Edexcel GCSE Geography A notes on climate and climate change by Savemyexams

Edexcel GCSE Geography A: Weather Hazards & Climate Change

Contents

• 2.1.1 The Atmosphere as a Global System
• 2.1.2 Changes in the Global Climate
• 2.1.3 Human Activity & Global Climate Change
• 2.1.4 Climate of the UK

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The Atmosphere as a Global System

Atmospheric Heat Transfer

The atmosphere is constantly moving solar heat energy FROM the equator TO the poles to reach a
balance in temperature
Different areas of the Earth get different amounts of energy from the sun, known as insolation
The Earth is a sphere with a permanent tilt and a slight bulge at its equator
Therefore, the equator gains solar energy but the poles have a deficit of solar energy

Angle of Insolation

ANGLE OF INSOLATION
LOW ANGLE OF INSOLATION -
HEAT SPREAD OVER LARGER
AREA
ARCTIC CIRCLE
60° N
CONCENTRATED HEAT
30° N
TROPIC OF
CANCER
SUN'S RAYS
SUNLIGHT STRIKES
MOST DIRECTLY
EQUATOR
CONCENTRATED HEAT
TROPIC OF
CAPRICORN
30° S
LOW ANGLE OF INSOLATION -
HEAT SPREAD OVER LARGER
AREA
60° S
ANTARCTIC CIRCLE
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Diagram showing how solar radiation is spread over a wider area at the poles than the equator
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Wind Formation

To circulate the warm air around the Earth, specific wind and pressure patterns exist
Air always moves from high pressure to lower pressure

• This movement of air generates wind
  Winds are large-scale movements of air due to differences in air pressure
• Pressure differences happen because the Sun heats the Earth's surface unevenly
  The global circulation system begins at the equator because it is the hottest part of the Earth
  Air rises at the equator, leading to low pressure and rainfall at the surface
  When the air reaches the edge of the atmosphere, it cannot go any further and so it travels north and
  south
  The air in the atmosphere becomes cold and begins to sink back towards the surface, creating high
  pressure and dry air
• The cool air will then 'rush' from the high pressure zone to the low pressure zone at the equator to be
  warmed again by the Sun, at the same time creating wind
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Wind Pressure Cell System

WIND PRESSURE CELL
Your notes
4. AS THE AIR COOLS
IN THE ATMOSPHERE IT
BECOMES DENSER AND
BEGINS TO SINK,
LOWERING THE
ATMOSPHERIC PRESSURE
3. AS THE AIR RISES,
INTO THE ATMOSPHERE
IT ADDS PRESSURE
LOW
PRESSURE
ATMOSPHERIC
WINDS
PRESSURE
2. AS THE AIR RISES,
THE SURFACE
PRESSURE LOWERS
5. AS THE AIR SINKS,
THE SURFACE
PRESSURES RISES
HIGH
PRESSURE
SURFACE
WINDS
LOW
PRESSURE
SURFACE
1. AS THE SUN HEATS
THE SURFACE, AIR
EXPANDS AND BEGINS
TO RISE
6. THERE IS A PRESSURE
DIFFERENCE NOW. TO
BALANCE THIS, AIR
RUSHES TO THE LOW
PRESSURE AREA. THE
GREATER THE PRESSURE
DIFFERENCE, THE
STRONGER THE WINDS
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The wind pressure cell system shows the distribution of pressure at Earth's surface and upper
atmosphere
Air movement within the cell is roughly circular and helps move surplus heat around the Earth

• Each cell generates different weather patterns

Examiner Tips and Tricks: Weather vs. Climate

What is weather?
Remember that weather is what you get locally on a day-to-day basis, but climate is what you
expect a place to be over time (usually 30 years).
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You expect the UK to be wet and cold (not always but mostly!), but you would expect the
Mediterranean to be warm-that is climate.
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Pressure Differences and Air Movement

Pressure differences
Air moves in the atmosphere either towards the ground (subsidence) or up into the atmosphere
(convection)
These movements influence air pressure and rainfall

• The sea and land heat up differently
• Sea:
• Forms high pressure in summer and low pressure in winter
• It takes longer to heat and cool
• Air is denser and cooler in summer but warmer in winter
• Land:
  Generally, it forms areas of lower pressure in summer and higher pressure in winter
  It heats quickly in summer and the air is lighter and rises
• It cools quickly in winter

Influence of Air Movement on Weather Conditions

Table Showing Influence of Air Movement on Weather Conditions

Air Movement	Cause	Weather Conditions
Subsidence (sinking air)	It occurs in areas with low-intensity solar radiation, such as the poles or at high altitudes where the air is very cold. Air becomes denser and sinks towards the ground. As air sinks, it begins to warm and can therefore hold more moisture, preventing clouds from forming.	Forms high-pressure areas where the air is descending. Brings clear skies or very thin clouds. Creates arid or semi-arid conditions due to very little precipitation.
Convection (rising air)	It occurs in areas with high levels of solar radiation. The ground heats the air above and rises. As air rises, it cools and condenses into water droplets, which form clouds.	Low-pressure areas are created as air moves upward. Thick, heavy cloud cover with heavy rainfall creates wet tropical regions.

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Global Pressure Belts

• Abroad pattern of latitudinal high and low pressure belts are created via the horizontal bands of the
  Hadley, Ferrel and Polar cells
• However, the distribution of land and sea affects the location of these pressure zones, so the pattern is
  not symmetrical in each hemisphere, despite the mirroring of the cells
  Global pressure belts
  90°
  N
  HIGH
  f
  60°
  LOW
  HIGH
  LOW
  30°
  -HIGH
  HIGH
  0°
  - LOW
  -LOW ----
  EQUATOR
  30°
  - HIGH
  - - HIGH-
  -HIGH
  --.
  Exams
  DOWN
  LOW
  60°
  0
  3200
  HIGH
  km
  90°
  KEY:
  HIGH
  MEDIUM
  LOW
  AIR PRESSURE
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  Pattern of latitudinal high and low pressure belts created by the Hadley, Ferrel and Polar cells

Redistribution of Heat

Heat is transferred around the world by two main methods
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Your notes

• Circulation cells
• Ocean currents

Circulation Cells and the Tri-Cellular Model

Circulation cells
In both hemispheres, heat energy transfer occurs where 3 atmospheric circulation cells meet
These are the Hadley, Ferrel, and Polar cells and are shown via the tri-cellular model
GLOBAL ATMOSPHERIC CIRCULATION MODEL
RISING POLAR CELL
RISING COLD
WARM AIR
SINKING
COLD AIR
ATMOSPHERIC
WINDS
FERRELAIR
90°
POLAR
HIGH
1
CELL
60°
SINKING
COLD AIR
SUB POLAR LOWA
PRESSURE
DIRECTION OF
SURFACE WINDS
HEAT IS
TRANSFERRED
FROM
HADLEY
CELL
SUB - TROPICAL HIGH PRESSURE
EQUATORIAL
REGIONS TO
POLAR
REGIONS
RISING
HOT AIR
EQUATORIAL LOW PRESSURES
TRADE WINDS
3
HADLEY
30°
VCELL
SUB -ITROPICAL HIGH PRESSURE
4
SINKING
COLD AIR
SUB POLAR LOW
PRESSURE 60°
EASTERLIES
WINDS
FERREL
CELL
90° POLAR HIGH
AIR
RISING RISING
WARM COLD
SINKING
COLD AIR
POLAR CELL
AIR
1
HEAVY PRECIPITATION
2
VARIABLE PRECIPITATION, WINDS AND CALMS
3
HEAVY RAINFALL WITH VARIABLE WINDS AND CALMS
4
HIGH RATES OF EVAPORATION, VARIABLE WIND AND CALMS
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2
30°
WESTERLIES
WINDS4
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The tri-cellular model
Each hemisphere has three cells (the Hadley cell, Ferrel cell and Polar cell)
These circulate air from the Earth's surface through the atmosphere and back again

• The Hadley cell is the largest and extends from the equator to between 30° and 40° north and south
  Trade winds blow from the tropical regions to the equator and travel in an easterly direction
• Near the equator, the trade winds meet, and the hot air rises and forms thunderstorms (tropical
  rainstorms)
  From the top of these storms, air flows towards higher latitudes, where it becomes cooler and
  sinks over subtropical regions
  This brings dry, cloudless air, which is warmed by the Sun as it descends
  The climate is warm and dry (hot deserts are usually found here)
  Ferrel cell is in the middle and occurs from the edge of the Hadley cell to between 60° and 70° north
  and south of the equator
  This is the most complicated cell, as it moves in the opposite direction from the Hadley and Polar
  cells
  Air in this cell joins the sinking air of the Hadley cell and travels at low heights to mid-latitudes,
  where it rises along the border with the cold air of the Polar cell
  This occurs in the mid-latitudes and is the reason for lots of unsettled weather (particularly in the
  UK)
• The polar cell is the smallest and weakest of the atmospheric cells
  It extends from the edge of the Ferrel cell to the poles at 90° north and south
  The air in these cells is cold and sinks, creating high pressure over the highest latitudes
  The cold air flows out towards the lower latitudes at the surface, where it is slightly warmed and
  rises to return at altitude to the poles

Coriolis Effect and Global Wind Belts

Coriolis effect

• Each cell has prevailing winds associated with it
  These winds are influenced by the Coriolis effect
  The Coriolis effect is the appearance that global winds and ocean currents curve as they move
  The curve is due to the Earth's rotation on its axis, and this forces the winds to actually blow diagonally
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• The Coriolis effect influences wind direction around the world in this way:
  In the northern hemisphere it curves winds to the right
• In the southern hemisphere it curves them left
• The exception is when there is a low-pressure system:
  In these systems, the winds flow in reverse (anti clockwise in the northern hemisphere and
  clockwise in the southern hemisphere)
  Global wind belts - surface winds
  . The combination of pressure cells, the Coriolis effect and the 3-cells produce wind belts in each
  hemisphere:
  The trade winds: Blow from the subtropical high-pressure belts (30 degrees N and S) towards the
  Equator's low-pressure zones and are deflected by the Coriolis force
  The westerlies: Blow from the sub-tropical high-pressure belts to the mid-latitude low areas, but
  again, are deflected by the Coriolis force
• The easterlies: Polar easterlies meet the westerlies at 60 degrees S
  Global atmospheric circulation affects the Earth's climate
  It causes some areas to have certain types of weather more frequently than other areas:
  The UK has a lot of low-pressure weather systems that are blown in from the Atlantic Ocean on
  south-westerly winds, bringing wet and windy weather

Ocean Conveyor Belt

Ocean conveyor belt
Ocean currents move heat energy around the globe
Currents (warm or cold) act like 'rivers' of water in the sea
Cold currents move towards the equator and warm currents move towards the poles

• Each ocean has its own pattern of current
  E.g. the warm Atlantic Ocean waters of the low latitudes are moved to high latitudes via the North
  Atlantic Drift
  The direction of all ocean currents occur because of the Coriolis effect and prevailing surface winds
  Circulation occurs through convection currents
  These are driven by cold water freezing into ice at the poles
• The polar cold waters are denser, saltier sea water which sinks to the ocean floor
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