I. Climate and Weather
pages 55–56A.
Weather is the condition of the atmosphere in a certain place at aspecific time. (p. 55)
B.
The climate of an area is its long-term typical weather pattern. (p. 55)C.
The climate of an area is determined by many things; the most importantis the earth’s position in relation to the sun. (p. 56)
Discussion Question
Think about your location and the earth’s relationship to the sun. How does the earthsun
relationship affect your life?
(Answers may vary somewhat depending on location. Students should demonstrate an
understanding of climate and its effects on food, clothing, housing, energy consumption, and
transportation, among many other factors.)
II. Earth’s Tilt and Rotation
page 56Earth’s axis is currently tilted at an angle of about 23
1/2°. Because of the tiltof this axis, not all places on Earth receive the same amount of direct sunlight
at the same time. (p. 56)
Discussion Question
Which places on Earth receive the most direct sunlight? How does this phenomenon
affect their climates?
(Regions in the tropics receive the most direct sunlight. These regions are generally warm
or hot year-round, depending on their elevation.)
III. Earth’s Revolution
page 56A.
Earth travels in an orbit around the sun, completing one trip aboutevery 365 days. (p. 56)
B.
The seasons are caused by the earth’s revolution around the sun andthe earth’s tilt. (p. 56)
C.
The Equator divides Earth into the Northern and Southern Hemispheres.When one hemisphere experiences winter, the other experiences summer.
(p. 56)
Discussion Question
How does the reversal of seasons in the Northern and Southern Hemispheres affect
the lives of people on Earth?
(Accept reasonable responses. Students might note, for example, that food crops can be
produced year-round, so fresh fruits and vegetables generally are available all year long.)
IV. The Tropics of Cancer and Capricorn
pages 56–57The line of latitude at 23
1\2°N is called the Tropic of Cancer—the northernmostlatitude on the earth to receive the sun’s direct rays. (p. 56) The line of latitude
at 23
1\2°S is called the Tropic of Capricorn—the southernmost latitude toreceive the sun’s direct rays. (p. 57)
Discussion Question
What do you think the climate is like in the tropics? Why do you think so?
(Because the tropics receive direct sunlight all the time, they are probably very warm year-round.)
V. The Poles
pages 57–58The North Pole and the South Pole are located at either end of the earth’s
axis. Each Pole receives continuous indirect sunlight six months each year.
While one receives continuous sunlight, the other receives little to no
sunlight. (p. 57)
Discussion Question
Why do very few people live in polar climate areas?
(Accept reasonable responses. Students may mention extreme temperatures, frozen soils
which cannot support crops, great variations in light, and frozen precipitation.)
VI. The Greenhouse Effect
page 58A.
Part of the sun’s radiation passes through Earth’s atmosphere. Like theglass in a greenhouse, the atmosphere keeps the heat from escaping
back into space too quickly. (p. 58)
B.
Humans have altered Earth’s atmosphere by burning fuels that releasecarbon dioxide and other greenhouse gases into the atmosphere. They
also have cut down the forests that absorb carbon dioxide. (p. 58)
C.
Many scientists claim that in recent decades rising carbon dioxide levelshave coincided with a rise in global temperatures. This trend known as
global warming is believed to be caused in part by human activities,
such as the burning of coal, oil, and natural gas. As more fossil fuels
are burned, greenhouse gases enter the atmosphere and trap more
heat. (p. 58)
Discussion Question
How might global warming affect your community over the course of the next several
years?
(Answers will vary according to local climate conditions. Sample answer: It will rain in the
winter instead of snowing. Temperatures will be hotter year-round. People will stay indoors
more in the summertime because it will be too hot to go outside. Local vegetation will change
as the climate changes. Patterns of precipitation may change, causing floods or droughts.
Rising sea levels may flood low-lying areas along coasts.)
I. Latitude and Climate
pages 59–61A. Low Latitudes
The low latitudes are between the Tropic of Cancer and the Tropic
of Capricorn. Portions of the low latitudes receive direct sunlight
year-round. (p. 60)
B. High Latitudes
The high latitudes are the polar areas. They receive continuous but
indirect sunlight for six months each year, and the climate is always cold.
(p. 60)
C. Mid-Latitudes
The mid-latitudes are the zones between the Tropics and the polar
areas. They have a temperate climate ranging from fairly hot to fairly
cold, with dramatic seasonal changes. (pp. 60–61)
Discussion Question
Which zone would you prefer to live in? Why?
(Some students will say the low latitudes because the weather is always warm and sunny.
Others will like the change of seasons that comes in the mid-latitudes. Most will agree that
the high latitudes are too cold and dark.)
II. Elevation and Climate
page 61A.
The higher the altitude of a place, the colder its climate will be. (p. 61)B.
At high altitudes, the air is thinner and retains less heat.
Discussion Question
Explain why high mountaintops are always covered by snow, even in the Tropics.
(The thinner atmosphere in higher altitudes retains less heat. Therefore, temperatures are
lower at high altitudes. If the mountaintops are high enough, it will always be too cold for
the snow to melt.)
III. Wind and Ocean Currents
pages 61–63A. Wind Patterns
Prevailing winds, global winds that blow in fairly constant patterns, are
affected by the direction of the earth’s rotation and latitude. The trade
winds of the tropics blow diagonally toward the Equator. The westerlies
of the middle latitudes blow diagonally from west to east. The polar
easterlies of the high latitudes blow diagonally from east to west. (p. 62)
B. The Horse Latitudes
At the Equator is a narrow, generally windless band called the doldrums.
Just north and south of the Tropics are other narrow bands of calm air.
Wind-powered sailing ships were in danger if they were stranded in
these windless areas. To lighten their vessels in order to take advantage
of any breeze, livestock were thrown overboard, which accounts for the
name
horse latitudes. (p. 62)
C. Ocean Currents
Ocean currents move warm and cold water just as winds move warm
and cold air. (p. 62)
D. Weather and the Water Cycle
A drop in temperature causes the water vapor in the atmosphere to
form clouds and eventually to condense and fall as rain or snow. (p. 62)
E. El Niño
A periodic reversal of the pattern of mid-Pacific ocean currents and water
temperatures can cause trade winds to diminish or even change direction,
leading to worldwide climate alterations. This phenomenon is called El
Niño. It has become more frequent and may be linked to global warming.
(p. 63)
Discussion Question
Why is an El Niño year a bad year for most people across the globe?
(Farmers depend on the weather and have learned to adapt to normal climate variations.
They choose certain crops and plant at certain seasons, according to their knowledge of local
weather patterns. In an El Niño year, the weather may be dramatically different, causing crop
failures and therefore food shortages. El Niño years also may cause damaging storms or
severe droughts.)
IV. Landforms and Climate
pages 63–64A.
Earth’s surface features, such as mountains and bodies of water, canaffect and be affected by climate. (p. 63)
B.
Large bodies of water are slower to heat and cool than land, so bodiesof water tend to moderate coastal land temperatures. (p. 63)
C.
When wind meets a mountain range, it is forced upward. This rising aircools and brings precipitation to the windward side (the side facing the
wind) of the range. After the rain falls on the windward side, the air is
warmer and drier as it descends on the leeward side (the side facing
away from the wind) of the mountain range. Areas on the leeward
sides of mountains receive little precipitation and are often very dry
because of this rain shadow effect. (p. 64)
Discussion Question
What kinds of effects do El Niño phenomena have on the earth’s people?
(Accept reasonable answers. Students may say that increased precipitation and warmer
winters along the coasts of North and South America, for example, cause flooding in some
areas, increase storm damage, lead to crop failures from drought, and make desert areas
bloom with wildflowers. Droughts in Southeast Asia and Australia cause massive forest fires,
and their smoke spawns additional weather phenomena and adversely affects human health.)
I. Climate Regions
pages 65–69A. Tropical Climates
Tropical climates are found in or near the low latitudes. The two types
of tropical climates are tropical rain forest and tropical savanna. (p. 66)
Tropical rain forests are densely wooded areas that are hot and wet
year-round. Tropical savannas are grasslands that are hot year-round,
dry in winter, and wet in summer. (p. 67)
B. Dry Climates
Dry climates include deserts and steppes. Deserts are always dry with
sparse vegetation; temperatures vary greatly from day to night and season
to season, and rainfall is 10 inches (about 25 cm) or less per year. Steppes
are dry grasslands that receive from 10 to 20 inches (25 to 51 cm) of
rain annually. (p. 67)
C. Mid-latitude Climates
Earth’s mid-latitude climates include four temperate climate regions.
Regions with a marine west coast climate are cool in summer, damp
in winter, and forested. Mediterranean climate regions have mild, rainy
winters and hot, sunny summers. Humid subtropical climate regions have
short, mild winters and year-round rain. Those having humid continental
climates are inland; ocean currents do not moderate their climates. Winters
in these areas are generally cool to very cold; summers are hot. (p. 68)
D. High Latitude Climates
The surfaces of ice cap regions are constantly covered with snow and
ice. Tundra climate regions are slightly warmer than ice cap regions
and can support short grasses. Subarctic climate regions, experiencing
bitterly cold winters, have a long enough growing season for needled
evergreens. (pp. 68–69)
E. Highlands Climates
At high altitudes, climates vary with elevation. The higher the altitude,
the cooler the temperatures. The natural vegetation of these areas also
varies with elevation. (p. 69)
I. Climate Regions
pages 65–69
Discussion Question
Which of the climate regions do you think are most heavily populated? Why do you
think so?
(Mid-latitude climate regions tend to be temperate, and the tropical climate regions are
generally warm to hot with lush vegetation. Mid-latitude and tropical regions are the most
heavily populated.)
II. Climatic Changes
page 69A.
Climates change gradually over time. (p. 69)
B.
Humans have altered climates by burning fossil fuels, building dams,and cutting down forests. (p. 69)
Discussion Question
Give an example of one change you think humans have made to climates.
(Accept reasonable responses. One possible answer: People build a dam to irrigate a dry area
in which they want to farm. The dam may cause new areas to flood or dry out, and this
may affect climate over time.)