Driving Forces of Climate
and Weather
Adapted from The Knowledge Project
Stevens, A. (2010) Introduction to the Basic Drivers of Climate. Nature Education Knowledge 3(10):10
Climates on Earth vary from the warm, wet
tropics to the cold, dry Arctic and Antarctic.
What drives this variation?
What is Climate?
Every day, we note the weather: temperature, rain, cloud cover, wind and
humidity. Climate is the long-term common weather in an area and is largely
determined by temperature and precipitation. The climate in a desert is hot and
dry. The climate in the tropics is warm and wet. The climate of a particular area is
the largest determinant to the life found there. Climate is a key focus in ecology.
Variations in climate include daily and seasonal cycles. Climate variation also
includes changes over several years or even decades. Droughts and El Niño
events are examples of climate variation.
What is Climate?
Variations in climate include daily and seasonal cycles.
Think about it…
In Laguna Niguel, how do temperatures change throughout the day? Is there a
regular pattern to those temperature changes? How do daily cycles of temperature
change in Laguna Niguel compare to those near Las Vegas?
How does temperature change with the seasons?
Climate variation also includes changes over several years or even decades.
Droughts and El Niño events are examples of climate variation.
Sunlight Intensity Is a Key Component of Climate
The sun drives our planet’s weather and climate
patterns.
Because Earth is spherical, energy from the sun
does not reach all areas with equal strength. Areas
that are exposed more directly to the sun’s rays (i.e.
those nearest to the equator) receive greater solar
input.
In contrast, those in higher latitudes (closer to the
poles) receive sunlight that is spread over a larger
area and that has taken a longer path through the
atmosphere.
As a result, these higher latitudes receive less solar
energy and generally have colder climates.
Review Energy Lab Station #6. How does
Earth’s revolution around the sun affect the
amount of direct sunlight the surface
receives?
Sunlight Intensity Is a Key Component of Climate
North pole is tipped away from
sun; it is winter in the northern
hemisphere
Because the Earth is tilted on its axis by 23.5˚,
the amount of direct sunlight on some parts of the
Earth changes a lot over the course of the year
causing different seasons to occur.
Winter in the northern hemisphere occurs as
the northern tip of the planet tilts away from the
sun; during this time, the southern hemisphere
receives more direct sunlight and experiences
summer. As Earth reaches the opposite point of
its orbit, the northern hemisphere becomes
angled toward the sun, and the seasons reverse.
Closer to the equator, tropical areas experience
relatively minor changes in temperature, and their
seasons are characterized by the presence or
absence of rain.
As Earth reaches the opposite point of its orbit,
the North Pole is pointed at the sun; it is summer
in the northern hemisphere. Note how the sun
strikes the North and South differently in each
position.
Think it over...
At the equator, the Earth
receives ____________
exposure to the sun’s rays.
The ____________ direct
sunlight at the equator
causes the oceans and air to
_________________.
Think it over...
At the equator, the Earth
receives greater exposure to
the sun’s rays.
The greater direct sunlight at
the equator causes the
oceans and air to warm-up.
Think it over...
At which position does the southern
hemisphere receive the greatest direct
sunlight?
Would this cause temperatures to be
warmer or cooler?
Would the days be longer or shorter?
A
B
D
What season would this be in the
southern hemisphere?
C
Think it over...
At which position does the southern
hemisphere receive the greatest direct
sunlight? Position D
Would this cause temperatures to be
warmer or cooler? Warmer
Would the days be longer or shorter?
Longer
What season would this be in the
southern hemisphere? It would be
summer in the southern hemisphere.
With more of the southern hemisphere pointed at the
sun, it receives a great amount of direct sunlight AND
has longer days. Both these conditions allow the land
and water to absorb and store greater amounts of
energy, and as such, have warmer temperatures.
A
B
D
C
Position D: Summer in the southern hemisphere
Climate basics...Heat Rises, Cold Sinks!
Molecules behave differently when energy is added. When cold, molecules are
more closely packed together than when they are warm. As such, warm fluids like
air and water are less dense than cold air and water.
This difference in relative density causes heat to rise and cold to sink. We
discovered this in our Energy Station Labs!
Climate Basics: Sunlight Intensity Drives the Water Cycle,
Global Winds, Precipitation Patterns, and Ocean Circulation
The warm air that rises in the tropics is
wet, because there is a lot of water in
plants, soils and bodies of water for the
strong sunlight to evaporate.
These water molecules rise to become
part of the warm air which is not very
dense.
As the air gains altitude it cools and
decreases the space for water. The water
molecules condense to form clouds and
eventually fall as precipitation. It rains a
lot in the tropics, leaving dry air in the
atmosphere moving toward the poles.
Climate Basics: Sunlight Intensity Drives the Water Cycle, Global Winds,
and Ocean Circulation
As warm air moves
upward, colder air from
neighboring areas rushes
in to fill the void left
behind. The air moves
just like the water did in
Energy Station Lab #2.
Air and water are both fluids. When fluids of different
temperatures meet, warm fluids rise, cool fluids sink.
Climate Basics: Sunlight Intensity Drives Global Winds
As warm air moves
upward, colder air from
neighboring areas rushes
in to fill the void left
behind.
Climate Basics: Sunlight Intensity Drives Global Winds
Tropical air moves away
from the equator and
toward the poles. As it
travels, it cools, becomes
denser, and eventually
sinks around 30˚ northor south-latitude.
Climate Basics: Sunlight Intensity Drives Global Winds
This dry air mass, having lost its
moisture in the tropics, absorbs
moisture from the ground,
creating arid (dry) conditions at
these latitudes.
Some of the air is drawn back
toward the equator, and some is
drawn toward the pole as part of
a new air mass.
As the tropical air moves toward the poles, it
cools and sinks to form trade winds here
Climate Basics: Sunlight Intensity Drives Global Winds
At latitudes around 60° north and
south, the air again rises, cools and
releases precipitation (though less
than in the topics).
Some of the cold, dry rising air then
flows to the poles, where it absorbs
moisture creating the cold, dry
climates of the polar regions.
Differences in temperatures at
various regions cause warmer
air to rise and colder air to sink
resulting in global wind patterns.
Climate Basics: Sunlight Intensity Drives Global Winds
Think about it…
Why does air rise in some regions
and sink in other regions?
How could this affect global winds?
How could the same activity be
happening in the oceans?
Climate Basics: Sunlight Intensity Drives Global Winds
Think about it…
Why does air rise in some regions and sink in
other regions?Unequal heating of the Earth’s
surface causes air in warmer regions to rise, and
air in cooler regions to sink.
How could this affect global winds?As warm air
rises, cooler air rushes in to fill the empty space
left behind, creating wind.
How could the same activity be happening in the
oceans? Air and water are both fluids, so they
behave in similar ways. Warm water rises, cooler
water moves in to fill the space, and currents
occur.
Global winds occur due to difference is air
temperatures over various regions
Climate Basics: The World Turns...The Coriolis Effect
This is weird…
Because the Earth spins on it axis, global winds and ocean currents move
to the right in the northern hemisphere and to the left in the southern
hemisphere.
Climate Basics: The World Turns…
The Coriolis Effect
Because the Earth spins on it axis, global winds and
ocean currents move to the right in the northern
hemisphere and to the left in the southern
hemisphere.
Study the illustration to the right.
Imagine you are gliding in the wind. The white arrow
shows the direction the wind is traveling. Because
the Earth is turning counter clockwise, the wind
direction will change as shown by the red arrows.
If wind is traveling toward the equator, it will be
turned clockwise; if the wind is moving toward the
poles, it will move counter clockwise.
Climate Basics: The World Turns…
The Coriolis Effect
Because the Earth spins on it
axis, global winds and ocean
currents move to the right of
the wind direction in the
northern hemisphere and to
the left of the wind direction
in the southern hemisphere.
These winds are predictable
and named by the direction
they come from
Climate Basics: The World Turns…
The Coriolis Effect
Think about it…
South East Trade winds
come from the __________
__________ and move in a
__________ ___________
direction.
Westerlies come from the
___________ and move
toward the ___________ .
Climate Basics: The World Turns…
The Coriolis Effect
Think about it…
South East Trade winds
come from the South East
and move in a North West
direction.
Westerlies come from the
West and move toward the
East.
Climate Basics: The World Turns…
The Coriolis Effect
The Coriolis Effect explains
why hurricanes always turn
counter-clockwise and
cyclones always turn
clockwise.
Climate Basics: The World Turns…
How the Earth’s Winds and Ocean Currents Drive Weather and Climate