Transcript Lecture Outlines Natural Disasters, 5th edition

Chapter 12
Climate Change
Lecture PowerPoint
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Early Earth Climate –
An Intense Greenhouse
Inner planets atmospheric compositions:
• Venus:
– Intense solar radiation, trapped by dense CO2-rich atmosphere
 surface temperatures 477oC
• Mars:
– Less solar energy, but thin atmosphere is rich in CO2, so holds
heat effectively, surface temperature -53oC
• Venus’, Mars’ atmospheres changed little in last 4 billion years
• Earth’s atmosphere: radical change from CO2-rich to CO2-poor
Early Earth Climate –
An Intense Greenhouse
Insert Table 12.1 here.
Early Earth Climate –
An Intense Greenhouse
• Changes in Earth’s atmosphere caused by life processes
– Plants remove CO2 from atmosphere by photosynthesis
– Atmospheric CO2 dissolves in water, is absorbed by marine life
– CO2 is chemically tied up in limestone (CaCO3 from shells,
reefs, mineralized tissue of invertebrate animals, algae)
– Early photosynthesizing life on Earth removed enough CO2
from atmosphere for other animal life to survive  animals
made skeletons of CaCO3  further reduced atmospheric CO2
 lessened greenhouse effect on Earth  lowered temperatures
Early Earth Climate –
An Intense Greenhouse
• Changes in Earth’s atmosphere caused by life processes
Figure 12.1
Early Earth Climate –
An Intense Greenhouse
• Before life, atmosphere full of CO2, greenhouse effect 
surface temperature about 290oC
• Greenhouse effect:
– Incoming visible light is admitted at short wavelengths
– Atmosphere warms up, heat is given off as infrared (longer
wavelength) radiation
– Longer-wavelength outgoing energy is trapped
– Greenhouse effect produced by glass (in greenhouse, windows
of car) or by gases in atmosphere (CO2, H2O vapor, methane
(CH4), chlorofluorocarbons (CFCs))
– CO2 is most important greenhouse gas
Early Earth Climate –
An Intense Greenhouse
• Present: CO2 is 0.039% of atmosphere  weakened
greenhouse effect
• Average temperature is 34oC higher than without CO2
• Earth has always been influenced by greenhouse effect
• Life has always been in dynamic equilibrium with
greenhouse effect
• Humans now changing atmospheric CO2 concentration
– Burning tremendous volumes of living plants (trees and
shrubs) and dead plants (coal, oil, natural gas)
– Relatively small amounts but may be enough to trigger climate
shifts
Climate History of the Earth:
Timescale in Millions of Years
• Sedimentary rocks contain information about climate at time they
formed
• Warm climates indicated by:
– Fossil reefs, limestones
– Aluminum ore bauxite (tropical soils)
– Evaporite minerals
• Cold climates indicated by:
– Erosion by glaciers (distinctive marks and debris deposition)
• Certain fossil organisms indicate paleo-temperatures
• Can derive history of Earth’s climate
In Greater Depth: Equilibrium Between
Tectonics, Rock Weathering and Climate
• Volcanism is a major source of carbon dioxide to the
atmosphere
• During tectonically active periods more carbon dioxide enters
the atmosphere
• Mountain building resulting from the tectonic activity leads to
more rock weathering which removes carbon dioxide from the
atmosphere
• The result is a negative feedback that helps to maintain an
equilibrium of climate
Climate History of the Earth:
Timescale in Millions of Years
• Climate depends on balance between
incoming and outgoing heat – may
be gaining or losing overall
• Earth divided into belts of frigid,
temperate and torrid by latitude
• Ice Age:
– frigid zone expands to larger area
– torrid zone shrinks but does not
disappear
• Torrid Age:
– torrid zone expands to larger area
– frigid zone shrinks but does not
disappear
Figure 12.4
Climate History of the Earth:
Timescale in Millions of Years
Late Paleozoic Ice Age
• 360 – 260 million years ago
• Major factors (requirements for Ice Age to occur):
– Large landmasses near poles to accumulate snowfall, build
continental ice sheets
• In late Paleozoic, Pangaea (supercontinent) moved across
south polar region
Climate History of the Earth:
Timescale in Millions of Years
Late Paleozoic Ice Age
• 360 – 260 million years ago
• Major factors (requirements for Ice Age to occur):
– Continents blocking equatorial (east-west) ocean circulation
• Water must first evaporate from ocean for clouds to form and
precipitate snow (to build ice sheets)
• Warm water evaporates more easily than cold water
• If continents divert warm ocean currents to flow north and
south to the poles, more water will evaporate to form clouds,
to drop more snow
• Ice Age may have ended because Pangaea broke apart
Climate History of the Earth:
Timescale in Millions of Years
Late Paleocene Torrid Age
• 65 – 55 million years ago
• Equatorial zones similar to today, poleward latitudes much warmer
• Less temperature difference between tropical and polar ocean
waters
– Absence of cold, dense, sinking water at poles
• Less temperature difference between surface and deep ocean
waters
– Sluggish ocean circulation
• Less temperature difference in atmosphere
– More peaceful weather, absence of strong seasons, evenly
distributed rainfall  warmer and wetter
Climate History of the Earth:
Timescale in Millions of Years
Late Paleocene Torrid Age
Factors to create Torrid Age:
• Equatorial zones were oceans, allowing more absorption of solar
radiation by water
• As oceans warmed, snow and ice melted  more land was exposed
– Land absorbs more heat than snow and ice
• Opening North Atlantic Ocean erupted huge amounts of lava and
huge volumes of gases to atmosphere, increasing global warming
by greenhouse effect
Climate History of the Earth:
Timescale in Millions of Years
Late Paleocene Torrid Age
Factors to create Torrid Age:
• Heaviest ocean water may have been dense, salty, oxygen-poor
tropical water, as polar waters became warmer
– Tropical waters would have sunk to bottom, warming oceans
from bottom up  massive extinction of ocean life
• Warming of ocean water may have
melted methane hydrates on seafloor,
releasing methane gas (CH4) to
atmosphere over 10,000 years
– Methane gas is powerful greenhouse
gas, caused further warming
Figure 12.7
In Greater Depth:
Oxygen Isotopes and Temperature
•
•
•
•
•
•
•
•
Use ratio of stable isotopes of oxygen in CaCO3 sea life fossils
Oxygen may be 16O, 17O or 18O
Evaporation removes more light 16O, leaves behind more heavy 18O
Atmospheric water becomes depleted in 18O
18O-depleted water is trapped on land as snow or ice during Ice Age
Oceans become 18O-enriched
Marine organisms use 18O-enriched water in making CaCO3 shells
Measurement of 18O/16O ratio in CaCO3 fossils is indicator of
climate when organism lived
– High 18O/16O  colder climate
– Low 18O/16O  warmer climate
Climate History of the Earth:
Timescale in Millions of Years
Late Cenozoic Ice Age
Long-term cooling from temperature peak at 55 million
years ago  current Ice Age
• 55 million years ago: methane reduced in atmosphere, began
cooling
• 40 million years ago: Antarctica surrounded by cold water
• 34 million years ago: glaciers widespread in Antarctica
• 14 million years ago: continental ice sheet on Antarctica, mountain
glaciers in northern hemisphere
• 5 million years ago: Antarctic ice sheet expanded
• 2.7 million years ago: continental ice sheets in northern hemisphere
Climate History of the Earth:
Timescale in Millions of Years
Late Cenozoic Ice Age
Factors in cooling:
• Ongoing breakup of Pangaea
• Opening and closing of seaways  altered ocean circulation and
heat distribution around globe
• Continental masses in polar regions (Antarctica at South Pole and
Eurasia near North Pole) to build ice sheets
• Accumulation of snow and ice at poles increased albedo  more
sunlight reflected
Climate History of the Earth:
Timescale in Millions of Years
Late Cenozoic Ice Age
Factors in cooling:
• Closing of Mediterranean and uplift of Isthmus of Panama stopped
east-west ocean circulation, forcing warm water to poles
• Less area of shallow ocean  less water surface to absorb sunlight
• Uplift of Tibetan plateau and Colorado plateau deflected west-toeast atmospheric circulation in midlatitudes
Climate History of the Earth:
Timescale in Millions of Years
The Last 3 Million Years
• Old, stable ice sheet on Antarctica – little short-term
climate effect
• North American and Eurasian ice sheets expand and
shrink, affecting global climate
• Formation of Isthmus of Panama 3 million years ago
blocked westward-flowing ocean water, forcing it north
• Warm water in north Atlantic Ocean increased
evaporation and snowfall, to build glaciers
• Continental ice sheets in northern hemisphere undergo
complex cycles of advance and retreat
Glacial Advance and Retreat:
Timescale in Thousands of Years
• Last 1 million years: about 10 glacial advances, retreats
• Worldwide glacial advances lasting almost 100,000 years
• Followed by retreats lasting decades to few thousand
years – much faster than advance
• Caused by cycles in Earth’s
orbit around Sun affecting
amount of solar energy
received by Earth
– Changes postulated in 1920s
by Serbian astronomer Milutin
Milankovitch and supported
recently by Greenland ice cores
Figure 12.10
Glacial Advance and Retreat:
Timescale in Thousands of Years
Milankovitch defined changes in Earth’s orbit, tilt and
wobble  changes in amount of solar radiation
received by Earth
– Amount of solar
radiation at high
latitudes during
summers determines
how much snow
remains from winter
to next winter,
allowing glaciers to
grow
Figure 12.12
Glacial Advance and Retreat:
Timescale in Thousands of Years
• Changes in Earth’s orbit:
– Eccentricity of orbit around
Sun: varies every 100,000 years
from circular to elliptical (less
solar radiation received when
elliptical) as dominant control of
glacial advance and retreat
– Tilt of Earth’s axis: 21.5 – 24.5o
off vertical in 41,000 year cycle
– Precession of tilt: direction of tilt
changes (wobble in spin of toy
top) in double cycle of 23,000
and 19,000 years
Figure 12.11
Glacial Advance and Retreat:
Timescale in Thousands of Years
Around 20,000 years ago:
• Glaciers at maximum extent, covered 27% of today’s land
– Virtually all of Canada, part of northeastern U.S.
• Seawater necessary to build glaciers lowered sea level 130 m
• Current Ice Age continues (current glacial retreat)
– 10% continents still buried under ice
– If ice melts, sea level would rise 65 m
Glacial Advance and Retreat:
Timescale in Thousands of Years
Around 20,000 years ago:
Figure 12.13
Figure 12.14
Climate Variations:
Timescale in Hundreds of Years
Temperature conditions following 20,000 years ago:
• Warming began, then interrupted by Older Dryas cold stage
• Cold interval replaced by warmth of Bolling period
• Temperatures fell through Allerod interval and bottomed in Younger
Dryas stage 12,900 to 11,600 years ago
• Current interglacial period
• Temperature changes of 3o to 5oC occurred in several years
Figure 12.16
Climate Variations:
Timescale in Hundreds of Years
Cause of sudden drops or jumps in temperature:
• Melting of continental ice sheets left behind huge cold lakes with
ice dams
• Failure of ice dams released
enormous amounts of fresh,
cold water into surface layers
of ocean, disrupting oceanic
circulation pattern for 1,100
years
• Constant rise in sea level from
melting of glaciers
Figure 12.15
Climate Variations:
Timescale in Hundreds of Years
At 7,000 years ago:
– Warmer global temperatures, higher rainfall totals  climatic
optimum
– Since then average global temperatures have fallen 2oC
– Smaller cycles of
glacial expansion and
contraction within
cooling trend
Figure 12.17
Shorter-Term Climatic Changes:
Timescale in Multiple Years
El Nino
• Typical conditions in Pacific (without El Nino effect):
– High pressure over eastern Pacific causes trade winds blowing
west and toward equator from north and south
– Westward winds ‘push’ surface water to western Pacific
– Western Pacific water absorbs solar energy, evaporates easily
– Heavy rainfalls in Indonesia and southeast Asia
– Eastern Pacific has upwelling of cold, deep water to replace
surface water blown westward
Shorter-Term Climatic Changes:
Timescale in Multiple Years
El Nino
• Typical
conditions
in Pacific
(without
El Nino
effect):
Figure 12.18
Shorter-Term Climatic Changes:
Timescale in Multiple Years
• Ocean-atmosphere coupling: arrival of warm ocean water
to Peru, Ecuador near Christmastime, affecting climate,
every 2 to 7 years
• El Nino conditions in Pacific:
– When westward blowing trade winds are absent, piled-up warm
surface water flows ‘downhill’ from western to eastern Pacific
– Warm surface water evaporates easily and causes increased
rainfall to western North and South America
– Decreased hurricane risk to Atlantic Ocean
Shorter-Term Climatic Changes:
Timescale in Multiple Years
• El Nino conditions in Pacific:
Figure 12.19
Shorter-Term Climatic Changes:
Timescale in Multiple Years
• El Nino 1982-83:
– Cold-water fisheries off Peru and Ecuador collapsed
– More evaporation  torrential rainfall, floods, landslides killed
600 people in Peru and Ecuador, economic loss
– Heavy rainstorms in western U.S.: $300 million in damages,
10,000 people evacuated, 12 people killed in California
– Tropical rain belt in central Pacific formed hurricanes hitting
Tahiti and Hawaii
– Australia and Indonesia had lower rainfall and droughts 
bushfires killed 75 people, $2.5 billion in damages
Shorter-Term Climatic Changes:
Timescale in Multiple Years
• El Nino 1997-98:
– Winds flowing eastward caused heavy rains and floods in
California
– Higher rainfall, tornadoes to southeastern U.S.
– Helped break apart Atlantic and Caribbean storms  fewer
hurricanes
– Warmer winter in midwestern and northern states
– More economic gains than losses, fewer fatalities in U.S.
Shorter-Term Climatic Changes:
Timescale in Multiple Years
• Cause of El Nino:
– Southern Oscillation in south Pacific Ocean: usual low pressure
replaced by high pressure, migrating from Indian Ocean (ENSO)
– Globally connected
weather system
• Tropical atmosphere
goes through
changes that link up
around world
• Takes four years to
circuit globe
Figure 12.21
Shorter-Term Climatic Changes:
Timescale in Multiple Years
La Nina
• Occurs when cooler waters move into equatorial Pacific
• Brings cold air and high rainfall to northwestern U.S. and
western Canada, below average rainfall to rest of North
America
• Encourages hurricanes in Atlantic Ocean, wildfires in
southwestern U.S.
Shorter-Term Climatic Changes:
Timescale in Multiple Years
Pacific Decadal Oscillation
• Lasts 20-30 years
• Midlatitude Pacific Ocean conditions, secondary tropical effects
– El Nino: lasts 6-18 months, conditions of tropics, secondary
effects on mid-latitudes
• Warm phase with increased storms and rainfall
• Occurred from 1925 to 1946, from 1977 to 1998
Insert Figure 12.23
Figure 12.23
Volcanism and Climate
• Large Plinian eruptions blast fine ash and gas to
stratosphere, above troposphere where weather occurs
• Ash and sulfuric acid (from sulfur dioxide gas) remain in
stratosphere as haze for years, blocking incoming
sunlight
Volcanism and Climate
El Chichon, 1982: Four big Plinian eruptions
– Smaller than eruption of Mount St. Helens, but more than 100
times SO2 gas emitted into stratosphere
– SO2 cloud took 23 days to circle globe  spectacular sunsets
– Lowered global average temperature 0.2oC
– Followed by El Nino (may be more likely after major eruption)
Figure 12.24
Volcanism and Climate
Mount Pinatubo, 1991
• Eruption pumped 20 million tons of
SO2 into stratosphere
• Reflected 2-4% of incoming solar
radiation  20-30% decline in solar
radiation reaching ground
• Average global temperatures dropped
0.5oC
– Included 1oC drop in U.S.,
offsetting global warming
Figure 12.25
Volcanism and Climate
Tambora, 1815: Eruptions reduced 4,000 m volcano to 2,000 m high
caldera, producing 175 km3 of ash and debris
• Made 1816 “the year without a summer”
• Average global temperatures lowered 0.3oC
• Triggered cholera epidemic
• Combined with 1809 “mystery eruption” to make the 1810s an
extremely cold decade
Toba, Indonesia, ~74,000 years ago: erupted 2,000 km3 of ash and
debris
• Youngest known resurgent caldera eruption
• Ash and sulfuric acid cloud estimated to have lasted in stratosphere
up to six years
• Global cooling possibly as much as 3-5oC  volcanic winter
Volcanism and Climate
Volcanic Climate Effects
• Plinian eruptions affect climate for few years, resurgent
caldera eruptions for several years
• Possible for several different volcanoes to erupt over
several successive years in a row (by chance)
• Might have long-term effects on climate  Little Ice Age
– Greenland ice-core record shows high acid during this time
• Factors in volcanism’s effect on climate:
–
–
–
–
Size, rate of eruptions
Height of eruption columns
Types of gases, atmospheric level of placement
Low latitude vs. high latitude (weather patterns spread debris)
Volcanism and Climate
Volcanic Climate Effects
• Worst-case scenario: Flood basalt eruptions such as
Deccan Plateau (India) 65 million years ago (extinction of
dinosaurs)
– 2.6 million km3 of basaltic lava erupted in only 500,000 years
– Possible effects:
• Increase in atmospheric CO2  temperature increase of
10oC
• More acidic ocean waters
• Depleted ozone layer
In Greater Depth: The Mayan
Civilization and Climate Change
• Great accomplishments in agriculture, irrigation, social
organization, mathematics, astronomy over 1,000 years
• Century-long pattern of decreased rainfall  droughts
 abandonment of urban areas, stop in monument
construction, breakdown of social and political order 
wars, return to life of rural subsistence
• Significant decline in Mayan civilization due to string of
events triggered by long-term climate change
The Last Thousand Years
• Combined effects of eccentricity, tilt, wobble caused
cooling trend with numerous variations
• Variations studied to learn more about:
– Extent of temperature fluctuations
– Whether regional or simultaneous around globe
– Causes of changes
• Other variations within cooling trend being studied with:
–
–
–
–
–
–
–
Oxygen isotopes in glacial ice layers
Annual growth rings of corals
Tree ring widths and densities
Tax records of grain and grape crops
Advances and retreats of mountain glaciers
Paintings of frozen lakes, rivers, ports
Weeks per year of sea ice around Iceland
The Last Thousand Years
Variations within cooling trend:
• Medieval Maximum: warm period from 1000 to 1300 C.E.
• Little Ice Age: cold period from 1400 to 1900 C.E. – “epoch of
renewed but moderate glaciation”
– Smaller scale coolings and warmings within Little Ice Age
– Maunder Minimum: cooler period from 1645 to 1715 C.E.
• Minimal sunspot activity  Sun possibly .25% weaker
Figure 12.28
The Last Thousand Years
Processes in climate changes of last thousand years:
• Changes in Earth’s orbital patterns caused cooling
• Lessened solar-energy production caused cooling
• Volcanism caused changes
• Interactions between ocean, atmosphere, ice sheets
• Millennium cycle? Warm centuries followed by cold centuries
– Twentieth century may have been beginning of warm centuries
Side Note: Stradivari Violins
• Most famous violins: increased size, secret varnish 
superior tones
• May have benefited from Maunder Minimum cold
temperatures
– Longer winters and cooler summers promoted slow, even tree
growth  dense wood with narrow rings
– May be cause of superior tones of Stradivari violins
The 20th Century
• 20th c. began as warm as any time in past 1,000 years
• Average global surface temperatures rose 0.6oC in 20th
century, from 1910-1944 and since 1977
• 1910-1944 warming: hotter Sun, lack of volcanism
• Warming since 1977 twice that of 1910-1944: likely
mostly due to greenhouse gases in atmosphere
• Natural causes 0.2oC:
– Changes in Earth’s orbital patterns  0.02oC decrease
– Hotter Sun  more than 0.2oC increase
• Human activities 0.4oC increase
Greenhouse Gases and Aerosols
• Greenhouse effect has always acted to warm Earth
climate; strength has varied
• Greenhouse gases (currently being added to atmosphere
by humans):
–
–
–
–
–
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (N2O)
Ozone (O3)
Industrial gases such as CFCs
Greenhouse Gases and Aerosols
Water Vapor
• Water vapor is Earth’s most abundant Greenhouse gas
• It is a vast, natural control on temperature
• The warmer the air, the greater the percentage of water
vapor it can hold.
• Greater volume of water vapor  greater amount of
trapped heat (positive feedback cycle)
In Greater Depth: When Did Humans Begin
Adding to Greenhouse Warming?
• Burning oil, natural gas, coal, and wood currently releases
huge amounts of CO2 to atmosphere
• 8,000 years ago: cutting, burning forests for agriculture
began adding CO2 to atmosphere
• 5,000 years ago: wetlands technique of rice-growing
began adding methane to atmosphere
• These agricultural practices may have warmed climate by
as much as 0.8oC over thousands of years
– May have prevented some Little Ice Ages, kept climate stable
• Occurred over thousands of years, unlike current
changes over decades
Greenhouse Gases and Aerosols
Carbon Dioxide (CO2)
• Causes over 50% of greenhouse warming caused by
humans
• Carbon cycle:
–
–
–
–
Major building block of life on Earth
20% of CO2 removed from atmosphere by photosynthesis
At plant death, oxidation returns CO2 to atmosphere, into water
Humans decompose plants at faster rates (burning wood and
fossil fuels)  CO2 increases in atmosphere and water
Greenhouse Gases and Aerosols
Carbon Dioxide (CO2)
• Carbon cycle:
– 1800: CO2
concentration in
atmosphere 280 ppm
– 2010: CO2
concentration in
atmosphere 390 ppm
– CO2 removed from
atmosphere: 20% by
photosynthesis, 30%
dissolves in ocean
water, but 50% stays
in atmosphere
Insert figure 12.33
Figure 12.33
Greenhouse Gases and Aerosols
Methane (CH4)
• Causes about 16% of greenhouse warming
• 21 times higher heat-trapping ability than CO2
• Risen more than 150% since 1750 (700 ppb)
• Released during decomposition of vegetation in oxygenpoor environments, by “mud volcanoes”
• 70% given off by human activities:
– Burning fossil fuels
– Growing rice
– Maintaining livestock
– Landfills
– Burning wood
– Rotting animal waste and
human sewage
• Melting of methane hydrates  torrid climate
Greenhouse Gases and Aerosols
Nitrous Oxide (N2O)
• Produced naturally by bacteria removing nitrogen from
organic matter, especially in soil
• Produced by humans in agricultural activities
– Chemical fertilizers
– Combustion burning of fuels in engines
Ozone (O3)
• Ozone in stratosphere absorbs UV radiation, shields life
• Principal component of smog in urban atmospheres
• Produced by gases interacting with sunlight
• Irritates eyes and lungs  shortens lives
Greenhouse Gases and Aerosols
Chlorofluorocarbons (CFCs)
• Produced solely by humans (do not occur naturally)
• Coolants in refrigerators and air conditioners, foam
insulation in buildings, solvents, etc.
• Aid in destruction of ozone in stratosphere
• Remain in atmosphere for up to century (catalyst)
Twentieth-Century Greenhouse Gas Increases
• Byproducts of industrial and domestic energy production,
rice and livestock agriculture
• 20th century population growth (doubled twice)
• Lifestyle of industrialized world
The 21st Century
Intergovernmental Panel on Climate Change (IPCC)
Insert Table 12.7 here
Global Climate Models
• Climate change involves complex questions and
many variables
• Questions are addressed by constructing global
climate models (GCMs)
Insert Revised Table 12.8 here
Drought and Famine
• Times of abnormal dryness in region, without usual rain
• Expected rains do not arrive  vegetation begins to die
 food supplies shrink  famine
• Tends to drive people apart rather than bring together
• Early stage: food available but inadequate
– Lose up to 10% body weight, still alert and vigorous
• Advanced stage: body weight decreases by about 20%,
body reduces activity levels, apathy
• Near-death stage: 30% or more body weight lost,
indifference to surroundings and others
Drought and Famine
U.S Dust Bowl, 1930s
• Several years of drought turned grain-growing central
U.S. into dust bowl
• Position of jet stream caused upper-level, high-pressure
dry air to sink  hot, dry winds killed plants and eroded
soil into dust clouds
• Drought began in 1930
• Dust storms increased in 1934, 1936
• Blame mistakenly put on farmers for plowing up native
grasses
– May have exacerbated situation
– Droughts typical but infrequent in North America
Ice Melting and Sea-Level Rise
•
•
•
•
Glacial ice holds 2.15% of water on earth
If all melted, sea level would rise 65 m (210 ft)
This will not happen in foreseeable future
However, there are regions of concern
– Arctic sea ice has been shrinking every decade (2009 was 13th
consecutive September with below-average sea-ice extent)
• Possible tipping point
– Greenland continental glacier melting has increased, large-scale
catastrophic collapses are possible
• Possible tipping point
• A sea level rise of 4-6 m in upcoming centuries would cause
major problems worldwide for major cities and low-lying deltas
Ocean Circulation
• Major climatic shift if present deep-ocean circulation pattern is
altered by inflow of fresh water from melting glaciers in north
Atlantic Ocean
• Unpredictable natural changes may offset or accentuate human
effects
Figure 12.41
Signs of Change
Insert revised Table 12.9 here
In Greater Depth: Tipping Points
• Change is usually a gradual process, but not always
• Points at which small changes suddenly produce large
effects
• History of change may not predict future
In Greater Depth: Lag Times
• Changes in climate are occurring slowly
• Full effects will not be felt for decades
• IPCC estimates oceans will continue to warm
throughout 21st century (0.6ºC)
• There are lag times in temperature changes and in the
melting of the ice sheets
Mitigation Options
• Widely perceived need to reduce greenhouse gas emissions
• Will require changing energy-usage technologies
• Cap-and-trade
– Emission allowances are placed on companies
– Companies can by or sell credits
• Drastic Engineering
– Imitate volcanoes, fertilize oceans, air scrubbing, cloud brightening
– Efforts may create bigger problems than they solve
• Fast-Action Strategies
– Reduce emissions of black carbon, tropospheric ozone, methane and
hydrofluorocarbons
End of Chapter 12