Download Earth,Notes,RevQs,Ch21

Global Climate Change
21
Global Climate Change begins with an examination of the climate system and the various techniques for
analyzing Earth’s climate. Following a discussion of the composition of air, electromagnetic radiation is
explained in detail. Climate change and the effect of humans on global climate are discussed at length. The
chapter concludes with a brief look at the complexity of climatic systems.
Learning Objectives
After reading, studying, and discussing the chapter, students should be able to:
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Explain the climate system.
Describe the composition of the atmosphere.
Discuss the various aspects of electromagnetic radiation.
Briefly discuss how Earth is heated by solar radiation.
Discuss the various ideas that have been formulated to explain climate change.
List and briefly discuss carbon dioxide and other gases added to the atmosphere by humans.
Explain how climatic systems are altered, including climate feedback mechanisms.
Briefly discuss the role of aerosols in affecting global climate change.
Discuss the complexity of the climate system.
Understand how such complexity may prevent the prediction of future changes in climate.
Chapter Outline___________________________________________________________________
I.
The shoreline: a dynamic interface
A. The shoreline is a dynamic interface
(common boundary) among air, land,
and sea
B. Constantly being modified by waves
C. Today the coastal zone is experiencing
intense human activity
II.
The coastal zone
A. Clarification of terms used to describe the
land-sea boundary
1. Shoreline is the line that marks the
contact between land and sea
2. The shore is the area that extends
between the lowest tide level and the
highest elevation on land that is
affected by storms
3. The coast extends inland from the
shore as far as ocean related features
are found
4. Coastline marks the coast’s seaward
edge
B. Shore is divided into the
1. Foreshore – area exposed at low tide
2. Backshore – landward of the hightide shoreline
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3. The nearshore zone lies between the
low tide shoreline and the point
where waves break at low tide
4. Seaward of the nearshore is the
offshore zone
C. Beach – an accumulation of sediment
found along the landward margin of the
ocean or a lake
1. The relatively flat platform
composed of sand and marked by a
change in slope at the seaward edge
is a berm
2. Beach face is the wet sloping surface
that extends from the berm to the
shoreline
III. Waves
A. Wind-generated waves provide most of
the energy that shapes and modifies
shorelines
B. Characteristics of waves
1. Waves derive their energy and
motion from the wind
2. Parts of a wave
a. Crest – top of the wave
b. Trough – low area between waves
3. Measurements of a wave
a. Wave height – the distance
between a trough and a crest
b. Wavelength – the horizontal
distance between crests
c. Wave period – the time interval
between the passage of two
successive crests
4. Height, length, and period of a wave
depend on
a. Wind speed
b. Length of time wind has blown
c. Fetch – the distance that the wind
has traveled across open water
C. Types of waves
1. Wave of oscillation
a. Wave energy moves forward, not
the water itself
b. Occur in the open sea in deep
water
2.
Wave of translation
a. Begins to form in shallower water
when the water depth is about
one-half the wavelength and wave
begins to “feel bottom”
b. As the speed and length of the
wave diminish, the wave grows
higher
c. The steep wave front collapses
and the wave breaks along the
shore
d. Turbulent water advances up the
shore and forms surf
IV. Wave Erosion
A. Breaking waves exert a great force
B. Wave erosion is caused by
1. Wave impact and pressure
2. Abrasion by rock fragments
V.
Sand movement on the beach
A. Movement perpendicular to the shoreline
1. Waves seldom approach the shore
straight on, but rather at an angle
2. When waves reach shallow water
with a smoothly sloping bottom they
are bent and tend to become parallel
to the shore
B. Wave refraction
1. Bending of a wave
2. Causes waves to arrive nearly parallel
to the shore
3. Consequences of wave refraction
a. Wave energy is concentrated
against the sides and ends of
headlands
b. Wave energy is spread out in bays
and wave attack is weakened
C. Moving sand along the beach
1. Waves that reach the shoreline at an
angle cause the sediment to move
along a beach in a zigzag pattern
called beach drift
2. Oblique waves also produce
longshore currents
Global Climate Change
a.
b.
c.
VI.
Currents in the surf zone
Flow parallel to the coast
Easily moves fine suspended sand
and rolls larger sand and gravel
along the bottom
Shoreline features
A. Features vary depending on
1. The rocks of the shore
2. Currents
3. Wave intensity
4. Whether the coast is
a. Stable
b. Sinking
c. Rising
B. Features caused by wave erosion
1. Wave-cut cliffs
2. Wave-cut platform
3. Features associated with headlands
a. Sea arch
b. Sea stack
C. Features related to beach drift and
longshore currents
1. Spits
a. Elongated ridges of sand
extending from the land into the
mouth of an adjacent bay
b. Often the end of a spit hooks
landward in response to wave
generated currents
2. Baymouth bar – a sand bar that
completely crosses a bay
3. Tombolo – a ridge of sand that
connects an island to the mainland or
another island
D. Barrier islands
1. Mainly along the Atlantic and Gulf
coasts
2. Low ridges of sand that parallel the
coast 3 to 30 kilometers offshore
3. Probably form in several ways
E. If the shoreline remains stable the result
of shoreline erosion and deposition is to
eventually produce a straighter coast
VII. Stabilizing the shore
A.
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Influenced by the local factors
1. Proximity to sediment-laden rivers
2. Degree of tectonic activity
3. Topography and composition of the
land
4. Prevailing wind and weather patterns
5. Configuration of the coastline and
near shore areas
B. Three basic responses to erosion
problems
1. Building structures
a. Types of structures
1. Jetties
a. Usually built in pairs to
develop and maintain
harbors
b. Extend into the ocean at the
entrances to rivers and
harbors
2. Groin
a. Built to maintain or widen
beaches
b. Constructed at a right angle
to the beach to trap sand
3. Breakwater
a. Barrier built offshore and
parallel to the coast
b. Protects boats from the
force of large breaking
waves
4. Seawall
a. Barrier parallel to shore and
close to the beach to protect
property
b. Stops waves from reaching
the beach areas behind the
wall
b. Often the building of structures is
not an effective means of
protection
2. Beach nourishment
a. The addition of large quantities of
sand to the beach system
b. Only an economically viable longrange solution in a few areas
3. Relocation
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a.
Instead of building structures such
as groins and seawalls to hold the
beach in place or adding sand for
replenishment, another option is
available
b. Such proposals are controversial
C. Contrasting the Atlantic and Pacific
Coasts
1. Shoreline erosion problems are
different along the opposite coasts
2. Atlantic and Gulf coasts
a. Broad, gently sloping coastal
plains
b. Tectonically quiet regions
c. Development occurs mainly on
the barrier islands (also called
barrier beaches or coastal barriers)
1. Barrier islands face the open
ocean and
2. Receive the full force of
storms
3. Pacific Coast
a. Relatively narrow beaches backed
by steep cliffs and mountain
ranges
b. A major problem is a significant
narrowing of many beaches
1. Sediment for beaches has been
interrupted by dams and
reservoirs
2. Narrow beaches allow for the
erosion of the sea cliffs
c. Shoreline erosion varies
considerably from one year to the
next largely because of the
sporadic occurrence of storms
VIII. Coastal classification
A. Emergent coasts
1. Develop because of
a. Uplift of an area, or
b. A drop in sea level
2. Features of an emergent coast
a. Wave-cut cliffs
b. Wave-cut platforms
B. Submergent coasts
1.
Caused by
a. Land adjacent to the sea subsides,
or
b. Sea level rises
2. Features of a submergent coast
a. Highly irregular shoreline
b. Estuaries – drowned river mouths
IX.
Tides
A. Daily changes in the elevation of the
ocean surface
B. Causes of tides
1. Tidal bulges are caused by the
gravitational forces of the
a. Moon, and to a lesser extent the
b. Sun
C. Spring and neap tides
1. Spring tides
a. Occur during new and full moons
b. Gravitational forces of the Moon
and Sun are added together
c. Especially high and low tides
d. Large daily tidal range
2. Neap tides
a. Occur during the first and third
quarters of the moon
b. Gravitational forces of the Moon
and Sun are offset
c. Daily tidal range is least
D. Other factors that influence tides
1. Shape of the coastline
2. Configuration of the ocean basin
E. Tidal currents
1. Horizontal flow of water
accompanying the rise and fall of the
tide
2. Types of tidal currents
a. Flood current – advances into the
coastal zone as the tide rises
b. Ebb current – seaward-moving
water as the tide falls
3. Areas affected by the alternating tidal
currents are called tidal flats
4. Occasionally form tidal deltas
F. Tides and Earth’s rotation
1.
Tidal friction against the ocean floor
acts as a weak brake that is steadily
slowing Earth’s rotation
Global Climate Change
a.
b.
The day is increasing by 0.002
second per century
Over millions of years this small
effect becomes very large
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2. The length of each day must have
been shorter and the number of days
per year must have been longer in the
geologic past
Answers to the Review Questions
1. The climate system includes the atmosphere, hydrosphere, geosphere, biosphere, and cryosphere.
2. Proxy data refers to indirect evidence of past climate changes. Examples of proxy data include seafloor
sediments, glacial ice, fossil pollen, and tree-growth rings. Proxy data are necessary in the study of
climate change because recorded historical data are lacking beyond recent history.
3. Seafloor sediments are useful recorders of worldwide climate change because the numbers and types of
organisms living near the sea surface change with the climate.
4. The characteristics of each tree ring, such as size and density, reflect the environmental conditions
(especially climate) that existed during the year when the ring formed.
5. Clean, dry air is composed mainly of nitrogen and oxygen. A small percentage is made up of the inert gas
argon. Two significant variable components of air include water vapor and liquid particles.
6. Most of the Sun’s energy is emitted as shorter wavelength electromagnetic radiation.
7. Approximately 50 percent is absorbed by Earth’s surface, 30 percent is reflected back into space, and 20
percent is directly absorbed by clouds and the atmosphere’s gases. These percentages can vary greatly
because the percentage of light reflected and scattered back to space will vary greatly depending on
atmospheric conditions.
8. The atmosphere is heated mainly by terrestrial radiation from Earth because the gases in the atmosphere
readily absorb the longer wavelength terrestrial energy. The shorter wavelength rays emitted by the sun
pass through the atmosphere without much of the energy being absorbed.
9. Carbon dioxide and water vapor are the primary heat absorbers in the lower atmosphere.
10. The greenhouse effect refers to the heating of the lower atmosphere by the absorption of terrestrial
radiation by carbon dioxide and water vapor. These gases act much like the glass in a greenhouse in that
they allow shorter wavelengths to pass through them while absorbing longer wavelength.
11. Large volcanic eruptions, such at Mount Pinatubo in the Philippines, appear to have measurable shortterm effects on global temperatures. It is thought that fine-grained debris and huge quantities of gases
erupted from such volcanoes will filter out a portion of the incoming solar radiation, which in turn will
lower temperatures in the troposphere.
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12. Two examples of possible climate change linked to solar variability include sunspot frequency related to
temperature and drought conditions on Earth. Despite much research, no connection between solar
variations and weather has yet been well established.
13. Carbon dioxide levels in the atmosphere have been rising for more than 150 years due to the use of coal
and other fossil fuels.
14. Based on the increase in global average surface temperature during the twentieth century when carbon
dioxide levels were increasing, temperatures in the lower atmosphere are likely to increase in the future as
carbon dioxide levels continue to increase.
15. Other trace gases that are contributing to future global temperature change include methane, nitrous
oxide, and chlorofluorocarbons.
16. Climate feedback mechanisms are those possible outcomes when the climate system is altered. Some
examples include warmer surface temperatures and increased cloud cover.
17. The main sources of human generated aerosols are the sulfur dioxide emitted during combustion of fossil
fuels and also as a consequence of burning vegetation to clear agricultural land. Aerosols have a net
cooling effect on the atmosphere because they reduce the amount of solar radiation by influencing cloud
formation. Aerosols, once released into the troposphere, will remain there for only a few days.
18. Four potential consequences of global warming are 1) increases warming due to increased greenhouse
gases; 2) a wide difference in the impact of climate change on various regions; 3) the disappearance of
vulnerable ecosystems, and 4) widespread water shortages and associated food supply issues.
Lecture outline, art-only, and animation PowerPoint presentations for each chapter of Earth,
9e are available on the Instructor’s Resource Center CD (0131566911).