CHAPTER
17
Vocabulary
Weather
climate
Prevailing winds
Surface currents
Tropical zone
Temperate zone
Microclimate
Ice age
Global warming
latitude
elevation
biome
evergreens
polar zone
deciduous
greenhouse effect
BELLRINGER
You have just entered a contest
for a free trip to a place with a
perfect climate. To win, you need
to describe in 25 words or less
your idea of a perfect climate
Bell Ringer
1. What Is Climate?
Pretend you are entering a contest for a free trip to a place
with perfect climate. To win, write a description of your
idea of the perfect climate in 25 words or less.
Record your response in your Science Log.
2. Climates of the World
Describe the differences between the plant life where you
live and the plant life in an area you have visited. Think
about how climate influences the vegetation in these
areas.
Write your response in your Science Log.
Ellsworth
Huntington
In the early 1900s, a geographer named
Ellsworth Huntington conducted research to
see if he could determine the ideal climate for
human beings—the type of climate that would
result in optimal physical and mental wellbeing. He concluded that a climate with
considerable daily and seasonal weather
changes and an average temperature of 18°C
was ideal.
CLIMATE
What
is Climate?
Climates of the World
Changes in Climate
Climatology
Climatology can be divided into three branches:
 Global- investigates the general circulation of
wind and water circulation.
 Regional- studies the characteristic weather
patterns and related phenomena of a particular
region.
 Physical- analyzes statistics concerning climatic
factors such as temperature, moisture, wind and
air pressure
What is Climate?
Weather is the condition of the
atmosphere at a particular time and place.
Weather conditions vary from day to day.
Climate, on the other hand, is the
average weather conditions in an area
over a long period of time. Climate is
determined by two main factors,
TEMPERATURE
PRECIPITATION.
and
Latitude
Latitude is the distance north or south,
measured in degrees, of the equator. In
general, the temperature of an area
depends on its latitude. The higher the
latitude is, the colder the climate. For
example, the North Pole is at 900 latitude
and is cold while the equator, at latitude
00 is hot.
Is That a Fact!
 Tutenendo,
Colombia, is the rainiest place
in the world. It averages almost 12 m of
rain per year.
 The hottest day ever recorded occurred in
Libya, where the temperature reached
580C (1360F) in 1922.
 The coldest place on Earth is Antarctica,
with temperatures reaching -890C (-1280F)
Seasons and Latitudes
Most places in the United States, the
year consists of four seasons. But,
there are places that have only one
season. Can you name one? The
Earth is tilted on its axis at a 23.50
angle. This tilt affects how much solar
energy an area receives as the earth
moves around the sun.
ALERT!
The distance between the Earth and the
Sun does not determine the seasons.
The Earth’s tilt as it orbits the sun
determines where solar radiation is
concentrated and thus determines the
seasons.
For example; Australia has it’s summer
during our winter months in the northern
hemisphere.
Prevailing Winds
Prevailing winds are winds that
blow mainly from one direction.
These winds influence an area’s
moisture and temperature. Let’s
review some basic properties of
air.
Because warm air is less dense, it tends to rise. Cooler,
denser air tends to sink
Prevailing Winds
The amount of moisture in prevailing
winds is also affected by whether the
winds blow across land or across a
large body of water. Winds that travel
across water tend to absorb water
and winds that travel across land
tend to be dry.
Geography
Geography can influence an area’s climate by
affecting both temperature and precipitation.
Such as Mt. Kilimanjaro, the tallest mountain
in Africa, has snow covered peaks yearround, even though it is only about 30 south of
the equator. The temperature can be affected
by elevation. As elevation increases, the
atmosphere becomes less dense and it’s
ability to hold thermal energy from the sun
and Earth decreases. Mountains also affect
the climate of nearby areas by influencing the
distribution of precipitation.
Rain Shadow
Winds that travel across large bodies of
water, such as the ocean, absorb
moisture. As the winds approach mountain
ranges they are blocked and the amount
of moisture changes. Mountains force air
to rise and cool releasing moisture as
snow or rain. The land on the windward
side of the mountain is usually lush and
green. Due to the wind losing its moisture.
Rain Shadow
After dry air crosses the mountain, the air
begins to sink, warming and absorbing
moisture as it sinks. The dry conditions
created by this effect usually produce a
desert. This side of a mountain is in Rain
Shadow.
Ocean Currents
Surface currents in the ocean carry warm
or cool water to different locations. The
surface temperature of the water affects
the air temperature above it. Because of
the water’s ability to absorb and release
thermal energy, the circulation of the
ocean surface currents has an enormous
effect on an area’s climate
Climates of the World
There are three major climate zones:
 Tropical
 Temperate
 Polar
Each zone has a temperature range that relates
to its latitude. However, in each of these zones
there are several types of climates due to
differences in the geography and the amount of
precipitation. Because of the various climates in
each zone, there are different biomes.
Biomes
A biome is a large region
characterized by a specific
type of climate and the plants
and animals that live there.
Tropical Zone
The tropical zone is the warm zone located
around the equator. This zone extends
from the tropic of Cancer (23.50 N) to the
tropic of Capricorn (23.50 S) and receives
most of the solar radiation. Temperatures
are usually hot except at higher
elevations. Within the tropical zone there
are three types of biomes.
Tropical Zone
Biomes
Tropical Rain Forest
Average Temperature range: 77 82 degrees F
Avg. Yearly Precipitation: 200cm or more
Soil Characteristics: thin and nutrient poor
They are always warm and wet. They
contain the largest number of plant
and animal species of any biome with a
poor soil with lush vegetation.
Tropical Zone Biomes
Tropical Deserts
 Avg.
Temp. Range: 61-120 degrees F
 Avg. Yearly Precip.: 0-25cm per year
 Soil Characteristics: poor in organic matter
A desert is an area that receives less than
25cm per year and are the driest places
on earth.
The world’s largest desert, the Sahara,
covers more than 9 million square
kilometers----about the size of the United
States. In contrast, the largest desert in
the United States, is the Mojave Desert. It
covers 38,000km2, which is nearly twice
the size of New Jersey.
Tropical Zone Biomes
Tropical Savannas
 Avg.
Temp. Range: 80-90 degrees F
 Avg. Yearly Precip.: 100cm
 Soil Characteristics: generally nutrient
poor
Tropical savannas are dominated by
grasslands and tall grasses.
Temperate Zone
The temperate zone is the climate zone
between the Tropics and the polar zone.
Temperatures tend to be moderate as they
are in the United States. There are four
biomes:
 Temperate forest
 Temperate grassland
 Chaparral
 Temperate desert
Temperate Zone
Temperate Forests
 Avg. Temp. Range: 32-82 degrees F
 Avg. Yearly Precip.: 76-250cm
 Soil Characteristics: very fertile, organically rich
The temperate forest biomes tend to have very
high amounts of rainfall and seasonal
temperature differences. Because of these
distinct seasonal changes, summers are usually
warm and winters are cold.
Environmental
Connection
The settlement of humans in temperate
forests around the world has greatly
fragmented these forests. Much of the
temperate forest has been converted to
cropland or logged. Fragmentation has a
negative impact on many plants and
animals and has led to the extinction of
many species. Acid rain and ozone have
damaged many of the remaining
temperate forests.
Temperate Zone
Temperate Grasslands



Avg. Temp. Range: 21-78 degrees F
Avg. Yearly Precip.: 38-76cm
Soil Characteristics: most fertile soils of all
biomes.
Much of the temperate grasslands has been
plowed to make room for croplands. This biome
has warm summers and cold winters. “The
Prairies of North America.”
Temperate Zone
Chaparrals
 Avg.
Temp. Range: 51-78 degrees F
 Avg. Yearly Precip.: 48-56cm
 Soil Characteristics: rocky, nutrient poor
soils.
Chaparral regions, have cool wet winters
and hot, dry summers.
Environmental Connection
Chaparral vegetation is particularly
vulnerable to damage from air
pollution. Ozone and other pollutants
damage plants such as, the coastal
sage shrub, making them less able to
recover from the frequent chaparral
fires.
Temperate Zone
Temperate Deserts
Avg. Temp. Range: 34-120 degrees F
 Avg. Yearly Precip.: 0-25cm
 Soil Characteristics: poor in organic matter

The temperate desert biomes tend to be
deserts. Like all deserts, they receive less
25cm precipitation per year. They can be
hot in the day time, but unlike hot deserts,
tend to be very cold at night.
cold
than
very
they
Brain Food
Chile’s arid northern desert land is one of
the driest places on Earth. It receives so
little rainfall that it is listed as
“immeasurable”. Surprisingly, people live
there. They get drinking water by
harvesting the fog. The village of
Chungungo has built 75 fog-catching nets
that supply 11,000 L of clean water a day!
Polar Zone
The
polar
zone
includes
the
northernmost and southernmost climate
zones. Polar climates have the coldest
average temperatures. The temperatures in
the winter stay below freezing, and the
temperatures during the summer months
remain chilly.
Polar Zone
Tundra
Avg. Temp. Range: -17 to 41 degrees F
 Avg. Yearly Precip.: 0-25cm
 Soil Characteristics: frozen

Next to deserts, the tundra, is the driest place
on Earth. This biome has long, cold winters with
almost 24 hours of night and short, cool
summers with almost 24 hours of daylight.
Tundra continued;
In the summer, only the top meter of soil
thaws. Underneath the thawed soil lies a
permanently frozen layer of soil, called
permafrost. This frozen layer prevents the
water in the thawed soil from draining and is
therefore muddy and an excellent breeding
ground for mosquitoes and insects. Many
birds migrate there to feed on the insects.
Polar Zone
Taiga
 Avg.
Temp. Range: 14 - 59 degrees F
 Avg. Yearly Precip.: 40 - 61cm
 Soil Characteristics: acidic soil
Just south of the tundra lies the taiga
biome. The taiga has long, cold winters
and short, warm summers. The majority
of the trees are conifers (pine, spruce and
fir).
Microclimates
Microclimates are small regions with
unique
climatic
characteristics.
For
example, elevation can affect an area’s
climate and therefore its biome. Tundra
and tiaga biomes exist in the Tropics on
high
mountains.
Cities
are
also
microclimates as the temperature can be
10 C to 20 C warmer than the surrounding
rural areas.
QUIZ
1.
2.
3.
What are the three major climate zones?
Can a climate zone contain more than
one biome?
What is a microclimate?
1. Tropical, temperate and polar
2. Yes, may contain several different biomes
3. A small region with unique climate
characteristics
Changes in Climate
As you know, the weather constantly
changes --- sometimes --- several times in
one day. What causes climate to change?
Until recently, climatic changes were
connected only to natural causes.
However, studies indicate that human
activities may have an influence on
climatic change.
Ice Ages
An ice age is a period during which
ice collects in high latitudes and
moves towards lower latitudes.
Scientists have found evidence of
many major ice ages throughout
Earth’s geologic history. The most
recent ice age began about 2 million
years ago.
Glacial Periods
During an ice age there are periods of cold
and periods of warmth. The periods of
cold are called glacial periods. During
glacial periods, the enormous sheets of ice
advance, getting bigger and covering a
larger area. Because a large amount of
ocean water is frozen during glacial
periods, sea level drops. Glaciers
Spread!
Interglacial Periods
Interglacial periods are warmer and
occur between glacial periods. During this
time ocean level rises as the glacial ice
melts. The glaciers retreat! The last
interglacial period began about 10,000
years ago and is still occurring. Why do
these periods occur? Will there be another
ice age? These questions have been
debated by scientists for over 200 years.
Motions of the Earth
There are many theories about the causes
of ice ages. The Milankovitch theory
explains why an ice age isn’t just one long
cold spell but instead alternates between
cold
and
warm
periods.
Milutin
Milankovitch proposed that changes in
Earth’s orbit and tilt of the Earth’s axis
cause ice ages.
Volcanic Eruptions
There are many natural factors that
can affect global climate. Catastrophic
events, such as volcanic eruptions,
can influence climate. Volcanic
eruptions send large amounts of dust,
smoke and ash particles act as a
shield, blocking out so much of the
sun’s rays that the Earth cools.
Plate Tectonics
The Earth’s climate is further influenced
by plate tectonics and continental drift.
One theory proposes that ice ages occur
when continents are positioned near the
polar regions. For example, approx. 250
million years ago, all the continents were
connected near the south pole in one
giant landmass called Pangea. During this
time, ice covered a large area of Earth’s
surface.
Weird Science
During the last glacial period,
animals that live in the northern
part of North America, such as
the Arctic fox, wolf, grizzly bear
and caribou were living in
Oklahoma, Texas and Missouri!
Brain Food
When the climate starts to cool, ice
sheets grow and creep over the
Earth. Ice sheets act as reflectors,
reflecting solar radiation away from
the Earth, causing it to cool even
more. The more the earth cools, the
larger the glaciers grow.
Global Warming
Global warming is a rise in the average
global temperatures that can result from
an increase in the green house effect. The
green house effect is the Earth’s natural
heating process, in which gasses in the
Earth’s atmosphere trap thermal energy.
Greenhouse gasses allow sunlight to pass
through the atmosphere. It is absorbed by
the Earth’s surface and reradiated as
thermal energy.
Deforestation
Deforestation is the process of clearing
forests. All types of burning releases CO2
into the atmosphere, thereby increasing
the greenhouse effect. Plants use CO2 to
make food. As plants are removed from
the Earth, the CO2 that would have been
used by the plants builds up in the
atmosphere.
Consequences
Many scientists think that if the
average
global
temperature
continues to rise, some regions of
the world might experience flooding.
Warmer temperatures could cause
the ice caps to melt, raising the sea
level and flooding low-lying areas,
such as coasts.
Connection
There are many consequences to global
warming. One possibility is the spread of
tropical diseases, such as malaria and
dengue fever. Both of these diseases are
carried by a specific species of mosquito.
These mosquitoes have a minimum
temperature at which they can survive.
Quiz
1.
Why does the sea level fall during glacial
periods?
2.
How might a major volcanic eruption
have brought about an ice age?
3.
How might global warming affect coastal
areas?
Answers
1.
2.
3.
Because much of Earth’s water is frozen
during a glacial period
Dust, smoke and ash act as a shield
blocking the sun’s rays
Ice caps could melt causing the ocean
water level to rise