?
Factors affecting temp: Distance from 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
Factors affecting temp: Distance from 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
Factors affecting temp: Distance from 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/WhatisClimatology/ClimographsforSelectedInternationalCities.aspx
What are the elements of weather? Weather
Temperature
Relative humidity
Clouds
Rainfall
Pressure & winds
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: 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
What are the elements of weather? Weather
Temperature
Relative humidity
Clouds
Rainfall
Pressure & winds
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 vapour2. When water vapour rises, it cools to dew point
temperature3. Condensation: water vapour changes to liquid form4. 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) RainfallConvectional• 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) RainfallRelief• 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.
What are the elements of weather? Weather
Temperature
Relative humidity
Clouds
Rainfall
Pressure & winds
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
5) Pressure and winds
• 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.
5) Pressure and winds
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)
5) Pressure and winds
Wind direction• The direction which the wind blows from• Measured by a wind vaneWind 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
RegionalMonsoon 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
Localised wind systemsLand 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
Localised wind systems
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 systemsWind 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
Regional wind systems
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
Regional wind systems
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
Section ObjectivesWeather vs. Climate
Elements of weather
Climatic types: Characteristics & Location
KGQ 1: Why do different places experience different weather and climate?
Climatic types
Equatorial Monsoon Cool temperate
Warm temperate Dry Other cool
temperate
Polar Highlands
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
KGQ 2: What is happening to the Earth’s climate?
Chapter 2: Variable Weather and Changing Climate – A Continuing Challenge
Section ObjectivesHow 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=9kFHQpZpgdg
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 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
Natural causes of climate change: Variations in solar output
• 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
Natural causes of climate change: Variations in solar output
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.
What are the natural causes of climate change?
Natural causes of climate
change
Variations in solar output
Volcanic eruptions
Natural causes of climate change: Volcanic eruptions
http://www.youtube.com/watch?v=WecgO8cBcZY
Natural causes of climate change: 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
Natural causes of climate change: 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.
Section ObjectivesHow 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
What is greenhouse effect and how 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.
What is greenhouse effect and how 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
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)
Burning Fossil Fuels
• 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
Burning 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)
How do human activities lead to the Enhanced Greenhouse Effect?
Burning fossil fuels
Deforestation Changing land use
▪ Agriculture▪ Industries
▪ Urbanisation
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)
How do human activities lead to the Enhanced Greenhouse Effect?
Burning fossil fuels
Deforestation Changing land use
▪ Agriculture▪ Industries
▪ Urbanisation
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 CO2Use 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 gases in the atmosphere?
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.
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 riseFrequent 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
Impacts of Climate change
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
Impacts of Climate change
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
Impacts of Climate change
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
Impacts of Climate change
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
Impacts of Climate change
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)
Impacts of Climate change
Lengthening the growing season in certain areasAdvantages 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.
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
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)