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CHAPTER 2
Weather, Climate, and Climate Change
Weather, Climate, and Climate Change starts with the roles of solar radiation and movements of
Earth in determining patterns of weather and climate. Following an explanation of heat storage,
transfer, and exchange is a discussion of the causes of different types of precipitation. Circulation
patterns related to atmospheric pressure variations emphasizing the four zones of global
circulation, seasonal variations, effects on ocean currents, and regional storms are covered next.
Then the role of temperature and precipitation in describing climate is explained. The
classification and description of Earth’s many important climate regions precede a concluding
section on climate change emphasizing causes and consequences of global warming.
A Global and Local box discusses El Niño/La Niña, whereas a Rapid Change box examines
Warming in West Antarctica.
Learning Outcomes
After carefully studying this chapter, students should be able to:
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Describe the difference between weather and climate
List the ways that solar energy varies in time and space, and how it affects the weather
Discuss convection and its relationship to weather
Describe fronts, including the difference between a cold front and a warm front
Describe the general circulation patterns of the atmosphere
Describe oceanic circulation patterns
Explain the purpose of classifying climates, and major climate types
Describe three major causes of climate change
Chapter Review
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Weather is day-to-day conditions; climate is the summary of weather over time.
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Energy and Weather
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Solar energy drives atmospheric processes creating patterns of weather and climate.
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Earth’s orbit around the Sun, tilt, and rotation affect the insolation or amount of solar
energy at a particular location. The angle at which the Sun’s rays strikes Earth’s
surface is the angle of incidence. The more perpendicular the angle of incidence, the
more solar energy received. The number of hours a day of sunlight depends on
latitude and season. Places tilted toward the Sun have more hours of sunlight. There
are always 12 hours of daylight and 12 hours of night at the equator.
Water stores more heat than land. Land temperatures are more changeable and
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extreme.
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Solar energy is radiant energy. Radiant energy is energy transmitted by
electromagnetic waves. Most insolation is shortwave radiation where successive
waves are close together, whereas most of the energy reradiated back into space is
longwave. The atmosphere contains greenhouse gases that allow shortwave to reach
the surface, but block a portion of the outgoing longwave.
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Latent heat is heat stored in the different states of water and is often responsible for
large transfers of energy.
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Convection occurs when part of a fluid is heated. Heated air will rise and cooled air
will descend. Rising or descending air causes advection, the horizontal movement of
air. Differences in insolation cause differences in heating and cooling, which in turn
produce many of the basic patterns of the atmosphere.
Precipitation
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Humans expect precipitation amounts to be normal. Droughts, floods, and other
problems occur when precipitation is not what is expected.
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Precipitation occurs when there is enough condensation around tiny particles in
clouds. Condensation occurs when the pressure of moisture in the air exceeds
saturation.
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There are three ways precipitation develops. Convectional has humid air heated
near the surface, rising, being cooled adiabatically, latent heat being released,
more rising, more cooling, and ultimately precipitation often in a thunderstorm.
Orographic is caused when air is pushed upward over mountains. Cooling leads to
condensation and precipitation, especially on the windward side. The leeward side has
a rain shadow. Frontal is when warm air rises over cool air when air masses meet.
Again the warm air is cooled and precipitation results.
Circulation Patterns
· Atmospheric pressure reflects the weight of the atmosphere’s air above a given point.
Differences in pressure create wind.
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The Coriolis effect is the deflection of air due to the rotation of Earth. Deflection to
the right, or clockwise, exists in the Northern Hemisphere. The opposite is true for the
Southern Hemisphere.
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Global scale convection creates the intertropical convergence zone, trade winds,
subtropical high-pressure zones, westerlies, midlatitude low-pressure zones, polar
easterlies, and polar high-pressure zones. For example, in the polar regions, cold causes
dense air, high pressure, and outward (toward the equator) moving winds that are
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deflected by the Coriolis effect.
The tilt of Earth causes seasonal shifts in the previously mentioned zones and the winds.
January and July can be compared. The monsoon circulation of South Asia has winter
high pressure over Asia creating land to sea winds that allow little rain and summer low
pressure over Asia yielding sea to land winds that produce much rain (the monsoon).
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Winds and differences in water temperature and in salinity produce ocean currents
and ocean circulation patterns. For example, the Gulf Stream moves northward along
the east coast of North America, bringing heat into the north Atlantic. When El Niño
occurs, weather patterns change.
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Tropical cyclones (hurricanes), midlatitude cyclones, and tornadoes are storms that
start as low-pressure centers with rising air. Hurricane-induced storm surges are often
very devastating.
Climate
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Climate is the summary of weather conditions over many years. Climate affects the
vegetation, natural resources, and human activities of an area. Climate changes over
time due to natural processes and human actions.
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Air temperature and precipitation are the two most important aspects of climate. Both
vary over time and location in response to many factors such as insolation, elevation,
and movements of air masses. Humans need to adapt to variations in temperature and
precipitation.
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Water availability in an area is also affected by transpiration by plants.
Classifying Climate
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Climates are classified using temperature, precipitation, and vegetation information.
The Köppen scheme with five basic climates and letter codes is most commonly used.
Earth’s Climate Regions
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Humid tropical, seasonally humid tropical, desert, semiarid, humid subtropical,
marine west coast, Mediterranean, humid continental, subarctic, tundra, and ice-cap
are the 11 principal climates that are described.
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A climograph is provided for a representative location for each type of climate.
Climate Change
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Climate changes in response to temperature change over geologic time. The
Quaternary Period has had relatively many periods of warmer temperatures
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followed by colder ones. The last period of colder temperatures and glaciation
peaked about 18,000 years ago. Currently, Earth is in a warmer period.
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Astronomy and geology offer possible natural reasons for climate change.
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Humans contribute to climate change by adding to the amount of carbon dioxide
in the atmosphere. Burning of fossil fuels is a major contributor.
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Based on climate models, consensus exists that Earth is warming, but there is much
uncertainty concerning details and logical responses. Tipping points may be reached,
leading to rapid or irreversible changes. Ice in the Arctic and Greenland is melting.
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Responses to global warming include adapting to the warmer conditions, reducing
carbon emissions to slow the process, and geoengineering the atmosphere to reduce the
warming. Dealing with global warming will be expensive.
Chapter Outline
I. Introduction
A. Weather is the day-to-day changes
B. Climate is the statistical summary of weather over time
II. Energy and weather
A. Solar energy
1. Drives atmospheric processes
2. Derived from thermonuclear reactions in the Sun
B. Amount of incoming solar radiation varies
1. Earth’s orbit and tilt
a. Time of day
b. Latitude
c. Season
2. Amount intercepted at a given location
a. Angle of incidence
b. Day length
c. Distance from the Sun
3. Equinoxes (March and September) and solstices (June and December)
C. Storage of heat
1. Water stores large amounts
2. Land stores small amounts
3. Land temperature changes faster than water temperature
D. Heat transfer between the atmosphere and Earth
1. Radiation
a. Radiant energy is transmitted by electromagnetic waves
b. Most incoming solar radiation is shortwave
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c. Most outgoing energy is longwave
d. Most shortwave passes through the atmosphere
e. Some longwave is trapped by greenhouse gases
2. Latent heat
a. Heat stored in water and water vapor
b. Transfers large amounts of energy
E. Heat exchange and atmospheric circulation
1. Convection
a. Movement in any fluid when part of the fluid is heated
b. Warm air (and water) rises
2. Advection
a. Horizontal movement of air
b. Moves large amounts of air and latent heat
III. Precipitation
A. Variations in precipitation affect human activities
B. Condensation
1. Water from vapor to liquid
2. Relative humidity
3. Leads to precipitation
a. When the pressure of moisture exceeds the saturation vapor pressure
b. When clouds contain tiny particles (condensation nuclei)
C. Rising air causes precipitation
1. Convection
a. Rising air leading to adiabatic cooling
b. Clouds form and condensation occurs
c. Thunderstorms with gusty winds and intense rain develop
d. Major cause of precipitation
2. Orographic precipitation
a. Mountains force air upward
b. Cooling, clouds, condensation, precipitation
c. Windward side has precipitation
d. Leeward side is rain shadow with less precipitation
3. Frontal uplift
a. Cold air mass pushes under a warm air mass
b. Warm air rises
c. Cooling, clouds, condensation, precipitation
d. Cold fronts and warm fronts
IV. Circulation patterns
A. Fundamental causes
1. Atmospheric pressure
a. Weight of air above a location
b. Varies with altitude
2. Wind
3. Coriolis effect
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B. Global atmospheric circulation
1. Intertropical convergence zone (ITCZ)
a. Much solar radiation causes air to rise, creating low pressure and rain
b. Pushes warm, dry air toward the midlatitudes
2. Trade winds
3. Subtropical high-pressure zones
a. Air descends, causing high pressure
b. Creates arid climate
4. Westerlies
5. Midlatitude low-pressure zones
a. Convergence of warm air and polar air
b. Causes the westerlies
6. Polar easterlies
7. Polar high-pressure zones
a. Cold causes high pressure
b. Very little moisture
C. Seasonal variations
1. January
a. ITCZ is a few degrees south of the equator
b. Pattern of the other zones is more consistent in the Southern Hemisphere
2. July
a. ITCZ is north of the equator
b. Low pressure over Asia causing the monsoon circulation
D. Global ocean circulation
1. Winds are the main cause of currents
2. Currents form circular patterns (gyres)
a. Warm water moved toward the poles
b. Cold water moved toward the equator
E. Storms
1. Vary from huge monsoons to local thunderstorms
2. Modified by El Niño/La Niña
3. Tropical cyclone (hurricane or typhoon or cyclone)
a. Intense low pressure
b. Strong winds, much rain, and storm surges
c. Weakens over land
4. Midlatitude cyclone
a. Low pressure along polar fronts
b. Weaker than tropical cyclones
c. Sometimes leads to tornadoes
V. Climate
A. Summary of weather conditions over many years
B. Two main components
1. Temperature
a. Varies over time and space
b. Affected by elevation and topography
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2. Precipitation
a. Varies over time and space
b. Transpiration and potential evapotranspiration
VI. Classifying climate
A. Uses patterns of temperature and precipitation as related to water availability for
vegetation
B. Köppen system
a. Most recognized system
b. Used distribution of vegetation to reflect temperature and precipitation
c. Uses A, B, C, D, E to identify five main types
VII. Earth’s climate regions
A. Humid low-latitude tropical climates
1. Humid tropical (Af, Am)
a. Beneath the ITCZ
b. Warm, humid, rainy
c. Little seasonal variation
d. Tropical rainforests
2. Seasonally humid tropical (Aw)
a. Has a distinct dry season
b. Often caused by shifts in the ITCZ
c. Sometimes caused by the monsoon circulation
d. Less plant growth during dry season
B. Dry climates
1. Desert (BWh, BWk)
a. Beneath subtropical high-pressure zones
b. Very dry, especially on western sides of continents, high temperatures
c. Little vegetation
2. Semiarid (BSh, BSk)
a. More rainfall
b. Between deserts and humid regions
c. Steppes or grasslands
C. Warm midlatitude climates
1. Humid subtropical (Cfa, Cw)
a. Beneath subtropical high-pressure zones, especially on eastern sides of continents
b. More seasonal variations
c. Mostly deciduous vegetation
2. Marine west coast (Cfb, Cfc)
a. On west coasts
b. Moderate temperatures
c. Plentiful precipitation, drizzle
d. Mostly evergreen vegetation
3. Mediterranean (Cs)
a. Dry summers
b. Cool, rainy winters
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c. Vegetation has to survive dry period
D. Cold midlatitude climates
1. Humid continental (Dfa, Dwa, Dfb, Dwb)
a. Only in Northern Hemisphere
b. Warm summers
c. Cold winters
d. Deciduous and some evergreen vegetation
2. Subarctic (Dfc, Dwc, Dfd, Dwd)
a. Very cold winters
b. Modest precipitation
c. Conifers (boreal forest)
E. Polar climates
1. Tundra (ET)
a. Cold throughout the year
b. Permafrost
c. Treeless tundra vegetation
2. Ice-cap (EF)
a. Very cold, quite dry
b. No vegetation
F. Climographs quantitatively describe different climates
VIII. Climate change
A. Long-run changes in the underlying determinants of climate cause climate change
B. Over geologic time
1. Glacial periods during the Pleistocene Epoch
a. Shifts in temperature back and forth
b. Most recent colder episode was about 18,000 years ago
2. Little Ice Age from 1500 to 1750
C. Causes
1. Astronomical hypotheses
2. Geologic hypotheses
3. Human activities
a. Burning fossil fuels
b. Adding other pollutants
D. Global warming
1. Consensus that it is truly occurring
2. Caused by increased carbon dioxide
3. Climate models are used
4. Uncertainties
a. Limited understanding of the climate system
b. Tipping points being reached, leading to rapid change
c. Unknown future conditions
5. How to respond to global warming
a. Adapt to climate change
b. Reduce carbon emissions
c. “Geoengineer” the global carbon cycle, the atmosphere
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d. Substantial costs involved
Possible Questions and Topics for Discussions and Exams
1. Describe what climographs show and do not show.
2. Explain how the trade winds, westerlies, and polar easterlies are formed.
3. What is the name and Köppen code for the climate where your college is located? What are
its characteristics? Explain what causes those characteristics.
4. Compare and contrast the characteristics of hurricanes and tornadoes.
5. Look up the worst natural disasters in human history. How many were caused by weather
extremes? Using a world map, locate these disasters. Explain reasons for any patterns.
6. Compare the patterns of average January temperatures in Australia and North America.
7. Looking at Figure 2-34, which of the 11 climates covers the most area? Which covers
the least area?
8. Find climate data for your favorite foreign vacation destination. When would be the best
and worst times of the year to visit? Why?
9. Using Weatherbase.com, look up Dhaka, Bangladesh. Describe Dhaka’s temperature and
precipitation variations throughout the year.
10. Suggest reasons why weather forecasts are often inaccurate.
11. Describe the best weather for sailing, playing soccer, and sleeping. Do all students agree?
12. What are likely negative consequences of global warming? What are possible positive
consequences? Do the negatives outweigh the positives or not?
Answers for Checkpoints
Checkpoint: Variations in Solar Energy
For any given location, the angle of incidence for solar radiation is much more important than
the distance to the Sun.
Checkpoint: Heat Transfers
In general, morning temperatures are lower after a cloudless night because less longwave
radiation is trapped when there are less water vapor and fewer clouds in the atmosphere.
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Checkpoint: Convection and Clouds
During a more humid day clouds would be lower since there would more water vapor
available to condense into clouds.
Checkpoint: Weather Patterns
Looking at the national forecast high-resolution map for July 2, 2013, from weather.gov, there
are six low-pressure and two high-pressure areas shown. There is a long mostly stationary front
running from Maine to south Texas to Wyoming and a cold front beginning to move down from
Canada. The link to the map legend should be used.
Checkpoint: Circulation Patterns
Looking at weather.com–Map Room–Satellite Map for July 2, 2013, for the Western
Hemisphere there are three storm systems along 30 degrees south or near the subtropical highpressure zone. The pattern is also affected by the northward shift of the ITCZ in July.
Checkpoint: Climate and Circulation
Comparing Indianapolis and New Orleans, which are about 800 miles apart, Indianapolis has
an average annual temperature of 53 degrees and New Orleans has 69 degrees. Average annual
precipitation is 40 inches and 61 inches, respectively. These differences are not surprising and
the data are from weatherbase.com.
Checkpoint: Climate
Answer depends on location. Using Seattle, the climate is marine west coast (Cfb). Seattle’s
average annual temperature is 53 degrees, whereas its average annual precipitation equals 34
inches. These values are fairly typical for a marine west coast climate, although summers in
Seattle would be a little colder.
Checkpoint: Climate Change
Examining Chicago’s historical record, the record high is 105 degrees in July 1934 and the
record low is minus 27 degrees in January 1985. Looking at the 50-year periods of 1913 to 1962
and 1963 to 2012, there were 34 years with above-average temperatures in the first period and
30 years above average in the next. The decades before 1913 were cooler. Based on 100 years of
temperatures in Chicago, there is little evidence of global warming. Data are from
ClimateStation.com.
Answers to Questions for Review and Discussion
1. Using Figure 2-6 and a latitude of 40 degrees, minimum solar radiation occurs at the winter
solstice and maximum amounts at the summer solstice. As the angle of incidence becomes
less perpendicular, the intensity of solar radiation also declines. More hours of daylight
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mean more solar radiation. The angle of incidence and day length do not vary by latitude at
the time of the equinoxes.
2. Radiation, or the energy transmitted by electromagnetic waves; movement of water and
water vapor containing latent heat; convection, or the movement in any fluid when part of
the fluid is heated; and advection, or horizontal movement of air are the major processes.
3. Hurricanes occur mostly over oceans and during the late summer and fall because these
storms depend on large amounts of warm, moist air. Oceans add moisture and ocean
temperatures are the warmest in the late summer and into fall.
4. In comparison to continental interiors, climatic conditions are usually more moderate in
coastal areas. The nearby body of water slows the heating or cooling of the coastal lands.
Similarly, the continental interiors are less moderate, meaning that annual temperature
variations are greater.
5. Midlatitude cyclones occur in the midlatitudes and are centers of low pressure that develop
along a polar front. Midlatitude cyclones are more common and weaker than most
hurricanes. The passage of a front associated with a midlatitude cyclone normally causes
changes in temperatures, precipitation, and winds. In some cases, these storms become
tornadoes.
6. Related to the fact that warm air holds more moisture than cold air, higher temperatures
mean more rainfall is needed for the place to be classified as having a humid climate.
7. Humid tropical—the ITCZ is there all the time.
Seasonally humid tropical—the ITCZ shifts away during part of the year and for Asia the
monsoon circulation applies.
Desert—located in subtropical high-pressure zones, especially in western parts of
continents where high-pressure zones over adjacent oceans make the land drier.
Semiarid—subtropical high-pressure zones are not as strong, and, in some cases, mountains
block air masses containing moisture.
Humid subtropical—the subtropical high-pressure zone brings moisture to eastern sides
of continents.
Marine west coast—westerlies bring air masses to west coasts of some areas.
Mediterranean—shifts in the subtropical high-pressure and midlatitude low-pressure zones
cause dry summers and cool, wet winters.
Humid continental—seasonal contrasts between the subtropical high-pressure and the
midlatitude low-pressure zones.
Subarctic—polar edge of midlatitude low-pressure zones draws in cold air.
Tundra—polar high-pressure zone has little moisture and warmth.
Ice-cap—polar high-pressure zone is strongest.
8. Over the last 1,000 years, global temperatures were warmer in about A.D. 900, cooler
with the Little Ice Age (A.D. 1500 to A.D. 1750), and warming over the last 200 years.
Warmer conditions and melting of glaciers was true between 15,000 to 5,000 years ago.
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Based on Figure 2-56, there were two glacial and three interglacial periods over the last
100,000 years.
9. Earth–Sun geometry, sunspots, continental drift, volcanic eruptions, burning fossil fuels,
creation of methane, use of halocarbons, and removing vegetation are possible causes of
global warming. Consequences include sea-level rises and changes in precipitation patterns
affecting agriculture and other human activities.
Answers for Thinking Geographically
1 There are too many varying aspects to answer this question specifically. It is likely that the
daily weather journal will be generally consistent with the daily weather maps, but with
more details and specifics. The daily weather journal is likely to be less quantitative.
2. Living near Kenosha, Wisconsin, the topography is flat, meaning that it is more windy and
that orographic precipitation effects do not exist. Kenosha is on the shoreline of Lake
Michigan,which causes summer temperatures to be cooler and winter temperatures to be
warmer. Kenosha is an urban area with a population of about 125,000, so there are some
modest urban heat island effects.
3. Answers will vary.
4. An annual average increase of 9 degrees (F) would be a huge increase in temperature. One
way to think about this is that every day throughout the year would be 9 degrees warmer.
People would wear more warm weather clothes, run their air conditioners more, water their
lawns more often, avoid outdoor activities during the hottest times, not have to deal with
winter driving conditions as often, celebrate a white Christmas less often, be more irritable,
not sign up for skiing lessons, and so forth.
5. Warm midlatitude climates (Cfa, Cw, Cfb, Cfc, Cs) have the highest population densities.
Humid low-latitude climates (Af, Am, Aw) are a close second. Dry climates (B), polar
climates (E), and highland (H) have much lower densities. The climates with high densities
have temperature and precipitation levels that are favorable for agriculture and settlement.
For example, the hundreds of millions of people who live in East China are aided by the
Cfa climate.
For additional review and test prep materials visit the Study Area in MasteringGeography™.
Students can enhance their geographic literacy, spatial reasoning skills, and understanding of this
chapter’s content by accessing a variety of resources including MapMaster interactive maps,
videos, RSS feeds, flashcards, web links, self-study quizzes, and an e-Text version of the text.
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Introduction to Geography.
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