ST. ANDREW’S HIGH SCHOOL
GEOGRAPHY DEPARTMENT
HIGHER GEOGRAPHY
Higher Geography
Atmosphere
Atmosphere
INTRODUCTION
Acid rain
Skin
cancers
Global
warming
Atmosphere
in the news
Hole in the
ozone layer
Climate change
Greenhouse
gases
CFC’s
Although considered a difficult topic, this is the most up-to-date
of the basic units!
Atmosphere
In this unit we will be covering the following
topics:
Topic 1: Global Insolation
Topic 2: Atmospheric Circulation
Topic 3: Oceanic Circulation
Topic 4: Air Masses
Topic 5: Climatic Change
Atmosphere
Today we are going to find out:
What the atmosphere is and why it is important.
What global insolation and the heat budget are.
Why variations in insolation occur.
Atmosphere
What is the atmosphere?
Originally formed as the earth cooled, the
atmosphere is a blanket of gases which contains
solid material, such as volcanic dust and blown
soils, and is attached to earth by the force of
gravity.
This atmosphere is a mixture of oxygen (21%), nitrogen Atmosphere
(78%),
carbon dioxide (0.037%) and other gases such as hydrogen, helium,
argon, neon, krypton, xenon and ozone. It also contains water
vapour.
These gases are densest at the Earth's surface and get less dense
with increasing height. Around 90% of the atmosphere by weight
lies in the lowest 15 km (9 miles) above the surface and it is only a
very thin skin of air that keeps all life on Earth alive.
There are five main layers in the atmosphere.
1) The troposphere contains approximately 75% of the
atmosphere's mass, and has an average depth of about 16
km. The troposphere is is where weather systems develop.
Atmosphere
Atmosphere
2) The stratosphere 16-50km is dry with rising temperatures.
It contains large amounts of ozone gas which protects life
on earth by filtering out most of the Sun’s harmful rays.
3) Many rock fragments from space burn up in the
mesosphere 50-90km (middle sphere).
As it lies between the maximum altitude for aircraft and
the minimum altitude for orbital spacecraft, this is the
most poorly understood part of the atmosphere.
4) The thermosphere is directly above the mesosphere. Within thisAtmosphere
layer,
ultraviolet radiation causes ionization. The thermosphere, named from the
Greek (thermos) for heat, begins about 80 km above the earth and can
experience temperatures of 2,500°C.
5) The upper limit of our atmosphere is the exosphere. The
main gases within the exosphere are the lightest gases,
mainly hydrogen, with some helium, carbon dioxide, and
atomic oxygen.
Atmosphere
Atmosphere
Topic 1: Global Insolation
Insolation: incoming solar energy
Less than half the incoming solar energy actually penetrates to
the surface of the earth. The rest is lost in a variety of ways.
Atmosphere
The Global Heat Budget
Incoming heat being absorbed by the Earth, and
outgoing heat escaping the Earth in the form of
radiation are both perfectly balanced.
If they were not balanced, then Earth would be getting
either progressively warmer, or progressively cooler
with each passing year. This balance between incoming
and outgoing heat is known as Earth’s heat budget.
As the sun’s
rays pass
through the
atmosphere,
some are
reflected,
some
absorbed
and some
pass
through to
reach the
earth’s
surface.
Atmosphere
Atmosphere
Variations in Insolation
Because the earth is a sphere, there are variations in the
amounts of insolation received in different places.
Both bands of solar radiation are
of the same strength.
The band near the north pole
though has to heat a large area
(D-E) due the curve of the earth.
AGAIN, COPY AND
MEMORISE THIS
DIAGRAM!
The band at the equator can
concentrate its heat in a smaller
area A-B
Atmosphere
Latitudinal Variations in insolation
Radiation Budget
Atmosphere
We can also compare energy received by the earth
(insolation) with energy lost by radiation (terrestrial
radiation).
Insolation: solar energy received by the earth.
Terrestrial radiation: solar energy lost by radiation.
At the equator: insolation is greater than terrestrial
radiation (due to darker forest material and higher
land concentration), leading to a surplus in energy.
At the polar zones, insolation is weak and terrestrial
radiation is high (due to lighter light-reflecting snow +
lower land concentration), leading to an energy deficit.
Atmosphere
Seasonal Insolation
Not only does insolation vary with latitude, it also varies
with season.
Because of the earth’s tilt, during the northern summer
the sun is overhead at the Tropic of Cancer, and the Artic
regions receive insolation 24 hours per day.
However, in the northern winter, the sun does not shine
on the Artic, so there is no insolation at all.
Factors Affecting Insolation
The Green House Effect
Atmosphere
What were the key points for
‘Variations in Isolation’
Albedo Affect
◦ Equator’s surface – low reflection (high insolation)
◦ Pole’s surface – high reflection (high terrestrial radiation)
◦ (land cover)
Earth’s tilt
◦ Earth’s orbit around the sun
◦ Winter solstice – polar region – no solar insolation
◦ Tropics – yearly solar insolation
Earth is a sphere
◦ Concentrated rays at equator
◦ Intensity from vertical rays
Atmosphere
Topic 2 Atmospheric Circulation
This diagram
shows how heat
from the
Equatorial area is
transferred to
the polar regions
by the
circulation of the
atmosphere in
the Northern
Hemisphere.
Atmosphere
CELLS AND HEAT TRANSFER
INSOLATION
The 3 CELL MODEL: The
Formation of a Hadley Cell
Insolation in tropical
areas causes warm air
to rise and spread
polewards, carrying
heat energy.
SOLAR ENERY
Nb; lots of new
terms to learn!
Atmosphere
Atmosphere
Air cools and begins to
fall at about 30ºN and
30ºS of Equator.
Cooled air returns to
the Equator.
NORTHERN HADLEY CELL
SOLAR ENERGY
Heat energy is therefore
transferred from the
Equator to sub-tropical
latitudes.
SOUTHERN HADLEY CELL.
Atmosphere
FORMATION OF THE POLAR CELL
Intensely cold, dense
air sinks at the poles,
then blows as surface
winds towards the
Equator.
Atmosphere
At about 60ºN and 60 ºS,
the cold polar air is
warmed in contact with
the earth’s surface.
This warmed air rises and
returns polewards,
carrying heat energy.
This circular motion is
called the POLAR CELL.
NORTHERN POLAR CELLS.
SOUTHERN POLAR CELLS.
FORMATION OF THE FERREL CELL
Unlike the Hadley and
Polar Cells, the Ferrel
Cell is not driven by
differences in heat
energy.
The Ferrel Cell is caused
by friction where air is in
contact with the other
two cells.
(The Hadley Cell drags air
down at about 30ºN and
S.
The Polar Cell causes an
uplift at about 60ºN and S.
)
Atmosphere
Atmosphere
THE THREE
CELLS
TOGETHER
Polar Cell
Ferrel Cell
Hadley Cell
Hadley Cell
Ferrel Cell
Polar Cell
Atmosphere
ASSOCIATED PRESSURE BELTS
Rising air at the equator
causes the equatorial belt of
low pressure
Polar high pressure
Mid latitude low pressure
Descending air at about
30ºN and 30ºS causes the
sub-tropical belt of high
pressure
Rising air at about 60ºN and
60ºS causes a mid-latitude
belt of low pressure
Sub-tropical high pressure
Equatorial low pressure
Sub-tropical high pressure
Descending air at the poles
causes the polar high
pressure areas
Mid latitude low pressure
Polar high pressure
ASSOCIATED SURFACE WIND PATTERNS
Atmosphere
Winds always blow from high
pressure to low pressure.
They are deflected because of
the Coriolis Force which come
about because of the rotation
of the earth. ( see later slide)
Winds in Northern
Hemisphere are deflected to
the right.
Winds in the southern
hemisphere are deflected to
the left.
These wind belts shift
seasonally. (See next section)
Polar high pressure
Mid latitude low pressure
Sub-tropical high pressure
Equatorial low pressure
Sub-tropical high pressure
Mid latitude low pressure
Polar high pressure
Answer these questions fully in sentences.
Q1. What kind of pressure has rising air?
A. Low pressure has rising air.
Q2. What kind of pressure has falling air?
A. High pressure has falling air.
Q3. Name two latitudes with rising air.
A. The Equator and 60 degrees N/S have rising air.
Q4. Name two latitudes with falling air.
A. 30 degrees N/S and the Poles have falling air.
Atmosphere
Q5. Explain the two factors that make the NE trade winds
blow in the direction they do.
( You will need to be able to do this for any of the winds in
diagram 13 !)
i) Air is flowing from a high pressure area at 30 degrees
north towards a low pressure area at the Equator.
ii). The winds are being deflected by the Coriolis
force/ effect to the right as the area is in the northern
hemisphere.
Atmosphere
Atmosphere
Rossby waves and the Jet Stream
Not far above our
heads in the northern
UK is where the Ferrel
and Polar cells meet.
This turbulence is
mainly responsible for
the series of
depressions and
anticyclones that
happen over Britain.
Here is where powerful
waves of turbulence
occur called Rossby
waves.
What are Rossby waves and jet streams?
Rossby waves are high altitude, fast moving westerly
winds, which often follow an irregular path. The path that
they take changes throughout seasons, as shown in the
diagram below:
See the website for more information on
Rossby Waves and the Jet Stream.
Atmosphere
THE CORIOLIS EFFECT
What happens when you set off in a plane to fly to
somewhere?
The earth turns beneath you, and you have to keep
adjusting your direction ! Watch……….
Atmosphere
Destination
Direction of Earth-spin
has moved
Got the idea?
Note the
runners path is
curved!
Destination
has moved
Thirty
minutes in
Twenty
minutes in
Destination
has moved
Ten
minutes in
Initial direction
start
destination
Atmosphere
Watch Episode 1 of ORBIT
Atmosphere
Ocean Currents
Ocean Currents
You need to know how the ocean
currents work in one ocean. The
Atlantic will do.
You need to remember the names of
the currents and the directions in
which they travel.
You must know whether they are hot
or cold.
Note how the ocean currents also
obey the Coriolis Force Laws.
Atmosphere
Atmosphere
Atmospheric Circulation
So far, we have concentrated on the circulation of the air
throughout the depth of the atmosphere.
Now it is time to look in detail at air movements near the earth’s
surface.
It is easier to understand and remember this movement if we start
with the global pressure belts.
In theory, the global pressure belts are perfectly balanced north
and south of the Equator.
Atmosphere
The Main Global Pressure Belts
There is a band of Low
Pressure at the equator.
There are two bands of
High Pressure between
300 and 400 north and
south of the Equator.
There are two bands of
Low Pressure around 600
north and south of the
Equator.
There are two bands of High Pressure over
the North and South Poles.
Atmosphere
OCEAN CURRENTS and HEAT TRANSFER
Water heats up and cools
down very slowly.
But once it has stored it, it
holds on to that temperature
for a long time.
As currents move, they
transport heat and cold
around the globe.
The pattern of ocean currents is linked to the
pressure belts and wind patterns.
Land masses disrupt an otherwise straightforward water flow pattern.
Winds blowing over currents assist them in
transferring heat from warm to cool areas and vice
versa.
Winds deflected by the Coriolis force help to
create the currents.
The nature of the current affects the land masses
it flows beside.
Copy this
CASE STUDY AREA- the ITCZ in AFRICA
You will need to be able to give
very detailed answers to a
question on this area in an
assessment.
This case study shows the way that the movement of the wind
belts between their summer and winter positions has a
profound effect on the lives – indeed the very survival- of
people who live in the Sahel zone of northern Africa.
You will need an atlas for most of this
section. Get one now.
The ITCZ is an area where
two air masses meet- it
brings heavy rain to the
areas it passes over.
It happens all round the
world between the Equator
and about 20 degrees N/S.
Copy text
Its full name is the Inter
Tropical Convergence Zone.
It is part of the Hadley
convection cells, and has
the Doldrums within its
boundary.
The AFRICAN ITCZ REGION
The ITCZ does not stay in
the same area all year
round but migrates to
the north and then back
south again.
It is this movement that
matters so much to the
people and animals of
the area.
Discuss
this
diagram
The trade winds ( mT air mass) come into the zone from cooler
areas in the southern mid- latitudes and have travelled over
oceans; they are therefore carrying a lot of moisture.
This is their position in January.
Once in the hotter latitudes, they are energised into huge
towering cumulo-nimbus thunderclouds. These can be anything
up to 10kms across, and groups of clouds can form covering
1000kms. In between the clusters are often sunny cloud-free
areas.
The clusters are particularly found over land, not sea.
Copy diagram
S
Wet
warm
mT air
IN JANUARY
N
Hot
dry
cT
air
Moves this way
‘Harmattan’ wind
HEAVY RAINS
Gulf of
Guinea
Coastal
areasequatorial
climate
Inland areassavanna
climate type
SaharaDesert
climate
type
In January, the sun is
overhead near the Tropic
of Capricorn, in the
southern hemisphere.
The ITCZ zone of
meeting air lies well to
the south, as seen here.
The rains brought by the
zone are confined to the
very coastal areas of
Nigeria, Togo, Ghana and
their neighbours.
Case study area
ITCZ
JANUARY
Atmosphere
The Inter Tropical Convergence Zone- The ITCZ
The movement of the ITCZ and its effects on rainfall can be best
understood by examining the situation in Africa.
23.50N
NE Trade Winds
Warm, Dry Winds (cT)
23.50N
Warm, Dry Winds
Warm, Moist Winds (mT)
Equator
SE Trade Winds
23.50S
July
The ITCZ in
Africa In July
Equator
Warm, Moist Winds
23.50S
January
The ITCZ in
Africa In
January
Atmosphere
The Changing ITCZ
The ITCZ moves north and south over Africa to “follow the sun”.
However, the ITCZ sticks over the land areas since the land is warmer
than the sea causing lower pressure over he land than over the area.
ITCZ
ITCZ
ITCZ
July
September
November
Atmosphere
The Changing ITCZ
The ITCZ moves north and south over Africa to “follow the sun”.
However, the ITCZ sticks over the land areas since the land is warmer
than the sea causing lower pressure over he land than over the area.
ITCZ
ITCZ
January
ITCZ
March
May
ATMOSPHERE
Here, the moist warm mT air from the Atlantic Ocean
meets the hot dry cT air coming out of the Sahara
Desert. Note that the desert is an area of HIGH pressure in winter and
particularly strong winds blow AWAY from such areas.
The cT wind is called the HARMATTAN and is extremely
hot, dry and dusty. Of course, the Harmattan cannot bring any rain
to the area it travels over, and all the northern part of Africa is influenced
totally by it. No crops can grow.
In the south, however, the wet moist winds from the sea
are forced upwards over the land where they drench the
land in life-giving torrential rains. Here crops can be easily
grown, providing the soil is fertile enough and not washed away.
ATMOSPHERE
During the spring, the ITCZ moves slowly northwards,
the Harmattan losing its dominance over the land bit
by bit.
Places further and further inland get the rains that
they so desperately need for people, crops and
animals alike. The slight drawback is that the further the ITCZ
travels north, the less water it can bring to the rainy area, so crops to
the north get less than those to the south.
By mid spring, places like northern Ghana, northern
Benin and central Nigeria are getting the rains. The
wells are re-filled, the grass for feeding animals starts to grow and
farmers can start off their crops.
ATMOSPHERE
S
IN JULY
Compare the January and July diagrams.
Hot
dry
cT
air
Wet
warm
mT air
Moves this way
HEAVY RAINS
Gulf of
Guinea
Coastal
areasequatorial
climate
N
‘Harmattan’ wind
LIGHT RAINS
Inland areassavanna
climate type
Copy diagram
SaharaDesert
climate
type
ATMOSPHERE
There is a handout illustrating the two main
climate types mentioned on the previous
slide, affected by the ITCZ.
You will need to be able to recognise the
differences between them in an exam
question.
ATMOSPHERE
By July the ITCZ has reached as far
north as it will go, reaching central
Mali, northern Niger and northern
Chad. There the Harmattan is confined to the
very edges of the Sahara desert, the weakest it
ITCZ JULY
gets all year.
This is the Sahel zone, the area most
prone to DESERTIFICATION that you
learned about in Standard Grade.
Without these rains most years, the desert will take
over yet more land, forcing poverty-stricken, hungry
people to migrate southwards into other peoples’
territory, with their thirsty cattle and goats.
ATMOSPHERE
After July, the belt moves back down south
again, giving a second rainy spell to the lucky
areas in its path.
No more rain will fall this far inland until next
year!
The people rely on these rains that arrive within a
week or two of the same time every year.
Recently, there have been several years where
the rain has not got as far inland as normal !
What do you think has been the result of this?
ATMOSPHERE
Read the article on the handout which
highlights the human consequences of
the failure of this pattern of rainfall.
Answer the 12 questions in your
jotters.
ATMOSPHERE
Lesley Monk
Balfron High School
Session 2005/6
ATMOSPHERE
GLOBAL WARMING – ARE WE TO BLAME ?
This is one of the most frequently asked
environmental questions in recent times.
That the planet’s climate is changing, there is no
doubt. But who or what is the reason for this is a
hotly debated point.
We shall put the evidence in front of you and let
you decide!
So what is the
answer ?
ATMOSPHERE
Graph 1 shows the
temperature of the Earth
over 1 million years. Note
the line showing today’s
average temperatures, and
the arrow to the last Ice
Age.
Graph 2 is a close-up from
the last few years of the
Ice Age till today.
Graph 3 shows the time
since the Vikings began
raiding Britain.
ATMOSPHERE
1. ICE CORE ANALYSISAir trapped in ancient
snow- now ice- can show
what the atmosphere was
like millions of years ago.
2. TREE RING ANALYSISTree rings record good and
bad years for tree growth
and can go back to
prehistoric times.
WHAT EVIDENCE IS THERE OF GLOBAL WARMING ?
Copy text
3. OCEAN FLOOR
SEDIMENTS-The mud in
the ocean deep has been
there for millennia and can
be analysed for oxygen
isotopes.
4. POLLEN ANALYSISThis will show the types of
plants that were growing in
an area millions of years
ago, and we can work out
the likely conditions from
comparison with today’s
plant needs.
ATMOSPHERE
So you can see that our
planet hasn’t exactly had
a stable climate !
But are we responsible for
the changes, or is it natural
forces at work?
Read pages 25 and 26 of the booklet. You will need to
be able to discuss each of these factors in a way that
shows you appreciate their potential importance.
ATMOSPHERE
There are different possible
causes of these raised
temperatures. They fall into
two categories- Physical and
Human.
•
•
•
•
Physical Factors
Human Factors
Solar variation
Volcanic activity
Ocean currents
Milankovitch
cycles
Burning fossil fuels
Increased output of
methane etc.
Deforestation
Let’s look at each in turn.
ATMOSPHERE
PHYSICAL 1 - SOLAR VARIATION
Sunspots: an increase in
sunspot activity may lead to a
very slight increase in the
sun’s output and a temporary
warming of the earth.
Sunspot activity follows 11
and 22 year cycles.
The Little Ice Age of 14501700 may have been linked to
periods of very low sunspot
activity.
ATMOSPHERE
PHYSICAL 2 - VOLCANIC ERUPTIONS
• Eruptions of volcanoes
can throw millions of
tonnes of ash,dust and
sulphur dioxide into the
atmosphere.
• This produces aerosols
that can reduce the
amount of sunlight
reaching the earth.
• This can lead to a
temporary cooling of the
earth.
ATMOSPHERE
VOLCANIC ERUPTIONS 2
• Major eruptions in the
past which have been
linked to short periods of
global cooling include;•
•
•
•
Tambora (1815),
Krakatoa (1883),
Mt. St Helens (1980)
Pinatubo (1991)
ATMOSPHERE
PHYSICAL 3 – OCEAN CURRENTS
Changes in the pattern
and strength of ocean
currents may lead to
changes in the
distribution of heat
around the planet.
A short term example
would be El Niño, which
appears every few
years.
A longer term example
would be the North
Atlantic Drift, which may
change position every few
thousand years.
ATMOSPHERE
ENSO - the El Niño Southern Oscillation
The “normal” conditions,
with cool surface water off
the coast of Peru.
A La Niña year
Every 2-7 years the western
Pacific becomes much warmer,
disrupting weather patterns possibly on a global scale.
An El Niño year
ATMOSPHERE
One theory
suggests that
global warming
will increase the
number of
icebergs in the
Atlantic, cooling
the sea and
switching off the
North Atlantic
Drift / Atlantic
Conveyor system.
This would be
bad news for us!
ATMOSPHERE
PHYSICAL 4 - MILANKOVITCH CYCLES
•Milankovitch cycles
are three variations in
the earth’s orbit.
Although they may be
linked to very long term
changes in the climate,
their effect would not
be noticed on a scale of
a few hundred years.
ATMOSPHERE
HUMAN FACTORS
THE ENHANCED GREENHOUSE EFFECT.
ATMOSPHERE
These are the main
greenhouse gases
See how they have
increased over the
years of industrial
activity.
HOW ?
ATMOSPHERE
HUMAN 1 - BURNING FOSSIL FUELS
The fossil fuels are: COAL
 OIL
 NATURAL GAS
They are called fossil
fuels because they
are formed from the
remains of ancient
plants (coal) and
marine animals (oil).
ATMOSPHERE
When we burn
these fuels,
we release
millions of
tonnes of
Carbon Dioxide
(CO2) into the
atmosphere.
There has
been an
enormous
increase in
these
greenhouse
gases since
the Industrial
Revolution
began about
200 years
ago.
ATMOSPHERE
Power stations are one of the main producers
of greenhouse gases such as Carbon Dioxide.
ATMOSPHERE
Environmental
campaigners all over
the world are
demanding cuts in
CO2 emissions. Here
Greenpeace uses a
light display to get
its message across.
ATMOSPHERE
Vehicle
exhausts are
the main
source of
Nitrous
Oxides.
ATMOSPHERE
HUMAN 2 - INCREASED METHANE
A cow can burp / fart about a
quarter of a kg. of methane a
day.
The number of cattle has doubled
in the past 40 years. Sheep,
goats and camels are also
ruminants.
There are now 1.3 billion cattle,
each burping / farting methane
several times a minute!
The New Zealand government is
proposing to bring in a
“flatulence” tax on cattle farms.
I am a
ruminant when I
digest
grass, I
produce
methane lots of it!
ATMOSPHERE
The huge increase in world population and in the
area of land given over to crops in general and
to rice production in particular, has led to a
rapid rise in global methane production.
Farmland for rice has doubled in 45 years.
ATMOSPHERE
HUMAN 3 - DEFORESTATION
Forests absorb CO2 and
release oxygen:
...if they are cut down, atmospheric levels of CO2 must rise as
a consequence.
ATMOSPHERE
This is known as a
double- whammy !
• Clearing forest
by burning
releases huge
amounts of
stored CO2
back into the
atmosphere.
• The smoke
from the fires
also adds to
global air
pollution.
ATMOSPHERE
KEY TERMS TO REMEMBER
Solar variation / Sunspots
Volcanic eruptions /Sulphur dioxide /Aerosols
Milankovitch cycles
El Niño
Enhanced Greenhouse effect
Carbon Dioxide / Methane / Nitrous Oxides
The Industrial Revolution / burning fossil fuels
Padi fields / cattle / methane production
Deforestation
CONGRATULATIONS !!
You have now finished the Higher
Geography Course!
All that remains is to learn it all!
Lesley Monk
Balfron High School
Session 2005/6
ATMOSPHERE REVISION
There are only a few
types of questions
they ask about;-
The principles
of energy movement
around the planet
Energy budget diagrams
like in slide 4
Cells and the way
they move heat aroundnot done for a few years !
The contribution made
by ocean currents to
heat transfer.
ATMOSPHERE REVISION
The principles explained
The ITCZ and
its effects
Data like maps and
graphs described and
explained.
ATMOSPHERE REVISION
The causes and
effects of climate
change, including
global warming.
World temperature
fluctuation graph described
and explained
The human and physical
causes of the greenhouse
effect named and
explained.
These are
often
combined!
ATMOSPHERE REVISION
Energy budget diagam-
Describe and explain
the exchanges that
result in only 50% of
the potential Sun’s
energy reaching the
surface. (4)
ATMOSPHERE REVISION
Atmospheric winds
circulation
diagram
Explain how the cells A,B
and C, and their associated
surface winds, help to
distribute energy around
the Earth. (4)
ATMOSPHERE REVISION
Ocean circulation
diagram
Explain how the ocean currents operate to maintain
an energy balance. (3 or 4 )
This question has been known to focus on one ocean
only to explain !
ATMOSPHERE REVISION
Using the information on the maps
and the graph, and referring to the
characteristics of the two air masses
shown, describe and account for the
annual seasonal variations in rainfall
in West Africa. (4)
The principles
of the ITCZ
ATMOSPHERE REVISION
The effects
of the ITCZ
Describe in
detail and
account for
the pattern of
annual rainfall
shown in the
diagrams. (5)
ATMOSPHERE REVISION
World temperature
fluctuation graph
described
and explained
Describe and give both human and physical reasons
for the fluctuation in world temperatures shown in
the graph. (5)