Download Earth Systems – Chapter 2

Atmosphere Resources and
Climate Change
Chapter 14
© 2011 Pearson Education, Inc.
You will learn
• The nature of atmospheric resources, including the
atmosphere’s composition, physical character, and
role in Earth systems interactions
• The nature and sources of atmosphere pollutants,
including NOx, SO2, VOCs, low-level ozone, CO, and
greenhouse gases, especially CO2
• The effects of atmospheric pollution, including smog,
acid rain, and changes in the natural stratospheric
ozone layer
• How variations in Earth’s orbit influence climate by
changing the amount of solar radiation Earth
receives
© 2011 Pearson Education, Inc.
You will learn (cont.)
• How variations in the atmosphere’s composition
influence climate, what greenhouse gases are,
where they come from, and how they work
• How scientists study climate change
• How human activities have changed the composition
of the atmosphere, how these changes have altered
climate and contributed to global warming, and what
future challenges people will face as a result
• How science is helping people understand global
warming and develop ways of dealing with it,
including the capture and storage of CO2
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Composition of the Atmosphere
FIGURE 14-2 Composition of the Atmosphere, Including
Variable Components (by Volume)
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Composition of Atmosphere (cont.)
• Three elements (N, O, Ar)—make up over 99.9% of the
atmosphere
• Pure nitrogen (N2) is used in its very cold, liquid state
• Instantly freezes biological specimens
• Nonreactive; used to purge vessels of reactive gases like
oxygen
• Prevents food spoilage, and refrigerate perishables during
shipping
• Prevents corrosion of metal surfaces
• Pure oxygen (O2)—is used in iron and steel smelting
• Cutting and welding torches to achieve higher temperatures
• Oxidizing agent in processes that produce a variety of
chemicals
• Increases the efficiency of waste incinerators
• Medical applications
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Composition of Atmosphere (cont.)
• Argon (Ar)—is a colorless, odorless, nontoxic,
and nonreactive gas
• Creates inert environments for growing crystals—in
semiconductors
• Protects materials against corrosion
• Fills the air space in double-pane insulating windows
• The gas in incandescent and fluorescent lightbulbs.
• Water vapor, methane, carbon dioxide—
greenhouse gases
• Keep Earth’s climate from being unbearably cold
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The Structure of the Atmosphere
FIGURE 14-3 The Structure of the Atmosphere
Temperature variations define the atmosphere’s four principal layers:
the troposphere, stratosphere, mesosphere, and exosphere. The
ozone layer is within the stratosphere.
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Ozone
• Ozone layer—within the stratosphere, some 15
kilometers (9 mi) up at higher latitudes and 35
kilometers (22 mi) up at low latitudes
• Ozone molecules = (O3) rather than the usual two
(O2).
• forms when UV radiation breaks apart some O2
• makes O—combines with other O2 to form O3
• Ozone layer (few ppm) screens out
• harmful, shortest-wavelength UV radiation
• longer-wavelength UV radiation
• (causes sunburn and skin cancer)
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The Atmosphere Screens Earth from
Harmful Solar Radiation
FIGURE 14-4 The Atmosphere Screens Earth from Harmful Solar Radiation
Shorter wavelength gamma and X-ray radiation and large amounts of infrared radiation are
completely absorbed by the atmosphere. The ozone layer absorbs the most harmful
ultraviolet wavelengths. Only radio waves, visible light, and some ultraviolet radiation reach
Earth’s surface relatively unimpeded.
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Air Pollution
• The EPA considers common air pollutants to
be:
• Volatile organic compounds (vocs)
• Nitrogen oxides (NO and NO2)
• Sulfur dioxide (SO2)
• Carbon monoxide (CO)
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Air Pollution (cont.)
• Common greenhouse gases are:
• Water vapor (H2O), methane (CH4), CO, nitrous oxide
(N2O)
• Volatile organic compounds—(VOCs)
• Chemicals that contain carbon and hydrogen and
vaporize easily
• Benzene, toluene, butane, and propane are
examples
• Paint thinners, solvents, plastics, and gasoline
• VOCs evaporate from crude oil when exposed to
atmosphere
• In the presence of sunlight—chemical reactions that
lead to smog
© 2011 Pearson Education, Inc.
NOx and SO2
• Nitrogen oxides—NOx
• Family of nitrogen-oxygen compounds where N:O ratio
varies
• Nitrogen oxide (NO) and nitrogen dioxide (NO2)
• Nitrous oxide (N2O) is not toxic like NO and NO2—
effective greenhouse gas
• Produced during combustion of fossil fuels
• Key ingredient in the formation of smog, contributes to
developing acid rain, and causes respiratory problems
for people
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NOx and SO2 (cont.)
• Sulfur dioxide
• Oil and coal combust and S combines with O = sulfur
dioxide (SO2)
• In the atmosphere, SO2 + H2O + O = sulfuric acid
(H2SO4)
• Source of acid rain
• Causes respiratory problems for people
• Reacts with nitrogen in the atmosphere to form
ammonium sulfate
• Creates atmosphere haze
• Volcanic eruptions may release SO2 into the
atmosphere
• Special effect—global cooling
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Emissions
FIGURE 14-5 Emission Trends
Regulations developed by the EPA have had a
major influence on pollutant emissions in the
United States. A a result, air pollution levels
are near or significantly below national
standards and the trends continue downward.
FIGURE 14-6 Sources of SO2
Pollution in the Atmosphere
Although SO2 emissions in the
United States have significantly
decreased, over 10 million tonnes
(11 million tons) are released into
the atmosphere each year.
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CO and CO2
• Carbon monoxide—CO
• Colorless, odorless, tasteless, and dangerous
gas
• 75% of CO—produced by incomplete
combustion of fossil fuels
• CO is a good general indicator of air pollution
• Can be detected and mapped by satelliteborne instruments
• EPA vehicle regulations—effective at lowering
levels of CO
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CO and CO2 (cont.)
• Carbon dioxide—CO2
• Source of CO2 emissions—burning fossil fuel with CO2
as product
• Metabolism of food—source of CO2 that we exhale
• Volcanic eruptions may release large amounts of CO2
• The Supreme Court—greenhouse gases are atmospheric
pollutants
• EPA can regulate under the clean air act
• This ruling signals changes for CO2 emitters
• Example—EPA permits for new coal-fired power
plants must now consider a “best available control
technology” for CO2 emissions—as for other air
pollutants
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Smog
• Combination of smoke and fog
• Originally referred to the haze from extensive burning of coal
• CO, NOx, and VOC emissions cause most of today’s smog
problems
FIGURE 14-9 Two of the Reactions Involved in Forming Ozone (O3)
and Smog There are several other reactions involving NOx, VOCs, CO,
and O (in the presence of sunlight) that also contribute to ozone and smog
formation.
© 2011 Pearson Education, Inc.
Photochemical Smog and Acid Rain
• Photochemical smog—brownish haze over cities
on warm, sunny days
• Brownish color comes from Nox, smell comes from
ozone
• Most dangerous component is low-level ozone
• Irritates lungs—damages vegetation
• Cause—photochemical reactions involving VOCs, NOx,
and CO
• Solution—more efficient combustion of fossil fuels
• Reformulating gasoline
• Catalytic converters, electronic engine controls,
exhaust gas recirculators
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Photochemical Smog and Acid Rain (cont.)
• Acid rain
• NOx and SO2 react with water (atmosphere) to form
droplets of acid
• SO2 emissions = principal cause of acid rain
• Coal-burning power plants—release 70% of SO2 emitted
each year
• Acid rain has a ph less than 5.6; NE U.S.—rain can
have ph = 3.6 !!
• Acid rain in NE has affected vegetation, aquatic
systems, buildings—damaging plant leaves, degrading
soil, dissolving nutrients
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Formation of Acid Rain
FIGURE 14-11
Both NOx and SO2 can react with water in the atmosphere to form droplets of acid,
but SO2 emissions have been the principal cause of acid rain
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Acid Rain in the NE U.S.
Where acid rain accumulates in
surface waters, acidity can reach
levels that are unhealthful for fish and
other aquatic life. Some lakes in the
northeast U.S. have pH levels <5.
Acid rain falls on limestone and
marble (buildings, tombstones, etc.)
and dissolves bits of the building
stone and pits, etches, and discolors
the building surfaces. In places,
structural components are weakened
and need to be replaced.
FIGURE 14-13 Acid Rain and Power Plant
Emissions (a) The location of coal-burning power
plants. (b) The acidity of rainwater in different parts
of the United States. The distribution of plants
combined with prevailing winds (from west to east)
make acid rain common in the east and northeast
parts of the country.
© 2011 Pearson Education, Inc.
The Ozone Layer
• The ozone layer in the stratosphere absorbs shorterwavelength UV radiation in sunlight that would otherwise
be lethal to surface life
• Photosynthesis releases oxygen
• Migrates to high altitudes—reacts with UV radiation to form ozone
• Ozone layer effectively shields surface life
• Is carried to higher latitudes by stratospheric winds
• Chlorofluorocarbons (CFCs)—destroy ozone
• UV radiation breaks cfcs down in stratosphere
• Releasing Cl and Br atoms that react with ozone
• Cl and Br atoms—very effective at destroying ozone
• Seasonal depletion over Antarctica is known as the ozone hole
• The ozone hole—well developed between August and late
November
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How Chlorine Destroys Ozone
FIGURE 14-15 How Chlorine Destroys Ozone
CFCs have such a devastating effect on ozone because the reactions
involved form a cycle. Once a single chlorine atom is dislodged from a CFC
molecule, it can just keep reacting with one ozone molecule after another.
© 2011 Pearson Education, Inc.
Atmosphere and Climate Change
• Earth’s climate is strongly influenced (forced) by:
1) atmosphere composition; 2) solar radiation Earth
receives
• Composition—greenhouse gases
• Let shorter-wavelength incoming sunlight through to Earth’s
surface
• Warm the ground, the ocean, and lower regions of the
atmosphere
• Reradiate some of their heat energy back at longer
wavelengths
• Infrared wavelengths are absorbed by greenhouse gases
• Trapping energy in the atmosphere
• Part of this trapped energy is, in turn, reradiated back to
Earth
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Atmosphere and Climate Change (cont.)
• This trapping of heat in the atmosphere is often likened
to the effect of glass in a greenhouse—hence the term
greenhouse effect
• This greenhouse effect keeps Earth’s surface habitable
• CO2—low warming potential—very abundant, hence
important
• Methane—56x warming potential of CO2—not abundant
• Nitrous oxide—280 warming potential of CO2—not
abundant
• Water vapor too is a very potent greenhouse gas—
temperature-dependent
© 2011 Pearson Education, Inc.
The Greenhouse Effect
FIGURE 14-18 The Greenhouse Effect
Solar radiation reflected or reradiated by Earth’s surface is absorbed by greenhouse
gases and warms the atmosphere. The warmed atmosphere reemits radiation back to
Earth, causing surface warming.
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How Axis Tilt Affects the Intensity of
Solar Radiation
FIGURE 14-19 It is because the axis is
tilted that we have seasons.
(a) The tilt of Earth’s axis of rotation
changes from 22.1 to 24.5 degrees and
back in a 41,000-year cycle.
At higher latitudes, even the shift of a few
degrees can cause a significant change in
the intensity of solar radiation.
(b) Solar radiation reaching Earth’s
surface is strongest when the Sun is
directly overhead and becomes weaker
when Sun's rays strike at a more oblique
angle.
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How Axis Tilt Affects the Intensity of
Solar Radiation (cont.)
FIGURE 14-19 How Axis Tilt Affects the Intensity of Solar Radiation
In (c), the Northern Hemisphere is tilted toward the Sun and experiences summer while the
Southern Hemisphere experiences winter. Six months later, when Earth is on the opposite
side of its orbit (d), the Northern Hemisphere is tilted away from the Sun and experiences
winter while the Southern Hemisphere experiences summer.
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Influence of Orbital Eccentricity
FIGURE 14-20
How Orbital Eccentricity Changes the
Amount of Solar Radiation Earth
Receives
Earth’s orbit around the Sun changes
from more elliptical (a) to less elliptical (b)
and back about every 100,000 years.
(The extent of the elongation in part (a)
has been exaggerated.) When the orbit is
more elliptical, the Earth moves both
closer to and farther from the Sun during
a year than it does when the orbit is less
elliptical.
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Precession
FIGURE 14-21 Precession
Earth wobbles as it orbits the Sun, much as a top wobbles as it spins. This wobble
gradually rotates the poles in a circle. Precession changes the direction of Earth’s tilt
about its axis, but not the amount of tilt. Rotation of the poles shifts them slightly toward
or away from the Sun. A complete precession cycle takes 22,000 years.
Milankovitch Cycles—cyclic changes in axis tilt, orbital
eccentricity, and precession cycles lead to cycles of colder climate
(glacial maximums) and warmer climate (interglacial periods)
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Tectonic Processes and Climate
• Continent size and distribution
• The size and distribution of these landmasses directly affect
circulation patterns
• Affect the concentration of CO2 in the atmosphere
• Influence on the chemical weathering of silicate minerals
• Atmosphere transfers dissolved CO2 to the geosphere through
rain
• Reacts with water to give carbonic acid (H2CO3)
• Chemical-weathering processes break down silicate
minerals
• Reactions work to decrease atmospheric CO2
concentrations
• Silicate weathering is likely to be more extensive:
• Continents split into smaller fragments surrounded by
oceans—wetter
• Continentals are located at lower latitudes—warmer
conditions
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Tectonic Processes and Climate (cont.)
• Mountain ranges
• Direct influences on atmosphere circulation and
precipitation
• Increase exposure of silicate minerals to chemical
weathering
• Decrease CO2 concentrations in the atmosphere
• Volcanoes
• Volcanic gases (e.g., SO2) reach high altitudes—cool
Earth
• May release enough CO2 to affect global climate for long
periods of time.
© 2011 Pearson Education, Inc.
Average Past Global Temperatures
FIGURE 14-22 Average Global Temperature during the Phanerozoic
Over the last 540 million years, Earth was mostly warmer than it is now.
Earth’s geologic record shows evidence of past climates both colder and warmer
than today. These past climates are related to interactions involving geosphere
processes, greenhouse gas cycles, the distribution and size of continents and
oceans, and variations in the amount of solar radiation Earth receives.
© 2011 Pearson Education, Inc.
Paleoclimatology—Studying Past
Climates
• Sedimentary records
•
•
•
•
Evaporites (salt-rich sediments) indicate arid conditions
Coal seams commonly indicate warm, moist conditions
Tillite indicates cold, glacial conditions
Cores of deep-sea sediments with continental rock
debris (from icebergs)
• Fossils
• Remains of organisms help determine environmental
conditions
• Zooplankton and algae—indicators of water
temperatures
• Fossil plant spores and pollen
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Paleoclimatology—Studying Past
Climates (cont.)
• Oxygen isotopes
•
•
•
•
Almost all oxygen has an atomic mass of 16 (16O, or O-16 atoms)
Two other stable oxygen isotopes are: O-17 and O-18.
O-18 is five times more abundant than O-17—easier to use
O-18 is slightly heavier than O-16
• Water containing O-18 does not evaporate as easily as water with O-16
• The escaping water vapor is slightly enriched in O-16
• Seawater left behind is slightly enriched in O-18
• During cold periods
• O-16-enriched water vapor is added to ice sheets
• Ratio of O-18 to O-16 in seawater increases
• Marine organism incorporate this O-18 : O-16 into shells and skeletons
• Locking in ratio for time they grew
• Expanding ice sheets—higher O-18 to O-16 ratios
• Contracting ice sheets—decreasing O-18 to O-16 ratios
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Oxygen-16 in Glacial Ice
FIGURE 14-25
How Oxygen-16 Becomes More
Concentrated in Glacial Ice
(a) Because O-16 is lighter than O-18,
water vapor evaporated from the
oceans is slightly enriched in O-16.
Because most of this water eventually
finds its way back to the oceans in rain
and runoff, however, the ratio of the
two isotopes in seawater is largely
unaffected.
(b) During times of glaciation, water
vapor enriched in O-16 becomes
trapped in ice accumulations and
doesn’t return to the oceans. As a
result, the relative concentration of
O-18 in seawater increases.
© 2011 Pearson Education, Inc.
The Phanerozoic Oxygen Isotope Record
of Seawater
FIGURE 14-26 The Phanerozoic Oxygen Isotope Record of Seawater
The variation in the ratio of O-18 to O-16 is determined from measurements of
oxygen isotopes in fossil marine shells and skeletons. A greater O-18 to O-16
ratio indicates colder periods.
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Paleoclimatology—Studying Past
Climates (cont.)
• Atmosphere samples in ice cores
• Air is trapped in snow each year on ice sheets
• Snow becomes compressed under the weight of new
snow and turns into ice
• Enclosed air becomes trapped in the ice as bubbles
of ancient air
• Bubbles can be analyzed for their content of
greenhouse gases
• Determine prehistoric atmospheric concentrations of
methane and CO2
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Paleoclimatology—Studying Past
Climates (cont.)
• Sea level history
• Shifts from cold to warm climate marked a change from
expanding permanent ice sheets to melting ice sheets.
• Major cold periods make major continental-scale ice
sheets
• Trap tremendous volumes of water evaporated from
the oceans
• Lower sea level
• Warm periods melt the great ice sheets
• Send tremendous amounts of water back to the oceans
• Sea level rises
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Atmospheric Gases Trapped in Ice at
Vostok Station, Antarctica
FIGURE 14-27 Atmospheric Gases Trapped in Ice at Vostok Station, Antarctica
Higher concentrations of methane (a) and carbon dioxide (b) in air bubbles trapped in
ice cores indicate warmer interglacial times. Earth entered a warming interglacial
period 20,000 years ago.
© 2011 Pearson Education, Inc.
Shifts between Warm and Cold
Periods during Last 3 Million Years
FIGURE 14-30
Shifts between Warm and Cold Periods during the Last 3 Million Years
The plots are based on deep-sea sediment oxygen isotope data. Up to 0.9
million years ago, shifts from warm to cold climates occurred every 41,000 years
(the axis tilt cycle). Since then the shifts have been every 100,000 years.
© 2011 Pearson Education, Inc.
The Last 10,000 Years of
Greenhouse Gas Concentrations
FIGURE 14-31 The Last 10,000 Years of
Greenhouse Gas Concentrations
The curves represent the concentrations of
atmospheric CO2 (a) and methane (CH4) (b) as
determined from ice cores.
Note the shift from the longer-term natural trends at
about 7000 years ago for CO2 and at 5000 years ago
for methane. Could this be related to an increase in
farming practices?
If data for the last 200 years were included, the CO2
concentration would go off the chart—CO2
concentrations increased to 380 ppm during this
time!
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Climate Models—IPCC
• A scientific model is a physical or mathematical
representation of system relationships and
processes
• General Circulation Models, GCMs, represent the
interactions of the major components of climate
system: solar radiation, atmosphere, oceans, land,
and ice
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Climate Models—IPCC (cont.)
• GCMs share characteristics of all models, including:
• They are incomplete. Models represent what scientists consider to
be the most important components: ocean temperature, solar
radiation levels, atmosphere and ocean circulation patterns, and
greenhouse gas concentrations, for example
• They require assumptions. Scientists must assume many
quantitative aspects of the climate system components and their
relationships to one another—for example, the rate at which CO2
is being added to the atmosphere each year. They base such
assumptions on what they can reasonably project from past
experience and on the best existing information
• They incorporate variable parameters. The components of the
climate system vary in their physical character through space and
time; for example, ocean water temperatures vary around the
world
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Climate Models—Feedback Loops
• Sophisticated models take changes into consideration
as they simulate future conditions. Feedback
mechanisms respond to a change in the climate
system and either amplify or diminish the change.
• positive feedbacks—amplify the change
• negative feedbacks—diminish the change
• Increasing ocean temperatures decrease the amount
of CO2 oceans can absorb. This in turn increases
atmospheric CO2 concentrations and their
greenhouse gas effect causes additional ocean
temperature warming. This is an example of a
positive feedback.
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Climate Models—Feedback Loops (cont.)
• With climate warming, ice sheets melt and reflect less
solar radiation. This in turn causes more surface
warming, a positive feedback
• Increasing air temperatures enable more water vapor to
be stored in the atmosphere. As water vapor has a
significant greenhouse gas effect, more water vapor
increases surface and air temperatures, a positive
feedback.
• If increased air temperatures lead to increased water
vapor in the atmosphere, an outcome can be increased
cloudiness. Clouds reflect incoming solar radiation and
decrease surface and air temperatures, negative
feedback
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FIGURE 14-35 Atmospheric CO2 Concentrations Increased Very Rapidly
during the Last 200 Years
The change from about 280 ppm in 1800 to 380 ppm today reflects the impact of
the Industrial Revolution and the increased use of fossil fuels.
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FIGURE 14-37 The Global Climate System Is Very Complex
This figure shows some of the many interlocking feedback mechanisms that
affect global climate. (You don’t need to worry about the details—the purpose of
the figure is just to suggest why the system is so challenging to model.)
© 2011 Pearson Education, Inc.
IPCC Story Lines and Scenarios
• Define the scope of possible changes the world may experience by 2100:
• A1—very rapid economic growth, low population growth, and the rapid
introduction of new and more efficient technologies. Themes are
convergence among regions, capacity building, and increased cultural
and social interactions, with a substantial reduction in regional
differences in per capita income.
• A2—very heterogeneous world. Theme is self-reliance and preservation
of local identities. High population growth. Economic development is
regionally oriented, and per capita economic growth and technological
change are more fragmented and slower than in other story lines.
• B1—convergent world with the low population growth (like A1), but with
rapid changes toward a service and information economy, with
reductions in material intensity, and the introduction of clean and
resource-efficient technologies. The emphasis is on global solutions to
economic, social, and environmental sustainability, including improved
equity, but without additional climate initiatives.
• B2—emphasis is on local solutions to economic, social, and
environmental sustainability. Moderate population growth, intermediate
levels of economic development, and less rapid and more diverse
technological change.
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FIGURE 14-36 Average Global Temperature Rise over the Past Century
Instrument-measured air temperatures are compared to the average from 1961
to 1990 (the zero line) to calculate the observed temperature anomaly.
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The IPCC 2007 Assessment
• Warming of the climate system is unequivocal, as is now
evident from observations of increases in global average
air and ocean temperatures, widespread melting of
snow and ice, and rising global average sea level.
• Global GHG (greenhouse gas) emissions due to human
activities have grown since preindustrial times.
• Most of the observed increase in global average
temperatures since the mid-20th century is very likely
due to the observed increase in anthropogenic GHG
concentrations.
• It is likely that there has been significant warming
caused by human activities over the past 50 years
averaged over each continent (except Antarctica).
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The IPCC 2007 Assessment (cont.)
• There is high agreement and much evidence that with
current climate change mitigation policies and related
sustainable development practices, global GHG
emissions will continue to grow over the next few
decades.
• Continued GHG emissions at or above current rates
would cause further warming and induce many changes
in the global climate system during the 21st century—
would very likely be larger than those observed during
the 20th century.
• A wide array of adaptation options are available, but
more extensive adaptation than is occurring is required to
reduce vulnerability to climate change.
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FIGURE 14-40 Examples of Impacts Associated with
Different Amounts of Global Average Temperature Change
Projected here by the IPCC.
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Kyoto Protocol and Carbon
Sequestration
• The Kyoto Protocol
• Identified CO2 emission reduction goals for all
participating countries.
• As of May 2008, 181 countries are parties to
the agreement
• Developing countries are not required to limit
their emissions
• Countries with a lot of CO2 emissions are not
participating
• Carbon sequestration
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Kyoto Protocol and Carbon
Sequestration 9 (cont.)
• Capturing and storing CO2 emitted by hydrocarbon
burning
•
•
•
•
Physical membranes that separate CO2 from exhaust streams
Use of sorbents that chemically react with emitted CO2
A bigger challenge is storing CO2 after it’s captured.
Reacting CO2 with Ca, Mg, Fe to form stable carbonate
minerals
• Storage in underground geologic reservoirs—geosequestration
• Injects captured CO2 into permeable reservoirs
• Depleted oil fields, saline water-filled formations
• Overlain by impermeable layers to trap CO2 and prevent
leaking
• Making of methanol (wood alcohol, CH3OH)
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FIGURE 14-43 An Example of Carbon Capture Technology
CO2 emissions from a large point source first combine with solid sodium carbonate
in the carbonation reactor. The resulting sodium bicarbonate is heated in the
decarbonation reactor. This releases concentrated CO2 and regenerates sodium
carbonate that is recycled back to the carbonation reactor.
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SUMMARY
• The atmosphere supports life and supplies useful elements
(e.g., O, N, Ar).
• The atmosphere absorbs gamma rays, X-rays, and
ultraviolet radiation.
• Atmospheric pollutants include NOx, SO2, VOCs, low-level
ozone, CO, CO2.
• Greenhouse gases include CO2, methane, water vapor, and
N2O.
• Smog = reactions with VOCs and NOx that produce lowlevel ozone.
• Acid rain forms from reactions between NOx and SO2 and
H2O vapor.
• Stable Cl- and BR-bearing compounds, CFCs, are emitted
to the atmosphere.
© 2011 Pearson Education, Inc.
SUMMARY (cont.)
• Greenhouse gases in Earth’s atmosphere absorb heat radiated by
Earth, trap it in the atmosphere, and reradiate it back to Earth,
causing surface and ocean temperature increases.
• Variations in solar radiation caused by cyclic changing of the tilt of
Earth’s axis, Earth’s distance from the Sun due to orbital
eccentricity, and Earth’s wobble as it orbits the Sun are significant
controls on global climate.
• Shifts between warm and cold climates have occurred for large parts
of Earth’s history (e.g., 40–50 cycles during the last 2 to 3 million
years)
• The last glacial maximum occurred 20,000 years ago—incoming
solar radiation increased between 20,000 and 10,000 years ago, the
ice sheets melted, and sea level rose some 110 to 125 meters (360
to 410 ft).
• Addition of greenhouse gases has led to global warming.
© 2011 Pearson Education, Inc.