Earth Science 21.2 World Climates
World Climates
Earth Science 21.2 World Climates
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If you were to travel around the
world , you would find an incredible
variety of climates.
So many climates in fact, that one
might find it hard to conceive that
they could all occur on one planet.
Despite this diversity, climates can
be classified according to their
average temperatures, and amounts
of precipitation.
In this lesson, we will examine the
Koppen climate classification
system.
Earth Science 21.2 World Climates
The Koppen Climate Classification
System:
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Many classification systems have
been used to classify climates.
Perhaps the best known and most
commonly used system is the
Koppen Climate Classification
System.
The Koppen climate classification
system uses mean monthly and
annual values of temperature and
precipitation to classify climates.
This system is often used
because it classifies the world
into climatic regions in a realistic
way.
Earth Science 21.2 World Climates
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The Koppen system has five
principal groups
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Humid tropical climates
Dry climates
Humid mid-latitude climates
Polar climates
highland climates
All of these groups, except
those classified as dry, are
defined on the basis of
temperature.
Dry climates are classified
partly according to the amount
of precipitation that falls over
an area.
Each of these five major groups
is than subdivided further.
Earth Science 21.2 World Climates
Humid Tropical Climates
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Humid tropical climates are climates
without winters.
Every month in such a climate has a
mean temperature above 18 degrees
Celsius.
There are two types of tropical
climates
○ Wet tropical climates
○ Dry tropical climates
Earth Science 21.2 World Climates
Wet Tropical Climates
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The tropical rain forests of Costa Rica
are typical of a wet tropical climate.
Wet tropical climates have high
temperatures and much annual
precipitation.
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Recall what we have already learned
about how latitude effects climate.
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The intensity of the sun’s rays in the
tropics is consistently high.
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Because the sun is directly overhead
much of the time, changes in the length
of daylight throughout the year are
very slight.
Earth Science 21.2 World Climates
Wet Tropical Climates
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The wind that blows over the
tropics cause the warm,
humid, unstable air to rise,
cool, condense, and fall as
precipitation.
Note that these areas of wet
tropical climates fall on a belt
centered on the equator when
one looks at a world climate
map.
Earth Science 21.2 World Climates
Tropical Wet and Dry Climates:
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Bordering the wet tropics are
climates classified as tropical wet
and dry climates.
Tropical wet and dry climates have
temperatures and total
precipitations similar to those in the
wet tropics , but experience distinct
dry seasons (periods of no or little
rain).
Savannas, which are tropical
grasslands with drought resistant
trees, are typical of tropical wet and
dry climates.
An African savanna can be seen at
right.
Earth Science 21.2 World Climates
Humid Mid-latitude climates:
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Humid mid-latitude climates fall
into two groups:
 Climates with mild winters
 Climates with severe winters
Climates with mild winters have
an average temperature in the
coldest month that is below 18
degrees Celsius but above -3 C.
Climates with severe winters
have an average temperature in
the coldest month that is below
-3C.
Earth Science 21.2 World Climates
Humid Mid-latitude
climates:
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There are three types of
humid mid-latitude
climates:
 Humid subtropical
 Marine west coast
climates
 Dry-summer subtropical
climates
Earth Science 21.2 World Climates
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Located between 25 degrees and 40
degrees latitude on the eastern sides
of continents are the humid
subtropical climates.
Notice that a humid subtropical
climate dominates the southeastern
side of the United States.
In the summer, these areas
experience hot, humid weather as
daytime temperatures often soar.
Although winters here are generally
mild, frosts are common in the higher
latitude areas.
The temperatures and precipitation
data in the graph at right are typical
of a subtropical climate.
Earth Science 21.2 World Climates
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Coastal areas between about 40
degrees and 65 degrees north and
south latitude have marine west coast
climates.
Maritime air masses over these
regions result in milder winters and
cool summers with an ample amount of
rainfall throughout the year.
In North America, the marine west
coast climate extends as a narrow
belt from northernmost California
into southern Alaska.
The data table at right for Vancouver
shows average temperature (in red)
and precipitation (in blue) amounts for
this zone.
Earth Science 21.2 World Climates
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Regions with dry-summer
subtropical climates are
generally located between 30
degrees and 45 degrees
latitude.
These climatic regions are
unique because they are the
only humid climate that has a
strong winter rainfall maximum.
In the United States, dry
summer subtropical climate is
found only in California.
It is sometimes referred to as
a Mediterranean climate.
Earth Science 21.2 World Climates
Humid Mid-latitude with severe
winters:
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There are two types of humid midlatitude climates with severe
winters: the humid continental
climates and the subarctic climates.
Continental landmasses strongly
influence both of these climates.
As a result, both of these climates
are absent from the Southern
Hemisphere. There, oceans
dominate the mid-latitude zone.
Earth Science 21.2 World Climates
Humid Mid-latitude with severe
winters:
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Looking at the map at right we can
see that the winter temperatures
are quite severe while the summers
are warm.
Note as well that precipitation is
generally greater in the summer
than the winter.
Earth Science 21.2 World Climates
Humid Mid-latitude with severe
winters:
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North of the humid continental
climate and south of the tundra
is an extensive subarctic
continental climate region. (show
in purple)
This climate zone covers a large
swath of North America,
stretching from western Alaska
to Newfoundland in North
America.
Earth Science 21.2 World Climates
Humid Mid-latitude with severe
winters:
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Winters in these regions are long
and bitterly cold.
In contrast, summers in the
subarctic areas are relatively warm
but very short.
The extremely cold winters and
warm short summers combine to
produce the highest annual
temperature ranges on Earth.
Earth Science 21.2 World Climates
Dry Climates:
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A dry climate is one in which the
yearly precipitation is not as great
as the potential loss of water by
evaporation.
The dryness of a climate is not only
related to the amount of rain that
falls; it also is based on the amount
of evaporation of water that takes
place within the zone.
Evaporation, in turn, is heavily linked
to the temperature of an area.
There are two types of dry climates:
arid (desert) and semi-arid climates
(steppe) .
Earth Science 21.2 World Climates
Dry Climates:
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Arid and semi-arid climates have
much in common between them.
In fact, the difference between
them is actually very slight.
The steppe is a marginal, slightly
more humid variation of the desert
environment.
The steppe is a transition zone that
isolates the desert and creates a
transition between it and the more
livable humid climates.
Earth Science 21.2 World Climates
Dry Climates:
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Dry climates exist as the result of
the global distribution of air
pressure and winds.
In regions near the Tropics of
Cancer and Capricorn, air is
subsiding, sinking from above.
When air sinks, it becomes
compressed and warms. These
conditions are the exact opposite of
the conditions that produce rain
clouds.
As a result, these regions
experience clear, sunny skies and dry
climates with little rain.
Earth Science 21.2 World Climates
Dry Climates:
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Other dry areas of the world include
the Gobi Desert in Africa, the Great
Basin of North America and the
Sahara desert.
These arid areas are called rain
shadow deserts.
Some of the Earth’ driest climates
occur where a cold ocean current
effects the west coast of a continent.
A cold current cools the air above it.
This strengthens the sinking of air in
the warm, dry air masses that cause
deserts.
The Namib desert of Africa is an
example of this type of dry coastal
desert.
Earth Science 21.2 World Climates
Polar Climates:
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Polar climates are those in which
the mean temperature of the
warmest month is below 10
degrees Celsius.
Polar winters are periods of
perpetual night, or nearly so.
During the summer, temperatures
remain cool despite the long hours
of daylight.
Very little precipitation falls in
polar regions.
Earth Science 21.2 World Climates
Polar Climates:
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There are two types of polar
climates: the tundra climate and
the ice cap climate.
The tundra climate is a treeless
region found almost exclusively in
the Northern Hemisphere.
The ice cap climate does not have
a single monthly mean above 0
degrees Celsius. The landscape is
covered with permanent snow and
ice.
Ice cap climates occur in high
mountain areas and in Greenland
and Antarctica.
Earth Science 21.2 World Climates
Highland Climates:
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Highland climates are localized.
This means they are much
different from climates in nearby
surrounding areas.
Conditions of highland climates
often vary abruptly from one
place to another.
Earth Science 21.2 World Climates
Highland Climates:
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For example, southern facing
slopes are warmer than north
facing slopes, and air on the
windward sides of mountains is
wetter than air on the leeward
sides of mountains.
In general, highland climates are
cooler and wetter than nearby
areas at lower elevations.