24.7 Climate This postcard shows a warm coastal climate.

24.7 Climate

This postcard shows a warm coastal climate.

24.7 Climate

How is climate different from weather?

Classifying Climates

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.

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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.


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Scientists divide the world’s climates into six major climate groups. Those groups are

• tropical• temperate marine• temperate continental• polar• dry • highlands


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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.


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What factors determine the climate of a region?

Factors Affecting Temperature

Factors that affect a region’s temperature include its latitude, distance from large bodies of water, ocean currents, and altitude.

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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.


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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.


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Areas that are high above sea level have lower average temperatures than areas at the same latitude closer to sea level.


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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.


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What factors determine the climate of a region?

Factors Affecting Precipitation

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.

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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.


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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.


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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.


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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.


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A mountain range can form a barrier to the movement of humid air.


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How has Earth’s climate changed over time?

Natural Climate Change

Climates change over the long term, and they vary somewhat over the short term.

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Natural forces cause climates to change.

Scientists are also concerned that human activities may cause changes in the world’s climates.


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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.


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Glaciers covered much of North America in the past. The rock in the front shows deep scratches made by a glacier.


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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.


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• 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.


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• 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.


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How can human activities affect Earth’s climate?

Global Warming

One cause of climate change is the addition of carbon dioxide and other greenhouse gases into the atmosphere.

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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.

Global Warming

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• 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.

Global Warming

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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.

Global Warming

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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.

Global Warming

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Carbon dioxide emissions from motor vehicles, power plants, and other sources may contribute to global warming.

Global Warming

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Assessment Questions

1. Climate is mainly determined by a region’s a. air pressure and humidity.

b. latitude and winds.

c. temperature and precipitation.

d. temperature and air pressure.

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1. Climate is mainly determined by a region’s a. air pressure and humidity.

b. latitude and winds.

c. temperature and precipitation.

d. temperature and air pressure.

ANS: C

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2. The addition of greenhouse gases to the atmosphere may cause a. global warming.b. monsoons.c. an ice age.d. El Niño.

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2. The addition of greenhouse gases to the atmosphere may cause a. global warming.b. monsoons.c. an ice age.d. El Niño.

ANS: C

24.7 Climate This postcard shows a warm coastal climate.

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