1 What Is Climate ?

What Is Climate? How is weather different from climate? Weather is the condition of the atmosphere at a certain time. The weather can change from day to day. In contrast, climate describes the average weather conditions in a region over a long period of time. The climate of an area includes the area’s average temperature and amount of precipitation. Different parts of the world have different climates.


PREVAILING WINDS
Prevailing winds are winds that blow mainly in one direction.The wind patterns on Earth are caused by the uneven heating of Earth's surface.This uneven heating forms areas with different air pressures.Wind forms when air moves from areas of high pressure to areas of low pressure.
Prevailing winds affect climate and weather because they move solar energy from one place to another.This can cause the temperature in one place to decrease and the temperature in another place to increase.
Prevailing winds also affect the amount of precipitation an area gets.They can carry water vapor away from the oceans.The water vapor can condense and fall to the land somewhere far from the ocean.
The figure on top of the next page shows the major prevailing winds on Earth.Notice that most prevailing winds blow from west to east or from east to west.

ES 3d
The sun is the major source of energy for phenomena on the earth's surface, such as growth of plants, winds, ocean currents, and the water cycle.Seasons result from variations in the amount of the sun's energy hitting the surface, due to the tilt of the earth's rotation on its axis and the length of the day.

Word Help: major of great importance or large scale
Word Help: energy the ability to make things happen Word Help: phenomenon any fact or event that can be sensed or described scientifi cally (plural, phenomena)

TOPOGRAPHY
The sizes and shapes of the land-surface features of a region form its topography.The topography of an area affects its climate because topography can affect temperature and precipitation.For example, elevation is a feature of topography that can have a large impact on temperature.Elevation is the height of an area above sea level.As elevation increases, temperature tends to decrease.
Mountains can also affect precipitation.As air rises to move over a mountain, it cools.The cool air condenses, forming clouds.Precipitation may fall.This process causes the rain-shadow effect, which is illustrated in the figure below.
Air rises to flow over mountains.The air cools as it rises, and water vapor can condense to form clouds.The clouds can release the water as precipitation.Therefore, this side of the mountain tends to be wetter, with more vegetation.
The air on this side of the mountain contains much less water vapor.As the air sinks down the side of the mountain, it becomes warmer.The warm air absorbs moisture from the land.Therefore, this side of the mountain tends to be drier and more desert-like.

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Class Date What Is Climate? continued

LARGE WATER BODIES
Large bodies of water can affect an area's climate.Water absorbs and releases heat more slowly than land.This quality helps regulate the air temperature over the land nearby.This is why sudden temperature changes are not very common in areas near large bodies of water.
An example of this effect is the climate of Michigan.Michigan is surrounded by the Great Lakes.It has moremoderate temperatures than other places at the same latitude.However, the lakes also increase the humidity of the air.This can cause heavy snowfalls in the winter.

OCEAN CURRENTS
Surface currents can have a big effect on a region's climate.Surface currents are paths of flowing water found near the surface of the ocean.As surface currents move, they carry warm or cool water to different places.The temperature of the water affects the temperature of the air above it.For example, warm currents can heat the surrounding air.
An example of the effects of ocean currents on climate can be seen in Iceland.Iceland is an island near the Arctic Circle.The Gulf Stream, a warm surface current, flows past Iceland.The warm water in the Gulf Stream causes Iceland's climate to be fairly mild.In contrast, the island of Greenland is at a similar latitude but is not affected by the Gulf Stream.Greenland's climate is much colder than Iceland's.Each climate zone has a certain range of temperatures.The tropical zone, near the equator, has the highest temperatures.The polar zones, located at latitudes above 66.5°, have the lowest temperatures.

BIOMES
Each climate zone contains several different kinds of climates.The different climates are the result of topography, winds, and ocean currents.The different climates affect the organisms that live in an area.A large area with a certain climate and types of organisms is called a biome.
This map shows some of the major land biomes on Earth.After you read this section, you should be able to answer these questions:

Polar ice
• Where is the tropical zone?
• What are three biomes found in the tropical zone?

What Is the Tropical Zone?
Remember that latitudes near the equator receive more solar energy than other areas.The area between 23.5°N latitude and 23.5°S latitude receives the most solar energy.This region is called the tropical zone.It is also known as the Tropics.Because areas in the Tropics receive so much solar energy, they tend to have high temperatures.
There are three main biomes in the Tropics: tropical rain forest, tropical savanna, and tropical desert.All the tropical biomes have high temperatures.However, they receive different amounts of rain and have different types of soil.Therefore, different organisms live in each biome.The figure below shows where each of these biomes is found.

STUDY TIP
Compare After you read this section, make a chart comparing the three kinds of tropical biomes.

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Class Date The Tropics continued

TROPICAL RAIN FORESTS
Tropical rain forests are warm and wet.They are located close to the equator, so they receive about the same amount of solar energy all year long.Therefore, there is little difference between the seasons.
Tropical rain forests are homes to many different kinds of living things.Animals that live in tropical rain forests include monkeys, parrots, frogs, tigers, and leopards.Plants include mahogany trees, vines, ferns, and bamboo.
Many organisms live in tropical rain forests.When dead organisms decay, nutrients return to the soil.However, the nutrients are quickly used up by plants or washed away by rain.As a result, the soil is thin and poor in nutrients.

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Class Date The Tropics continued

TROPICAL DESERTS
A desert is an area that receives less than 25 cm of rainfall per year.Deserts are the driest places on Earth.Tropical desert plants, such as shrubs, are adapted to living in places with little water.Animals such as camels, lizards, snakes, and scorpions also have adaptations for living in the desert.
Most tropical deserts are very hot in the daytime.They can be up to 50°C (120°F) during the day.However, the temperatures at night may be much lower.Therefore, organisms that live in deserts are also adapted to changing temperatures.After you read this section, you should be able to answer these questions: • What biomes are found in the temperate zone?
• What biomes are found in the polar zone?
• What are two examples of microclimates?
What Is the Temperate Zone?
The climate zone between the tropical and the polar zones is the temperate zone.This zone extends from about 23.5° to about 66.5° north or south latitudes.Most of the continental United States is in the temperate zone.The temperate zone receives less solar energy than the Tropics.Therefore, temperatures in the temperate zone tend to be lower than those in the Tropics.
The four main biomes in the temperate zone are temperate forests, temperate grasslands, chaparrals, and temperate deserts.All of these biomes show seasonal changes in weather.However, some biomes have more extreme weather changes than others.For example, some areas in the United States have similar temperatures all year long.Other areas have very low temperatures in the winter and very high temperatures in the summer.Temperate forests tend to have high amounts of rainfall and large seasonal temperature differences.The summers are warm, and the winters are cold.Animals that live in temperate forests include foxes, deer, and bears.Some trees in temperate forests lose their leaves each winter.These trees are called deciduous trees.Other trees, called evergreens, do not lose all of their leaves at once.

STUDY TIP
The soils in most temperate forests are very rich in nutrients.This is because the deciduous trees drop their leaves every winter.As the leaves decay, nutrients are added to the soil.Of all the land biomes, temperate grasslands have the most fertile soil.As a result, much of the grassland on Earth has been plowed up to make room for crops.Temperate and Polar Zones continued

CHAPARRALS
Chaparral regions have cool, wet winters and hot, dry summers.Animals that live in the chaparral include mountain lions, coyotes, and quail.
Fires are common during the summers in chaparrals.Some chaparral plants are adapted to these fires.Chaparral plants also have adaptations that prevent water loss during dry conditions.For example, the main kinds of plants in the chaparral are evergreen shrubs.These shrubs have thick leaves with waxy coatings.The coatings help prevent the leaves from losing water.Like tropical deserts, temperate deserts are hot in the daytime and receive little rainfall.However, temperate deserts tend to have much colder nights than tropical deserts.This is because temperate deserts tend to have low humidity and cloudless skies.These conditions allow solar energy to heat the surface a lot during the day.They also allow heat to move into the atmosphere at night.
Plants that live in temperate deserts include cacti, shrubs, and thorny trees.Animals include lizards, snakes, bats, and toads.

What Is the Polar Zone?
The polar zone is located between 66.5° and 90° north and south latitudes, near the North and South Poles.This zone has the coldest temperatures of all climate zones.There are two biomes in the polar zone: tundra and taiga.

TUNDRA
The tundra has long, cold winters and short, cool summers.In the summer, only the top meter of soil thaws out.Below this depth is a permanently frozen layer called permafrost.It prevents water in the thawed soil from draining away.Therefore, the upper soil is muddy in the summer.Insects like mosquitoes thrive there.Birds migrate there in the summer to eat the insects.
Other animals that live in the tundra include caribou, reindeer, and polar bears.Only small plants, such as mosses, live in the tundra.Temperate and Polar Zones continued TAIGA Taiga biomes are found just south of tundra biomes in the Northern Hemisphere.The taiga has long, cold winters and short, warm summers.Animals that live in the taiga include moose, bears, and rabbits.
Evergreen trees called conifers, such as pine and spruce, are the main plants that grow in the taiga.The needle-like leaves from these trees contain acidic substances.When the needles die and decay on the ground, these substances make the soil acidic.Not very many plants can grow in acidic soils.Therefore, few plants grow on the forest floor of the taiga.Remember that latitude, topography, and water help determine the climate of an area.Local conditions can also affect the climate in smaller areas.A microclimate is the climate of a small area.Two examples of microclimates are alpine biomes and cities.
Alpine biomes are cold microclimates found near the tops of mountains.In winter, the temperatures are below freezing.In summer, they range from 10°C to 15°C.It is the high elevations of alpine biomes that cause them to be so cold.Alpine biomes are even found on mountains in the Tropics.
Cities are also microclimates.Buildings and pavement are made of dark materials.They absorb solar energy and stay warm.City temperatures can be 1°C to 2°C warmer than temperatures in other areas.

Say It
Share Experiences In a small group, talk about different biomes that you or your classmates have visited.After you read this section, you should be able to answer these questions:

Math Focus
• How has Earth's climate changed over time?
• What factors can cause climates to change?
How Was Earth's Climate Different in the Past?
The geologic record shows that Earth's climate in the past was different from its climate today.During some periods in the past, Earth was much warmer.During other periods, Earth was much colder.In fact, much of Earth was covered by sheets of ice during some times in the past.
An ice age happens when ice at high latitudes expands toward lower latitudes.Scientists have found evidence of many major ice ages in Earth's history.The most recent one began about 2 million years ago.
Many people think of an ice age as a time when the temperature is always very cold.However, during an ice age, there can be periods of colder or warmer weather.A period of colder weather is called a glacial period.A period of warmer weather is called an interglacial period.
During glacial periods, large sheets of ice grow.These ice sheets form when ocean water freezes.Therefore, sea level drops during glacial periods.The figure below shows the coastlines of the continents during the last glacial period.Notice that the continental coastlines extended further into the ocean than they do today.

CHANGES IN EARTH'S ORBIT
A Serbian scientist, Milutin Milankovitch, found that changes in Earth's orbit and tilt can affect Earth's climate.He modeled the way Earth moves in space and found that Earth's movements change in a regular way.These changes happen over tens of thousands of years.For example, Earth's orbit around the sun is more circular at some times than others.
These variations in Earth's orbit and tilt affect how much sunlight Earth gets.Therefore, they can also affect climate.The figure below shows how these factors can change the amount of sunlight Earth gets.
A circular orbit causes less variation in sunlight.
A less-circular orbit causes more variation in sunlight.Plate tectonics and continental drift also affect Earth's climate.When a continent is closer to the equator, its climate is warmer than when it is near the poles.Also, remember that continents can deflect ocean currents and winds.When continents move, the flow of air and water around the globe changes.These changes can strongly affect Earth's climate.

Pangaea
The locations of the continents can affect their climate.When India, Africa, South America, and Australia were part of Pangaea, they were covered with large ice sheets.

THE SUN
Some changes in Earth's climate are caused by changes in the sun.Many people think that the sun is always the same, but this is not true.In fact, the amount of energy that the sun gives off can change over time.The sun follows a regular cycle in how much energy it gives off.Because the sun's energy drives most cycles on Earth, these changes can affect Earth's climate.

IMPACTS
Sometimes, objects from outer space, such as asteroids, crash into Earth.An asteroid is a small, rocky object that orbits the sun.If a large asteroid crashed into Earth, the climate of the whole planet could change.
When a large object hits Earth, particles of dust and rock fly into the atmosphere.This material can block some sunlight from reaching Earth's surface.This can cause temperatures on Earth to go down.In addition, plants may not be able to survive with less sunlight.Without plants, many animals would die off.Many scientists believe that an asteroid impact may have caused the dinosaurs to become extinct.Much of the CO 2 in the atmosphere comes from natural processes, such as volcanic eruptions and animals breathing.However, human activities can also increase the amount of CO 2 in the atmosphere.
When people burn fossil fuels for energy, CO 2 is released into the atmosphere.When people burn trees to clear land for farming, CO 2 is released.In addition, plants use CO 2 for food.Therefore, when trees are destroyed, we lose a natural way of removing CO 2 from the atmosphere.

PROBLEMS WITH GLOBAL WARMING
Many scientists think that if global warming continues, the ice at Earth's poles could melt.This could cause sea levels to rise.Many low-lying areas could flood.Global warming could also affect areas far from the oceans.For example, the Midwestern part of the United States could become warmer and drier.Northern areas, such as Canada, may become warmer.

WHAT PEOPLE CAN DO
Many countries are working together to reduce the effects of global warming.Treaties and laws have helped to reduce pollution and CO 2 production.Most CO 2 is produced when people burn fossil fuels for energy.Therefore, reducing how much energy you use can reduce the amount of CO 2 produced.Here are some ways you can reduce your energy use: • Turn off electrical devices, such as lights and computers, when you are not using them.
• Ride a bike, walk, or take public transportation instead of using a car to travel.
• Turn the heater to a lower temperature in the winter.
• Turn the air conditioner to a higher temperature in the summer.

TAKE A LOOK 2 .
Explain Why do areas near the equator tend to have high temperatures?
three major climate zones are determined by latitude.

3 .
savannas, or grasslands, contain tall grasses and a few trees.The climate is usually very warm.Tropical savannas have two main seasons.The dry season lasts four to eight months.It is followed by a wet season that contains short periods of rain.Because savannas are often dry, fires are common.These fires can help to enrich the soil in the savanna.Many plants in the savanna have adapted to yearly fires and rely on them for growth.For example, some plants need fire to break open their seeds' outer skin.Animals that live in tropical savannas include giraffes, lions, crocodiles, and elephants.The figure on the top of the next page shows a tropical savanna.READING CHECK Explain Why is there little difference between the seasons in a tropical rain forest?TAKE A LOOK 4. Explain Why is the soil in tropical rainforests thin and nutrient-poor?Critical Thinking 5. Predict Consequences What could happen to a tropical savanna if people stopped all fi res from spreading?Explain your answer.Climate SECTION 2

TAKE A LOOK 5 . 6 .
Identify How was the climate of India different when it was part of Pangaea?READING CHECK Explain Why do changes in the sun's energy affect the climate on Earth?Critical Thinking

continued What Are the Different Climates Around the World?
Earth has three major climate zones: tropical, temperate, and polar.The figure below shows where these zones are found.

Section 1 Review NSES ES 1f, 1j, 3d SECTION VOCABULARY
2. Apply Concepts Nome, Alaska, lies at 64°N latitude.San Diego, California, lies at 32°N latitude.Which city receives more sunlight?Explain your answer.3. Explain What causes some places on Earth to have seasons?4. Identify What are four things that can affect climate? 5. Explain Describe how the rain-shadow effect works.SECTION 2 The Tropics CHAPTER 17

• Average Temperature Range 16°C to 50°C (61°F to 120°F) • Average Yearly Precipitation 0 cm to 25 cm • Soil Characteristics poor in organic matter Tropical Desert
What are the three biomes found in the Tropics?2.IdentifyWhat is one thing that all the biomes in the Tropics have in common?3.Compare Fill in the missing information about the features of each tropical biome.An area is located at 30°N latitude.It receives less than 25 cm per year of rain and has temperatures as high as 50°C during the day.Is the area a tropical desert?Explain your answer.
5. IdentifyOn which continent are most tropical savannas found?

Section 2 Review Climate SECTION 3 Temperate and Polar Zones
CHAPTER17

• Average Temperature Range 0°C to 28°C (32°F to 82°F) • Average Yearly Precipitation 76 cm to 250 cm • Soil Characteristics very fertile, organically rich Temperate Forest TEMPERATE GRASSLANDS
Temperate grasslands have warm summers and very cold winters.Few trees grow in temperate grasslands because they do not receive enough rain.Animals that live in temperate grasslands include bison and kangaroos.

• Average Temperature Range -6°C to 26°C (21°F to 78°F) • Average Yearly Precipitation 38 cm to 76 cm • Soil Characteristics most-fertile soils of all biomes Temperate Grassland
TAKE A LOOK4.Identify What is the main kind of plant that grows in temperate grasslands?

• Average Temperature Range 1°C to 50°C (34°F to 120°F) • Average Yearly Precipitation 0 cm to 25 cm • Soil Characteristics poor in organic matter Temperate Desert READING CHECK 5 Describe
What adaptation do evergreen shrubs in the chaparral have to survive dry conditions?READING CHECK 6. Compare How are temperate deserts different from tropical deserts?Give one way.
Scientists have several theories to explain ice ages and other forms of climate change.Factors that can cause climate change include Earth's orbit, plate tectonics, the sun's cycles, asteroid impacts, volcanoes, and human activities.

7 .
Identify RelationshipsWhy may animals die off if there are fewer plants around?