Weather and Climate — Key Concepts
1. Weather
Definition: The state of the atmosphere at a specific time and place.
Elements: Temperature, wind, cloud cover, and rainfall.
Characteristics:
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Changes frequently — hour to hour, day to day, and season to season.
Caused by interactions between the atmosphere, hydrosphere, and
lithosphere.
Can include extreme events such as heatwaves, droughts, or cyclones.
2. Climate
Definition: The long-term average of weather conditions over many years (usually 30 years
or more).
Measured by: Data such as temperature, rainfall, and wind speed averages.
Includes: Records of extreme events like cyclones and droughts.
Changes slowly — over decades or centuries.
Climate change = Changes in long-term weather patterns.
Influences on Climate
1. The Sun – The Main Source of Energy
Provides energy that:
 Drives weather patterns.
 Supports life by maintaining warmth.
Although solar energy is mostly constant, other factors influence Earth’s climate.
2. Earth’s Surface
Determines how much solar energy is reflected or absorbed.
Reflection (albedo):
 Ice and clouds reflect a lot of sunlight.
 Ice reflects about 84% of incoming solar energy.
Darker surfaces (like oceans or forests) absorb more heat.
3. Gases in the Atmosphere (The Greenhouse Effect)
Short-wave radiation:
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Comes from the Sun.
Passes through the atmosphere to reach Earth’s surface.
Long-wave radiation:
Heat energy re-radiated from Earth’s surface back to space.
Greenhouse Gases:
Include water vapour (H₂O), carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and
ozone (O₃).
These gases:
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Allow short-wave solar radiation to pass through.
Absorb long-wave heat radiation and re-emit it in all directions — some back
to Earth.
Effect:
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Traps heat in the atmosphere — keeps Earth warm enough for life.
Without it, Earth’s average temperature would be –18°C.
This natural warming is called the greenhouse effect.
Analogy:
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A greenhouse traps heat the same way — sunlight (short-wave radiation) passes through
glass, but re-radiated heat (long-wave radiation) cannot escape.
Ocean Currents and Their Role in Climate
Definition:
Continuous movements of ocean water that circulate heat and nutrients around the Earth.
Types of Currents:
1. Surface Currents – caused mainly by wind.
2. Deep Currents – caused by temperature and salinity differences.
Causes of Ocean Currents:
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Wind.
Temperature differences.
Variations in salinity (salt concentration).
Earth’s rotation.
Gravitational pull of the Sun and Moon.
1. Surface Currents
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Wind pushes surface water until it hits land and moves sideways.
Form circular patterns called gyres:
 Clockwise in the Northern Hemisphere.
 Anticlockwise in the Southern Hemisphere.
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Caused by Earth’s rotation (Coriolis effect).
2. Deep Currents
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Begin at the poles.
When sea ice forms:
 Salt is left behind → water becomes saltier and denser.
 Dense water sinks → replaced by surrounding water → creates a deep current.
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These deep currents carry cold water along the ocean floor.
3. The Gulf Stream
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A warm ocean current flowing from the Caribbean Sea to Western Europe.
Effect: Makes Europe’s winters milder compared to other regions at the same latitude.
4. Ocean Currents and Ecosystems
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Phytoplankton – microscopic, photosynthetic organisms living near the ocean’s surface.
They:
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Form the base of ocean food chains.
Produce half of Earth’s oxygen.
Ocean currents:
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Bring nutrients from the deep ocean to the surface.
Support marine life and maintain ecosystem balance.
Changing Climate Over Earth’s History
1. Past Climate of Australia
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62 million years ago – part of Gondwana, with a warmer and wetter climate.
Cycles of cooling and warming have occurred throughout Earth’s history.
2.5 million years ago – ice sheets covered southern Australia and Tasmania (glaciation).
20,000 years ago – current warming period began.
During ice ages, sea levels fell because more water was stored in ice caps.
2. Evidence for Climate Change
A. Glaciers
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Advance (grow) during cooler periods.
Retreat (shrink) during warmer periods.
Leave behind moraines (rocky debris) showing where ice once was.
B. Ice Cores
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Cylindrical samples drilled from ice sheets (e.g., Antarctica).
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Each layer represents snowfall from a different year.
Provide data on:
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Past temperatures.
Carbon dioxide (CO₂) and oxygen levels.
Sea level changes.
Show clear links between temperature and atmospheric CO₂ over thousands of years.
C. Ocean Currents
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Antarctic Circumpolar Current affects Australia’s rainfall.
Climate change may shift the current, directing warm moist air away from Australia,
causing reduced rainfall.
D. Pollen Analysis
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Fossilised pollen shows what plants grew in an area long ago.
Changes in pollen types reveal changes in vegetation and climate.
E. Sea Level Changes
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Sedimentary rocks and marine fossils found inland (like in central Australia) show that
these areas were once underwater.
Indicates that sea levels have changed many times throughout Earth’s history.