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24.7 Climate
This postcard
shows a
warm coastal
climate.
24.7 Climate
Classifying Climates
How is climate different from weather?
Climate is a description of the pattern of
weather over many years.
The two main factors that determine a
region’s climate are temperature and
precipitation.
24.7 Climate
Classifying Climates
Climate is the long-term weather conditions
of a place or region.
Climate includes average weather conditions
as well as how weather varies over time.
24.7 Climate
Classifying Climates
Scientists divide the world’s climates into six
major climate groups. Those groups are
•
•
•
•
•
•
tropical
temperate marine
temperate continental
polar
dry
highlands
24.7 Climate
Classifying Climates
One of the six major groups, the dry climates,
is determined mainly by precipitation.
Another group, the highland climates, is
determined mainly by elevation.
The four remaining groups are determined
mostly on the basis of temperature.
24.7 Climate
Classifying Climates
24.7 Climate
Factors Affecting Temperature
What factors determine the climate of a
region?
Factors that affect a region’s temperature
include its latitude, distance from large
bodies of water, ocean currents, and
altitude.
24.7 Climate
Factors Affecting Temperature
The latitude of a region is perhaps the most
important factor affecting temperature.
Places at the same latitude experience the
same seasonal changes in solar radiation.
24.7 Climate
Factors Affecting Temperature
Another important factor affecting the
temperature of a region is its distance from a
large body of water.
• The air above large bodies of water has much
less variation in temperature than the air over
land.
• The moderating effects of water are felt in
coastal regions.
• The temperature of coastal regions is also
influenced by nearby ocean currents.
24.7 Climate
Factors Affecting Temperature
Areas that are high above sea level have
lower average temperatures than areas at the
same latitude closer to sea level.
24.7 Climate
Factors Affecting Temperature
Giraffes inhabit the
grasslands near
Mount Kilimanjaro,
Tanzania. Although
Mount Kilimanjaro is
near the equator, its
top is covered by
snow all year
because of its high
altitude.
24.7 Climate
Factors Affecting Precipitation
What factors determine the climate of a
region?
Factors that affect a region’s precipitation
include its latitude, the distribution of air
pressure systems and global winds, and the
existence of a mountain barrier.
24.7 Climate
Factors Affecting Precipitation
The warm air over the equator usually
contains more moisture than the cold air over
the poles.
Precipitation is generally higher near the
equator than near the poles.
24.7 Climate
Factors Affecting Precipitation
A desert is an extremely dry region, receiving
less than 25 centimeters of rain per year.
• Deserts may be hot or cold.
• Many deserts receive almost no rain because
they are located within high-pressure belts. A
series of deserts can be found around 30° north
and south of the equator.
24.7 Climate
Factors Affecting Precipitation
The direction of prevailing winds can play an
important role in the amount of precipitation a
region receives.
• A coastal region where the wind generally blows
from the ocean onto land will receive a large
amount of precipitation.
• If prevailing winds blow from the land toward the
ocean, the region will receive much less
precipitation.
24.7 Climate
Factors Affecting Precipitation
The very dry high plains of western North
America are the result of a mountain barrier.
• The moist air from the Pacific Ocean loses its
moisture as it rises over the mountains of the
West.
• As the air rises, it cools and its water vapor
condenses.
• Rain or snow falls on the ocean side of the
mountains.
• The air that reaches the far side of the
mountains is much drier.
24.7 Climate
Factors Affecting Precipitation
A mountain range can form a barrier to the
movement of humid air.
24.7 Climate
Natural Climate Change
How has Earth’s climate changed over time?
Climates change over the long term, and
they vary somewhat over the short term.
24.7 Climate
Natural Climate Change
Natural forces cause climates to change.
Scientists are also concerned that human
activities may cause changes in the world’s
climates.
24.7 Climate
Natural Climate Change
Ice Ages
Glaciers once covered much of North America.
Ice ages were periods when climates were colder
than usual and glaciers covered a large portion of
Earth’s surface.
Possible causes of ice ages include variations in
Earth’s orbit around the sun, changes in the angle
of Earth’s axis, and global levels of volcanic
activity.
24.7 Climate
Natural Climate Change
Glaciers covered much
of North America in the
past. The rock in the
front shows deep
scratches made by a
glacier.
24.7 Climate
Natural Climate Change
El Niño
There are short-term natural variations in climate
patterns.
El Niño, the periodic warming of water in the
central and eastern Pacific Ocean, happens every
three to eight years.
• A deep cold-water current flows northward along the
Pacific coast of South America.
24.7 Climate
Natural Climate Change
• The water rises to the surface near Peru,
and a strong current moves the water west
across the Pacific.
• The temperature of these currents affects
the atmosphere above the ocean and,
therefore, the weather in that part of the
world.
• Every few years, for reasons that are not
well understood, conditions change.
24.7 Climate
Natural Climate Change
• The normal direction of winds changes,
causing ocean surface currents to shift
direction.
• During some El Niño years, these changes
have caused abnormal weather patterns in
many parts of the world.
24.7 Climate
Global Warming
How can human activities affect Earth’s
climate?
One cause of climate change is the addition
of carbon dioxide and other greenhouse
gases into the atmosphere.
24.7 Climate
Global Warming
Human activities may also change climate
over time.
The burning of fossil fuels such as coal
releases large quantities of carbon dioxide
into the air.
• Carbon dioxide (CO2) is one of the gases that
absorb radiation from Earth’s surface.
• This process, known as the greenhouse effect,
keeps the troposphere at normal temperatures.
24.7 Climate
Global Warming
• The amount of CO2 in the atmosphere has
increased.
• Evidence suggests an greater amounts of
CO2 will increase the greenhouse effect
and cause the temperature of the
atmosphere to rise, a process called global
warming.
24.7 Climate
Global Warming
The effects of global warming are widespread.
• Sea level rises as water in the oceans heats
and expands and glaciers melt.
• A continued rise in sea level will flood low-lying
regions.
• Other regions may be at greater risk of drought
or more frequent and violent storms.
24.7 Climate
Global Warming
Energy conservation and a greater reliance
on solar, nuclear, or geothermal power would
reduce the amount of carbon dioxide
released.
This might reduce or delay global warming.
The issue of global warming will be an
important topic for science and public policy
for decades to come.
24.7 Climate
Global Warming
Carbon dioxide emissions
from motor vehicles,
power plants, and other
sources may contribute to
global warming.
24.7 Climate
Assessment Questions
1. Climate is mainly determined by a region’s
a.
b.
c.
d.
air pressure and humidity.
latitude and winds.
temperature and precipitation.
temperature and air pressure.
24.7 Climate
Assessment Questions
1. Climate is mainly determined by a region’s
a.
b.
c.
d.
air pressure and humidity.
latitude and winds.
temperature and precipitation.
temperature and air pressure.
ANS: C
24.7 Climate
Assessment Questions
2. The addition of greenhouse gases to the
atmosphere may cause
a.
b.
c.
d.
global warming.
monsoons.
an ice age.
El Niño.
24.7 Climate
Assessment Questions
2. The addition of greenhouse gases to the
atmosphere may cause
a.
b.
c.
d.
global warming.
monsoons.
an ice age.
El Niño.
ANS: C