ALSO COVERS: MA.912.S.3.2 Defining...

376 Chapter 14 Climate

Section 1 144.1 .1

Objectives

Recognize limits associated with the use of normals.

Explain why climates vary. Compare and contrast tempera-

tures in different regions on Earth.

Review Vocabularyjet stream: a high-altitude, narrow, westerly wind band that occurs above large temperature changes

New Vocabularyclimatologynormaltropicstemperate zonespolar zones

Defining Climate

MAIN Idea Climate is affected by several factors including latitude and elevation.

Real-World Reading Link Just because you observed someone eating a steak dinner, you probably would not assume that they ate steak for every meal. In nature, taking a one-day snapshot of the weather does not necessarily describe what that location experiences over the course of many days.

Annual Averages and VariationsFifty thousand years ago, the United States had much different weather patterns than those that exist today. The average tempera-ture was several degrees cooler, and the jet stream was probably far-ther south. Understanding and predicting such climatic changes are the basic goals of climatology. Climatology is the study of Earths climate and the factors that affect past, present, and future climatic changes.

Climate describes the long-term weather patterns of an area. These patterns include much more than average weather condi-tions. Climate also describes annual variations of temperature, pre-cipitation, wind, and other weather variables. Studies of climate show extreme fluctuations of these variables over time. For exam-ple, climatic data can indicate the warmest and coldest tempera-tures recorded for a location. Figure 14.1 shows weather differences between summer and winter in Chicago, Illinois. This type of information, combined with comparisons between recent conditions and long-term averages, can be used by businesses to decide where to build new facilities and by people who have medi-cal conditions that require them to live in certain climates.

Figure 14.1 Climate data include the warmest and coldest temperatures recorded for a location. The highest temperature on record for Chicago, IL, is 40C, which occurred in June 1988. The lowest temperature on record for Chicago, IL, is 33C, which occurred in January 1985.

Chicago, IL, in the summer Chicago, IL, in the winter

(l)Kelly-Mooney Photography/CORBIS, (r)Charles Bennett/AP Images

SC.912.E.7.1: Analyze the movement of matter and energy through the different biogeochemical cycles, including water and carbon. SC.912.E.7.3: Differentiate and describe the various interactions among Earth systems, including: atmosphere, hydrosphere, cryosphere, geosphere, and biosphere. SC.912.E.7.4: Summarize the conditions that contribute to the climate of a geographic area, including the relationships to lakes and oceans. ALSO COVERS: MA.912.S.3.2

Section 1 Defining Climate 377

Careers In Earth Science

Climatologist Scientists who study long-term trends in climate are called climatologists. Climatologists might collect data by drilling holes in ice or sampling ocean water temperatures. To learn more about Earth science careers, visit glencoe.com.

Normals The data used to describe an areas climate are compiled from meteorological records, which are continuously gathered at thousands of locations around the world. These data include daily high and low temperatures, amounts of rainfall, wind speed and direction, humidity, and air pressure. The data are averaged on a monthly or annual basis for a period of at least 30 years to determine the normals, which are the standard values for a location.

Reading Check Identify data that can be used to calculate normals.

Limitations of normals While normals offer valuable informa-tion, they must be used with caution. Weather conditions on any given day might differ widely from normals. For instance, the nor-mal high temperature in January for a city might be 0C. However, it is possible that no single day in January had a high of exactly 0C. Normals are not intended to describe usual weather condi-tions; they are the average values over a long period of time.

While climate describes the average weather conditions for a region, normals apply only to the specific place where the meteoro-logical data were collected. Most meteorological data are gathered at airports, which cannot operate without up-to-date, accurate weather information. However, many airports are located outside city limits. When climatic normals are based on airport data, they might differ from actual weather conditions in nearby cities. Changes in elevation and other factors, such as proximity to large bodies of water, can cause climates to vary.

Data A y lab Data Analysis labBased on Real Data*Interpret the Data

What is the temperature in Phoenix, Arizona? The table contains temperature data for Phoenix, Arizona, based on data collected from July 1, 1948, through December 31, 2005.

Analysis1. Plot the monthly values for average maxi-

mum temperatures. Place the month on the x-axis and temperature on the y-axis.

2. Repeat Step 1 using the monthly values for the average minimum temperatures.

Think Critically3. Identify the months that were warmer than

the average maximum temperature.4. Identify the months that were colder than

the average minimum temperature.5. Infer What is the climate of Phoenix,

Arizona, based on average temperatures?

Monthly Temperature Summary for Phoenix, AZ

Temperature (C) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average

Average maximum 19 21 24 29 34 39 41 39 37 31 24 19 29.8

Average minimum 5 7 9 13 18 22 27 26 22 16 9 6 15

*Data obtained from: Western Regional Climate Center. 2005.

Data and Observations

SC.912.E.7.4: Summarize the conditions that contribute to the climate of a geographic area, including the relationships to lakes and oceans. MA.912.S.3.2: Collect, organize, and analyze data sets, determine the best format for the data and present visual summaries from the following: bar graphs, line graphs, stem and leaf plots, circle graphs, histograms, box and whisker plots, scatter plots, cumulative frequency (ogive) graphs.

http://glencoe.mcgraw-hill.com/sites/0078746361/student_view0/unit4/chapter14/web_links.html

Suns rays

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Temperate zones Polar zones

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Causes of ClimateYou probably know from watching the weather reports that cli-mates around the country vary greatly. For example, on average, daily temperatures are much warmer in Dallas, Texas, than in Minneapolis, Minnesota. There are several reasons for such cli-matic variations, including differences in latitude, topography, closeness of lakes and oceans, availability of moisture, global wind patterns, ocean currents, and air masses.

Latitude Recall that different parts of Earth receive different amounts of solar radiation. The amount of solar radiation received by any one place varies because Earth is tilted on its axis, and this affects how the Suns rays strike Earths surface. The area between 23.5 S and 23.5 N of the equator is known as the tropics. As Figure 14.2 shows, tropical areas receive the most solar radiation because the Suns rays are nearly perpendicular to Earths surface. As you might expect, temperatures in the tropics are generally warm year-round. For example, Caracas, Venezuela, located at about 10 N, enjoys average maximum temperatures between 24C and 27C year-round. The temperate zones lie between 23.5 and 66.5 north and south of the equator. As their name implies, tem-peratures in these regions are moderate. The polar zones are located from 66.5 north and south of the equator to the poles. Solar radiation strikes the polar zones at a low angle. Thus, polar temperatures tend to be cold. Thule, Greenland, located at 77 N, has average maximum temperatures between 20C and 8C year-round.

Figure 14.2 Latitude has a great effect on climate. The amount of solar radiation received on Earth decreases from the equator to the poles.Describe what happens to the angle at which the Suns rays hit Earths surface as one moves from the equator to the poles.

VOCABULARYACADEMIC VOCABULARYImplyto indicate by association rather than by direct statementThe title of the movie implied that it was a love story.

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As air on the windward side of a mountain risesand cools, it condensesand precipitation occurs.

Dry air warms as itdescends the leewardside of a mountain,commonly resultingin desert conditions.

Cloud

Windward sideCool and wet

Leeward sideWarm and dry

Rain

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Section 1 Defining Climate 379

Topographic effects Water heats up and cools down more slowly than land. Thus, large bodies of water affect the climates of coastal areas. Many coastal regions are warmer in the winter and cooler in the summer than inland areas at similar latitudes.

Also, temperatures in the lower atmosphere generally decrease with altitude. Thus, mountain climates are usually cooler than those at sea level. In addition, climates often differ on either side of a mountain. Air rises up one side of a mountain as a result of oro-graphic lifting. The rising air cools, condenses, and drops its mois-ture, as shown in Figure 14.3. The climate on this side of the mountain the windward side is usually wet and cool. On the opposite side of the mountain the leeward side the air is drier, and it warms as it descends. For this reason, deserts are common on the leeward side of mountains.

Reading Check Explain how large bodies of water affect the climate of coastal areas.

Figure 14.3 Orographic lifting leads to rain on the windward side of a mountain. The leeward side is usually dry and warm.

Windward side of mountains on Maui, Hawaii Leeward side of mountains on Maui, Hawaii

(l)Mike Severns/Getty Images, (r)Bill Ross/CORBIS


Self-Check Quiz glencoe.com

Major Air Masses Over North America

Maritimepolar

Continentalpolar

Continentaltropical

Maritimetropical

Maritimetropical

Maritimetropical

(Atlantic)

Maritimepolar

Arctic

Cool,humid

Cool,humid

Warm,humid

Warm,humid

Warm,humid

Dry,hot

Dry


Air masses Two of the main causes of weather are the movement and interaction of air masses. Air masses also affect climate. Recall from Chapter 12 that air masses have distinct regions of origin, caused primarily by differences in the amount of solar radiation. The properties of air masses also depend on whether they formed over land or water. The air masses commonly found over North America are shown in Figure 14.4.

Average weather conditions in and near regions of air-mass formation are similar to those exhibited by the air masses themselves. For example, consider the island of Dominica, shown in Figure 14.4, in the tropical Atlantic Ocean. Because this island is located in an area where maritime tropical (mT) air masses dominate, the islands climate has maritime tropical characteristics, such as warm temperatures, high humidity, and high amounts of precipitation.

Section 1 144..11 AssessmentSection Summary Climate describes the long-term

weather patterns of an area.

Normals are the standard climatic values for a location.

Temperatures vary among tropical, temperate, and polar zones.

Climate is influenced by several dif-ferent factors.

Air masses have distinct regions of origin.

Understand Main Ideas1. MAIN Idea Describe two factors that cause variations in climate.

2. Identify What are some limits associated with the use of normals?

3. Compare and contrast temperatures in the tropics, temperate zones, and polar zones.

4. Infer how climate data can be used by farmers.

Think Critically5. Assess Average daily temperatures for City A, located at 15 S, are 5C cooler

than average daily temperatures for City B, located at 30 S. What might account for the cooler temperatures in City A, even though it is closer to the equator?

Earth Science

6. Write a hypothesis that explains why meteorological data gathered at an airport would differ from data gathered near a large lake. Assume all other factors are constant.

Figure 14.4 Air masses affect regional climates by transport-ing the temperature and humidity of their source regions. The warm and humid maritime tropical air mass supports the lush vegetation on the island of Dominica.

Lush vegetation on the Caribbean island of Dominica

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Section 2 Climate Classification 381

Section 1 4.14.2 2

Objectives

Describe the criteria used to clas-sify climates.

Compare and contrast different climates.

Explain and give examples of microclimates.

Review Vocabularyprecipitation: all solid and liquid forms of water including rain, snow, sleet, and hail that fall from clouds

New VocabularyKppen classification systemmicroclimateheat island

Climate Classification

MAIN Idea Climates are categorized according to the average temperatures and precipitation amounts.

Real-World Reading Link What sort of place comes to mind when you think of a vacation in a tropical climate? A place with hot weather and a lot of rain? If so, you already know something about a tropical climate, even if you have never visited one.

Kppen Classification SystemThe graph on the left in Figure 14.5 shows climate data for a desert in Reno, Nevada. The graph on the right shows climate data for a tropical rain forest in New Guinea. What criteria are used to classify the climates described in the graphs? Temperature is an obvious choice, as is amount of precipitation. The Kppen classification system is a classification system for climates that is based on the average monthly values of temperature and precipitation. Developed by German climatologist Wladimir Kppen, the system also takes into account the distinct vegetation found in different climates.

Kppen decided that a good way to distinguish among different cli-matic zones was by natural vegetation. Palm trees, for instance, are not located in polar regions, but instead are largely limited to tropical and subtropical regions. Kppen later realized that quantitative values would make his system more objective and therefore more scientific. Thus, he revised his system to include the numerical values of temper-ature and precipitation. A map of global climates according to a modi-fied version of Kppens classification system is shown in Figure 14.6.

Precipitation Temperature

Reno, Nevada

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Figure 14.5 These graphs show tem-perature and precipitation for two different climates a desert in Reno, Nevada, and a tropical rain forest in New Guinea.Describe the difference in temperature between these two climates.

SC.912.E.7.4: Summarize the conditions that contribute to the climate of a geographic area, including the relationships to lakes and oceans.

Master Page used: NGS


Visualizing Worldwide Climates

Figure 14.6 Kppens classification system, shown here in a modified version, is made up of five main divisions based on temperature and precipitation.Estimate Use the map to determine the approximate percentage of land cov-ered by tropical wet climates.

Tropical climates

Tropical wetTropical wet and dry

Dry climates

SemiaridArid

Mild climatesMediterraneanHumid subtropicalMarine west coast

Continental climatesWarm summerCool summerSubarctic

Polar climates

TundraIce capHighland

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75 7560 6045 4530 3015 15090 90105 105120 120135 135150 150165 165

To explore more about climate classification, visit glencoe.com.

Highland polar climate, Canada

Arid dry climate, Australia

Semiarid dry climate, Argentina

(tl)John E Marriott/Alamy Images, (tr)Theo Allofs/zefa/CORBIS, (br)Michael Lewis/CORBIS


http://glencoe.com/sec/science/earthscience/2007/concept_motion/NGS/Visualizing_Worldwide_Climates_14.swf


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Normanton, Australia

3632282420161284

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Tropical climates Year-round high temperatures characterize tropical climates. In tropical wet climates, the locations of which are shown in Figure 14.6, high temperatures are accompanied by up to 600 cm of rain each year. The combination of warmth and rain produces tropical rain forests, which contain some of the most dramatic vegetation on Earth. Tropical regions are almost continu-ally under the influence of maritime tropical air.

The areas that border the rainy tropics to the north and south of the equator are transition zones, known as the tropical wet and dry zones. Tropical wet and dry zones include savannas. These tropical grasslands are found in Africa, among other places. These areas have distinct dry winter seasons as a result of the occasional influx of dry continental air masses. Figure 14.7 shows the average monthly temperature and precipitation readings for Normanton, Australia a savanna in northeast Australia.

Reading Check Explain the difference between tropical wet and tropical wet and dry climate zones.

Dry climates Dry climates, which cover about 30 percent of Earths land area, make up the largest climatic zone. Most of the worlds deserts, such as the Sahara, the Gobi, and the Australian, are classified as dry climates. In these climates, continental tropical (cT) air dominates, precipitation is low, and vegetation is scarce. Many of these areas are located near the tropics. Thus, intense solar radiation results in high rates of evaporation and few clouds. Overall, evaporation rates exceed precipitation rates. The resulting moisture deficit gives this zone its name. Within this classification, there are two subtypes: arid regions, called deserts, and semiarid regions, called semideserts. Semideserts, like the one shown in Figure 14.8, are usually more humid than deserts. They generally separate arid regions from bordering wet climates.

Figure 14.7 The graph shows the temperature and precipitation readings for a tropical savanna in Australia.Analyze How does the rainfall in this area differ from that of a tropi-cal rain forest?

Figure 14.8 This semidesert in Kazakhstan is another example of a transi-tion zone. It separates deserts from border-ing climates that are more humid.

Wolfgang Kaehler/Alamy Images



Mild climates Mild climates can be classified into three sub-types: humid subtropical climates, marine west-coast climates, and Mediterranean climates. Humid subtropical climates are influenced by the subtropical high-pressure systems that are normally found over oceans in the summer. The southeastern United States has this type of climate. There, warm, muggy weather prevails during the warmer months and dry, cool conditions predominate during the winter. The marine west-coast climates are dominated by the con-stant inland flow of air off the ocean, which creates mild winters and cool summers, with abundant precipitation throughout the year. Mediterranean climates, named for the climate that characterizes much of the land around the Mediterranean Sea, are also found in California and parts of South America. An example of this type of climate is shown in Figure 14.9. Summers in Mediterranean cli-mates are generally warm and dry because of their nearness to the dry midlatitude climates from the south. Winters are cool and rainy as a result of the midlatitude weather systems that bring storm sys-tems from the north.

Reading Check Compare and contrast humid subtropical and marine west-coast climates.

Continental climates Continental climates are also classified into three subtypes: warm summer climates, cool summer climates, and subarctic climates. Tropical and polar air masses often form fronts as they meet in continental climates. Thus, these zones experience rapid and sometimes violent changes in weather, including severe thunderstorms or tornadoes like the one shown in Figure 14.10.Both summer and winter temperatures can be extreme because the influence of polar air masses is strong in winter, while warm tropical air dominates in summer. The presence of warm, moist air causes summers to be generally more wet than winters, especially in latitudes that are relatively close to the tropics.

Figure 14.9 Olive trees thrive in the warm, dry summers and cool, rainy winters of the Mediterranean climate of Huesca, Spain.

Figure 14.10 Tornadoes, such as this one in Kansas, occur in continental climates.

(t)age fotostock/SuperStock, (b)Eric Nguyen/Jim Reed Photography/Photo Researchers


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FOLDABLESIncorporate information from this section into your Foldable.


Polar climates To the north of subarctic climate lies one of the polar climates the tundra. Just as the tropics are known for their year-round warmth, tundra is known for its low temperatures the mean temperature of the warmest month is less than 10C. There are no trees in the tundra and precipitation is generally low because cold air contains less moisture than warm air. Also, the amount of heat radiated by Earths surface is too low to produce the strong convection currents needed to release heavy precipita-tion. The ice-cap polar climate, found at the highest latitudes in both hemispheres, does not have a single month in which average temperatures rise above 0C. No vegetation grows in an ice-cap climate and the land is permanently covered by ice and snow. Figure 14.11 shows an ice-cap polar climate.

A variation of the polar climate, called a highland climate, is found at high elevations. This type of climate includes parts of the Andes Mountains in South America, which lie near the equator. The intense solar radiation found near such equatorial regions is offset by the decrease in temperature that occurs with altitude.

MicroclimatesSometimes the climate of a small area can be much different than that of the larger area surrounding it. A localized climate that differs from the main regional climate is called a microclimate. If you climb to the top of a mountain, you can experience a type of microclimate; the cli-mate becomes cooler with increasing elevation. Figure 14.12 shows a microclimate created by the buildings and concrete in a city.

Heat islands Sometimes the presence of buildings can create a microclimate in the area immediately surrounding it. Many concrete buildings and large expanses of asphalt can create a heat island,where the climate is warmer than in surrounding rural areas, as shown in Figure 14.12. This effect was first recognized in the early nineteenth century when Londoners noted that the temperature in the city was noticeably warmer than in the surrounding countryside.

Figure 14.12 This diagram shows the difference in temperature between the downtown area of a city and the surround-ing suburban and rural areas.Analyze How much warmer is it in the city compared to the rural areas?

Figure 14.11 Icebergs float in the sea in the ice-cap polar climate of Greenland.

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Self-Check Quiz glencoe.com

Urban Suburban


Pavement, buildings, and roofs made of dark materials, such as asphalt, absorb more energy from the Sun than surrounding vege-tation. This causes the temperature of these objects to rise, heating the air around them. This also causes mean temperatures in large cities to be significantly warmer than in surrounding areas, as shown in Figure 14.13. The heat-island effect also causes greater changes in temperature with altitude, which sparks strong convec-tion currents. This, in turn, produces increased cloudiness and up to 15 percent more total precipitation in cities.

Heat islands are examples of climatic change on a small scale. In Sections 14.3 and 14.4, you will examine large-scale climatic changes caused by both natural events and human activities.

Section 1 14 .4.22 AssessmentSection Summary German scientist Wladimir Kppen

developed a climate classification system.

There are five main climate types: tropical, dry, mild, continental, and polar.

Microclimates can occur within cities.

Understand Main Ideas1. MAIN Idea Describe On what criteria is the Kppen climate classification

system based?

2. Explain What are microclimates? Identify and describe one example of a microclimate.

3. Compare and contrast the five main climate types.

4. Categorize the climate of your area. In which zone do you live? Which air masses generally affect your climate?

Think Critically5. Construct Make a table of the Kppen climate classification system. Include

major zones, subzones, and characteristics of each.

Earth Science

6. Write a short paragraph that explains which of the different climate types you think would be most strongly influenced by the polar jet stream.

Figure 14.13 These thermal images show differences in daytime temperatures between an urban area and a suburban area. The coolest temperatures are represented by blue; the warmest temperatures are repre-sented by red.

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