LESSON 4

Weather and Climate

Climates of Earth
Key Concept
• Why is one climate
different from another? What do you think? Read the two statements below and decide
whether you agree or disagree with them. Place an A in the Before
column if you agree with the statement or a D if you disagree. After
you’ve read this lesson, reread the statements to see if you have
changed your mind.
Before Statement After
Locations at the center of large continents
usually have the same climate as locations
along the coast.
Latitude does not affect climate.

Mark the Text

What is climate?
Summarize Write a short Weather is the atmospheric conditions and short term
phrase beside each changes of a certain place at a certain time. The weather
heading that summarizes
changes from day to day in many places on Earth. However, the
the main point of the
section. Use the summaries weather is more constant in other places. In Antarctica,
as you review the lesson. temperatures are rarely above 0°C. Areas in Africa’s Sahara have
temperatures above 20°C every day of the year.
Climate is the long-term average weather conditions that
occur in a particular region. A region’s climate depends on

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average temperature and precipitation. It also depends on how
these variables change throughout the year.

What is the most important influence

on climate?
Scientific Vocabulary Several factors determine a region’s climate. Large bodies of
coastline water, such as lakes and oceans, influence the climate of a
(noun) the part of land region. Along coastlines, weather is more constant throughout
that touches the ocean the year. Hot summers and cold winters often occur in the
center of continents. The altitude of an area also affects climate.
Scientific Vocabulary
Mountainous areas are often rainy and snowy. Yet, the most
altitude
(noun) vertical elevation important influence on climate is the amount of solar energy a
or height region receives.

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 Solar Energy on Earth Recall that because Earth is a sphere,
different areas receive different amounts of solar energy. As a Academic Vocabulary
result, locations near the equator tend to have warmer climates tend
than locations at higher latitudes. Polar regions are colder (verb) to behave or develop
because they receive less solar energy per unit of surface area in a particular way
annually. The snow and ice in these regions also contributes to
the climate. Recall that ice has a very high albedo and reflects Scientific Vocabulary
75 to 90 percent of the solar energy it receives. In the middle unit
(noun) an amount of
latitudes, between 30° and 60°, summers are generally hot and
something used as a
winters are usually cold. Thus, latitude—the distance north or standard for measuring,
south of the equator—largely determines the climate of most like meters
regions.

90°N

60°N

Sun’s rays
30°N

0°

30°S
90°S 60°S

90°
45° 30°
Earth’s surface Earth’s surface Earth’s surface
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Additionally, when exposed to a similar amount of solar

energy, the soil and rocks of the land warm to higher
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temperatures than the oceans. This means that temperatures are
more extreme on continents and vary over a smaller range in
the oceans.

How do mountains affect climate?

Mountains influence climate because they are barriers to
Scientific Vocabulary
prevailing winds. The wind is not able to flow straight through
the mountains, nor can it flow around the mountains. Thus, the precipitation
(noun) water, in liquid or
wind is forced up and over the mountains instead. This leads to solid form, that falls from
unique precipitation patterns called rain shadows. the atmosphere

Reading Essentials Weather and Climate 19

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 Scientific Vocabulary Rain Shadows An area of low rainfall on the downwind slope
downwind of a mountain is called a rain shadow. As shown in the figure
(adjective) in the direction below, rain shadows form as prevailing winds carry moist, warm
that the wind is blowing; air over Earth’s surface. As the air nears mountains, it rises and
leeward
cools. Water vapor in the air condenses and rain or snow falls
on the upwind slope. The dry air then passes over the
mountains. The air warms as it sinks. This causes dry weather
on the downwind slope.

1 Prevailing winds 2 As the air approaches mountains, it

rises and cools. Water vapor in the air 3 The now-dry air
carry moist, warm passes over the
air over Earth’s condenses. Precipitation falls as rain or
snow on the upwind slope of the mountains. As it 4 Dry weather
surface. sinks, it warms.
mountains. exists on the
downwind slope of
the mountains.

Altitude Altitude can also influence climate. Mountain climates

are usually cooler than those at sea level. Why? The molecules that
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make up atmospheric gases are fewer and fewer in number as you
go higher in altitude. This means that air pressure decreases with
altitude. Given the same amount of thermal energy, air at lower
pressures will have lower temperatures than air at higher
pressures. So, as you climb a tall mountain, you might experience
the same cold, snowy climate that is near the poles.

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How do oceans affect temperatures
and precipitation on land?
Continental areas tend to experience more extreme
temperature changes than coastal areas. Along coastlines,
Academic Vocabulary weather is more constant throughout the year. Why does this
phenomenon phenomenon occur? Recall that water has a higher specific heat
(noun) an observable fact than the rocks and soil of the surrounding land. A high specific
or event heat means that it takes much more thermal energy to raise the
temperature of water than it does to raise the temperature of
rocks and soil.

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 Large Bodies of Water The high specific heat of water causes
the climates along coastlines to remain more constant than
climates in the middle of a continent. Because a large body of
water tends to heat slowly, the climate in the area is more Academic Vocabulary
moderate in the summer. In winter, the warmed water releases moderate
heat slowly, so the area around the body of water or in coastal (adjective) not too much or
areas is less cold than inland areas. little of something; not too
hot or cold
Areas of land that are not near large lakes or an ocean are
generally warmer in the summer and cooler in the winter than
the areas near water. For example, the West Coast of the United
States has moderate temperatures year-round. On the other
hand, interior areas such as the Midwest experience hot
summers and cold winters.
Ocean Currents Ocean currents can also affect climate. Recall
that solar energy drives convection in the oceans causing warm-
water currents and cold-water currents. The temperature of
surface currents, combined with the prevailing winds, affects
weather and climate in different ways.
Regions near warm-water currents are often warmer than
regions near cold-water currents. For example, the Gulf Stream
is a warm current that flows northward along the coast of
eastern North America. This warm current causes temperatures
to be warmer along parts of the East Coast of the United States
and parts of Europe.

San Diego, CA Charleston, SC

July average high = 23.9°C July average high = 32.8°C
January average low = 9.4°C January average low = 3.3°C
Average temperature = 17.6°C Average temperature = 18.8°C
Average annual rainfall = 26.4 cm Average annual rainfall = 129.7 cm
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Ca Oklahoma City
lifo m
r San Diego Charleston
Gul Strea
ni
aC

f
urre

Oklahoma City, OK
nt

July average high = 34.4°C

January average low = −1.7°C
Average temperature = 16.4°C
Average annual rainfall = 92.3 cm

Reading Essentials Weather and Climate 21

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 Areas near warm-water currents are also often wetter than
regions near cold-water currents. When water from the ocean is
warmed by the Sun and evaporates, it releases moisture into the
atmosphere. This increases the humidity of the surrounding air
which forms rain and storms. These storms are carried by winds
to different locations.
Cold-water ocean currents make surrounding areas cooler
and drier. For example, the average temperatures and annual
rainfall in San Diego, California, is much lower than the average
temperatures and annual rainfall in Charleston, South Carolina.
The climate of San Diego is influenced by the cool California
Current. Charleston is influenced by the warm Gulf Stream.

Why do some regions have rain

forests and others deserts?
A forest with high annual rainfall, no freezing temperatures,
and a rich collection of plant and animal life is a rain forest.
Rain forests comprise only 2 percent of Earth’s land surface, yet
Scientific Vocabulary
hold nearly half of terrestrial life.
desert Deserts are dry lands that cover many parts of Earth’s land.
(noun) an area of land Vegetation is sparse in deserts, commonly covering less than
that gets little rain 15 percent of the ground.
Rain forests and deserts—what is the main feature that
distinguishes these regions? Precipitation, or rainfall, determines
whether or not a particular region will become a lush forest or a
barren desert. Across Earth, variations in precipitation and, to a
certain extent, temperature, determine what type of climate will
develop.
Precipitation and Pressure Systems Constant high-pressure
systems are present along 30°N and 30°S latitude. Recall that

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high-pressure systems keep air masses close to the ground. This
prevents clouds from forming and fair, dry weather prevails.
Earth’s great deserts have formed along these latitudes.
On the other hand, constant low-pressure systems are
present along the equator and at 60°N and 60°S latitude. Recall
that low-pressure systems allow air masses to rise. This results in
cloud formation and generally some sort of precipitation.
Regions along these latitudes experience wetter weather and
climates. For example, many of Earth’s rain forests are located
near the equator.

22 Weather and Climate Reading Essentials

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 60°N

30°N

EQ

30°S

Desert
Rain forest
60°S

Earth’s pressure systems result in a pattern of drier weather

and climates near latitudes with high-pressure zones, and wetter
weather and climates near latitudes with low-pressure zones.
Vegetation and Climate The amount of vegetation a region
has also affects climate and weather. Plants absorb solar energy, Scientific Vocabulary
keeping the land relatively cool. Plants also release water vapor transpiration
(noun) the process by
through transpiration into the atmosphere. This contributes to
which plants release
cloud formation and subsequent rainfall. water vapor into the
atmosphere
How are climates classified?
Many factors affect climate. In 1918, Wladimir Köppen (vlah Academic Vocabulary
DEE mihr • KAWP pehn) developed a system for classifying the classify
world’s many climates. Köppen, a German scientist, classified a (verb) to assign things to
region’s climate by its temperature, precipitation, and native a particular group
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vegetation.

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 Academic Vocabulary Native vegetation is often limited to particular climate
native conditions. For example, you would not expect to find a warm-
(adjective) living or desert cactus growing in the cold, snowy Arctic. Wladimir
growing naturally in a Köppen identified five climate types. Their distribution is shown
particular region
in the map below. Polar climates are cold year-round and have
little precipitation. Continental climates have warm summers
and cold winters. They experience moderate precipitation. Dry
climates have hot summers and cooler winters. They experience
very little precipitation. Tropical climates are warm all year
round and have high precipitation. Mild climates have warm
summers and mild winters.

75°
60°

45°

30°

15°

0°

15°

30°
165° 150° 135° 120° 105° 90° 75° 60° 45° 30° 15° 0° 15° 30° 45° 60° 75° 90° 105°120° 135° 150° 165°
45°

60°
75°

Tropical climates Mild climates Dry climates Continental climates Polar climates
Tropical wet Mediterranean Semiarid Warm summer Tundra
Tropical wet and dry Humid subtropical Arid Cool summer Ice cap
Marine west coast Subarctic Highland

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RE_E170_411A_NGMSS-BANK Reread the statements at the beginning of the lesson. Fill in

the After column with an A if you agree with the statement or a
D if you disagree. Did you change your mind?

24 Weather and Climate Reading Essentials

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